[Age and reduction in the sensitivity of the hypothalamo-hypophyseal complex to the inhibiting effect of dexamethasone. Effect of stress, polypeptide epiphyseal extract and phenformin].

It was shown in experiments on rats that sensitivity of the hypothalamo-hypophysial complex to the inhibitory action of dexamethazone decreased in adult and old rats in comparison with the young sexually mature animals. Single administration of l-tryptophane and L-DOPA decreased, and 5-day administration of the both preparations potentiated the inhibitory action of dexamethazone. Resistance to dexamethazone action occurred under conditions of other stress, whereas potentiation of the inhibitory effect of dexamethazone took place under the effect of acetic acid polypeptide extract from the epiphyses and the antidiabetic biguanide--phenoformine. Arguments are presented in favour of the role of biogenic amines in the age-related increase of the sensitivity threshold of the central structures to the corticosteroid inhibition.