Moderate and severe nutrient restriction has divergent effects on gonadotroph function in orchidectomized sheep

The effect of plane of nutrition and estradiol (E-2) on pituitary concentrations of GnRH receptor and GnRH receptor mRNA was assessed in orchidectomized sheep (wethers). As detailed in the companion paper, 36 wethers were fed to gain, maintain, or lose body weight. Six animals from each feeding group received E-2 (0.31 mu g E-2/50 kg per h) or vehicle during Days 51-54 of controlled feeding. Anterior pituitary tissue was collected at the end of infusion. Both moderate and severe nutrient restriction increased (p < 0.05) tissue concentrations of FSH and FSH beta mRNA. Conversely, concentrations of GnRH receptor and receptor mRNA were not affected (p > 0.05) by plane of nutrition. Estradiol increased (p < 0.05) GnRH receptor and receptor mRNA in wethers fed to gain or maintain weight. However, this E-2-induced response was not evident in wethers subject to severe nutrient restriction. These data demonstrate that severe, but not moderate, nutrient restriction suppresses E-2-induced augmentation of tissue concentrations of GnRH receptor and GnRH receptor mRNA. Collectively, the data presented here and in the companion paper suggest that severe nutrient restriction leads to physiologic changes that render the hypothalamus increasingly sensitive to estrogenic stimulation, while the pituitary is made less responsive to steroidal inputs.