Baroreceptor influences on oxytocin and vasopressin secretion

Abstract

The objective of these studies was to investigate the role of arterial baroreceptors in the control of neurohypophyseal secretion. The effect of sinoaortic denervation on basal and osmotic-induced release of oxytocin and vasopressin and on blood pressure was determined. Hypertonic or isotonic saline was infused intravenously into sham-operated or denervated rats 3 days after surgery. Plasma oxytocin and vasopressin were measured at 5 and 15 minutes after the infusion. The control levels of oxytocin were increased in the denervated rates, but vasopressin levels were not significantly altered. The vasopressin and oxytocin responses to hypertonic saline were greater after baroreceptor denervation. Plasma oxytocin was increased from 4.7 ± 0.9 to 72.2 ± 8.7 pg/ml in the denervated rats and from 1.8 ± 0.3 to 39.9 ± 6.7 pg/ml in the sham-operated control group at 5 minutes after the infusion (p < 0.01). The plasma vasopressin response to hypertonic saline was 7.1 ± 0.6 pg/ml in the sham-operated versus 11.1 ± 1.6 pg/ml in the denervated rats (p < 0.05). There was no difference between sham-operated and denervated rats in the effect of hypertonic saline on plasma sodium and hematocrit. Mean arterial blood pressure was increased after sinoaortic denervation (116.3 ± 4.2 mmHg in the sham-operated vs. 138.2 ± 8.3 mmHg in the denervated rats, p < 0.05); however, there was no difference in the pressor response to hypertonic saline. These results show that the baroreceptor system influences the secretion of both oxytocin and vasopressin, with effects on basal secretion as well as the response to an osmotic stimulus. These changes may be important in the regulation of cardiovascular and fluid balance under conditions of barorecptor deficiency.