1. Cholinergic mechanisms in the systemic vasculature of the rainbow trout have been pharmacologically analysed using an isolated trunk preparation perfused at constant flow. 2. Acetylcholine (ACh) causes a two component vasoconstriction comprising a rapid initial peak (response A) and a long-lasting tail on the initial peak (response B). Skeletal muscle contraction is not involved in either response. 3. Response B has a high dose threshold, is nicotinic in nature, and is blocked by α-adrenoreceptor antagonists, procaine, and 0 mM Ca++ plus 20 mM Mg++, indicating a classical indirect action of ACh on sympathetic neurons or chromaffin tissue to cause the release of an adrenergic transmitter. 4. Response A has a lower dose threshold, is nicotinic in nature, is resistant to α-adrenergic, muscarinic cholinergic, and adrenergic neuron blockade, is insensitive to tetrotoxin and 0 mM Ca++ plus 20 mM Mg++, but is blocked with some specificity by procaine. 5. The properties of the nicotinic receptors of response A differ from those of the traditional ganglionic and skeletal muscle types of higher vertebrates. 6. Response A is mimicked by ATP, which appears to act by a direct mechanism in the preparation. 7. It is concluded that response A reflects either direct stimulation of nicotinic receptors on vascular tissue or an indirect nicotinic effect resulting in the release of a non-adrenergic, non-cholinergic transmitter such as ATP. 8. Unlike the situation in higher vertebrates, no muscarinic dilatory responses to ACh occur in the preparation.
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics
- Animal Science and Zoology