Acute aortic coarctation hypertension: role of vasopressin and angiotensin II.

The role of vasopressin (AVP) and angiotensin II (ANG II) in the onset of acute (45 min) aortic coarctation hypertension was studied in conscious rats. Changes in mean carotid pressure (MCP) and heart rate (HR) were measured in four groups of rats. Control rats presented a hypertensive response that attained a plateau 5 min after coarctation and remained near this level throughout the experiment. Rats treated with AVP V1-vascular receptor antagonist [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid), 2-(O-methyl)tyrosine]arginine vasopressin [d(CH2)5Tyr(Me)AVP] presented a prompt rise in MCP similar to the control rats, but in contrast to this group, the MCP started to decline progressively. Rats treated with saralasin presented a delay in the onset of hypertension right after coarctation but slowly attained values similar to those for control rats. In contrast, the rats treated with AVP antagonist plus saralasin showed a blunted MCP elevation throughout the experiment. Reflex bradycardia observed in the rats treated with saralasin or the AVP antagonist plus saralasin was similar to that observed in the control rats, whereas for the group treated only with AVP antagonist, the reflex bradycardia was more intense than for the other three groups, indicating an increased sensitivity of the baroreflex. These data demonstrate that in addition to the mechanical effect of aortic constriction, both ANG II and AVP participate in the onset of acute aortic coarctation hypertension. Moreover, the results indicate that ANG II acts on the prompt (5 min) rise in pressure, whereas AVP is responsible for the maintenance (30-45 min) of the arterial pressure elevation.