Levels of testosterone and luteinizing hormone in the plasma of young post-pubertal bulls after injection of human chorionic gonadotrophin or dexamethasone and human chorionic gonadotrophin.

Abstract

Institut National Agronomique Paris-Grignon, Centre de Grignon, Franceand *Laboratoire d'Hormonologie, U.N.C.E.L.A., 13 Rue Jouet, 94700 Maisons-Alfort, France (Received 21 July 1977) There is now very good evidence that in young or adult bulls, as in many species, the secretion of luteinizing hormone (LH) and testosterone is episodic (Katongole, Naftolin & Short, 1971; Thibier, 1975, 1976). Each individual discharge of LH can result in transient stimulation of the testes and hence in an associated increase in the level of testosterone. It has recently been shown that administration of dexamethasone dramatically reduces the level of testosterone in the plasma, with no fluctuations during the next 30h; simultaneously, the level of LH also tends to decrease (Thibier & Rolland, 1976). We have now examined the levels of testosterone and LH in the peripheral plasma of young post-pubertal bulls after treatment with human chorionic gonadotrophin (HCG) alone, or HCG and dexamethasone. Twelve French Friesian