PERIPHERAL INHIBIN LEVELS IN RELATION TO CLIMATIC VARIATIONS AND STAGE OF ESTROUS-CYCLE IN BUFFALO (BUBALUS-BUBALIS)

The present study investigated the peripheral plasma inhibin levels in relation to 1) the stage of estrous cycle and the effect of climatic variations. Blood samples were collected from cyclic buffalo (n=5) onc e daily for 32 consecutive days during the tropical hot humid (summer) and cold (winter) seasons. Estrus was recorded by parading a vasectom ized bull as well as by plasma progesterone determination. In the wint er season, peripheral inhibin concentrations which were lowest (0.35 /- 0.02 ng/ml) during the mid-luteal phase of estrous cycle (Day 6 to Day 14, Day 0 = day of estrus) increased significantly (P<0.02) to 0.4 7 +/- 0.04 ng/ml during the late luteal phase (Day -4 to Day -2) and t hen further to 0.52 +/- 0.03 ng/ml (P<0.02) during the periestrus phas e (Day -1 to Day 1). Inhibin concentrations then decreased significant ly (P<0.02) to 0.40 +/- 0.03 ng/ml during the early luteal phase (Day 2 to Day 5). In the summer season the differences in peripheral inhibi n concentrations among different phases of estrous cycle were found to be nonsignificant. A comparison of the circulating inhibin concentrat ions between the two seasons indicated that inhibin concentrations wer e significantly higher in the late luteal phase (P<0.01) and periestru s phase (P<0.05) during the winter season compared with corresponding periods during the summer season. The present study suggests that peri pheral inhibin concentrations change in the estrous cycle during coole r breeding season and that environmental heat stress can cause a reduc tion in peripheral inhibin concentrations. (C) 1997 by Elsevier Scienc e Inc.