Abstract
In male rats, LH pulse frequency and amplitude increase dramatically by 24 h after gonadectomy; in females they increase only slightly by this time. Mean FSH levels increase significantly in both sexes by 24 h after gonadectomy. The objectives of the present studies were to compare pulsatile LH, FSH, and prolactin (PRL) secretion in intact versus gonadectomized and in male versus female rats, and to determine whether the acute postovariectomy lag in LH rise is due to a lingering effect of the higher PRL and/or progesterone (P) levels seen in intact females. LH pulse amplitude, frequency, and mean levels increased significantly by 24 h after gonadectomy in both sexes, but the increases were greater in the males. FSH mean levels, but not pulse amplitude or frequency, increased similarly in both sexes by 24 h after gonadectomy. PRL did not change with gonadectomy. Treatment with CB-154 (a dopamine agonist), with or without RU486 (a P antagonist), 1 h before gonadectomy significantly suppressed pulsatile PRL secretion 1 day later in both sexes. There was no effect of either treatment on LH secretion. We have demonstrated that there is a sex difference in LH, but not FSH or PRL, pulsatility at 24 h after gonadectomy, and that female rats' higher PRL and P levels do not account for their slow rate of LH rise after ovariectomy.
Highlights
Serum LH pulse frequency and amplitude increase significantly by 24 h after gonadectomy in both male [1] and female [2] rats; the rate of increase is much more rapid in males than in females
LH pulse frequency and amplitude in male rats respond to the removal of negative feedback with 3-fold increases by 24 h after castration [1], whereas in females they increase by only 1.5- to 2-fold [3], if at all [4], by this time after ovariectomy
[23] was used to determine significant UI and PRL pulses. This program takes as input the series of data values, the coefficients of variation (CV) of the concentration ranges of the assay, and a threshold expressed in terms of number of assay CVs
Summary
Serum LH pulse frequency and amplitude increase significantly by 24 h after gonadectomy in both male [1] and female [2] rats; the rate of increase is much more rapid in males than in females. We hypothesized that the higher average levels of PRL in intact females compared to levels in intact males may account for the delayed LH rise after ovariectomy. Diestrous levels of P replacement given at the time of ovariectomy on metestrus cause W pulse amplitude to be suppressed 24 h later [3] and mean LH levels [16] to be suppressed 4 days later compared to untreated ovariectomized rats. The aims of the following studies, were to compare pulsatile LH, FSH, and PRL secretion in intact versus gonadectomized rats and in male versus female rats in the same study; and to determine whether, given the higher levels of P and PRL in intact female than in male rats, the acute postovariectomy lag in the rate of LH rise is partially caused by continued occupancy by P and/or PRL of their receptors.
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