Interactions between the effects of endothelin-1, clonidine and yohimbine on electrically-induced contractions in rat vas deferens

Mutafova-Yambolieva, V.; Petkov, O.; Staneva-Stoytcheva, D.; Lasova, L.

General Pharmacology 23(3): 529-534


ISSN/ISBN: 0306-3623
PMID: 1511861
DOI: 10.1016/0306-3623(92)90123-2
Accession: 040468967

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1. The relationship between endothelin-1(ET-1)-induced effects on the contractile responses of epididymal portion of rat vas deferens elicited by field electrical stimulation (FES: 80 V, 1 msec, 0.1 Hz) and the effects of the alpha 2-adrenoceptor agonist clonidine and the alpha 2-adrenoceptor antagonist yohimbine were studied. 2. ET-1 (0.01 nM-0.1 microM) concentration-dependently increased the FES-induced contractions. 3. ET-1 (0.1 nM-0.1 microM) reversed the inhibitory effect of clonidine on the FES-evoked contractions whereas ET-1 applied before clonidine exerted a dual effect on the clonidine-induced inhibition of the FES-evoked contractions. 4. The ET-1-induced enhancement of FES-induced contractions was potentiated in the presence of 1 microM yohimbine and was not observed at all in the presence of 10 microM yohimbine. Yohimbine, applied at concentrations of 1 and 10 microM exerted similar blocking effects on the alpha 1-adrenoceptor agonistic effects of phenylephrine. However, yohimbine at a concentration of 10 microM markedly potentiated the contractile effect of exogenous adenosine 5'-triphosphate (ATP), 30 microM. Tetrodotoxin abolished this effect of yohimbine. 5. The results presented here suggest the existence of modulating interactions between the ET-1-evoked increase of FES-induced contractions of rat vas deferens and the alpha 2-adrenoceptor drugs clonidine and yohimbine.