Ovulation Induced by LH-RH in Rats Made Anovulatory by Various Experimental Procedures

Abstract

The injection of LH-RH induced ovulation in constant estrous rats (CEA), made anovulatory either by frontal hypothalamic deafferentation (FHD), or by exposure to continuous light (CL), or by neonatal androgenization (NA) with 0.500 mg testosterone propionate (NA500). Rats neonatally treated with 1.250 mg testosterone (NA1250) were almost unable to ovulate. 100% of FHD-CEA rats ovulated in response to 10 ng LH-RH, which is 1/3 of the lowest dose able to determine 100% of full ovulation in control pro-estrous rats. NA500-CEA rats, on the other hand, ovulated in response to doses comparable to those effective in the controls, whereas in CL-CEA rats the doses required for full ovulation were 2–3 times higher than in the controls. The results of these experiments demonstrate that the pituitary glands of CEA rats respond to the stimulation by the specific hypothalamic releasing factor. The pituitary response, however, appears enhanced in FHD-CEA rats and markedly depressed in CL-CEA animals.

Preovulatory changes in luteinizing hormone releasing hormone concentrations in peripheral plasma in constant estrous rats at induced ovulation.

“…The duration of this "autonomous" LH secretion might have some relationship to the so-called responsiveness of the pituitary to LHRH or the amount of LH released in response to a certain LHRH stimulation. The much shorter length of LH secretion maintained at a plateau level in this study (70min at most) than that in proestrous rats during the preovulatory period (approximately 2h, Blake, 1976) could partly be attributed to the depressed pituitary responsiveness to LHRH in lightestrous rats (Trentini et al, 1977). The plasma concentration of LHRH sharply declined between 10 and 20min post-stimulation.…”