EFFECT OF CHRONIC FOOD RESTRICTION ON PULSATILE LUTEINIZING-HORMONE SECRETION AND HYPOTHALAMIC NEUROPEPTIDE-Y GENE-EXPRESSION IN CASTRATE MALE SHEEP

Castrate male sheep (wethers, average liveweight 38 +/- 0.6 kg) were g iven one of the following diets for 10 weeks followed by euthanasia (n =8/group): high-energy high-protein providing 1.5 times the energy req uired to maintain Liveweight (maintenance) (group 1.5M), low-energy lo w-protein at 0.5 maintenance (0.5M), or low-energy high-protein at 0.5 maintenance (0.5M+P). 1.5M wethers gained 22% liveweight whereas 0.5M and 0.5M+P wethers lost 18 and 13% liveweight respectively. Relative to the 15M group, the 0.5M and 0.5M+P soups had similar plasma concent rations of glucose and cortisol throughout, but elevated non-esterifie d fatty acids (P<0.001) and reduced IGF-I and insulin (P<0.05, 0.01 or 0.001) from 1 week onwards. Each week blood samples were taken every 12 min for 4 h and plasma assayed for LH. Mean concentration over 4 h, LH pulse frequency and LH pulse amplitude showed no progressive chang e in 1.5M sheep. However, in both 0.5M and 0.5M+P groups mean LH incre ased (P<0.001 and P<0.01 respectively), pulse frequency decreased (P<0 .01 and P<0.01) and pulse amplitude increased (P<0.001 and P<0.01) ove r the 10-week period. Anterior pituitary LH content was greater in 0.5 M (P<0.01) and 0.5M+P (P<0.05) than in 15M sheep. Coronal sections (20 mu m) of hypothalamic brain tissue were subjected to in situ hybridis ation to determine gene expression for neuropeptide Y (NPY). NPY mRNA was concentrated in the arcuate nucleus and median eminence, with tota l amounts greater in both 0.5M (310%, P<0.001) and 0.5M+P (333%, P<0.0 1) groups than in 1.5M sheep (100%). These data reveal that chronic lo w dietary energy intake by long-term castrates, with high or low prote in intake, reduces LH pulse frequency but increases the circulating le vels of LH by virtue of an increase in pulse amplitude, and concomitan tly increases hypothalamic NPY gene expression.