Effects of metoclopramide and isoprenaline in the rat vas deferens; interactions with alpha-adrenoceptors.
1 Metoclopramide (2.8 to 280 microM) augmented contractions of rat vas deferens preparations induced by field stimulation (6 Hz for 1 s). This effect was antagonized by phentolamine (0.1 microM). Metoclopramide (2.8 to 280 microM) did not affect phenylephrine-induced contractions. 2 Metoclopramide (2.8 to 280 microM) antagonized the inhibitory effects of clonidine on the contractions induced by field stimulation, but not the inhibitory effects of purine nucleosides. 3 From these results it is concluded that metoclopramide (2.8 to 280 microM) is a presynaptic alpha-adrenoceptor antagonist in the rat vas deferens. 4 Following beta-adrenoceptor blockade with (+/-)-propranolol (3.3 microM), (-)-isoprenaline (0.47 to 14 microM) inhibited responses to field stimulation but not to phenylephrine. These propranolol-resistant effects of isoprenaline were antagonized by metoclopramide (2.8 to 280 microM) and by phentolamine (0.1 to 10 microM), indicating that isoprenaline may stimulate presynaptic alpha-adrenoceptors in this preparation.
D000818:Animals; D001549:Benzamides / Q000494:pharmacology; D003000:Clonidine / Q000494:pharmacology; D004558:Electric Stimulation; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D008787:Metoclopramide / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D011941:Receptors, Adrenergic / Q000187:drug effects*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D014649:Vas Deferens / Q000187:drug effects
D001549:Benzamides; D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D011433:Propranolol; D008787:Metoclopramide; D007545:Isoproterenol; D003000:Clonidine