The effect of changes in adrenal blood flow on adrenal cortical responses to adrenocorticotrophin in conscious calves.

1. The effect of varying adrenal blood flow on the rate at which it was estimated that adrenocorticotrophin (ACTH) was presented to the adrenal gland was related to right adrenal cortisol output in conscious calves fitted with 'adrenal clamps'. 2. Intra-aortic infusions of endothelin at either 15.0 or 7.5 pmol min-1 kg-1 produced a substantial fall in right adrenal blood flow which was dose-related over this range. There was an associated fall in right adrenal cortisol output and cortisol output was linearly related to estimated ACTH presentation to the gland over the whole range investigated. The changes in adrenal cortisol output were reflected by changes in the concentration of cortisol in the peripheral plasma, which could be attributed entirely to the fluctuations in adrenal cortisol output. 3. It is concluded that delivery of ACTH to the adrenal gland is flow dependent over the physiological range in these animals and that changes in adrenal cortical blood flow can therefore be expected to result in changes in adrenal output due to variations in the presentation rate of ACTH.