1. The adrenergic receptors in the systemic vasculature of the rainbow trout have been pharmacologically characterized using an isolated trunk preparation perfused at constant flow. 2. The dominant α-constrictory receptors in the trunk are similar to those of mammals in their adrenaline/noradrenaline potency ratio (3.2/1.0), and in the natures of their blockade by phenoxybenzamine and yohimbine. However they are more selective than mammalian α-receptors, responding directly to only adrenaline and noradrenaline, and not to phenylephrine, methoxamine, dopamine, or isoprenaline. 3. Tyramine and dopamine cause weak α-adrenergic constriction, apparently indirectly through the release of catecholamine stores. 4. The α-adrenergic response is susceptible to inhibition by competitive β-blocking agents, but this effect is due to non-competitive antagonism with a point of action beyond the adrenergic receptor. 5. β-dilatory receptors of the β2, as in the homologous systemic vasculature of mammals, also apparently occur, but their dilatory actions cn only be demonstrated against a background of α-adrenergic vasoconstriction. 6. The racemate d,l-isoprenaline is a more potent vasodilator than the pure isomer l-isoprenaline during α-adrenergic tone because of the competitive α-blocking activity of the d-isomer.
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics
- Animal Science and Zoology