Méthode de mesure des vitesses d'épuration métabolique et de sécrétion du cortisol chez l'anguille (Anguilla anguilla L.)

Abstract

Classical methods for the analysis of steroid dynamics were adapted to measure the metabolic clearance rate and the secretion rate of cortisol in the European eel using (1, 2-3H) cortisol as a tracer. 1. Measurements were made whilst the eels were in the steady state; stresses which usually result from anaesthesia and handling were avoided by chronic catheterization of the blood vessels of the swim bladder. In this way, the plasma cortisol level were constant; thus, it was possible to obtain valid measurements of the cortisol secretion rate knowing the metabolic clearance rate and the plasma cortisol level. 2. In the eel, cortisol and cortisone together form a chemical compartment', derived originally from cortisol secreted by the interrenal gland and subsequently transformed partially into cortisone in the plasma and maintained thenceforth in dynamic reversible equilibrium. Consequently, the metabolic clearance rate of cortisol has been calculated from the known changes in concentration of both (1, 2-3H) cortisol and (1, 2-3H)cortisone in the plasma deduced from dichloromethane-extractable plasma radioactivity, 72% of which is always attributable to these two steroids from the moment that the radioactivity begins to decline regularly as a function of time (15-30 min after the injection). 3. After a single injection of (1,2-3H) cortisol, the interpretation of the disappearance curve by compartmental analysis is complicated by the delay of tracer distribution and by the evident variability in the initial portion of the curve. Disappearance curves have accordingly been analysed in a more rigorous fashion either by integrating the area under each curve which allows one to calculate individually the metabolic clearance rates, or by integrating according to Normand, M., and Fortier, C. (1970. Can. J. Physiol. Pharmacol. 48, 274-281) which allows one statistical treatment of data. 4. Estimates of the metabolic clearance rate of cortisol were made in a satisfactory manner by either one of the two integration methods. They were also very similar to estimates obtained by prolonged infusion of (1, 2-3H) cortisol to constant specific activity into eels maintained under identical experimental conditions.