Pharmacological Investigation of Ritodrine Hydrochloride, a Beta2-Adrenoceptor Stimulant

Abstract

Ritodrine hydrochloride (ritodrine) was effectively prescribed for the prevention of premature labor. The mode of action of ritodrine on the uterus and heart was investigated in comparison with those of isoxsuprine and isoproterenol. Ritodrine (10-8-10-6 M) suppressed the spontaneous motility of pregnant rat uterus and showed positive chronotropic action at the doses of 10-6-10-4 M in guinea-pig atria. In the Ca2+-free, K+-rich Tyrode solution, ritodrine suppressed the Ca2+ induced contracture of pregnant rat uterus, while it potentiated the carbachol induced contraction. Ritodrine increased the amount of cAMP in the uterus but not in the heart. This action of ritodrine was suppressed by pretreatment with propranolol (10-6 M). Ritodrine apparently causes actions through activation of cAMP production, as in the case of isoproterenol and it acts more selectively on .beta.2-adrenoceptors than on .beta.1-adrenoceptors.