Ovariectomy leads to a rapid increase in rat placental lactogen secretion

Serum placental lactogen (rPL) levels were measured by RIA in late pregnant rats subjected to a number of endocrine ablations. Adrenalectomy or unilateral ovariectomy had no significant effect on serum rPL levels. Hypophysectomy of the dam at midpregnancy resulted in a significant increase in serum rPL at late pregnancy. Bilateral ovariectomy of day-14 or -16 pregnant rats led to a rapid increase in serum rPL levels for 2 days followed by a gradual decrease as fetuses were reabsorbed or aborted. Adrenalectomy combined with ovariectomy led to sustained, elevated levels of serum rPL which were greater than those seen with bilateral ovariectomy alone. When progesterone (4 mg/rat X day) and estrone (500 ng/rat X day) or 17 beta-estradiol (100 or 200 ng/rat X day) were administered to ovariectomized pregnant rats, serum rPL remained elevated and the conceptuses were retained. In conclusion our studies have shown that ovarian and adrenal factors influence rPL secretion.