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

Oxytocin augments baroreflex bradycardia in conscious rats

Previous studies have demonstrated augmentation of baroreflex-mediated bradycardia by arginine vasopressin (AVP). However, the specific receptor subtype responsible for mediating this augmentation has not been determined. In the present study, experiments were performed in conscious rats to determine the possible involvement of oxytocin receptors in this response. Infusion of oxytocin at a dose that had no effect on baseline hemodynamic values significantly augmented the bradycardic response to IV bolus doses of methoxamine. Prior treatment with selective antagonists to either oxytocin, V1 vasopressinergic or V2 vasopressinergic receptors reversed this enhancement. In a separate set of experiments, baroreflex-mediated bradycardic responses to IV bolus doses of AVP were assessed. Pretreatment with the selective oxytocin receptor antagonist reversed vasopressinergic augmentation of baroreflex sensitivity. Finally, combined vasopressinergic and oxytocinergic stimulation of the baroreflex was assessed. Treatment with both AVP and oxytocin did not augment baroreflex-mediated bradycardia greater than AVP alone. We conclude from these experiments that AVP and oxytocin both augment baroreflex sensitivity, although the receptor type(s) responsible are not clear.

Increased neuropeptide Y (NPY) receptor binding in hippocampus and cortex of spontaneous hypertensive (SH) rats compared to normotensive (WKY) rats

Specific 125I-NPY binding in various brain regions of spontaneous hypertensive (SH) rats and age-matched normotensive (WKY) rats was compared. SH rats exhibited significantly greater 125I-NPY binding than WKY rats in the hippocampus (43%) and cortex (18%), but not hypothalamus, midbrain, striatum or pons-medulla. Scatchard analysis indicated that the increased 125I-NPY binding in the hippocampus of SH rats represents a greater number of NPY binding sites.

Central cardiovascular regulation and the role of vasopressin: a review

This paper will review the current state of knowledge concerning interactions between vasopressin and central neural mechanisms of cardiovascular regulation. The development of information concerning systemic cardiovascular effects of vasopressin and interactions between vasopressin and the peripheral autonomic system is outlined to provide an introduction to the topic. Major themes discussed in the rest of the paper include a survey of information suggesting direct central effects of vasopressin on autonomic control of blood pressure and heart rate and the possible localization of the central site of effect. Evidence that circulating vasopressin may act on central cardiovascular control, especially baroreflex function, is reviewed, as is the possibility of vasopressin effects on baroreflex control independent of circulating vasopressin. A survey of central pathways containing vasopressin which may be relevant to central cardiovascular actions of vasopressin is presented along with a discussion of possible regulation of activity in these pathways. Some evidence of an association between alterations in brain vasopressin levels and hypertension in experimental animals is also introduced.