The action of oxytocin and synthetic analogues on the isolated mammary-gland myoepithelium of the lactating rat; effect of some ions.

Abstract

SUMMARY The contractile response of mammary-gland strips from lactating rats to oxytocin varied with the concentration of calcium ions in the organ bath; calcium could be partially substituted by strontium but not by magnesium. High concentrations of potassium did not substantially affect the response to oxytocin. In these and several other respects the mammary gland myoepithelium resembles uterine smooth muscle, notwithstanding the differences in morphology and embryonal origin. The effects of 12 synthetic analogues of oxytocin modified in sequence positions 1, 2, and 3 of the peptide chain on the rat mammary-gland strip were examined. None of the analogues showed a higher potency than oxytocin. However, the mammary-gland strip was less sensitive to the structural changes represented in this series of analogues than the rat uterus in vitro. The action of some of the analogues on the mammary-gland strip differs from that of oxytocin in the time-course of the response.