THE EFFECT OF OVINE CORTICOTROPHIN RELEASING FACTOR (oCRF), BROMOCRIPTINE AND TRH ON THE SECRETION OF ACTH AND α‐MSH IN NELSON'S SYNDROME AND CUSHING'S DISEASE

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Abstract
SUMMARY: The circulating levels of ACTH and α‐melanocyte stimulating hormone (α‐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 α‐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 α‐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 α‐MSH following either bromocriptine or TRH. Cultured tumour cells from one case of Cushing's disease showed a corticotrophic response but no change in α‐MSH to oCRF and the response was enhanced by vasopressin. Bromocriptine added to the same tumour depressed ACTH secretion without affecting the output of α‐MSH. The present data suggest that the tumours in these subjects are responsive to oCRF and arise from corticotrophs rather than melanotrophs.

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