THE EFFECT OF FRUSEMIDE ON OXYTOCIN-INDUCED CONTRACTIONS OF THE RAT MYOMETRIUM

Oxytocin-induced contractions of isolated strips of oestradiol-treated rat myometrium were found to be affected by exposure to the diuretic frusemide. At a concentration of 20 mu M, frusemide transiently increa sed the force of contraction over a period of approximately 10 min. Af ter this time there was a progressive fall in contractile force. At a higher concentration of 200 mu M, only the progressive fall in force w as seen until contractions were completely abolished. Frusemide has be en reported to increase the activity of cAMP-phosphodiesterase in tiss ue extracts from oestradiol-treated rat myometrium. Therefore, the cha nges in contraction due to exposure to frusemide may be a reflection o f the changes in intracellular cAMP resulting from a stimulation of cA MP-phosphodiesterase activity. In support of this idea, addition of di butyryl cAMP was found to partially restore contractions after frusemi de treatment. These data suggest that frusemide may be a useful tool i n the manipulation of tissue cAMP levels in order to determine the dif ferent roles of cAMP in the oestradiol-treated rat myometrium.