HYPER-SECRETION OF LUTEINIZING-HORMONE FOLLOWING OVARIECTOMY AND ESTROGEN ADMINISTRATION IN RATS BEARING ANTERIOR-PITUITARY TRANSPLANTS

Secretion of luteinizing hormone (LH) and prolactin was determined in rats bearing anterior pituitary transplants under the renal capsule and in cycling diestrous rats (controls). Control rats were ovariectomized (OVX) during the diestrous period of the estrous cycle and the rats bearing pituitary transplants were OVX during the diestrous period of recurring pseudopregnancies. Plasma LH was less than 30 ng/ml in intact animals and remained unchanged for several days following OVX in control rats. Plasma LH fluctuated for several days following OVX in 19 of 45 rats bearing pituitary transplants under the renal capsule. The plasma concentration of prolactin was 104 ± 6 ng/ml (mean ± SEM) in rats bearing pituitary transplants and remained unchanged following OVX. In control rats, plasma prolactin concentrations were 43 ± 4 ng/ml and fluctuated in 11 of 37 rats following OVX. Silastic capsules of estradiol-17β implanted on Day 2 following OVX on Day 1 stimulated surges of LH (but not of prolactin) in rats bearing anterior pituitary transplants; plasma LH reached peak concentrations of 776 ± 102 ng/ml on Day 3 and 433 ± 48 ng/ml on Day 4. In OVX control animals implanted with estradiol-17β, LH and prolactin surges were both observed. Peak concentrations in plasma LH were 116 ± 34 ng/ml on Day 3 and 213 ± 40 ng/ml on Day 4 and these values were significantly below those in rats bearing pituitary transplants. Plasma progesterone concentrations were significantly (P<0.01) higher in rats bearing pituitary transplants than in cycling diestrous rats and decreased in all animals following OVX. It is concluded that, in rats bearing pituitary transplants, an augmented secretion of LH can be initiated by OVX and estrogen administration.