The pattern of LH release in the adult ram influences the testicular steroidogenic response to individual LH pulses and is regulated by testosterone negative feedback.
Two experiments were conducted with adult intact rams (approximately 58 kg in body weight) in the nonbreeding season to investigate interrelationships between LH and testosterone secretion. In Experiment 1, LH pulse frequency was increased from approximately two to six peaks per 8 hours (for 56 hours) by injecting (iv) 10 micrograms NIH-LH-S18 every 80 minutes. Induction of a breeding season peak frequency produced a progressive 3-fold increase (P less than 0.01) in mean serum testosterone levels to values during the last 8 hours of treatment (12.6 +/- 1.2 ng/ml) that were 50% of those in the fall. In response to LH pulsing, testosterone peak amplitude increased (P less than 0.05) from 3.5 +/- 0.8 ng/ml to 6.7 +/- 0.7 ng/ml. In Experiment 2, the mean testosterone level was increased to breeding season values (for 96 hours) by injecting (im) 5 mg testosterone every 4 hours. Mean LH levels and LH peak frequency were decreased (approximately 70%, P less than 0.01) following 36 hours of treatment, and the LH response to exogenous GnRH was decreased (approximately 45%, P less than 0.01) by the final 4 hours Results indicate that for rams in the nonbreeding season, the testicular steroidogenic response to individual LH pulses is enhanced when pulse frequency is increased. When blood testosterone is elevated to breeding season levels, LH pulse frequency is severely impaired, while pituitary responsiveness to GnRH is diminished, as in the fall.
Sanford
L M
LM
McGill University Centre for the Study of Reproduction, Department of Animal Science, Macdonald College, Ste Anne de Bellevue, Quebec, Canada.
Ponzilius
K H
KH
D000818:Animals; D001947:Breeding; D005246:Feedback; D007986:Luteinizing Hormone / Q000097:blood / Q000494:pharmacology / Q000502:physiology*; D008297:Male; D012756:Sheep; D013737:Testis / Q000187:drug effects* / Q000378:metabolism; D013739:Testosterone / Q000097:blood / Q000494:pharmacology / Q000502:physiology*
D013739:Testosterone; D007986:Luteinizing Hormone