Inhibition of pressor responses induced by electrical stimulation of the mesencephalon by vasopressin and oxytocin.

Receptors for vasopressin are present in blood vessels, kidney and the brain. Earlier studies indicated that the memory and learning effects of vasopressin are exerted via receptor sites in the brain and that the classical hormonal effects in the periphery can be dissociated in the molecule from the central action. Vasopressin also affects blood pressure regulation. Arg8-vasopressin (AVP) and oxytocin upon intracerebroventricular administration reduced the pressor response elicited by electrical stimulation of the rat mesencephalic reticular formation. Desglycinamide-AVP also exerted this effect. Lesion and microinjection studies revealed that the dentate gyrus of the hippocampus may be a site of action of AVP or its active fragments, inhibiting central pressor responses. Oxytocin appeared to act on structures in the vicinity of the fourth cerebral ventricle.