CIRCADIAN AND PULSATILE VARIATIONS IN PLASMA-LEVELS OF INHIBIN, FSH, LH AND TESTOSTERONE IN ADULT MURRAH BUFFALO BULLS

The present study investigated pulsatile and circadian variations in t he circulatory levels of inhibin, gonadotrophins and testosterone. Six adult buffalo bulls (6 to 7 yr of age) were fitted with indwelling ju gular vein catheters, and blood samples were collected at 2-h interval s for a period of 24 h and then at 15-min interval for 5 h. Plasma con centrations of inhibin, FSH, LH and testosterone were determined by sp ecific radioimmunoassays. Plasma inhibin levels in Murrah buffalo bull s ranged between 0.201 to 0.429 ng/mL, with a mean of 0.278+/-0.023 ng /mL. No inhibin pulses could be detected during the 15-min sampling in terval. Plasma FSH levels ranged between 0.95 to 3.61 ng/mL, the mean concentration of FSH over 24 h was 1.66+/-0.25 ng/mL. A single FSH pul se was detected in 2 of 6 bulls. The LH levels in peripheral circulati on ranged between 0.92 to 9.91 ng/mL, with a mean concentration of 3.3 3+/-1.02 ng/mL. Pulsatility was detected in LH secretion with an avera ge of 0.6 pulses/h. Plasma testosterone levels in 4 buffalo bulls rang ed from 0.19 to 2.99 ng/mL, the mean level over 24 h were 1.34+/-0.52 ng/mL. Testosterone levels in peripheral circulation followed the LH s ecretory pattern, with an average of 0.32 pulses/h. The results indica te parallelism in inhibin, FSH acid LH, and testosterone secretory pat tern. Divergence in LH and FSH secretory patterns in adult buffalo bul ls might be due to the presence of appreciable amounts of peripheral i nhibin. (C) 1998 by Elsevier Science Inc.