Temporal relationships among peripheral blood concentrations of corticosteroids, luteinizing hormone and testosterone in bulls.

Interrelationships among peripheral blood concentrations of corticosteroids (CS), luteinizing hormone (LH) and testosterone (T) were evaluated over a 24-hr period in four Angus bulls (18 months of age and 450 kg in body weight). Concentrations of LH and T were determined by radioimmunoassay and concentrations of CS by competitive protein binding assay of blood samples collected via jugular cannula at hourly intervals for 24 consecutive hr. A positive temporal relationship was observed between LH and T as significant positive correlations were obtained between concentrations of LH at one hour and concentrations of T at the subsequent hour in 3 of 4 bulls. Although LH peaks preceded T peaks by 1 hr, variation in this temporal relationship was observed as LH peaks occurred which were not accompanied by T peaks in some bulls. LH peaks were usually preceded by basal or declining concentrations of CS and prolonged elevations in concentrations of CS were often coincident with basal concentrations of LH and T. Negative correlations were obtained between concentrations of CS at one hour and concentrations of LH and T at the subsequent hour. These data describe the positive regulatory role of LH in testicular T production in the bull and suggest that alterations in endogenous concentrations of CS may influence peripheral concentrations of LH and T in the bull.