Global Changes in Uterine Protein Secretion Are Associated With Differences in the Number of Antral Follicles in Heifers

Abstract Text: The numbers of antral follicles on the ovary have been reported to be associated with differences in beef cattle fertility. To further explore potential mechanisms for these differences, an experiment was undertaken to determine the association between numbers of antral follicles and differences in uterine protein secretion in beef heifers. Using ultrasonography, the number of antral follicles was determined twice (March and April, 2013) in beef heifers (n=104; 10-12 mo of age), which had been developed from weaning on a standard USMARC heifer development diet (65% mature weight by breeding). From the heifers determined to be cycling in April (presence of a corpus luteum at ultrasound), 10 heifers with the greatest and 10 heifers with the least antral follicles were identified. These heifers were synchronized with two injections of prostaglandin F2α given 11 days apart and slaughtered on day 15-16 of the estrous cycle. After slaughter, the uterus was flushed with 20 mL 0.9% saline. Uterine flushings were measured for total uterine protein using a bicinchoninic acid procedure. Flushings were dialyzed (10 mM Tris, pH 8.0) and then aliquots were lyophilized and subjected to SDS-PAGE (0.5 mL) and 2D-PAGE (1 mL). Gels were stained with coomassie, imaged, and protein bands or spots were quantified using densitometry. Of the 10 heifers in each group, 7 high and 8 low group heifers responded appropriately to estrous synchronization and were in diestrus. Retrospectively, the number of antral follicles determined by ultrasound differed between the high and low groups (33±2.1 and 15.2±1.9, respectively; P<0.01). Total uterine protein concentration also differed between high and low groups (524±47 and 293±44 µg/ml, respectively; P<0.05). After SDS-PAGE, densitometry was measured on 11 protein bands. All but one band (serum albumin) differed between high and low groups (high group 39-71% greater than low group; P<0.05). After 2D-PAGE, densitometry was measured on 223 spots. Of these, 66 spots were greater (P<0.05) in high compared to low groups, no spots were greater in low compared to high groups. These results suggest a generalized increase in uterine protein secretion in heifers with greater numbers of antral follicles. Possible mechanisms for this increase include greater prepubertal uterine gland development or increased stimulation of uterine protein secretion during the estrous cycle. Greater uterine protein secretion could contribute to the previously reported increased fertility of beef heifers with more antral follicles. USDA is an equal opportunity provider and employer.

Keywords: Endometrium, Follicle, Proteome