Inhibition of Hypothalamic Thyrotropin-Releasing Hormone Messenger Ribonucleic Acid during Food Deprivation*

Abstract

Food deprivation in laboratory rats induces profound changes in the neuroendocrine system. We have investigated the hypothalamic and pituitary responses of the hypothalamo-pituitary thyroid axis to 48-h food deprivation in Sprague-Dawley rats. Peripheral T3 and hypophysial portal TRH were measured by RIA, and TSH beta, PRL, and pro-TRH mRNA were measured using in situ hybridization histochemistry. Peripheral total T3 was greatly reduced in food-deprived rats. Hypothalamic portal blood TRH levels declined significantly with time in control animals. The initial level of TRH in the portal blood of food-deprived rats was significantly reduced compared to that in controls, but did not fall further with time. In situ hybridization histochemistry revealed significantly lower pro-TRH mRNA in the paraventricular nucleus of food-deprived animals, while pro-TRH mRNA in the reticular nucleus remained unaltered. Furthermore, in the anterior pituitary, TSH beta mRNA decreased significantly in food-deprived animals, while PRL mRNA was unaltered. We conclude that the reduction in circulating T3 after food deprivation appears to be due primarily to decreased hypothalamic TRH synthesis and release.

α-Melanocyte-Stimulating Hormone Is Contained in Nerve Terminals Innervating Thyrotropin-Releasing Hormone-Synthesizing Neurons in the Hypothalamic Paraventricular Nucleus and Prevents Fasting-Induced Suppression of Prothyrotropin-Releasing Hormone Gene Expression

“…These observations raise the possibilities that AGRP may have actions on pro-TRH neurons independent of its antagonism of ␣-MSH, either directly on the melanocortin receptor itself or through a separate receptor (Graham et al, 1997;Bures et al, 1998), and that only a subpopulation of hypophysiotropic pro-TRH neurons in the PVN is under direct control by ␣-MSH. Nevertheless, whereas fasted animals receiving only vehicle intracerebroventricularly showed a significant reduction in pro-TRH mRNA in the PVN compared with fed controls, as reported previously (Blake et al, 1991;Legradi et al, 1997), the administration of 300 ng of ␣-MSH intracerebroventricularly every 6 hr completely reversed the effect of fasting on pro-TRH gene expression, resulting in a hybridization pattern that was identical to that of the fed animals in all parvocellular subdivisions of the PVN. No selectivity for increased pro-TRH mRNA in periventricular parvocellular neurons was apparent.…”

Hormone and metabolite changes associated with extended breeding fasts in male northern elephant seals (Mirounga angustirostris)

“…Fasting is generally associated with down-regulation of metabolic rate via suppression of the thyroid axis (Spencer et al, 1983;Blake et al, 1991;Boelen et al, 2008). We found no changes in total thyroid hormones across the fast.…”

Daylong pituitary hormones in morbid obesity: effects of bariatric surgery

“…In fact, starvation acts, at least in part, by suppressing TRH expression in the PVN; TSH production falls, followed by a drop in T 4 and T 3 levels. 57 However, patients subjected to biliopancreatic diversion eat normal diets; thus, malabsorption rather than undereating should generate 'starvation' signals to the midbrain. In any case, a drop in circulating leptin levels stands out as the dominant, and perhaps sufficient, signal-suppressing TRH in the PVN.…”