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Endocrinology, Vol 132, 2399-2406, Copyright © 1993 by Endocrine Society

ARTICLES

Comparison of the effects of pulsatile and constant testosterone on the secretion of gonadotropins in the ram

TJ Rhim, DJ Schaeffer and GL Jackson
Department of Veterinary Biosciences, University of Illinois, Urbana- Champaign 61801.

The objective of the present study was to compare the effectiveness of a pulsatile vs. a constant pattern of testosterone (T) infusion to suppress LH and FSH secretion in wethers. Two separate experiments were conducted. In Exp 1, animals were subjected to each of four different iv infusion regimens for 3 days: 1) constant diluent, 2) constant T (768 micrograms/kg.24 h), 3) pulsatile (one pulse every 4 h) diluent, and 4) pulsatile T (768 micrograms/kg.24 h). Blood samples were collected at 10-min intervals for 4 h both before infusion and during the last 4 h of the infusion. Compared to diluent, T decreased (P < 0.001) mean LH and increased (P < 0.001) LH interpulse interval. The LH interpulse interval was increased more (P < 0.005) by constant T than by pulsatile T. Mean LH was slightly more suppressed (P = 0.052) by constant T than by pulsatile T. LH pulse amplitude did not differ between constant T and pulsatile T. In Exp 2, animals were subjected to each of three different iv infusion regimens for 4 days: 1) constant diluent, 2) constant T (384 micrograms/kg.24 h), and 3) pulsatile (one pulse every 6 h) T (384 micrograms/kg.24 h). Both LH the interpulse interval (P = 0.001) and LH pulse amplitude (P = 0.04) were increased more by constant T than by pulsatile T. Mean LH was suppressed more (P = 0.002) by constant T than by pulsatile T. In both Exp 1 and 2, none of the treatments significantly affected mean FSH. These results indicate that constant T is more effective than pulsatile T in suppressing LH secretion in the ram.


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