Plasma estradiol-17β concentration in ewes and cows after estradiol-17β administration

Abstract

Microgram doses of estradiol-17β (30 and 100 μg) that have marked effects on sperm transport and uterine motility when injected into estrous ewes resulted in transient increases in estradiol concentrations in plasma that peaked by one-half to 1 hr and that had begun to decline by 6 hr. One hundred micrograms of estradiol resulted in peak concentrations of estradiol in plasma of estrous heifers (45 pg/ml) that were similar to the peak plasma concentrations in estrous ewes (42 pg/ml) after the administration of a 30-gmg dose. Plasma clearance of estradiol was rapid in ewes with blood concentrations reduced by half at 10 to 11 min after injection. Concentrations of estradiol in plasma in heifers could be maintained at an elevated (estrous) concentration for up to 24 hr by a single injection of estradiol as estradiol benzoate. Estradiol-17β (estradiol) injected into ewes in doses as low as 30 or 40 μg, at or near the time of mating, increased the number of sperm in the anterior cervix, uterus and oviducts by 24 hr after mating (1). Estradiol injected into ewes in doses up to 150 μg at the time of mating did not have deleterious effects on fertilization or embryo survival up to 25 days (2). Doses of estradiol ranging from 6 to 150 μg prevented reversal of direction of movement of peristaltic contractions in the uterus of estrous ewes (3). The two experiments of the present study were to evaluate how these estradiol treatments, which alter uterine motility and sperm transport in the ewe, affect the concentration of estradiol in the plasma. In Experiment I, we evaluated estradiol concentrations in plasma of estrous ewes after the injection of microgram doses of estradiol. In Experiment II, we ascertained doses of estradiol injected into heifers that would give estradiol concentrations in plasma similar to those observed with the 30-μg dose of estradiol in ewes.