Interaction of vasopressin and of the atrial natriuretic peptide in blood pressure control.

Studies performed on normotensive (WKY) and spontaneously hypertensive (SHR) rats indicate that SHR are more sensitive to the hypotensive effects of atrial natriuretic peptide (ANP) administered as a bolus and in iv infusion as well as to pressor infusions (but not bolus injections) of vasopressin (VP). Elevation of blood ANP significantly enhanced reflex bradycardia elicited by bolus injections of VP in WKY, having no effect on pressor responsiveness to VP in any of the strains. Infusion of VP markedely enhanced the hypotensive action of ANP in both WKY and SHR, having no effect on reflex tachycardia elicited by ANP. V1 receptor blockade did not significantly influence effects of ANP on blood pressure and HR responses. The results suggest that under certain conditions ANP and VP may interact in blood pressure control and that this interaction is modified in SHR. In studies performed on conscious dogs central application of ANP exerted no effect on VP secretion in euhydrated animals and during iv infusion of hypertonic NaCl, stimulating thirst. A weak suppressing effect was observed in 24-h dehydrated dogs. The physiological role of ANP in inhibition of VP secretion and its relevance to blood pressure control remains to be established.