Suppression of ACTH secretion by synthetic MSH-release inhibiting factor Pro-Leu-Gly-NH2 in Addison's disease.

The regulation of release of MSH and ACTH seems to be closely related. The effect of Pro-Leu-Gly-NH2, the most active MSH-release inhibiting factor (MIF), was investigated on ACTH-hypersecretion in six patients suffering from primary adrenocortical insufficiency. MIF was infused at constant rates with stepwise increase in concentration (0.25 mg, 2.5 mg, 25.0 mg/30 min). Plasma ACTH-levels were measured radioimmunologically at 10 minutes intervals. In four cases there was a remarkable decrease (P less than 0.005) in the ACTH plasma level of more than 50% as compared to the elevated starting levels of 800 to 1400 pg/ml. It is concluded that under certain circumstances MIF could play a role in the regulation of ACTH-secretion.