Influence of Corticosteroids on Testosterone Production in the Bull1

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Abstract
Relationships of characteristics of 24 h profiles for concentrations of corticosteroids (CS), luteinizing hormone (LH) and testosterone (T) in peripheral blood with episodic and exogenously induced elevations of T were studied in bulls. Hourly blood samples were collected via jugular vein cannula for 24 consecutive h from 11 puberal Angus bulls. Exogenous bovine LH (1 mg) was injected at the end of the 24 h period. The overall lag correlation between concentrations of LH at one hour and concentrations of T at the subsequent hour (LAG-LHTCORR) was significant (r = 0.34). Prolonged maintenance of elevated concentrations of CS were coincident with baseline concentrations of LH (BASAL-LH) and T (BASAL-T). Episodic LH and T peaks occurred at the time of baseline concentrations of CS (BASAL-CS) or were preceded by the decline of elevated concentrations of CS. A significant negative correlation (r = -0.14) was obtained for the overall lag correlation between concentrations of CS at one hour and concentrations of T at the subsequent hour (LAG-CSTCORR). A negative relationship was observed between total area under 24 h profile of CS (CS-AREA) and total area under 24 h profile of LH (LH-AREA) and between CS-AREA and total area under 24 h profile of T (T-AREA). Peak concentration of T following LH injection varied among bulls; bulls were ranked according to T response to exogenous LH and particular characteristics of 24 h profiles of concentrations of T and CS. Profile characteristics associated with T response after exogenous LH was given were T-AREA, BASAL-T, CS-AREA and BASAL-CS. The results of this study provide evidence that adrenal corticosteroids may exert a regulatory influence upon both episodic and induced synthesis and secretion of T by the bovine testis.