Serum corticosterone as a quantitative test of the phlogistic potency of various agents topically applied in the rat.

The application into the rat conjunctiva of various phlogistic agents, such as croton oil, mustard oil and formaldehyde, elicits an increase of serum corticosterone linearly related to the log of the applied concentrations, so that from their parallelized regression lines it is possible to calculate the phlogistic potency of each tested agent in reference to croton oil. The time kinetic of such an increase (elicited by croton oil) is compared with that of two other parameters previously adopted as indirect quantitative indices of the phlogosis: the adrenal ascorbic acid depletion and the liver tyrosine-alpha-ketoglutarate transaminase increase. Serum corticosterone is shown to be the quickest and the most sensitive of the adopted indices, even if the phlogistic potency of the tested agents and the precision of these evaluations substantially coincides whatsoever the index adopted. Finally the pathways of adrenocortical activation are investigated and it is shown that the activation may be peripherally blocked by topical application of corticosteroids (but not of local anesthetics) and centrally by hypophysectomy or parenteral administration of pentobarbital plus morphine.