ISOPROTERENOL-INDUCED RELAXATION, PHOSPHORYLASE ACTIVATION AND CYCLIC ADENOSINE-MONOPHOSPHATE LEVELS IN POLARIZED AND DEPOLARIZED RAT UTERUS

  • 1 January 1976
    • journal article
    • research article
    • Vol. 198  (3) , 539-547
Abstract
Catecholamines are reported to relax uterine and other types of smooth muscle by increasing tissue levels of cyclic[c]AMP. Isoproterenol completely relaxed uterine strips obtained from estrogen-primed rats and also increased tissue levels of cAMP and phosphorylase a. In uterine strips depolarized and put into contracture for 15 min by 127 mM K+, isoproterenol did not increase phosphorylase a or cAMP but was still capable of producing relaxation. When uterine strips were exposed to the methoxy derivative of verapamil, D-600, a compound known to prevent the influx of Ca, the uterus relaxed completely without an increase in cAMP. The addition of isoproterenol at this stage resulted in an increase in cAMP similar to that noted in nondepolarized uterine strips. The addition of 127 mM K+ also resulted in time-dependent biochemical changes and contracture. cAMP was increased 3-fold after 2 min of K+ depolarization and phosphorylase a was also increased. The increase in cAMP was prevented by propranolol but propranolol did not affect the contracture response to K+. D-600 prevented contracture but did not affect the K+-induced increase in cAMP. An increase in whole tissue levels of cAMP were not necessary in order for isoproterenol to relax depolarized rat uterine strips. Intracellular Ca levels may affect the level of cAMP in the rat uterus.

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