Surfactant effects on adrenergic responses in the gills of the flounder (Platichthys flesus L.)

Summary

The interactions between catecholamines and surfactants was investigated in perfused gills of the marine teleostPlatichthys flesus L. The activity of the branchial ion pumps was monitored via the electrogenic transepithelial potential (inside positive) measured in gills bathed and perfused with identical saline. Vascular resistance of the arterio-arterial and arterio-venous pathway was also recorded simultaneously by measuring respectively the afferent perfusion pressure and venous flow in gills perfused at constant flow and at constant efferent pressure. The specific effects of respective α- and β-adrenergic receptor stimulation was investigated by the administration of discrete doses of either adrenaline in the presence of 10 μmol l⁻¹ propranolol or isoprenaline in the perfusate. In the absence of surfactants the α-adrenergic effects were an inhibition of electrogenic ion transport, a decrease in venous flow and an increase in the vascular resistance of the arterioarterial vascular pathway. In contrast the β-adrenergic effects consisted of a stimulation of electrogenic ion transport and a vasodilation of the arterio-arterial pathway. Both anionic (linear alkyl sulphonate; sodium lauryl sulphate) and non-ionic (nonyl phenol ethoxylate; synthetic alcohol ethoxylate) surfactants were administered in the perfusate at nominal concentrations of 1 μmol l⁻¹ (0.3–0.5 mg l⁻¹). None of these compounds had any effect on the affinity or the efficacy of the α-adrenergic responses. In contrast there was a significant reduction in the efficacy of isoprenaline in the presence of all of the surfactants used but only in the case of the synthetic alcohol ethoxylate was there an effect on the affinity of this agonist for the β-adrenergic receptor. The results are discussed in the context of the mechanism of action of these environmental contaminants and the nature of adrenergic receptors in the gill.