Effect of L-thyroxine and carbimazole on brain biogenic amines and amino acids content and circulating levels of thyroid hormones has been investigated in rats. L-thyroxine treatment caused marked elevation of 5-HT, histamine and glutamate along with the decline in the level of GABA whereas administration of carbimazole had a contrary effect on rat hypothalamus. Further, L-thyroxine administration also raised histamine as well as glutamate content and decreased GABA level in thalamic region of the rat brain but carbimazole treatment reduced 5-HT and glutamate content in this area of the rat brain. Similarly, cortical content of 5-HT and histamine also increased following L-thyroxine administration whereas carbimazole treatment lowered 5-HT, histamine and glutamate levels. Simultaneously, there was a considerable rise in the circulating levels of T3 and T4 in L-thyroxine-treated rats and a marked reduction in their levels in carbimazole-treated rats. There is a positive correlation between these amines and the thyroid hormone level. Thus, the results suggest that L-thyroxine and carbimazole administration cause marked alteration in biogenic amines and amino acids in rat brain, which may have an important role in the functioning of thyroid gland.

Circulating levels of T3, T4, \g=g\-amino-butyricacid, glutamate, 5-hydroxytryptamine, histamine, monoamine oxidase and histaminase were studied in 45 (2 5M, 20F) hyperthyroid patients and 46 (2 5M, 21F) normal healthy volunteers. Increased levels of blood 5-hydroxytryptamine, histamine and glutamic acid were observed along with elevated T3 and T4, whereas plasma \g=g\-aminobutyric acid, monoamine oxidase and histaminase activities were found to be low in both male and female patients.After three months of treatment, circulating levels of 5-hydroxytryptamine, histamine and glutamic acid decreased significantly along with normalization of thyroid hormones and with an increase in the concentrations of \g=g\-aminobutyric acid, monoamine oxidase and histaminase. There was a positive correlation between these amines and thyroid hormone levels. The findings thus suggest that alterations in the metabolism of biogenic amines may be related to an altered metabolism in thyrotoxicosis, and these parameters may prove to be useful markers for diagnosis and follow-up of these patients.Biogenic amines play an important role in the regulation of many physiological and psychological processes. Recently, considerable attention has been paid to eva¬ luating the effect of biogenic amines on thyroid function. It has been observed that not only TSH but also longacting thyroid stimulator (LATS) may interact with biogenic amines (1). Experimental studies have also shown a close association between biogenic amines and thyroid function. It has been reported that 5-hydroxy¬ tryptamine ( 5-HT) activity stimulates iodine metabolism in isolated thyroid cells which leads to the formation of iodothyronines, this effect being similar to that of catecholamines (2). Ericson et al.(3) showed that both 5-HT and catecholamines stimulate thyroid hormone release in vivo. Further, 5-hydroxytryptophane is known to elevate TSH secretion in rats and humans (4, 5), and it has been reported that intravenous injection of histamine H? agonist enhances Tj response to TRH and thus interacts with thyroid function. Sanchez Herrenz et al. (6) on the other hand reported that y-aminobutyric acid (GABA) inhibits TSH release in experimental ani¬ mals. Thus, it was considered to be of interest to study the metabolic status of these amines in hyperthyroid patients in order to elucidate the possible association of these amines with thyroid dysfunction.Patients and methods We studied 46 (2 5M, 2 IF) normal healthy volunteers (as controls), aged 25 to 45 years, non-obese, with normal endocrine and metabolic functions, and with no family history of thyrotoxicosis; and 45 (25M, 20F) hyperthyroid patients, aged 20 to 50 years. The diagno¬ sis of thyrotoxicosis was based on clinical profile and biochemical investigations including measurements of serum T? and T4 (RIA methods). All the subjects were selected from the Thyroid Clinic of S.S. Hospital, Institute of Medical Sciences, Bañaras Hindu University. None of the controls were taking any drug or intoxicants like alcohol, mar...

Circulating levels of 5-hydroxytryptamine (5HT), histamine, monoamine oxidase (MAO), histaminase, tri-iodothyronine (T3) and thyroxine (T4) were studied in L-thyroxine and carbimazole treated rats. Increased concentrations of 5-HT, histamine, glutamate, T3 and T4 were recorded in L-thyroxine-treated rats while plasma gamma-aminobutyric acid (GABA), MAO and histaminase levels were significantly decreased. Considerable reduction in 5-HT, glutamate, T3 and T4 with trend towards the rise in plasma levels of MAO and histaminase was noticed in carbimazole treated group. There was a significant correlation between these amines and thyroid hormone values. The findings suggest that alterations in the metabolism of thyroid hormones may have a link with the altered metabolism of biogenic amines.