Decrease in voluntary feed intake and pulsatile luteinizing hormone secretion after intracerebroventricular infusion of recombinant bovine leptin in mature male sheep

The aim of the present study was to determine whether leptin might play a r ole in the gonadotrophic response of mature merino rams to changes in the l evel of nutrition in rams fed ad libitum. Recombinant bovine leptin was inf used intracerebroventricularly and voluntary food intake (VFI) and luteiniz ing hormone (LH) pulse frequency were measured. In Experiment 1, rams (n = 5) were infused for 24 h per day for 5 days with vehicle or with leptin (0. 04, 0.4 and 4.0 pg h(-1)). All doses decreased both VFI and LH pulse freque ncy. In Experiment 2, rams were infused for 24 h per day for 5 days with ve hicle (n = 10) or leptin (4 mug h(-1); n = 5); a sub-group of 5 controls wa s pair-fed to the leptin-infused group to control for effects of changes in feed intake. LH pulse frequency was reduced equally in both the leptin-inf used and pair-fed groups. Leptin did not affect other systems controlled by the hypothalamic-pituitary axis. Thus. rather than stimulate LH secretion, intracerebral leptin specifically inhibits it by reducing food intake, so it is unlikely that effects of nutrition on the reproductive axis in mature rams involves leptin as a single blood-borne signal. A range of nutritiona l or metabolic inputs may be needed, and perhaps interconnections between n eural centres that control appetite and reproduction.