Short-term hormonal responses to food intake in peripubertal female rats

Abstract

These studies focused on the phenomenon of "catch-up" pubertal development. Circulating levels of several hormones were characterized in 8-wk-old female rats whose growth and reproductive development had been blocked before puberty by restricting their food intake. Some of these females were fed ad libitum for 24 h to initiate rapid pubertal development. Blood levels of luteinizing hormone (LH) and growth hormone (GH) were suppressed by food restriction and then partially restored to adult diestrus levels by 24 h of ad libitum feeding. Prolactin titers were also suppressed by food restriction but not significantly elevated by 24 h of ad libitum feeding. Circulating levels of follicle-stimulating hormone (FSH) and thyroid-stimulating hormone (TSH) were unaffected by either treatment. It is concluded that GH could play an active supplementary role to LH in eliciting catch-up pubertal development but that FSH and TSH could play only passive roles at best. The role of prolactin remains uncertain. On a finer time scale, when food-restricted females were examined in relation to the time of day at which they were fed, most showed high-amplitude LH pulses 2-4 h after eating but rarely at any other time. Thus under some conditions LH secretion can be modulated by food intake on an almost hour-by-hour basis. Overall, blood levels of corticosterone were generally but not always inversely correlated with the frequency of LH pulsing in these experiments. Finally, the present results argue against the concept that puberty is dependent on a critical whole body characteristic.(ABSTRACT TRUNCATED AT 250 WORDS)

Central infusion of leptin into well-fed and undernourished ewe lambs: effects on feed intake and serum concentrations of growth hormone and luteinizing hormone

“…Also of note is the dichotomy of neuroendocrine responses to the undernourished condition exhibited by ruminants and rodents, especially in the somatotrophic axis. Because nutrient-restricted rodents exhibit reduced GH concentrations (Tannenbaum et al 1979, Sisk & Bronson 1986, Bronson & Heideman 1990, Bruno et al 1990) whereas nutrient-restricted ruminants and most other livestock and primates exhibit increased GH concentrations (Vandergrift et al 1985, Phillips 1986, Gluckman et al 1987, Foster et al 1989, Thissen et al 1994, it may be premature to extrapolate the somatotrophic responses of rodents to nutrient restriction in order to predict responses within ruminants or other species.…”

Hypothalamic pathways linking energy balance and reproduction

“…GnRH pulses are readily suppressed by food restriction, high or low ambient temperature, or excessive exercise, and GnRH pulsatility returns rapidly when the energetic challenge is alleviated, usually in one to two hours. Both males and females of a large number of species exhibit this suppression despite the fact that a temporary halt to spermatogenesis is unlikely to have any long-term reproductive consequences in the male (11,39,73). …”

Fasting and Glucose Effects on Pituitary Leptin Expression

“…Also, Schneider et al report that LH pulses lost by fasting can be restored within a few hours by nutrition alone (Schneider et al 2000(Schneider et al ,2002. The timing of this response was too rapid for it to have been due to the restoration of adipocyte leptin (Bronson 1986;Bronson and Heideman 1990;Cameron 1996).…”