Luteolysis In Heifers Research Articles

Growth and differentiation of large antral follicles after spontaneous luteolysis in heifers: changes in concentration of hormones in follicular fluid and specific binding of gonadotropins to follicles.

The objective of the present study was to characterize changes in growth, concentrations of steroids in follicular fluid (FF) and gonadotropin receptors of individual antral follicles after spontaneous luteolysis in heifers and to reexamine our hormonal method of classifying healthy and atretic follicles. Groups of heifers were ovariectomized (OVX) before regression of corpora lutea on d 17, 18 and 19 of an estrous cycle and after regression of corpora lutea at time periods before, during and after preovulatory gonadotropin surges. Each follicle greater than or equal to 6 mm in diameter was examined for concentration of progesterone, androstenedione, testosterone and estradiol-17 beta in FF and capacities of granulosal and thecal cells to specifically bind 125I-bovine follicle stimulating hormone (bFSH) or 125I-human chorionic gonadotropin (hCG). Follicles were separated into two classes, estrogen-active (E-A) or estrogen-inactive (E-I). Concentrations of estradiol in FF were higher than both progesterone and androgens in E-A follicles, whereas either androgens or progesterone was higher than estradiol in E-I follicles. Diameters, volumes of FF and numbers of granulosal cells in E-A follicles increased from d 17 through the end of the preovulatory gonadotropin surges. During this time, concentrations of progesterone, androstenedione and estradiol in FF and specific binding of 125I-hCG to granulosal and thecal cells increased, whereas specific binding of 125I-bFSH to granulosal cells decreased. In E-I follicles, progesterone in FF decreased and androstenedione increased from d 17 through end of gonadotropin surges. The E-I follicles had a higher incidence of granulosal cells with pycnosis than E-A follicles. We concluded that changes in growth, concentration of steroids in FF and gonadotropin receptors in E-A follicles after spontaneous luteolysis were similar to changes we previously reported for E-A follicles after prostaglandin-induced luteolysis, and that ratio of concentration of estradiol in FF to both progesterone and androgens could be used to separate potential ovulatory (E-A) from atretic (E-I) follicles in heifers.

Development of antral follicles in cattle after prostaglandin-induced luteolysis: changes in serum hormones, steroids in follicular fluid, and gonadotropin receptors.

Changes in growth, concentrations of steroids in follicular fluid, and numbers of gonadotropin receptors in follicles 6 mm or more in diameter were examined 12, 24, 36, 48, 60, and 72 h after prostaglandin (PG)-induced luteolysis in heifers. Follicles with higher concentrations of estradiol than progesterone and androgens in follicular fluid (FF) were classified as estrogen active (E-A). Follicles with higher concentrations of progesterone or androgens than estradiol in follicular fluid were classified as estrogen inactive (E-I). Although E-A and E-I follicles were similar in size 12-72 h after PG treatment, before the preovulatory surge of LH, numbers of granulosa cells, estradiol concentrations, and capacities of follicles to specifically bind gonadotropins were markedly lower in E-I follicles. Most E-I follicles had histological signs of atresia, whereas E-A follicles did not. Sizes, concentrations of steroids in FF, and specific binding of gonadotropins to follicle cells did not change in E-A or E-I follicles 12-72 h after PG treatment but before the preovulatory surge of LH. However, diameters of E-A follicles were highly correlated with concentrations of estradiol and progesterone in FF and with capacities of granulosa and thecal cells to specifically bind [125I] iodo-hCG. In contrast, diameters of E-A follicles were highly negatively correlated with concentrations of testosterone in FF and with capacities of granulosa cells to specifically bind [125I] iodobovine FSH. We conclude that E-I follicles are atretic and E-A follicles are potentially ovulatory follicles. In addition, after a single injection of PG during an estrous cycle in heifers, the growth the differentiation of ovulatory follicles were not synchronized.

The release of prostaglandin F2α as reflected by 15-keto-13,14-dihydroprostaglandin F2α in the peripheral circulation during normal luteolysis in heifers

The release of prostaglandin F2α as reflected by 15-keto-13,14-dihydroprostaglandin F2α in the peripheral circulation during normal luteolysis in heifers

The release of prostaglandin F 2α as reflected by 15-keto-13,14-dihydroprostaglandin F 2α in the peripheral circulation during normal luteolysis in heifers

Progesterone and the main plasma metabolite of PGF 2α, 15-keto-13,14-dihydro-PGF 2α, were determined at hourly intervals in the peripheral circulation during luteolysis in two heifers. The prostaglandin release was found to occur during 2–3 days as rapid pulses with a duration of 1–5 hours prior to and during luteolysis, which was indicated by decreasing levels of progesterone.