Relaxin inhibits the pulsatile release of oxytocin but increases basal concentrations of hormone in lactating rats

Biology of Reproduction
A J SummerleeR S Poterski

Abstract

The effects of porcine relaxin were examined in urethane-anesthetized, lactating rats to clarify the actions of relaxin on basal levels and the pulsatile release of oxytocin during suckling. Baseline plasma oxytocin concentrations were 27.6+/-2.9 pM in unsuckled rats. They were significantly increased in rats after the onset of suckling (34.5+/-2.4 pM) compared with unsuckled animals. Oxytocin concentrations were increased further during reflex milk ejection (41.2+/-2.7 pM). Treatment with porcine relaxin (5 microg in 0.1 ml saline) caused a significant (p < 0.05) increase in plasma oxytocin compared with pretreatment concentrations or saline injection in all three groups. Frequent blood samples were taken before and during milk ejection to confirm pulsatile oxytocin associated with reflex milk ejection. Short-lived (5-10-sec) pulses with peak concentrations of oxytocin 392.4+/-122.1 pM were observed shortly before or at the time of the peak rise in intramammary pressure associated with reflex milk ejection. Relaxin (5 microg i.v.) completely suppressed the pulsatile release of oxytocin. These data suggest that relaxin increases basal secretion of oxytocin but inhibits the pulsatile secretion associated with reflex milk ejection.

Citations

Oct 24, 2006·Regulatory Peptides·Ulrike Friebe-HoffmannPhillip N Rauk
Apr 15, 2004·Endocrine Reviews·O David Sherwood
Sep 25, 2004·American Journal of Physiology. Regulatory, Integrative and Comparative Physiology·Alsadek H BogzilNick Ashton

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