The present study aims to clarify the role of fatty acids in regulating pulsatile LH secretion in rats. To produce an acute central lipoprivic condition, mercaptoacetate (MA), an inhibitor of fatty acids oxidation, was administered into the fourth cerebroventricle (4V) in ad libitum fed ovariectomized (OVX) rats (0.4, 2, and 10 micromol/rat) with or without an estradiol (E2) implant producing diestrus plasma E2 levels. Pulsatile LH secretion was suppressed by 4V MA administration in a dose-dependent manner in both OVX and OVX plus E2 rats. Mean LH levels and LH pulse frequency and amplitude were significantly reduced by the highest dose of MA in OVX rats, and by the middle and highest dose of MA in E2-treated rats, suggesting that estrogen enhanced LH suppression. Blood glucose levels increased immediately after the highest dose of MA in both groups. Fourth ventricular injection of trimetazidine (2 and 3 micromol/rat), another inhibitor of fatty acids oxidation, also inhibited pulsatile LH release, resulting in significant and dose-dependent suppression of LH pulse frequency and an increase in blood glucose levels in OVX plus E2 rats. In contrast, peripheral injection of the highest 4V dose of MA (10 micromol/rat) did not alter LH release or blood glucose levels. Microdialysis of the hypothalamic paraventricular nucleus (PVN) revealed that norepinephrine release in the region was increased by 4V MA administration. Preinjection of alpha-methyl-p-tyrosine, a catecholamine synthesis inhibitor, into the PVN completely blocked the lipoprivic inhibition of LH and the counter-regulatory increase in blood glucose levels in OVX plus E2 rats. Together, these studies indicate that fatty acid availability may be sensed by a central detector, located in the lower brainstem to maintain reproduction, and that noradrenergic inputs to the PVN mediate this lipoprivic-induced suppression of LH release.
A study was carried out on 16 indigenous ewes in Bangladesh in order to assess the reproductive physiology, the pattern of vaginal cell exfoliation and progesterone profiles during the estrous cycle period. The mean estrous cycle length and duration of estrus were 15.8±0.12 days and 31.1±0.57 h respectively. The exfoliated epithelial cells were categorized into parabasal, intermediate, superficial and keratinized and their relative occurrences. The percentages of parabasal, intermediate and superficial cell type during proestrus were similar. The percentage of superficial cell type during estrus was 61.7%, which was significantly (p<0.01) differ from other types of cells and stages of estrus cycle. Metoestrus was predominant with neutrophils in addition with other cell types. Dioestrus was dominated by neutrophils. On days 0 to 5 of the cycle the progesterone concentration was 0.09 to 1.6±0.07 ng/ml. The length of diestrus was 5∼10 days with a range of mean progesterone level of 1.6±0.07 to 2.8±0.11 ng/ml. Progesterone levels increased significantly (p<0.01) after Day 5 and maximum level was 2.8±0.11 ng/ml observed on Day 10 of the estrous cycle. Thereafter it dropped rapidly to basal level of 0.11±0.04 ng/ml on Day 0 (p<0.01). These results indicate that the pattern of exfoliation of vaginal cells along with progesterone concentration could be used to determine the reproductive stages of indigenous ewe.
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