Synthetic peptide octarphin (TPLVTLFK) inhibits the activity of the hypothalamus-pituitary-adrenal axis through nonopioid β-endorphin receptor

The synthetic peptide octarphin (TPLVTLFK) corresponding to the sequence 12-19 of β-endorphin, a selective agonist of nonopioid β-endorphin receptor, was labeled with tritium to specific activity of 29 Ci/mmol. The analysis of [3H]octarphin binding to rat pituitary and adrenal cortex membranes revealed the existence of one type of binding sites (receptors): Kd 5.9 and 35.6 nM, respectively. Octarphin at concentrations of 1-1000 nМ was shown to inhibit the adenylate cyclase activity of rat adrenocortical membranes, while its intramuscular injection at doses of 10-100 μg/kg was found to reduce the secretion of corticosterone from the adrenals to the bloodstream. Thus, the nonopioid receptor of β-endorphin may be involved in the regulation of the activity of the pituitary and adrenal glands.