STARVATION-INDUCED SUPPRESSION OF PITUITARY-TESTICULAR FUNCTION IN RATS IS REVERSED BY PULSATILE GONADOTROPIN-RELEASING-HORMONE SUBSTITUTION

This study was carried out to test the hypothesis that reduced hypothalamic GnRH release is responsible for the suppression of reproductive functions during starvation. Adult male rats were kept for 4 days under total fasting (only water allowed) and injected during this time at 2-h intervals with 100 or 500 ng/kg BW of GnRH or vehicle. Serum levels of LH and FSH decreased by 30% during starvation (p < 0.05), and these effects were fully reversed by either dose of GnRH treatment. Starvation reduced the pituitary mRNA contents of the gonadotropin common-alpha- and FSH-beta-subunits by 30% and 35% in starved animals (p < 0.05 for both), but the LH-beta-subunit mRNA was unaffected. The GnRH treatments partly or totally reversed these changes, but up-regulation of the mRNA levels by GnRH was seen only in controls ad libitum. Starvation reduced the testicular and serum levels of testosterone by 84% (p < 0.01) and 42% (p < 0.05), respectively. These changes were fully reversed by the 500-ng/kg dose of GnRH treatment during fasting, but only serum T was completely reversed by the 100-ng/kg GnRH treatment. To elucidate whether fasting per se had direct effects at the gonadal level, we blocked the secretion of gonadotropins by treatment with a GnRH antagonist, and replaced the gonadotropins by injecting of hCG (10 IU/kg BW once daily) and hFSH (75 IU/kg BW once daily). No differences were observed between starved and control animals in either testicular or serum levels of T, or in accessory sex gland weights. It is concluded that the reduction of pituitary-testicular function in male rats during short-term starvation results solely from decreased secretion of hypothalamic GnRH and that it is not accompanied by direct effects of starvation on endocrine functions of the pituitary or testes.