EFFECT OF RELAXIN ON CERVICAL DILATATION, PARTURITION AND LACTATION IN THE PIG

Porcine relaxin (600 U/day) was injected i.m. into intact and luteectomized Yorkshire pigs late in gestation in an attempt to elucidate physiological roles of relaxin in cervical dilatation, parturition and lactation. Porcine relaxin, given daily beginning either 105 or 107 days after mating and before surgical enucleation of corpora lutea (luteectomy) on day 110, significantly a) induced premature cervical dilatation, b) decreased the interval from surgery to delivery of the first neonate and c) reduced duration of delivery of all neonates in the litter compared with those parameters in luteectomized controls. Exogenous relaxin did not reduce peripheral serum progesterone concentrations and endogenous relaxin activity of the corpora lutea during late pregnancy. Although porcine corpora lutea secrete progesterone and accumulate relaxin after a prolonged period in hysterectomized pigs, there was no indication that exogenous relaxin reduced ovarian progesterone secretion. Lactation was reduced severely in intact and luteectomized dams given porcine relaxin during an extended period in late pregnancy and resulted in a severe reduction in litter survival to weaning.