The Effect of Nursing on Neurohypophyseal Hormone and Prolactin Secretion in Human Subjects*

Abstract

The effect of nursing on plasma levels of oxytocin (OT), arginine vasopressin (AVP) and PRL [prolactin] was studied in 6 normal women 2-3 days postpartum. Maternal blood samples were obtained for measurement of OT, AVP, PRL, Na and osmolality at 3 and 0 min before suckling , at 3 min intervals for 15 min during suckling and at 5 min after completion of suckling. Plasma OT rose during suckling from a mean (.+-. standard error of the mean) baseline value of 1.1 .+-. 0.2 to 3.6 .+-. 0.6 .mu.U/ml by 3 min (P < 0.001), reached a peak level of 6.4 .+-. 1.5 .mu.U/ml by 6 min (P < 0.005), and remained elevated for the entire 15 min period of suckling. Serial measurements of plasma OT during suckling failed to show a pattern consistent with episodic secretion. The baseline plasma AVP concentration was 0.4 .+-. 0.1 .mu.U/ml and was not significantly altered by suckling. Plasma Na and osmolality remained unchanged during the suckling period. The baseline serum PRL level was 268 .+-. 24 ng/ml and rose to 362 .+-. 31 ng/ml after 15 min of suckling (P < 0.05). Suckling apparently is a specific stimulus for OT and PRL secretion but has no effect on AVP release.