Adrenal responses to corticotrophin-releasing factor in conscious hypophysectomized calves

1. Adrenal responses to intra-aortic infusions of pure synthetic ovine corticotrophin-releasing factor (CRF) have been investigated in functionally hypophysectomized calves previously fitted with an adrenal clamp. 2. CRF caused an increase in the output of cortisol from the adrenal gland, which was dose related over the range 4-8 pmol min-1 and maximal at the higher of these doses; this response was observed at a dose below that which produced any change in adrenal vascular resistance. Cortisol output was also found to be related linearly to the rate at which CRF was estimated to be presented to the gland during these infusions. 3. The infusions of CRF also provoked the release of small, but readily detectable, amounts of adrenocorticotrophin-like peptides (ACTH) from the gland. This was mainly in the form of ACTH1-39 with some pro-opiomelanocortin (POMC) also being released. 4. Comparison of the adrenal steroidogenic response to exogenous CRF with that to synthetic ACTH1-24 showed that CRF was the more potent; in each case cortisol output was related linearly to the presentation rate of the peptide. 5. It is concluded that the adrenal cortex in the calf is capable of releasing cortisol in response to exogenous CRF at low concentrations and is even more sensitive to CRF than it is to exogenous ACTH over the dose range that was employed.