REDUCED RESPONSIVENESS OF THE HYPOTHALAMIC-PITUITARY-ADRENAL AXIS IN BORAN (BOS-INDICUS) CATTLE INFECTED WITH TRYPANOSOMA-CONGOLENSE

The response of the pituitary-adrenal axis to corticotrophin-releasing hormone (CRH) and the adrenal response to adrenocorticotrophin hormon e (ACTH) stimulation were studied during infection of Boran (Bos indic us) cattle with Trypanosoma congolense. For CRH, 15 animals were chall enged during pre-infection and infection phases, while for ACTH 10 ani mals were challenged during pre-infection, infection and post-treatmen t phases of the experiments. The axis showed a reduced responsiveness after CRH challenge during patent parasitaemia, manifested by low (p<0 .05) plasma ACTH and cortisol concentration as compared to the pre-inf ection CRH challenge concentrations. Cortisol concentration after ACTH challenge during pre-infection, infection and post-treatment phases d id not differ. The reduced pituitary-adrenal response to CRH challenge and the normal adrenal response to ACTH challenge found during trypan osomiasis indicates pituitary dysfunction due to infection.