Stress-Induced Alterations in Secretion of Corticosteroids, Progesterone, Luteinizing Hormone, and Testosterone in Bulls*

Abstract

Temporal relationships among the peripheral blood concentrations of corticosteroids, progesterone, LH₁ and testosterone and stress-induced alterations in the secretion of these hormones were examined in bulls. Blood samples were obtained via jugular cannula from eight bulls at 30-min intervals over a 12-h period. A rectal electroejaculation probe was then inserted with (EE; n = 4) or without (NE; n = 4) electrical stimulation, and ejaculation and blood samples were collected (5-, 15-, and 30-min intervals) over a second 12-h period. Treatments were reversed at the conclusion of this second 12-h period, and blood samples were collected over a third 12-h period. A positive temporal relationship was observed between concentrations of LH and testosterone during the initial 12-h period. During this time, a positive temporal relationship was also observed between concentrations of corticosteroids and progesterone. In contrast, concentrations of corticosteroids and progesterone were negatively correlated with concentrations of LH and testosterone during this period. For EE-NE bulls, concentrations of corticosteroids and progesterone increased concomitantly within bulls and synchronously among bulls within 5 min of EE, attained peak levels by 30 min, and returned to pre-EE levels between 2–3 h after EE. During this period, mean concentrations of LH and testosterone declined relative to pre-EE levels. Similar responses of corticosteroids, progesterone, LH, and testosterone to NE treatment were observed 12 h later. For NE-EE bulls, corticosteroid and progesterone responses observed post stress appeared similar to the responses of these hormones observed in EE-NE bulls. For both treatment groups, secretion of LH and testosterone decreased after each exposure to EE and NE, as indicated by fewer episodic LH and testosterone peaks relative to the initial prestress period. Negative correlations of -0.71, -0.54, and -0.43 were obtained between areas beneath corticosteroids and testosterone profiles during the first, second, and third 12-h periods, respectively. Taken together, these results indicate that both EE and NE treatments altered the secretion of adrenal hormones, which, in turn, temporarily altered the secretion of LH and testosterone.