The action of relaxin, fenoterol and etilefrine on uterine motility of the rat.

In uterine motility tests in virgin rats, the inhibitory action of the peptide hormone relaxin has been compared with the actions of fenoterol and etilefrine. At molecular levels, relaxin and fenoterol showed similar uterine inhibitory activity. Etilefrine was markedly less effective in inducing uterine relaxation. By pretreatment with propranolol, the inhibitory action of both fenoterol and etilefrine could be prevented but not the tocolytic effect of relaxin. Etilefrine, in higher doses, developed alpha-receptor activity as demonstrated by resumed uterine contractions. The doses required to induce beta 2- and alpha-activities differed by a factor of approximately 4,000.