EFFECTS OF TRYPANOSOMA-CONGOLENSE ON PITUITARY AND ADRENOCORTICAL FUNCTION IN SHEEP - RESPONSES TO EXOGENOUS CORTICOTROPIN-RELEASING HORMONE

To investigate whether the aberrations in adrenocortical and gonadal a ctivity observed in trypanosomiasis may be induced by the refractorine ss of the pituitary to hypothalamic liberins, the responses of the pit uitary and adrenal glands and the testes to stimulation with ovine cor ticotrophin-releasing hormone (oCRH) were studied in rams 23 days (acu te phase) and 65 days (chronic phase) after they were infected with Tr ypanosoma congolense. On both occasions a peak of plasma ACTH was obse rved within 20 minutes of the injection of CRH but the rate of increas e in ACTH and the mean peak values in the infected rams were significa ntly lower (P<0.001) on day 23 but higher (P<0.05) on day 65 than in t he uninfected control rams. Plasma cortisol concentration increased in all the rams after the injection of CRH. The rate of increase in plas ma cortisol and the mean peak values were not significantly different between the control and infected rams on day 23 but were significantly (P<0.001) higher in the infected rams on day 65. However, the post pe ak concentrations of ACTH declined more rapidly in the infected rams t han in the controls on both days 23 and 65. The plasma concentration o f luteinising hormone (LH) did not change after the injection of CRH, whereas the testosterone levels showed a delayed response and its conc entration increased when plasma ACTH and cortisol concentrations decli ned in both groups. On day 23, there was a greater increase in testost erone in the infected than in the control rams. These results demonstr ate that the responsiveness of the pituitary corticotrophs to CRH is d epressed during the acute phase and enhanced during the chronic phase of T congolense infection in rams, whereas the adrenal cortisol respon se is less affected. The results are also consistent with the hypothes is that the modulation of the pituitary-adrenal axis by infective tryp anosomes may exacerbate the changes in testicular steroidogenesis freq uently observed in trypanosomiasis.