Jan 1, 1989

Responses of the isolated rectum of the rainbow lizard (Agama agama) to sympathomimetics

Canadian Journal of Physiology and Pharmacology
A L Inyang, D T Okpako


The relaxant effects of isoprenaline, noradrenaline, and adrenaline on the isolated rectum of the rainbow lizard (Agama agama) were studied. Responses were measured as a reduction of carbachol-induced contractions for each sympathomimetic agent. Isoprenaline, adrenaline, noradrenaline produced a dose-dependent relaxation of this preparation and the order of potency was as given. The pD2 value of 8.15 +/- 1.88 obtained for isoprenaline was significantly different (p less than 0.05) from those for adrenaline (5.80 +/- 0.90) and noradrenaline (5.25 +/- 1.18). H35/25, propranolol, and practolol competitively antagonized the relaxant effects of isoprenaline on the isolated lizard rectum. The pA2 values for these beta-adrenoceptor antagonists did not differ significantly (at p less than 0.05). alpha-Adrenoceptor antagonists, phentolamine and phenoxybenzamine, failed to alter the relaxant responses of these sympathometics to any appreciable extent. These results are interpreted to suggest that the relaxant effect produced by these sympathomimetics are mediated predominantly by beta-adrenoceptors that are not significantly differentiated into subtypes. alpha-Adrenoceptors in this preparation contribute minimally to the observed inhibit...Continue Reading

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Mentioned in this Paper

Smooth Muscle
Norepinephrine, (+, -)-Isomer
Adrenergic alpha-Antagonists
Epinephrine Acetate
Beta-adrenergic receptor

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