Effects of Isoprenaline on the Time Course of the Cyclic AMP Level in Rat Uterus

Abstract

Isoprenaline markedly relaxed rat uterine muscle and increased its content of cyclic(c)AMP. The cAMP concentration reached its highest value, about 10 times the control after 3 min after which it declined rather quickly at first but later more slowly. After 60 min the cAMP content reached twice the prestimulation value. The muscle remained relaxed all the time. If the incubation medium from the uterus treated with isoprenaline for 60 min was added to a fresh muscle, a normal response was elicited. Addition of a new dose of isoprenaline to a muscle previously incubated with isoprenaline for 60 min only gave a minimal rise in cAMP after 3 min. The presence of catechol or corticosterone, which both decreased the inactivation of isoprenaline, showed no effect on the decrease of the isoprenaline-stimulated cAMP level. Nor could the decrease in the cAMP response be prevented in the presence of GTP, F-, adenosine or in Ca2+-deficient medium. The addition of theophylline and puromycin both lead to a slower decline of cAMP content, but after 60 min the value returned to near that seen after only isoprenaline. The change in the capacity of the preparations to accumulate cAMP may be a result of either changes in the .beta.-adrenoceptors or in the cyclase-system.