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

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

Mendoza

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

Sociedad de Biología de Cuyo

Oxytocin (OT) and prolactin (PRL) are essentialhormones for a successful lactation and OT acting at pituitary level wasproposed as a putative prolactin-releasing factor (PRF). An opioid restraint ofOT secretion is developed during late gestation but declines in the postpartum.Our aim was to evaluate if blockade of opioid action may influence OT regulationin response to suckling in hypoprolactinemic OFA hr/hr rats characterized by afailure in lactation compared with Sprague-Dawley rats (SD) their strain oforigin. Mid-lactating OFA and SD rats separated from their pups for 12 h andsubsequently subject to suckling during 2 and 4 h were treated with the opioidantagonist naltrexone (NTX; 5 mg/kg, ip; 8.00 h) or saline and decapitated at12.00 h. Serum OT levels were measured by RIA, weight gain of the litters wasdetermined and the expression of OT receptor (OTR) in the anterior pituitarywas measured by western blot. After suckling OT release and litter weight gainwere higher in SD rats compared with OFA rats. NTX treatment increased OTsecretion only in OFA rats and after 2 h of suckling an increase in weight gainwas observed. After suckling during 4 h an increase of OTR expression was observedin OFA rats. The results obtained show that the opioid restrain of OT secretionis still operating during lactation in OFA rats suggesting another mechanisminvolved in the failure of the lactation observed in these rats. The higher OTRexpression in anterior pituitary in suckling rat supports the proposal that OTmay act as a PRF.