Differential effects of phentolamine on the responsiveness of aortic and femoral smooth muscle from normotensive and DOCA/NaCl hypertensive rats.

The in vitro responsiveness of rat aortic and femoral arterial smooth muscle from normotensive and deoxycorticosterone acetate (DOCA)/NaCl-induced hypertensive rats to potassium chloride (KCl) and isoproterenol (ISO) in the presence and absence of the alpha-adrenergic blocker phentolamine was investigated. Femoral but not aortic smooth muscle from the DOCA/NaCl rat exhibited an enhanced sensitivity to KCl stimulation when compared to controls. Phentolamine had no effect on femoral smooth muscle from control or DOCA/NaCl rats. However, a significant decrease in the sensitivity of aortic smooth muscle responsiveness to KCl in the presence of phentolamine was observed in both the control and hypertensive groups. Isoproterenol-induced relaxation of both aortic and femoral smooth muscle was significantly attenuated in the DOCA/NaCl rat when compared to controls. Incubation with phentolamine resulted in a significant increase in the relaxation response to ISO in aortic and femoral smooth muscle from controls. This increased responsiveness, however, was not observed in DOCA/NaCl rats. The contractile response to high doses of ISO was attenuated with phentolamine in all groups. A significant increase in the sensitivity to norepinephrine (NE) was observed in both aortic and femoral smooth muscle from the DOCA/NaCl rat when compared to controls. Whereas aortic and femoral smooth muscle from the DOCA/NaCl rat which had been exposed to phentolamine previously in the experiment exhibited a significant decrease in the sensitivity to NE following a one hour washout of the phentolamine, no long-lasting effect of phentolamine was apparent in vessels from controls. The results of this study confirm previous studies that the vascular smooth muscle responsiveness to NE is increased and ISO-induced relaxation is decreased in the DOCA/NaCl rat and demonstrate that these altered adrenergic responses are similarly manifested in the femoral smooth muscle.(ABSTRACT TRUNCATED AT 400 WORDS)