Anovulation in postpartum suckled beef cows. II. Associations among binding of 125I-labeled gonadotropins to granulosa and thecal cells, and concentrations of steroids in serum and various sized ovarian follicles

To determine if specific binding of 125I-labeled gonadotropins to granulosa and thecal cells, or concentrations of steroids in ovarian follicles change during the postpartum anovulatory period, 21 suckled beef cows were slaughtered on d 7, 14, 28, 42 or 56 after parturition (n = 4 to 6 per d). After slaughter, 10 to 15 follicles were dissected from each pair of ovaries and categorized by diameter: small (1.0 to 3.9 mm), medium (4.0 to 7.9 mm) or large (greater than or equal to 8 mm). Progesterone (221 to 612 ng/ml), androstenedione (48 to 94 ng/ml) and estradiol (2.7 to 23.9 ng/ml) did not change (P greater than .10) in fluid of small or medium follicles from d 7 to 42 to 56 after parturition. Similarly, specific binding of human chorionic gonadotropin (125I-hCG) or follicle stimulating hormone (125I-oFSH) to homogenates of small, medium or large follicles did not change (P greater than .05). In contrast, progesterone in fluid of large follicles increased (P less than .05) 3.4-fold between d 7 and 14, but decreased (P less than .05) 55% between d 14 and 28. Concentrations of androstenedione in fluid of large follicles did not change (P greater than .10) from d 7 to 42 to 56. Concentrations of estradiol in fluid of large follicles remained constant between d 7 and 14, but increased (P less than .05) 4.2-fold between d 14 and 28. We conclude that during the postpartum anovulatory period, there is no change in steroidogenic capabilities of small or medium follicles, both of which predominantly produce progesterone.(ABSTRACT TRUNCATED AT 250 WORDS)