Follicular fluid immunoreactive-inhibin concentrations in relation to follicular diameter and estradiol-17 beta, progesterone and testosterone concentrations in individual ovarian follicles in buffalo, Bubalus bubalis.

The objective of this study was to measure the concentrations of immunoreactive inhibin (ir-inhibin) in follicular fluid from individual ovarian follicles and relate them to follicular diameter and follicular fluid concentrations of estradiol-17 beta, progesterone and testosterone in buffalo. Follicular size was measured with an ultrasound machine and follicles were categorized as small (4 to 5 mm diam.), medium (6 to 9 mm diam.) and large (10 mm and above in diam.). Ir-inhibin concentrations varied markedly between and within follicles of same size category. Follicular fluid ir-inhibin concentrations (microgram/ml) were positively related to follicular diameter (R = 0.32, n = 262, P < 0.001) and were significantly higher (P < 0.05) in large (8.32 +/- 0.56) in comparison to medium (7.02 +/- 0.31) follicles which, in turn had inhibin concentrations significantly higher (P < 0.001) than those in small follicles (5.13 +/- 0.48). Ir-inhibin and estradiol-17 beta concentrations were positively related in medium (R = 0.38, n = 128, P < 0.001) and large (R = 0.64, n = 35, P < 0.001) but not in small follicles. There was a negative relationship between ir-inhibin and progesterone concentrations in large follicles (R = 0.46, n = 33, P < 0.01), with no relationship between the two hormones in small and medium follicles. Ir-inhibin was positively related to molar ratios of estradiol-17 beta to progesterone in medium (R = 0.30, n = 124, P < 0.01) and large (R = 0.49, n = 24, P < 0.01) but not in small follicles. There was no relationship between ir-inhibin and testosterone concentrations in follicles of all size categories. The results of the present study suggest that follicular inhibin production is related to follicular size as well as intrafollicular estradiol-17 beta and progesterone concentrations.