Vascular Resistance Responses of an Eel Tail Preparation: Alpha Constriction and Beta Dilation

Abstract

1. An isolated, saline-perfused, eel tail preparation is described. This preparation was easily prepared and did not suffer from progressive deterioration, as indicated by stable baseline resistance with time and maintained responsiveness to drugs. 2. Elevation of caudal venous pressure caused a reduction in resistance of about 10% per 0·5 kPa. Addition of 3% or 5% human serum to the perfusate increased baseline resistance and imparted a degree of autoregulation to the preparation. 3. Full dose-response curves for the preparation's resistance responses to adrenaline (AD), noradrenaline (NA), and isoprenaline are presented. 4. AD and NA increased resistance, indicating the presence of alpha adrenergic receptors. AD was more potent than NA; the mean potency ratio was 2·78:1·00 (AD:NA). 5. Isoprenaline decreased resistance, indicating beta adrenergic receptors. From the relative potencies of isoprenaline << AD < NA in stimulating these receptors, they are classified as beta two adrenergic receptors. 6. The possible physiological functions of alpha and beta responses of the eel tail are discussed.