Original Article

Testosterone Alters Maternal Vascular AdaptationsNovelty and Significance

Role of the Endothelial NO System

Vijayakumar Chinnathambi, Meena Balakrishnan, Jayanth Ramadoss, Chandrasekhar Yallampalli, Kunju Sathishkumar
https://doi.org/10.1161/HYPERTENSIONAHA.111.00486
Hypertension. 2013;61:647-654
Originally published February 13, 2013

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Abstract

Sex steroid hormones estradiol and progesterone play an important role in vascular adaptations during pregnancy. However, little is known about the role of androgens. Plasma testosterone (T) levels are elevated in preeclampsia, mothers with polycystic ovary, and pregnant African American women, who have endothelial dysfunction and develop gestational hypertension. We tested whether increased T alters vascular adaptations during pregnancy and whether these alterations depend on endothelium-derived factors, such as prostacyclin, endothelium-derived hyperpolarizing factor, and NO. Pregnant Sprague Dawley rats were injected with vehicle (n=12) or T propionate [0.5 mg/Kg per day from gestation day 15–19; n=12] to increase plasma T levels 2-fold, similar to that observed in preeclampsia. Telemetric blood pressures and endothelium-dependent vascular reactivity were assessed with wire-myograph system. Phospho-endothelial NO synthase and total endothelial NO synthase were examined in mesenteric arteries. Mean arterial pressures were significantly higher starting from gestation day19 until delivery in T-treated dams. Endothelium-dependent relaxation responses to acetylcholine were significantly lower in mesenteric arteries of T-treated dams (pD2 [−log EC50]=7.05±0.06; Emax=89.4±1.89) compared with controls (pD2=7.38±0.04; Emax=99.9±0.97). Further assessment of endothelial factors showed NO-mediated relaxations were blunted in T-treated mesenteric arteries (Emax=42.26±5.95) compared with controls (Emax=76.49±5.06); however, prostacyclin- and endothelium-derived hyperpolarizing factor-mediated relaxations were unaffected. Relaxation to sodium nitroprusside was unaffected with T-treatment. Phosphorylations of endothelial NO synthase at Ser1177 were decreased and at Thr495 increased in T-treated mesenteric arteries without changes in total endothelial NO synthase levels. In conclusion, increased maternal T, at concentrations relevant to abnormal clinical conditions, cause hypertension associated with blunting of NO-mediated vasodilation. T may induce the increased vascular resistance associated with pregnancy-induced hypertension.

Introduction

Pregnancy is characterized by major cardiovascular adaptations, including marked decreases in systemic vascular resistance and mean arterial pressure (MAP) and an increase in maternal cardiac output and total blood volume.1,2 Studies in rats suggest that the enhanced endothelial vasodilatory actions allow peripheral vessels to accommodate these increases in blood flow and volume.3 Consistently, maternal vascular adaptations are accompanied by enhanced release of 3 major endothelium-derived vasodilatory factors, including NO,3–5 prostacyclin (PGI2),6–9 and endothelium-derived hyperpolarizing factor (EDHF).10,11 Further, there are concomitant pregnancy-induced increases in mRNA and protein expression of endothelial NO synthase (eNOS),4,5,12,13 prostaglandin H synthase,7,14 and EDHF activity.11 Altered vascular adaptations during pregnancy are directly related to several maternal/fetal vascular pathologies, such as increased systemic vascular resistance, hypertension, proteinuria, poor placental growth, decreased nutrient transport, and low birth weight, which are characteristics of preeclampsia.15

Most studies have investigated the beneficial role of sex steroid hormones, especially estradiol and progesterone on cardiovascular function during pregnancy.2 However, little is known about the role of androgens. The relation between testosterone and maternal cardiovascular function deserves special consideration because plasma levels of testosterone are increased ≈2- to 3-fold in pathological pregnancies, such as in preeclampsia,16–20 and androgen levels in preeclamptic women positively correlate with higher average systolic blood pressure.20 Also, pregnant hyperandrogenemia women with polycystic ovary syndrome21 and pregnant African American women have high maternal and cord blood testosterone levels22–24 and are at increased risk for developing preeclampsia.25,26 Previous studies have focused on the effects of increased maternal testosterone on cardiovascular consequences in the offspring,27–29 but, surprisingly, there is a paucity of literature about the effect of testosterone on the maternal cardiovascular system during pregnancy.

Most investigators have studied the effect of increased testosterone in cardiovascular function of males and nonpregnant females.30–32 Increased testosterone has been shown to decrease endothelial function through its influence on the production or function of NO,27,33–35 PGI2,36 and EDHF37 and affect vascular reactivity38,39 and systemic blood pressure.30–32 Thus, it is possible that the functions of endothelium in modulating the vascular adaptations associated with pregnancy are altered in response to increased testosterone. Therefore, we hypothesized that increased testosterone may decrease endothelium-mediated cardiovascular adaptations of pregnancy. We tested this hypothesis by injecting testosterone into pregnant rats, mimicking the 2-fold increase in plasma testosterone levels observed in preeclamptic women,27,28,40 to investigate (1) whether the systemic arterial pressure is enhanced in testosterone-treated compared with control pregnant rats; (2) whether endothelium-dependent vascular relaxation, particularly in the resistance mesenteric arteries, is inhibited in testosterone-treated compared with control pregnant rats; and (3) whether the testosterone-induced changes in vascular relaxation involve alterations in the endothelium-dependent PGI2-, EDHF-, or NO-mediated pathways.

Methods

Animals and Treatment

All experimental procedures were in accordance with National Institutes of Health guidelines (NIH Publication No. 85–23, revised 1996) with approval by the Animal Care and Use Committee at the University of Texas Medical Branch at Galveston. Timed pregnant Sprague Dawley rats (day 4 or day 12 of gestation; copulation plug on day 1; Charles River, Wilmington, MA) were used in the experiment. After acclimatization, on gestational day (GD) 13, dams were randomly divided into 2 groups. Dams in the treatment group were subcutaneously injected with testosterone propionate (0.5 mg/Kg per day; n=12) for 5 days from GD 15 to 19. The control group received vehicle (sesame oil; n=12). This dose and duration of exposure is commonly used to mimic plasma testosterone levels observed in preeclamptic women.27,28,40 Blood samples were drawn from the femoral vein 2 hours after testosterone injection on GD19 and analyzed for testosterone levels (Enzo Life Sciences, Farmingdale, NY) as reported previously.27,28 We injected rats with testosterone instead of dihydrotestosterone because it is the levels of testosterone and not dihydrotestosterone that are increased and correlate with complicated pregnancies.16–20 Moreover, this model is not associated with changes in levels of maternal estradiol, progesterone, or corticosterone.40 Detailed Methods for telemetric measurement of blood pressure, vascular reactivity studies, determination of eNOS expression and phosphorylation, and plasma nitrate/nitrite (NOx) analysis are described in the online-only Data Supplement.

Statistical Analysis

All data are presented as mean±SEM. Responses to acetylcholine (ACh) are expressed as percent relaxation of the initial phenylephrine contraction. Vasodilator concentration response curves were fitted to a log-logistic sigmoid relation, and pD2 values (negative logarithm of the molar concentration of vasodilator that produced 50% of the maximal response) and Emax (maximal relaxation effect) were calculated (GraphPad Prism, La Jolla, CA). Repeated measures ANOVA (treatment and time as factors) with a Bonferroni post hoc were used for comparisons of blood pressures and dose response curves between control and treatment groups. Percent maximal relaxation, pD2, NOx levels, eNOS mRNA expression, and protein levels were compared between control and treatment groups using unpaired Student t test. Statistical significance was defined as P<0.05. The letter n represents number of rats.

Results

The period of gestation and mean litter size were not significantly affected by testosterone treatment. Fetal weights (control: 2.62±0.06 g; testosterone-treated: 1.99±0.08 g), placental weights on GD 20 (control: 0.54±0.08 g; testosterone-treated: 0.43±0.13 g), and birth weight of pups (control: 6.30±0.19 g; testosterone-treated: 5.75±0.19 g) were significantly reduced (P<0.05; n=8 litters in each group) in the testosterone-treated group compared with controls, consistent with our previous reports.27,28,40 The plasma testosterone levels on GD 19 (2 hours after injection) from testosterone-treated dams were 2.1±0.17 ng/mL compared with 1.0±0.11 ng/mL in vehicle-treated control dams.

MAP and Heart Rate Measurements

Rats are nocturnal animals and continuous monitoring of blood pressure by telemetry revealed a characteristic circadian pattern with higher arterial pressure and heart rate values during the dark cycle (active phase) compared with the light cycle (Figure 1). In control animals (n=7), MAP was steady up to GD 17/18 and then progressively decreased as pregnancy advanced, reaching a nadir on GD21 and then increasing up to delivery on GD22. In testosterone-treated rats (n=7), MAP was similar to control rats during the early phase of treatment; however, the MAP did not show the expected decrease that occurred in control pregnant rats. Pregnant rats on testosterone had significantly higher MAP starting from GD19 until delivery on GD22 compared with the respective time point in controls (Figure 1A; P<0.05). Changes in both systolic and diastolic blood pressures were similar to that of MAP; therefore, data are not shown. No differences in heart rate were observed between controls and testosterone-treated dams (Figure 1B; n=7 rats in each group).

Figure 1.
Figure 1.

Mean arterial pressure (MAP) and heart rate in control and testosterone-treated pregnant rats. MAP (A) and heart rate (B) were continuously monitored via telemetry catheters in femoral artery from gestational day (GD) 14 until delivery in control and testosterone-treated (0.5 mg/kg per day, s/c from GD 15–19) pregnant rats. MAP and heart rate values are presented in 12-hour intervals showing circadian variation; night time periods are shaded. Data points represent the mean±SEM of measurements in 7 rats in each group. *P≤0.05 vs control.

Mesenteric Vasodilator Function

Testosterone treatment of pregnant rats did not alter phenylephrine-induced contractile responses but significantly decreased vessel sensitivity to ACh-induced vasodilation. The responses for ACh were significantly reduced in testosterone-treated pregnant rats (pD2: 7.05±0.06; n=9; P<0.05) compared with controls (pD2: 7.38±0.04; n=9; Figure 2; Table). The maximal responses to ACh were also significantly decreased in testosterone-treated pregnant rats (Emax: 89.4±1.89%; n=9) compared with controls (Emax: 99.9±0.97%; n=9).

View this table:
Table.

The Emax and pD2 of Concentration Response Curves Induced by ACh in PE-Precontracted Resistance Mesenteric Arteries of Control and Testosterone-Treated Pregnant Rats

Figure 2.
Figure 2.

Endothelium-dependent relaxation in mesenteric arterial rings. A submaximal phenylephrine contraction (EC80) was elicited, acetylcholine was added, and the percent relaxation of phenylephrine contraction was measured. Data points represent the mean±SEM of measurements in 18 to 24 vascular rings from 6 rats of each group. *P≤0.05 vs control.

To address the involvement of products generated by prostaglandin H synthase, EDHF, and eNOS activities in testosterone-impaired mesenteric endothelial vasodilation, we examined ACh-induced relaxation in the absence or presence of specific inhibitors. Inhibition of eNOS and EDHF pathways, leaving PGI2 as the only intact pathway, showed minimal relaxation to ACh, and there was no difference between control (n=7) and testosterone-treated pregnant rats (n=8; Figure 3A; Table). Inhibition of PGI2 and eNOS pathways, leaving EDHF as the only intact pathway, showed substantial relaxation to ACh; however, there were no significant differences between control (n=7) and testosterone-treated rats (n=8; Figure 3B; Table). However, inhibition of PGI2 and EDHF pathways, leaving NO as the only intact pathway, showed significant relaxation to ACh, and this relaxation response was significantly lower in the mesenteric arteries of testosterone-treated pregnant rats (Emax: 42.26±5.95%; n=9) compared with control pregnant rats (Emax: 76.49±5.06%; n=9; Figure 3C; Table). Blockade of all 3 pathways with inhibitors completely abolished ACh-induced relaxation (data not shown). Overall, these data imply that testosterone treatment does not affect PGI2 or EDHF components of relaxation, but only inhibits the NO component of relaxation responses to ACh. Sodium nitroprusside caused concentration-dependent relaxation of phenylephrine contraction that was not different in mesenteric arteries of control (n=6) and testosterone-treated (n=6) pregnant rats (Figure 4).

Figure 3.
Figure 3.

Prostacyclin (PGI2)-, endothelium-derived hyperpolarizing factor (EDHF)-, and NO-mediated endothelium-dependent relaxation in mesenteric arterial rings. Submaximal phenylephrine contraction (EC80) was elicited, acetylcholine was added to arterial rings in the presence of selective inhibitors as described in Methods, and then the percentage of relaxation to phenylephrine contraction was measured to determine (A) PGI2-, (B) EDHF-, and (C) NO-mediated mesenteric arterial relaxation. Data (mean±SEM) represent measurements from 14 to 24 vascular rings from 7 to 9 rats per treatment group. *P≤0.05 vs control. ChTx indicates charybdotoxin.

Figure 4.
Figure 4.

Endothelium-independent relaxation in mesenteric arteries. Submaximal phenylephrine contraction (EC80) was elicited in endothelium-denuded vascular rings, increasing concentrations of sodium nitroprusside were added, and then the percentage of relaxation to phenylephrine contraction was measured. Data points represent mean±SEM of measurements in 10 to 12 mesenteric arterial rings from 6 rats of each group.

eNOS Expression and Phosphorylation

eNOS mRNA levels were significantly reduced (P=0.0251; n=7 in each group) in mesenteric arteries of testosterone-treated pregnant rats compared with control pregnant rats (Figure5A). However, immunoblot analysis indicated that there were no significant differences in protein levels of total eNOS in mesenteric arteries between control and testosterone-treated pregnant rats (Figure 5B; n=5 in each group). Examination of phosphorylation status of eNOS, as an indicator activity state, demonstrated site-specific changes (Figure 6A). When expressed as a ratio of total eNOS, phosphorylation at Ser1177 was significantly lower (3.3-fold) in the mesenteric arteries of testosterone-treated pregnant rats compared with controls (Figure 6B; P=0.0021; n=5 in each group). Phosphorylation at Ser635 was unchanged with testosterone treatment (Figure 6C). In contrast, phosphorylation at Thr495 was significantly higher (1.3-fold) in testosterone-treated compared with control rats (Figure 6D; P=0.0117; n=5 in each group). Human umbilical vein endothelial cells in culture exposed to testosterone also resulted in similar alterations in eNOS phosphorylation (see online-only Data Supplement).

Figure 5.
Figure 5.

Endothelial NO synthase (eNOS) expression. A, Quantitative reverse transcriptase-polymerase chain reaction analysis of eNOS expression in mesenteric arteries isolated from testosterone-treated and control pregnant rats. B, Total eNOS protein expression in mesenteric arteries of testosterone-treated and control pregnant rats. Representative Western blots for eNOS and actin are shown at top; blot density obtained from densitometric scanning of eNOS normalized to actin is shown at bottom. Values are given as mean±SEM of 5 to 7 rats in each group. *P≤0.05 vs control.

Figure 6.
Figure 6.

Phosphorylation of endothelial NO synthase (eNOS) in mesenteric arteries isolated from control and testosterone-treated pregnant rats. Tissue lysates were immunoblotted with antibodies recognizing Ser1177-, Ser635-, or Thr495-phosphorylated eNOS, and blots were reprobed with anti-eNOS antibody. A, Representative Western blots of phospho-eNOS and total eNOS. The level of (B) Ser1177, (C) Ser635, and (D) Thr495phosphorylation of eNOS was quantified by scanning densitometry and normalized to total eNOS. Values are means±SE; n=5 for each group. *P≤0.05 vs control.

Plasma NOx Levels

The level of plasma NOx at GD20 was significantly lower in testosterone-treated dams compared with controls (control: 4.0±0.71 μmol/L; testosterone-treated: 2.6±0.37 μmol/L; P=0.002; n=12 in each group).

Discussion

To our knowledge, this is the first study evaluating the effect of increased testosterone levels on maternal vascular adaptations in pregnant animals together with a detailed investigation of the underlying mechanisms. Major findings are that increased testosterone levels in pregnant rats lead to (1) increases in MAP, (2) inhibition of endothelium-dependent mesenteric arterial relaxation, and (3) decreases in vascular mesenteric relaxations that are mediated by alterations in the endothelium-dependent NO-pathway, but not EDHF- or PGI2-mediated pathways. Moreover, testosterone-induced reductions in endothelial NOS activity are associated with decreased phosphorylation of excitatory eNOS at Ser1177 and increased phosphorylation of inhibitory eNOS at Thr495. Importantly, these testosterone effects in pregnant rats are observed at an in vivo concentration similar to that observed in pathological pregnancies, such as in preeclampsia.

The arterial pressure in normal pregnant rats is stable until GD17 or 18 and then gradually decreases until GD21. Similarly, in pregnant women, arterial pressure is stable during early stages of first trimester and then gradually decreases reaching a nadir during the second trimester.2,41 Interestingly, increased testosterone prevented the decrease in blood pressure observed in normal pregnancy such that the testosterone-treated pregnant rats have higher blood pressure compared with control pregnant rats. The lack of a pregnancy-related fall in blood pressure indicates a failure in normal cardiovascular adaptations and is considered to be a cardinal feature of preeclampsia.42 This failure suggests that the mechanisms controlling blood pressure during pregnancy are perturbed by increased testosterone. This effect on arterial pressure increase is without any changes in heart rate, indicating that testosterone does not affect the sympathetic activity. In the search for the possible mechanisms involved in the testosterone-induced increases in systemic arterial pressure, we found that increased testosterone caused inhibition of ACh-induced relaxation of resistance mesenteric arteries, suggesting that increased testosterone inhibits an endothelium-dependent relaxation pathway.

In the systemic circulation, the principal endothelium-dependent vasodilators are NO, PGI2, and EDHF. Studies have shown that PGI2 plays an important role in mediating vascular relaxation in uterine arteries43; however, its contribution in the mesenteric arterial relaxation, and in general to systemic blood pressure, is minimal, which is consistent with our findings and previous data illustrating that infusion of indomethacin into pregnant rats does not induce hypertension.44 Although a previous study reported that testosterone inhibits PGI2 production in cultured aortic vascular smooth muscle cells in vitro,36 we find that the PGI2-mediated relaxation was not affected by the presence of increased testosterone. This observation is also supported by similar levels of prostaglandin H synthase mRNA in the mesenteric arteries of testosterone-treated and control rats (data not shown). The current study shows that EDHF contributes substantially to mesenteric arterial relaxation during pregnancy, supporting earlier findings,43 but the presence of increased testosterone does not alter EDHF-mediated relaxation. However, in cerebral arteries of male rats, testosterone inhibited EDHF-mediated relaxation.37 The differences between our study and that of Gonzales et al37 may be attributable to the sex, pregnancy status, or vascular bed examined. Indeed, sex and, in particular, pregnancy status can play a major role in many aspects of vascular function.

The most striking finding of our study is that NO-mediated mesenteric vasodilation was significantly decreased in testosterone-treated pregnant rats compared with controls, suggesting that increased testosterone selectively blunts endothelial NO function. It has been suggested that during pregnancy there is a relative predominance of NO-dependent vasodilation45 that may increase its susceptibility to the effect of increased testosterone. The decreased NO-mediated arterial relaxation in testosterone-treated pregnant rats is not because of decreased vascular smooth muscle sensitivity to NO, as relaxation of mesenteric rings to sodium nitroprusside, an exogenous NO donor, was not different between control and testosterone-treated rats. This suggests that the decreased relaxation in the testosterone-treated rats is more likely a result of changes in the synthesis/release of NO. The current study demonstrates a significant decrease in basal eNOS mRNA expression, but a similar difference was not noted at the level of the protein. Similar differences in eNOS mRNA but not protein expression levels were reported in pigs and sheep.33,46,47

Testosterone-mediated decreases in the mesenteric vascular function via the NO-pathway were accompanied by concomitant decreases in the eNOS activity state. Immunoblotting demonstrated that the excitatory Ser1177eNOS was decreased whereas no differences were observed at the excitatory Ser635 levels. Ser1177eNOS is the most widely investigated excitatory phosphorylation site in the systemic vasculature and is regulated by numerous kinases including acutely transforming retrovirus AKT8 in rodent T cell lymphoma (AKT) and adenosine monophosphate-activated protein kinase (AMPK) and our studies suggest that testosterone specially affects the excitatory Ser1177 site. Our studies also show that testosterone increases phosphorylation at Thr495eNOS. Thr495eNOS, an inhibitory site in the Ca+2-calmodulin binding region of eNOS is reported to be significantly phosphorylated in the caveolar subcellular domain of endothelial cells and its dephosphorylation leads to increased enzyme activity.48 Expressing as a ratio of excitatory Ser1177 to inhibitory Thr495 eNOS would better suggest eNOS activity state. Testosterone treatment significantly decreased the Ser1177/Thr495 ratio (0.97±0.06; n=5; P<0.05) in mesenteric vessels compared with controls (3.6±0.7; n=5). However, the ratio of Ser635/Thr495 in mesenteric arteries of testosterone-treated rats (2.6±0.2) was not significantly different compared with controls (3.0±0.1). Thus, these findings suggest that chronic testosterone administration during gestation not only leads to decreased activity state of eNOS (as measured by decreased Ser1177 phosphorylation), but also produces decreased availability of eNOS (due to increased Thr495 phosphorylation) that is essential for eNOS activation. Endothelial cells in culture treated with testosterone also produced similar alterations in eNOS phosphorylation (see Figure S1 in the online-only Data Supplement). Consistent with the decreased eNOS activity state, the levels of plasma NOx were significantly lower in testosterone-treated dams compared with controls. Also, in vitro treatment of human umbilical vein endothelial cells with testosterone decreased NOx production (Figure S2). Future studies will be designated to examine testosterone-induced subcellular partitioning of eNOS and the signaling mechanisms, including the role of kinases that regulates the multisite phosphorylation state of eNOS.

Although this study demonstrates a role for NOS system, testosterone may also lead to increases in systemic blood pressure through other mechanisms including increase in renal tubular sodium and water reabsorption, activation of specific vasoconstrictor systems including the rennin-angiotensin,30,49,50 endothelin-1,51 and thromboxane,38,52 as well as increasing oxidative stress.53 Blood pressure increase in testosterone-treated animals may also be attributable to increase in sympathetic or decrease in the parasympathetic function. Numerous studies provide evidence that dysfunction in endothelial NO production is an important factor for the induction of gestational hypertension. For example, in pregnant rats, subcutaneous infusions of Nω-Nitro-L-arginine methyl ester (L-NAME) from day 17 to 22 of gestation resulted in sustained hypertension, proteinuria, and intrauterine growth retardation.54,55 Similarly, pregnant baboons showed an increase in MAP in middle and later pregnancy, but not early pregnancy, after administration of L-NAME.56 Many factors are proposed to play a role for impairing endothelial NO production during pregnancy; our study for the first time demonstrates a potential role for increased testosterone in causing endothelial dysfunction that may lead to hypertensive diseases of pregnancy. Also, it is possible that the decreased endothelial NO function may consequently decrease production and activity of other factors that cause pregnancy-associated vascular adaptations such as vascular endothelial growth factor57,58 and placental growth factor.59 Ultimately, placental blood flow and transfer of nutrients may be adversely affected, and this may contribute to abnormal fetal growth and development.40 In the current study, placental weights and pups born to testosterone-treated dams were significantly smaller than those born to control dams.

In conclusion, increased testosterone is associated with increased arterial pressure and selectively inhibits the endothelium-dependent NO-mediated vascular relaxation pathway in resistance vessels of pregnant rats. These results have important implications in determining the underlying factors for the adverse effects of testosterone on fetal growth and development.

Perspectives

Several studies show that the plasma levels of testosterone are 2-fold higher in preeclamptic pregnancies compared with normal pregnancies. Additionally, increased testosterone during pregnancy is associated with abnormal fetal growth and development leading to adult-life diseases, yet the mechanisms underlying the detrimental effects of testosterone remains unknown. In the current study, clinically relevant concentrations of testosterone produced increases in arterial pressure with significant effects on the mesenteric vasculature of pregnant rats. The endothelium-dependent relaxation pathway involving the NO production in endothelial cells is inhibited in systemic vessels of pregnant rats with elevated testosterone. The results suggest a role for testosterone as a possible mediator of increased vascular resistance and elevated blood pressure during pregnancy. Therefore, some of the vascular effects observed during preeclampsia may indeed be androgen-mediated. The ability of increased testosterone to influence cardiovascular function during pregnancy may contribute to some of the negative effects of testosterone on fetal growth and development. Understanding testosterone’s influences on the cardiovascular system could lead to new therapeutic approaches to antagonize some hypertensive effects during pregnancy. Furthermore, these results provide a novel approach to understanding the underlying factors that contribute to the pathogenesis of fetal origins of adult diseases.

Sources of Funding

Financial support from the National Institutes of Health through grants HD069750, HL58144, AA19446, and HL102866 is greatly appreciated.

Disclosures

None.

Footnotes

  • Received October 24, 2012.
  • Revision received December 19, 2012.
  • Accepted December 21, 2012.

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Novelty and Significance

What Is New?

  • In contrast to the well-studied beneficial roles of estrogen and progesterone in maternal cardiovascular adaptations to pregnancy, this study shows that increased maternal plasma testosterone at levels similar to those observed in preeclampsia, polycystic ovary syndrome mothers, and pregnant African American women leads to increases in mean arterial pressure and inhibition of endothelium-dependent mesenteric arterial relaxation in pregnant rats.

  • Testosterone-mediated decreases in vascular mesenteric relaxation are mediated by alterations in the endothelium-dependent NO—but not endothelium-derived hyperpolarizing factor and prostacyclin—components.

  • Testosterone-induced reductions in endothelial NO production are associated with decreased phosphorylation of excitatory endothelial NO synthase at Ser1177 and increased phosphorylation of inhibitory endothelial NO synthase at Thr495.

What Is Relevant?

  • Many pregnancy pathologies, like preeclampsia, that are associated with systemic hypertension and endothelial dysfunctions also have increased testosterone levels. Our studies imply that the cardiovascular dysfunctions observed in hypertensive disorders of pregnancy may indeed be androgen-mediated.

  • Novel compounds that may inhibit excessive androgen action might be used to reduce the severity of hypertension and endothelial dysfunction in preeclamptic patients.

  • Increased maternal testosterone levels affect fetal growth and program offspring to develop cardiovascular dysfunctions later in life. These effects of testosterone on maternal cardiovascular function may provide a novel approach to understanding the pathogenesis of fetal origins of adult diseases.

Summary

This article is the first to show that exogenous administration of testosterone to pregnant rats to increase plasma testosterone levels by 2-fold similar to that observed in abnormal clinical conditions like preeclampsia, affect cardiovascular adaptations to pregnancy. Increased testosterone impairs maternal vascular adaptations by causing hypertension and, specifically, blunting NO-mediated vasodilation in resistance mesenteric arteries.

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  • Testosterone Alters Maternal Vascular AdaptationsNovelty and Significance
    Vijayakumar Chinnathambi, Meena Balakrishnan, Jayanth Ramadoss, Chandrasekhar Yallampalli and Kunju Sathishkumar
    Hypertension. 2013;61:647-654, originally published February 13, 2013
    https://doi.org/10.1161/HYPERTENSIONAHA.111.00486
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