The intra-assay coefficient of variation for GnRH was described by the formulay= 3

The intra-assay coefficient of variation for GnRH was described by the formulay= 3.38X+ 3.14/100. GnRH release from male marmoset monkey hypothalamic tissue and compares release dynamics directly with those obtained from male rat, suggesting a species difference in feedback regulation of GnRH release. Keywords:hypothalamus, tissue culture, monkey, luteinizing hormone releasing hormone the hypothalamic decapeptidegonadotropin-releasing hormone (GnRH) I is responsible for controlling pulsatile gonadotropin release through its binding to pituitary gonadotrope cell membrane type I GnRH receptors in all vertebrates studied (14,25). In most mammals, the gonadotropins released are luteinizing hormone (LH) and follicle-stimulating hormone (FSH), but New World monkeys, such as common marmosets, utilize pituitary release of chorionic gonadotropin (CG) and FSH to control steroidogenesis and gametogenesis (15). Our focus in this study is to investigate GnRH release dynamics and testicular hormone-mediated feedback regulation of GnRH release in a small-bodied (350400 g) male New World primate, the common marmoset (Callithrix jacchus), in which pituitary gonadotropin stimulation of the testis differs from most mammalian species (15). We ascertained GnRH release dynamics from hypothalami isolated from testis-intact and gonadectomized male marmosets. In this regard, testosterone (T) provides the major testicular-mediated negative feedback regulation of gonadotropin release at the anterior pituitary, as exemplified by a number of animal models (14). Although male marmosets demonstrate Gimap5 expected changes in circulating gonadotropin levels following castration, postcastration estradiol replacement, and GnRH antagonist therapy (24), postcastration T replacement studies have not been performed. Broxyquinoline Investigations in male rhesus monkeys have been limited to measurement of GnRH tissue content; orchidectomy of rhesus monkeys decreases overall hypothalamic GnRH content while increasing GnRH content in the median eminence (35), and T treatment decreases GnRH content in the median eminence while increasing overall hypothalamic GnRH content (34). These studies are consistent with T-regulated negative feedback on GnRH release, but measurements of the effects of orchidectomy on GnRH release, either in vivo or in vitro, have not been performed in males of Broxyquinoline any primate species. The role of T in regulating hypothalamic release of GnRH has been investigated more extensively in model systems such as the rat and ram. The role of T, however, either mediated via androgen receptors or following aromatization to estrogen (17), in regulating hypothalamic GnRH release remains controversial. In an extensive review of this area, Kalra and Kalra (17) made a compelling argument refuting the notion that castration of male rats leads to an increase in hypothalamic GnRH secretion and that T replacement inhibits GnRH release. Our recent findings in male rats (50) are consistent with Kalra and Kalra’s (17) assertion. In vitro GnRH release from hypothalami collected from sham surgery (testis-intact) and gonadectomized male rats was similar in both male groups (50). In the ram, the only other animal model in which the direct effects of T on hypothalamic GnRH release have been assessed, Broxyquinoline T was demonstrated to show classical negative feedback on GnRH release (45). The issue of T-mediated negative feedback regulation of hypothalamic GnRH release in both male rats and primates is therefore still open to question. The present study employs a proven in vitro method for sequential sampling of GnRH release from hypothalamic explants, developed for both rats (46,48,49,51) and marmosets (42), to initiate an investigation of the regulatory control of reproductive neuroendocrine function in adult male marmoset monkeys and rats. In this first in vitro measurement of GnRH release from male marmoset Broxyquinoline hypothalamic explants, we also examine a novel physiological challenge to the neuronal network that regulates GnRH release in males. Oxytocin is implicated in the stimulation of hypothalamic GnRH release in.