Effect of angiotensin II on the reactivity of isolated mesenteric vessels to norepinephrine in rats poisoned with cadmium.
This study was designed to investigate the effect of cadmium on vascular response to norepinephrine (NE) administered before and during infusion of angiotensin II. The experiments were performed on isolated mesenteric vessels obtained from rats administered cadmium chloride intragastrically in doses of 20 mg Cd/kg body wt. once a week for 7 weeks. Changes in mesenteric vascular resistance due to NE were measured in the constant flow system as an increase in perfusion pressure. There was significant difference in the 50% effective doses (ED50) for NE between the two groups of rats when the dose-response curves were normalized to their respective maximal responses: ED50 NE for cadmium-exposed rats was lower and the dose-response curve was shifted to the left. Another change indicating an increased vasoconstrictor action of NE due to cadmium is more effective potentiation of exogenous NE responses produced by angiotensin II infused in dose of 5 mg/ml. In contrast to the controls in cadmium poisoned rats, propranolol in a dose of 300 ng/ml did not change significantly the vasoconstrictor response to NE and diminished the difference between angiotensin effect in vessels. Nifedipine (100 ng/ml), infused together with angiotensin II, inhibited pressor response to norepinephrine in preparation from both control and cadmium treated rats, to 60.5% and 69.3%, respectively. These results suggest an increase in the postsynaptic alpha adrenergic response and show a stronger potentiation of exogenous NE responses produced by angiotensin II, probably due to its influence on the calcium homeostasis in vessels of cadmium poisoned rats.