The aim of the present study was to determine whether leptin might play a role
in the gonadotrophic response of mature merino rams to changes in the level of
nutrition in rams fed ad libitum. Recombinant bovine
leptin was infused intracerebroventricularly and voluntary food intake (VFI)
and luteinizing 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 4.0g h
–1 ). All doses decreased both VFI and LH pulse
frequency. In Experiment 2, rams were infused for 24 h per day for 5 days with
vehicle (n = 10) or leptin (4 g h
–1; n= 5); a
sub-group of 5 controls was 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-infused 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 nutritional or metabolic inputs may be needed, and perhaps
interconnections between neural centres that control appetite and
reproduction.
Neural Determinants of Pulsatile Luteinizing Hormone Secretion in Male Mice
