CATECHOLAMINES: THYROID FUNCTION AND THE SEXUAL CYCLE IN RATS

Abstract

ABSTRACT Investigations were performed on the daily urinary excretion of noradrenaline (NA), adrenaline (A) and 4-hydroxy-3-methoxymandelic acid (vanillylmandelic acid) and on the concentration of both amines in different areas of the central nervous system, in control, triiodothyronine (T3), and 131I-treated Wistar rats in order to gain some knowledge about the interrelation between thyroid function, sexual hormones and catecholamines. Cyclic variations were observed in NA excretion and in the excreted NA/A relationship in the three groups of animals. T3 increased NA excretion and decreased vanillylmandelic acid excretion in both sexes. A excretion did not show cyclic changes, nor was it influenced by the thyroid function. In the hypothalamus, there was an increase of NA in experimental hyperthyroidism. No changes were observed in 131I-treated animals. Progesterone stimulated the synthesis and/or depletion of NA storage while oestrogens had the reverse effect, making it also possible for the latter to potentiate the activity of phenylethanolamine-N-methyltransferase. The thyroid hormones inhibited monoamine-oxidase and extended the half life of catecholamines, a fact which was corroborated by the increase in NA excretion and the decrease in vanillylmandelic acid.