Immunoreactive and bioactive LH release from pituitaries of intact or castrated male rats: Effect of in vitro GnRH and KCl administration

• Published in: Journal of endocrinological investigation 1997-07, Vol.20 (7), p.381-386
• Main Authors: VALENTI, S, SARKISSIAN, A, GIUSTI, M, GIORDANO, G, DAHL, K. D
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Gonadotropin-Releasing Hormone - pharmacology; Hormones and neuropeptides. Regulation; Hypothalamus. Hypophysis. Epiphysis. Urophysis; In Vitro Techniques; Luteinizing Hormone - secretion; Male; Orchiectomy; Pituitary Gland - drug effects; Pituitary Gland - secretion; Potassium Chloride - pharmacology; Rats; Rats, Sprague-Dawley; Vertebrates: endocrinology
• ISSN: 0391-4097; 1720-8386
• DOI: 10.1007/BF03347988

The in vitro immunoreactive (i-LH) and bioactive (b-LH) LH release from hemipituitaries of intact adult male rats (INT) or rats castrated 7 days earlier (CAS) was studied. Hemipituitaries were incubated for 30 min (time 1) plus an additional 30 min (time 2) with GnRH (10 nM) and/or KCl (50 mM), according to one of the following protocols: media alone (C), KCl+KCl (K/K), GnRH+GnRH (G/G), KCl+GnRH (K/G), GnRH+KCl (G/K). All of the hemipituitaries were further incubated in media alone for 120 min (time 3). I-LH, b-LH and i-FSH were assayed on the media. In both models, the highest bioactive:immunoactive (b/i) ratio was noted during time 1; however, CAS always secreted more b-LH than INT at any given time of the study. In INT, GnRH--but not KCl--administration during time 2 resulted in blunted i-LH. During the same time, the b/i ratios decreased in all groups but G/K. LH secretion recovered during time 3 in all groups. In CAS, i-LH levels comparable to those of time 1 were sustained by either stimulus during time 2, while the b/i ratios were markedly decreased. LH secretion recovered in the K/K group during time 3. These results suggest that: 1) promptly releasable pools of b-LH are available in both models; 2) CAS always secrete more b-LH; 3) in INT, desensitization occurs involving parallel changes in both i-LH and b-LH, while changes in b-LH rather than i-LH are noted in CAS; 4) prolonged KCl administration might play a role in new gonadotropin synthesis and/or release.