Technical and physiological problems rising from the application of the measurement methods of the peripheral metabolism of cortisol
Manin, M.; Delost, P.
Journal de Physiologie 73(1): 47-72
1977
ISSN/ISBN: 0021-7948 PMID: 886481 Document Number: 114079
Two techniques, continuous infusion and a single injection of radio-labeled hormone, were used to assess the cortisol metabolism parameters of the guinea pig under chronic cannulation. During continuous infusion carried out on the unanesthetized guinea pig, the concentration of radioactive cortisol in a steady state must be measured from samples of plasma taken after 120 min to avoid the risk of errors resulting from variations in appearance of the hormonal equilibrium. The establishment of a steady hormone state may be brought about by a previous injection of a single dose of radioactive hormone. The method of infusion, whether i.v. or intracarotidian, does not influence the metabolic clearance rate of cortisol. Anesthesia with chloral does not change the metabolic clearance rate of cortisol. Although it is difficult to obtain a basic cortisol level in the blood of the unanesthetized animal during infusion, the metabolic clearance rate of cortisol remains stable within the very large limits of blood cortisol levels. The continuous infusion of labeled cortisol is more satisfactory than a single injection of hormone. In the guinea pig, the cortisol metabolism shows physiological variations: the metabolic clearance rate and the cortisol production rate, in proportion to body weight, are higher in the young ones than the adult ones; there are sexual differences in the metabolic clearance rate of cortisol in favor of the male, both at puberty and in the adult.