Interactions between the effects of endothelin-1, clonidine and yohimbine on electrically-induced contractions in rat vas deferens.
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.
Mutafova-Yambolieva
V
V
Institute of Physiology, Bulgarian Academy of Sciences, Sofia.
Petkov
O
O
Staneva-Stoytcheva
D
D
Lasova
L
L
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D003000:Clonidine / Q000494:pharmacology*; D004558:Electric Stimulation; D016232:Endothelins / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D014649:Vas Deferens / Q000187:drug effects; D015016:Yohimbine / Q000494:pharmacology*
D016232:Endothelins; D010656:Phenylephrine; D015016:Yohimbine; D000255:Adenosine Triphosphate; D003000:Clonidine