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(Hypertension. 1995;26:290-293.)
© 1995 American Heart Association, Inc.

Articles

Insulin Modulation of Vascular Reactivity Is Already Impaired in Prehypertensive Spontaneously Hypertensive Rats

Giuseppe Lembo; Guido Iaccarino; Carmine Vecchione; Virgilio Rendina; Bruno Trimarco

From IRCCS Sanatrix, Pozzilli (G.L., C.V.), and the Department of Internal Medicine, School of Medicine, Federico II University, Naples (G.I., V.R., B.T.), Italy.

Correspondence to Bruno Trimarco, MD, Medicina Interna, Federico II University, via S. Pansini 5, 80131 Napoli, Italy.

Abstract Hyperinsulinemia reduces the vasoconstrictive response to norepinephrine in Wistar-Kyoto rats (WKY) but not in spontaneously hypertensive rats (SHR). It has been hypothesized that this difference in the vascular effect of insulin could be a hallmark of the hypertensive state. To test this hypothesis we studied SHR before (5 weeks old, n=10) and after (15 weeks old, n=10) the establishment of hypertension as well as two groups of age- and sex-matched WKY (5 weeks old, n=14; 15 weeks old, n=13). Blood pressure was significantly higher in SHR compared with WKY (181±5 versus 118±6 mm Hg, respectively, P<.001) in the 15-week-old rats but not in the 5-week-old rats (121±5 versus 117±3 mm Hg, P<NS). We tested vascular reactivity using increasing amounts of norepinephrine (from 10^-10 to 10^-5 mmol/L) on isolated aortic rings in control conditions and after 30 minutes of exposure to 715 pmol/L insulin. In WKY insulin reduced the vascular response to norepinephrine in both the 5-week-old (repeated-measures ANOVA with grouping factor: F=2.443, P<.05) and 15-week-old (F=9.667, P<.01) groups. In SHR at both ages insulin failed to modify the vascular response to norepinephrine (5 weeks: F=0.107, P<NS; 15 weeks: F=0.075, P<NS). Sodium nitroprusside was able to attenuate the vascular response to norepinephrine in WKY and SHR at 5 and 15 weeks. Our data demonstrate that in SHR the vascular resistance to insulin action is specific and not acquired with the hypertensive condition; thus, it seems to be a genetically inherited trait.

Key Words: insulin resistance • hyperinsulinemia • aortic rings • norepinephrine • hypertension, genetic

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