Pituitary Responsiveness to Luteinizing Hormone-Releasing Factor in Normal and Androgenized Female Rats¹

In order to compare directly the functional responsiveness of the pituitary gland in the androgenized rat with that of the normal female, luteinizing hormone-releasing factor (LRF) was administered intravenously and plasma and pituitary luteinizing hormone (LH) was measured utilizing a radioimmunoassay. Just prior to the critical period proestrous normal adult females received an ovulation blocking dose of pentobarbital; androgenized rats were similarly treated. Blood was collected by jugular puncture and then 0.1, 1.0, 10, 100 or 500 ng LRF/100 g body wt was administered. The rats were bled 15 minutes later and decapitated after 45 minutes at which time trunk blood and anterior pituitary glands were collected. Pituitary response to LRF as measured by plasma LH was identical in both groups of rats except at the 500 ng dose. Pituitary LH concentration was significantly reduced only in the androgenized rats given the 500 ng dose of LRF. Ovarian sensitivity to LH was also measured by studying the ovulatory response to exogenous LH. Ovarian sensitivity to LH in normal pentobarbital blocked proestrous females was found to be approximately 5–10 times greater than in similarly treated androgenized females. Thus, although the ovary of the androgenized rat is relatively insensitive to LH, the ability of the pituitary to respond to LRH is not affected by neonatal steroid exposure. Both the normal proestrous and androgen-sterilized female are capable of releasing equivalent amounts of LH in response to adequate LRF stimulation. (Endocrinology95: 412, 1974)