Increased LH pulse frequency and estrogen secretion associated with termination of anestrus followed by enhancement of uterine estrogen receptor gene expression in the Beagle bitch

摘要

In the 1st of 4 experiments, blood samples were collected from 30 bitches every 10 min for 8 h from a cephalic vein during different phases of the oestrous cycle. An increase (P<0.01) in mean plasma levels of LH occurred from mid to late anoestrus.The LH pulse frequency increased (P<0.01) from late anoestrus to pro-oestrus, and was highly correlated (r = 0.96, P<0.001) with the mean plasma level of oestradiol-17beta (E2). In experiment 2, middle uterine samples, including myometrium and endometrium, were collected from 18 bitches at 6 stages of the oestrous cycle. The total number of oestrogen receptors, and nuclear oestrogen receptor and its mRNA levels in the uterus increased (P<0.01) from late anoestrus to pro-oestrus. Mean plasma E2 level and the number of uterine oestrogen receptors were positively correlated (r = 0.81, P<0.05). In experiment 3, 9 bitches were ovariectomized in mid anoestrus. Two weeks later they received an i.m injection of 10 or 50μg/kg oestradiol benzoate. The number of uterine oestrogen receptors and their mRNA levels in ovariectomized bitches were low, but increased (P<0.05) after treatment with a low dose of oestradiol benzoate. It is suggested that increases in LH pulse frequency and oestrogen secretion are associated with termination of anoestrus, and that subsequent enhancement of uterine oestrogen receptor expression may be up-regulated by oestradiol.