Effect of anterior hypothalamic deafferentation on the negative feedback of gonadal steroids on luteinizing hormone pulse frequency in the ewe.

Three experiments were performed to determined the effect of anterior hypothalamic deafferentation (AHD) on the inhibitory actions of estradiol and progesterone on luteinizing hormone (LH) pulse frequency in ovariectomized ewes during the anestrous season. The first experiment tested the effects of AHD on LH secretion in the absence of gonadal steroids. AHD was accomplished by a 180 degree knife cut (Halasz knife) placed at the posterior border of the optic chiasm (n = 4). Control ewes received sham cuts or no surgery (n = 6). LH pulses were monitored in blood samples taken every 12 min for 4 hr before and after surgery. AHD reduced LH pulse amplitude (pre 7.4 +/- 2.9 ng/ml; post 1.2 +/- 0.3 ng/ml), but had no effect on LH pulse frequency (pre 3.5 +/- 0.3/4 hr; post 3.3 +/- 0.3/4 hr) in ovariectomized ewes. In the second experiment all ewes were given a Silastic implant containing estradiol (1 cm long) and 2 d later bled at 12 min intervals for 4 hr before and after administration of pimozide (PIM, 0.08 mg/kg), a dopamine antagonist. Estradiol decreased LH pulse frequency in controls (2.8 +/- 0.4 to 1.5 +/- 0.3/4 hr) and this was reversed by PIM (2.5 +/- 0.4/4 hr). In contrast, estradiol did not decrease pulse frequency in AHD ewes (3.3 +/- 0.3 to 2.8 +/- 0.5/4 hr) and PIM did not increase it (2.7 +/- 0.7/4 hr). In the third experiment, all ewes were given Silastic implants containing progesterone.(ABSTRACT TRUNCATED AT 250 WORDS)