Angiotensin II Induces Carbon Monoxide Production in Isolated Rat Kidney
Chronic angiotensin II (Ang II) infusion induces vascular expression of heme oxygenase (HO)-1. HO-dependent synthesis of carbon monoxide (CO) subserves vasodilatory mechanisms. We examined whether Ang II stimulates CO production in isolated rat kidneys perfused at 7 ml/min with oxygenated Krebs buffer. We monitored perfusion pressure (PP) continuously and measured the concentration of CO in the renal venous effluent by gas chromatography/mass spectroscopy. At the conclusion of perfusion for 120 min after the onset of treatment with Ang II or vehicle, the kidneys were processed for measurement of HO activity and isoform expression. In control experiment without experimental interventions, PP and concentration of CO in the venous effluent remained stable throughout the perfusion, ranging between 78 ± 7.7 and 83 ± 5.5, mmHg and 12.3 ± 5.7 and 15.1 ± 6.6 nM, respectively. Inclusion of Ang II (1μM) into the perfusion increased PP by 31.5 ± 14, 43.5 ± 14.5, 47 ± 13, 53 ± 11.2, after 30, 60,90,120 min, respectively. Ang II also increased (p<0.05) the concentration of CO in the venous effluent from 27.1 ± 11.9, to 45.6 ± 11.7, 62.6 ± 16.7, 94.8 ± 20.7, and 101.9 ± 13.1 nM after 30, 60, 90,120 min, respectively. Importantly, the ability of Ang II to increase PP and CO concentration in the effluent were greatly attenuated in the kidneys perfused with AT1 receptor antagonist, losartan (1 μM) or protein kinase C (PKC) inhibitor, staurosporine (100nM). HO activity in control kidneys (111.03 ± 2.25, pmol/mg/4h) was exceeded by HO activity in kidneys perfused with Ang II (162.40 ± 6.95, p<0.05). These data suggest that Ang II stimulates renal production of CO via a HO dependent pathway that is subject to stimulatory regulation by PKC. The known vasoregulatory actions of CO suggest that it may serve as a counter-regulatory influence to the constrictor actions of Ang II.