Prolactin administration during the follicular phase of cyclic sows

Abstract

This study was designed to examine the influence of exogenous prolactin (PRL) on ovarian steroid secretion, during the follicular phase in cyclic sows. Eleven multiparous sows were randomly assigned to a control ( n=4) or PRL-treated ( n=7) group. Sows were cannulated into the jugular vein (JV) and the utero-ovarian vein (UOV) on Day 11 of the estrous cycle. Blood was sampled hourly on Days 13–20. Samples taken via the JV were assayed for PRL and UOV samples were analyzed for progesterone (P 4), androstenedione (A 4), testosterone (T), estrone (E 1) and estradiol-17β (E 2). Porcine PRL (pPRL KK-3) was administered hourly (via UOV cannula) for 48 h commencing on Day 15 of the cycle. If administration of PRL started before luteolysis ( n=3), it did not affect the mean steroid concentrations except those of E 1, which were significantly elevated in comparison with controls. When PRL administration started after luteolysis ( n=4), it caused decreases in both of the estrogens, which were maintained until the end of the experiment. PRL also reduced A 4 concentrations, but only during PRL administration. The PRL effect on T concentrations was less pronounced in these sows. The present data indicate that exogenous PRL administered after luteolysis inhibits ovarian steroid secretion in sows.