EFFECTS OF METOCLOPRAMIDE AND ISOPRENALINE IN THE RAT VAS DEFERENS; INTERACTIONS WITH α‐ADRENOCEPTORS

E-ISSN： 1476-5381|71|1|113-120

ISSN： 0007-1188

Source： BRITISH JOURNAL OF PHARMACOLOGY (ELECTRONIC), Vol.71, Iss.1, 1980-01, pp. : 113-120

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Abstract

1Metoclopramide (2.8 to 280 μm) augmented contractions of rat vas deferens preparations induced by field stimulation (6 Hz for Is). This effect was antagonized by phentolamine (0.1 μm). Metoclopramide (2.8 to 280 μm) did not affect phenylephrine‐induced contractions.2Metoclopramide (2.8 to 280 μm) antagonized the inhibitory effects of clonidine on the contractions induced by field stimulation, but not the inhibitory effects of purine nucleosides.3From these results it is concluded that metoclopramide (2.8 to 280 μm) is a presynaptic α‐adrenoceptor antagonist in the rat vas deferens.4Following β‐adrenoceptor blockade with (±)‐propranolol (3.3 μm), (‐)‐isoprenaline (0.47 to 14 μm) inhibited responses to field stimulation but not to phenylephrine. These propranolol‐resistant effects of isoprenaline were antagonized by metoclopramide (2.8 to 280 μm) and by phentolamine (0.1 to 10 μm), indicating that isoprenaline may stimulate presynaptic α‐adrenoceptors in this preparation.