RESUMEN
Long-term administration of nitrendipine [N] in DOCA hypertensive rats for four weeks led to a significant decrease in systolic blood pressure [SBP] accompanied by a temporary increase in heart rate [HR]. the relationship between Alpha adrenoreceptors and the sensitivity of contractile responses induced by norepinephrine [NE], phenylephrine [PE] and clonidine [CL] in the presence of [N] was also investigated on isolated aortic strips from normotensive and DOCA hypertensive rate. Nitrendipine [10-5 M] suppressed NE, PE and CL induced responses both in DOCA hypertensive and normotensive rats only in the presence of each agonist [starting from 10-7 M]. this might be due to a decrease in the slow component of the contractile responses which depend mainly on the extracellular ca-influx. NE, PE and CL elicited contractile responses with greater magnitude in aorta from DOCA rats than from normotensive rats, probably due to increased vascular responsiveness in the hypertensive rats. It can be concluded that [N] is an effective antihypertensive agent which caused minor increase in HR eventually attenuated. The differential responses to NE, PE and CL in DOCA hypertensive and normal rats may be due to increased sensitivity of the postsynaptic Alpha adrenoreceptors in the DOCA hypertensive rats