Interrelationships of Serum Corticosteriods, LH, and Testosterone in Male Bovine

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Abstract
Temporal interrelationships of endogenous peripheral blood concentrations of corticosteriods (CS), luteinizing hormone (LH), and testosterone (T) were evaluated in bulls. Concentrations of CS, LH, and T were quantitated in blood samples collected at hourly intervals via jugular cannula from four bulls during a single 24-hr period in January and again in June. Alterations in hormone profile characteristics were noted within bulls between January and June. An increased number of LH peaks and increased area beneath entire 24-hr LH profile suggested that LH secretion was higher during the June sampling period than the January sampling period. However, no significant alteration in T secretion in June was observed, as number of T peaks and area under T peaks were essentially unchanged relative to January. An inconsistent relationship between secretion of LH and T was observed in June, with only 47% of LH peaks associated with elevations in concentration of T whereas in January 80% of LH peaks were associated with T peaks. A higher lag correlation over all bulls between concentration of LH at one hour and concentration of T at the subsequent hour for all such combinations throughout the 24-hr period (LAG-LHTCORR) in January (r = 0.45, p < 0.001) than in June (r = 0.12,p < 0.24) also indicated that the temporal relationship between LH and T changed between these two periods of time. Coincident with the inconsistent relationship between LH and T during June was an increased secretion of CS as the area beneath entire 24-hr CS profile and the height of CS peaks were greater in June. Prolonged elevations in concentration of CS were observed to be coincident with basal concentrations of LH and T and a negative value was obtained for LAG-CSTCORR in June (r = −0.10) but not in January (r = 0.06). Results of this study indicate that the major effect of LH upon blood concentration of T in the bull is usually exerted within 1 hr of a LH surge. However, failure of some LH peaks to be followed by T peaks suggests that the secretion of LH and T in the bull may be subject to modulation by adrenocortical hormones and other intrinsic and extrinsic factors.