Influence of starvation on testosterone-luteinizing hormone feedback in the rat

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Abstract
After 5 days of starvation, the body weight of adult male Wistar rats was on the average 34% lower than that of control animals. Luteinizing hormone (LH) and testosterone in plasma were significantly decreased in the starved animals (-95 and -82% on the average). The in vivo response to human chorionic gonadotropin (10 IU/animal for 3 days) was not diminished in the starved rats. The in vivo stimulation with synthetic LRH [luteinizing hormone-releasing hormone] (100, 200, 500 and 1000 ng/kg body wt i.v.) caused an increase of LH at all doses. The response, however, was quantitatively decreased in starved rats. The pituitary content of the LH and the LRH content in the preoptic area and in the hypothalamus were not influenced by starvation; the LRH content, however, was greatly increased in the median eminence (33.2 .+-. 11.7 vs. 15.5 .+-. 7.1 ng/mg protein). The feedback was studied by castrating the animals and implanting silastic tubes of various sizes which released testosterone. The plasma levels of testosterone were proportional to the length of the capsules used. LH levels increased greatly (> 90 ng/ml) when testosterone levels were lower than 1.80 ng/ml in the control rats. The starved rats tolerated testosterone levels as low as 1.00 ng/ml plasma before LH was elevated. The LRH content in the median eminence increased in starved and control animals when plasma levels of testosterone dropped below 1.80 ng/ml. The increased sensitivity of the testosterone-LH feedback may be caused by an impaired release of LRH from the median eminence.