Prolactin-releasing activity of dermorphin, a new synthetic potent opiate-like peptide, in normal human subjects

Dermorphins (D) are heptapeptides (H-Tyr-D-Ala-Phe-Gly-Tyr-X-Ser-NH2; X, Pro or Hyp) with powerful central and peripheral opiate-like activity, originally isolated from the skin of South American frogs. To study the effect of a synthetic D on PRL secretion in man, either D (5.5 micrograms/kg . min for 30 min) or D-placebo (0.9% saline) infusion over 30 min was administered iv in random sequence to 11 volunteers (6 women and 5 men). In all the subjects, D induced a significant increase in the levels of PRL, more consistently in women than in men. To investigate whether the increase in PRL was due to the opiate agonist properties of D, the study was repeated in the same subjects during naloxone infusion. The PRL response to D was completely suppressed, suggesting that the peptide exerts its effect on PRL release via an opiate receptor stimulation of the mu-type. These data allow us to conclude that D may affect PRL release in humans; however, further investigation is necessary before any physiological significance might be attributed to D in man.