PERIPHERAL INHIBIN LEVELS DURING ESTROUS-CYCLE IN BUFFALO (BUBALUS-BUBALIS)

A sensitive, specific RIA was validated and used for measurement of pe ripheral plasma immunoreactive inhibin (ir-inhibin) levels during the estrous cycle in Murrah buffalo. The RIA employed an 125-I iodinated i nhibin as tracer and an antiserum against dimeric inhibin. The procedu re had a sensitivity of 16 pg/tube, and the nonspecific effects of buf falo plasma were compensated for by including 200 ul bullock plasma in the standards. Separation of free and bound inhibin was affected by t he use of a second antibody and precipitation with polyethylene glycol . Blood samples were collected once daily for 30 d from Murrah buffalo (n = 6) during the hot month of July. Cyclic activity and estrus were confirmed by plasma progesterone determination. Peripheral plasma con centrations of ir-inhibin fluctuated between 0.40 +/- 0.07 and 0.67 +/ - 0.13 ng/ml during the estrous cycle in buffalo. During the same peri od, plasma progesterone levels increased from 0.21 +/- 0.01 ng/ml at D ay 0 to a peak of 3.30 +/- 0.72 ng/ml on Day 13, declining sharply by Day -5. Ir-inhibin levels exhibited an increase during the follicular phase, with the maximum concentration of 0.65 +/- 0.01 ng/ml occuring on the day of estrus, a decline thereafter, and no pattern during the luteal phase. The differences, however, were not statistically signifi cant throughout the estrous cycle.