Luteinizing Hormone in the Cat. I. Tonic Secretion*

Abstract

We have used a RIA system for measuring LH in the plasma of domestic cats and characterized the component of LH secretion which is controlled by negative feedback inhibition. Blood samples were collected at 6- to 10-min intervals from animals with chronically indwelling venous cannulae. The inhibitory influence (negative feedback) of gonadal secretion was evidenced by the increased plasma concentrations of LH seen 24 h after castration in 9 animals and within 5 days in all 15 cats. Restoration of negative feedback by either short or long term administration of 17 beta-estradiol reduced LH concentrations to precastration levels. In castrated animals of both sexes, the plasma concentrations of LH fluctuated episodically, with increases occurring at intervals of 20-30 min, presumably a reflection of intermittent periods of LH release. The dynamics of this pattern of LH release were simulated by the iv injection of gonadotropin-releasing hormone. In combination with our additional observation that plasma concentrations of LH decreased rapidly after treatment with four different anesthetic agents, the observations are suggestive of episodic secretion of gonadotropin-releasing hormone in the absence of negative feedback. The mechanisms regulating tonic LH secretion in this reflex ovulator appear to be more sensitive to neural stimuli but qualitatively similar to those previously described for other species in which ovulation occurs spontaneously.

Neuroendocrine Regulation of GnRH Release in Induced Ovulators

“…In cats (107), plasma LH levels increased rapidly after a single mating and peaked 20 min later. The pattern of the single matinginduced LH release was very similar to that occurring after a single injection of GnRH (106). However, a single mating bout induced ovulation in only 50% of the females studied (47,238).…”

“…Removal of the ovaries caused a rapid increase in pituitary LH secretion in rabbits (169), cats (106), ferrets (31), and voles (156). Conversely, administration of estradiol following ovariectomy suppressed plasma LH levels to those found in intact rabbits (169), cats (106), and ferrets (31). The few data (121,169) that are available on GnRH release after gonadectomy point to species differences among induced ovulators, as have been reported for spontaneously ovulating species (29,110,111).…”

“…Numerous studies (31,106,156,169) suggest that ovarian steroids exert primarily negative feedback actions on hypothalamic GnRH release and pituitary LH secretion in induced ovulators. Removal of the ovaries caused a rapid increase in pituitary LH secretion in rabbits (169), cats (106), ferrets (31), and voles (156).…”

“…This finding raises the possibility that the SCN-GnRH pathway is either absent or weakly orga-240 BAKKER AND BAUM nized in induced ovulators. In fact, ferrets show very weak circadian rhythms in locomotor activity levels (209) and in the display of maternal behavior (11).Numerous studies (31,106,156,169) suggest that ovarian steroids exert primarily negative feedback actions on hypothalamic GnRH release and pituitary LH secretion in induced ovulators. Removal of the ovaries caused a rapid increase in pituitary LH secretion in rabbits (169), cats (106), ferrets (31), and voles (156).…”

Avaliação da eficiência da eletroforese capilar como técnica analítica na prospecção de metabólitos de esteróides em extratos fecais de onça-pintada (Panthera onca)

“…Procedimentos anestésicos esporádicos para coleta de amostras de sangue podem não afetar o potencial reprodutivo, mas causam distúrbios temporários na dinâmica de secreção hormonal (amplitude do pulso e freqüência) dependendo da droga utilizada GAY, 1981;CLARKE;DOUGHTON, 1983;FULLER et al, 1984), além disso, a anestesia pode interferir ou bloquear a ovulação em gatos domésticos, por exemplo (HOWARD, 1992), contra-indicando a utilização de anestésicos no período peri-ovulatório em felinos não-domésticos.…”