The effect of ovine corticotrophin releasing factor (oCRF), bromocriptine and TRH on the secretion of ACTH and alpha-MSH in Nelson's syndrome and Cushing's disease.

The circulating levels of ACTH and alpha-melanocyte stimulating hormone (alpha-MSH) were measured in 9 patients with Nelson's syndrome after the administration of saline, ovine corticotrophin releasing factor (oCRF), bromocriptine or TRH. The concentrations of ACTH were grossly elevated and alpha-MSH levels ranged from undetectable to higher than the normal range. In seven of eight subjects there was a rapid corticotrophic response, but no change in the alpha-MSH level, following oCRF. This response was delayed in one subject. Following oCRF injection, the plasma oCRF profile was variable but circulating oCRF was detectable even at the end of the experiment in all cases. There was no significant change in circulating ACTH or alpha-MSH following either bromocriptine or TRH. Cultured tumour cells from one case of Cushing's disease showed a corticotrophic response but no change in alpha-MSH to oCRF and the response was enhanced by vasopressin. Bromocriptine added to the same tumour depressed ACTH secretion without affecting the output of alpha-MSH. The present data suggest that the tumours in these subjects are responsive to oCRF and arise from corticotrophs rather than melanotrophs.