Effect of starvation on gonadotrophin secretion and on in vitro release of LRH from the isolated median eminence of the male rat

Abstract

A perfusion system was developed in which isolated median eminences (ME) were stimulated in vitro by depolarizing agents such as potassium and veratridine. Potassium concentrations between 30 and 80 mm released increasing amounts of luteinizing hormone\x=req-\ releasing hormone (LRH) from the MEs of starved and control rats. Veratridine at a concentration of 50 \ g=m\ m caused a more prolonged LRH release in both starved and control animals. LRH secretion in vitro was slightly, though not under all conditions, significantly greater in rats starved for 5days. The testosterone ((T)-LHck was studied by castra¬castra-ting the animals and substituting various doses of throuT implantation of T-releasT-reldifferent. The Tconcentration in plasma, which can prevent the castration-induceds much smaller in starved than in control rats. The in vitro release of LRH evoked by 80 mM potassium was not different for starved and fed rats under various feedback conditions. Both groups revealed decreased in vitro release of LRH when castrated animals were not substitutT.The effect of castration was studied from 1to 28 days.The plasma LH values rapidly increased in starved and control animals, indicating that the hypothalamic responsestration is not delayed by starvation. The release in vitro of LRH decreased from the firsthe fifthand remained constant thereafter. No significant difference between starved and fed rats was observed. The experiments indicate that the 'releasable pool' of LRH in vitro is greater under conditions of reduced LH release in vivo. The basic mechanism of depolarization-inducedm the ME is intact in starved animals.

Effect of protein deficiency on some hypothalamic and pituitary hormones in growing male lambs. An immunohistochemical study

“…This increase occurred in the same way, in both the suprachiasmatic, and the paraventricular nuclei (Fig. 10) Spyra, 1981;Warnhoff et al, 1983). This LHRH material can be released in vitro, using a depolarizing agent (Warnhoff et al, 1983).…”

“…The central mechanisms responsible for regulating the luteinizing-hormone releasing-hormone (LHRH) pulse generator in cases of malnutrition are unknown. In starved rats, LHRH stored in the median eminence (ME) increases without increasing LHRH release (Warnhoff et al, 1983). Pubertal development in mammals seems to be directly related to whole body growth (e.g.…”

“…10) Spyra, 1981;Warnhoff et al, 1983). This LHRH material can be released in vitro, using a depolarizing agent (Warnhoff et al, 1983). (Haresign, 1981;Foster and Olster, 1985), where restricted food intake reduced the concentration of circulating LH in blood, but the LH levels were immediately restored after a LHRH injection (Haresign, 1981 (Wiggins et al, 1984).…”

The Actions of Prostaglandin E₂, Naloxone and Testosterone on Starvation-Induced Suppression of Luteinizing Hormone-Releasing Hormone and Luteinizing-Hormone Secretion

“…During starvation, although LH secretion is suppressed in rats, the mediobasal hypothala mus including the median eminences (ME) contains as much or even more LHRH than that of normally fed rats [34], This indicates a defect in the release mechanisms of the LHRH neurons. However, stimulation of isolated MEs from starved rats in vitro with potassium induced a strong release of LHRH which was even greater than that from MEs from fed rats [43]. The basic release mechanism of LHRH from the neuron terminals was obviously not dis turbed.…”

“…The MEs were dissected according to the method described by Negro-Vilarei al. [24], and were superfused immediately afterwards in plastic chambers, as described by Warnhoff et al [43].…”