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

Abstract

Incubated pituitary halves from ovariectomized, estrogen-implanted female rats were shown to be much more sensitive to LHRH than pituitaries from castrated, nontreated animals. LHRH in a concentration of 1,885 pg/ml increased the release of LH and FSH from 7.3 ± 0.9 and 0.91 ± 0.13 ng/h/hemipituitary respectively to 21.4 ± 1.9 and 1.97 ± 0.18 ng/h in animals implanted with the steroid. In contrast, 5,000 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 found to be over 20 times greater than that of pituitaries from nontreated castrates.

Biphasic Pattern of Follicle Stimulating and Luteinizing Hormone Responses to Gonadotropin-Releasing Hormone in vitro

“…Its presence appears to be testosterone-dependent in the male. The sec ond population has a lower affinity, which corresponds well to that found by other authors who assessed the biolog ical effect of LHRH [7,13] or binding properties of labelled LHRH to pituitary membranes [3,4,14]. Under our experi mental conditions, the active LHRH analog is about 7 times more potent than the naturally occurring peptide.…”

“…The lower affinity stimulation is comparable to that described previously [7,8,13]. The higher affinity stimulation is much smaller in amplitude, but consistent on both FSH and LH for all concentrations tested between 10 '-' and 10-*° M. This weak stimulation cannot be attributed to the tissue extract itself, since all baseline values were calculated after pitui tary incubation in the absence of LHRH, but with the same amount of ATE.…”

“…The higher affinity stimulation is much smaller in amplitude, but consistent on both FSH and LH for all concentrations tested between 10 '-' and 10-*° M. This weak stimulation cannot be attributed to the tissue extract itself, since all baseline values were calculated after pitui tary incubation in the absence of LHRH, but with the same amount of ATE. This does not contradict previous reports [13] showing a weak stimulating effect of acidic extracts on LH secretion, since 10-to 100-fold higher concentrations of tissue were necessary under those conditions to produce the effect.…”