CHANGES IN BETA-ADRENERGIC RECEPTORS UNDER LONG-TERM APPLICATION OF RITODRINE IN PREGNANT-RAT MYOMETRIUM

Changes in beta-adrenergic receptor density under long-term applicatio n of ritodrine were investigated using longitudinal muscle strips of d ay-21-pregnant-rat myometrium. Membrane (-)[H-3]dihydroalprenolol bind ing sites were increased by 3.1 X 10(-8) M ritodrine, with a maximum i ncrease at 3.1 X 10(-7) M, followed by a gradual decrease at higher co ncentrations. Under long-term application of a lower dose (1.5 X 10(-7 ) M) of ritodrine, the number of the binding sites increased up to 20 min, then decreased to the control level and fluctuated after 90 min. These results suggest that at lower doses, ritodrine might activate ad enylate cyclase, resulting in conformational changes in the receptors, and that receptor density might vary in parallel with cellular cAMP p roduction under long-term application of ritodrine.