Luteinizing hormone and growth hormone secretion in ewes infused intracerebroventricularly with neuropeptide Y

Neuropeptide Y (NPY) provides an important hypothalamic link between nutritional status and neuroendocrine mechanisms regulating growth and reproduction. The objective of the following series of experiments was to determine the effects of single or continuous administration of NPY on secretion of luteinizing hormone (LH) and (or) growth hormone (GH). In experiment 1, four ovariectomized (OVX) ewes and four OVX+estrogen-treated ewes each received, in a 4×4 Latin Square arrangement of treatments, a single injection of 0, 0.5, 5, or 50 μg NPY via an intracerebroventricular (i.c.v.) cannulae to determine the effects on secretion of GH. NPY significantly elevated serum GH at the 50 μg dose regardless of estrogen exposure ( P=0.003). In experiment 2, eight OVX ewes were infused i.c.v. with NPY or saline ( n=4/trmt) continuously for 20 h in a linearly increasing dose, ending at 50 μg/h NPY. Blood samples were collected via jugular cannulae every 10 min during hour –4–0 (interval 1, pre-treatment), hour 6–10 (interval 2) and hour 16–20 (interval 3) relative to the initiation of infusion (0 h). Mean LH and LH pulse frequency were lower in NPY- versus saline-infused ewes during intervals 2 and 3 ( P0.10). In experiment 3, four OVX ewes were continuously infused with NPY as in experiment 2, except that the maximum 50 μg/h dose was achieved after only 10 h of infusion. Blood samples were collected every 10 min, beginning 4 h before and continuing until 4 h after the NPY infusion. Mean serum LH changed significantly over time ( P=0.0001), decreasing below pre-treatment levels by hour 3 of NPY infusion ( P0.15). Serum GH also changed significantly over time ( P