Release of adrenocorticotrophin from the adrenal gland in the conscious calf.

1. The effect of stimulation of the splanchnic nerve on the output of ACTH-related peptides from the adrenal gland has been investigated in conscious, functionally hypophysectomized calves, previously fitted with an 'adrenal clamp'. 2. Stimulation of the splanchnic nerve elicited a small, but statistically significant, increase in the output of ACTH-like immunoreactivity at each frequency tested. This response was frequency-dependent over the range 40-70 Hz when stimulating intermittently for 1 s at 10 s intervals and was potentiated by stimulating intermittently. Thus, the average mean output during stimulation in burst at 70 Hz (25 +/- 5 fmol min-1 kg-1) was significantly higher than the corresponding value during continuous stimulation at 7 Hz (6 +/- 1 fmol min-1 kg-1; P less than 0.01) even though the total number of impulses delivered was identical in each case. 3. There was also a small but significant rise in the output of cortisol from the gland with intermittent stimulation, which was linearly related to the output of ACTH-like immunoreactivity at the lower frequencies (4 and 7 Hz). 4. Separation of the ACTH-related peptides which were extracted from the adrenal effluent plasma of these animals during splanchnic nerve stimulation revealed the existence of two clear forms: ACTH (1-39) accounted for about 60% of total ACTH immunoreactivity and pro-opiomelanocortin (POMC) for about 30%. 5. It is concluded that small amounts of ACTH are released within the adrenal gland during splanchnic nerve stimulation in the functionally hypophysectomized calf and that this may possibly contribute towards the steroidogenic effect of stimulating the splanchnic nerve.