The blockade of opioid system increases oxytocin secretion in suckling rats with deficient lactation.

PIETROBON EO; JAHN GA; NEIRA FJ; MACKERN-OBERTI JP; SOAJE M; PENNACCHIO GE; MORENO-SOSA MT; VALDEZ SR

Mendoza

Congreso; XXXIV Reunión Científica Anual de la Sociedad de Biología de Cuyo; 2016

Sociedad de Biología de Cuyo

Oxytocin (OT) and prolactin (PRL) are essential hormones for a successful lactation and OT acting at pituitary level was proposed as a putative prolactin-releasing factor (PRF). An opioid restraint of OT secretion is developed during late gestation but declines in the postpartum. Our aim was to evaluate if blockade of opioid action may influence OT regulation in response to suckling in hypoprolactinemic OFA hr/hr rats characterized by a failure in lactation compared with Sprague-Dawley rats (SD) their strain of origin. Mid-lactating OFA and SD rats separated from their pups for 12 h and subsequently subject to suckling during 2 and 4 h were treated with the opioid antagonist naltrexone (NTX; 5 mg/kg, ip; 8.00 h) or saline and decapitated at 12.00 h. Serum OT levels were measured by RIA, weight gain of the litters was determined and the expression of OT receptor (OTR) in the anterior pituitary was measured by western blot. After suckling OT release and litter weight gain were higher in SD rats compared with OFA rats. NTX treatment increased OT secretion only in OFA rats and after 2 h of suckling an increase in weight gain was observed. After suckling during 4 h an increase of OTR expression was observed in OFA rats. The results obtained show that the opioid restrain of OT secretion is still operating during lactation in OFA rats suggesting another mechanism involved in the failure of the lactation observed in these rats. The higher OTR expression in anterior pituitary in suckling rat supports the proposal that OT may act as a PRF.