The effect of oxytocin on contractile responses and 45Ca movements in rat isolated aortic strips.

The effects of oxytocin (Oxt) on contractile responses and transmembrane Ca fluxes were studied in rat isolated aortic strips. Oxt (50-1000 mu ml-1) induced a dose-dependent contractile response and spontaneous myogenic activity. The Oxt-induced contractile response was not inhibited by pretreatment of aortic strips with phentolamine plus practolol, atropine, diphenhydramine plus cimetidine or indomethacin, but was significantly reduced by verapamil or deamino-ethyl-Oxt. The dose-response curve for Oxt was shifted upwards and to the left by increasing the Ca concentration of the medium from 1.8 to 4 mM. Oxt also shifted upwards the dose-response curve to Ca (1 to 5 mM) in aortic strips incubated in K depolarizing Ca-free media. Oxt increased the La3+-resistant 45Ca content without altering 45Ca efflux. The present results suggest that in rat isolated aortic strips Oxt produces a contractile response which, as previously found with other neurotransmitters, can be partly attributed to an increase of Ca influx through receptor-operated channels and to the release of Ca from intracellular stores.