Summary. Concentrations of cortisol were determined in pooled fluid of small (< 10 mm) and large (≥ 10 mm) follicles of cyclic cattle (Exp. 1), and in fluid of the largest follicle of 17 post-partum anovulatory cows (Exp. 2). In Exp. 1, concentrations of cortisol in small follicles were greater (P < 0·05) than in large follicles (14·7 versus 13·2 ng/ml), and varied significantly with stages of the cycle; small and large follicles had the highest cortisol concentration during the early luteal phase of the cycle. Large follicles had 2-fold greater concentrations of oestradiol than did small follicles, whereas small follicles had 2-fold greater concentrations of androstenedione than did large follicles. Across pools of follicular fluid, cortisol concentrations were correlated only to androstenedione concentrations (r = 0·65, P = 0·07). In Exp. 2, concentrations of cortisol did not significantly differ between oestrogen-active (oestradiol > progesterone in follicular fluid) and oestrogen-inactive (progesterone > oestradiol) follicles, although oestrogen-active follicles had a 24-fold greater concentration of oestradiol than did oestrogen-inactive follicles. Cortisol concentrations were correlated to hCG binding capacity of thecal cells (r = − 0·35, P = 0·08) and to follicular diameter (r = 0·45, P < 0·05). These results suggest that normally fluctuating concentrations of cortisol in follicular fluid of cattle play little or no active role in follicular differentiation in vivo.
If the inline PDF is not rendering correctly, you can download the PDF file here.