CLONIDINE LOWERS ALPHA-MSH-LIKE IMMUNOREACTIVITY IN HUMAN PLASMA

In a group of seven healthy subjects, the effects of acute intravenous administration of clonidine, a selective alpha2 receptor stimulator, on plasma alpha-MSH-LI concentrations were measured. In comparison wit h saline, clonidine (0.075 mg) significantly reduced alpha-MSH-LI conc entrations, with a maximum fall between 30 and 60 min., followed by a return to basal concentrations at 120 min.; no significant variations in plasma ACTH and cortisol were seen. The precise mechanism of this e ffect is unclear. Our study suggests that separate regulatory mechanis ms exist for the secretion of POMC related peptides in the corticotrop h and melanotroph cells of the human pituitary gland.