Leptin attenuates the acute effects of centrally administered neuropeptide Y on somatotropin but not gonadotropin secretion in ovariectomized cows

We tested the hypothesis that recombinant ovine leptin would attenuate the acute effects of neuropeptide Y (NPY) on secretion of GH and gonadotropins (LH and FSH) in cows. Ovariectomized cows (n=6) fitted with third ventricle guide cannulas were assigned randomly to each of three groups in a Latin square arrangement: (1) control; saline treatment only, (2) NPY; saline followed by NPY, and (3) L-NPY; leptin pretreatment followed by NPY. Treatments were: s.c. injection of saline or leptin (30μg/kg BW) at time 0, i.v. injection of saline or leptin (30μg/kg BW) at 70min, and intracerebroventricular (i.c.v.) injection of saline or NPY (500μg) at 90min. Plasma leptin was elevated (P<0.01) at least four-fold throughout the experiment in the L-NPY group. Mean plasma concentrations of LH declined within 1h and were lower (P<0.03) than controls in both the NPY and L-NPY groups beginning 2h after NPY injection. An acute increase in plasma concentrations of GH was observed within 1h after NPY in the NPY group and mean values were greater (P<0.01) than controls. However, in the L-NPY group, leptin pretreatment attenuated the NPY effect on GH. Treatments had no effect on FSH secretion. Results confirm suppressive and stimulatory effects of NPY on LH and GH secretion, respectively, and indicate that leptin can attenuate the acute effects of NPY on GH secretion in cattle.