Kinetic Characteristics of LH and FSH Responses to LHRH in Incubated Pituitaries from Ovariectomized or Ovariectomized, Estrogen-Implanted Rats

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Abstract
Incubated pituitary halves from ovariectomized, estrogen-implanted female rats were much more sensitive to LHRH [luteinizing hormone releasing hormone] than pituitaries from castrated, nontreated animals. LHRH in a concentration of 1885 pg/ml increased the release of LH [luteinizing hormone] and FSH [follicle stimulating hormone] from 7.3 .+-. 0.9 and 0.91 .+-. 0.13 ng/h per hemipituitary, respectively, to 21.4 .+-. 1.9 and 1.97 .+-. 0.18 ng/h in animals implanted with the steroid. In contrast, 5000 pg/ml of LHRH increased LH secretion from 3.4 .+-. 0.3 to 8.4 .+-. 0.4 ng/h in ovariectomized, nontreated animals. In pituitaries from both steroid and nontreated animals a highly significant dose response for LH and FSH secretion to the actual concentration of LHRH measured in each incubation tube by radioimmunoassay was observed. When expressed as percent of the corresponding control release, maximal stimulation of LH and FSH was comparable. Pituitaries from implanted animals provided a very sensitive bioassay for LHRH, in which amounts of the peptide lower than 100 pg/ml were detected. The apparent responsiveness to LHRH of pituitaries from estradiol-treated rats was over 20 times greater than that of pituitaries from nontreated castrates.