Ovarian Progestin Secretion in Lactating Rats: Effect of Intrabursal Injection of Prolactin Antiserum, Prolactin and LH

Abstract

The control mechanism of progestin secretion by the rat ovary during lactation was studied by measuring levels of progesterone (P) and 20α-hydroxypregn-4-en-3-one (20α-OH-P) in ovarian venous blood of rats nursing 8 or 2 pups after intra-periovarian bursal (i.b.) injection of antiserum to rat prolactin (prol.AS), rat prolactin or ovine LH. Control groups receivednormal rabbit serum (NRS) or were untreated. The sera or hormone solution was injected i.b. on day7 of lactation. Twenty-four hr after the injection ovarian venous blood was collected and the steroids measured by gas-liquid chromatography. In control groups P secretion rate was significantly higher in the 8-pup than in the 2-pup group. P secretion rate was significantly lower in prol.AS-treated rats than in control NRS-treated rats, whereas 20α-OH-P secretion rate was not altered by the treatment. Rat prolactin did not increase P secretion over controls. A large dose of LH resulted in a significant decrease in P secretion in the 8-pup group, but it tended to increase in the 2-pup group. Treatment with prol.AS † LH resulted in a marked decrease in P secretion in both 8- and 2-pup groups, but the values were not significantly different from those obtained in prol.AS-treated groups. These results indicate that prolactin plays an important role in the P secretion of lactating rats arid the regulation of P secretion by LH is variable, depending on theintensity of lactation. The results also suggest that the luteotrophic complex can be of variable types as to the amount and ratio of LH and prolactin. (Endocrinology94: 829, 1974)