Effect of barbital on the pituitary-thyroid axis.

Barbital (diethylbarbituric acid), administered via the drinking water (0.1% solution), elicited mild goitrogenic responses in rats (p less than 0.05), accompanied by a slight depression in serum T4 titers (p less than 0.02). The goitrogenic responses appeared to be the result of slight elevations in the serum TSH levels and in the case of neonate rats, whose mothers were fed barbital during pregnancy and lactation, the elevations of TSH in the circulation were pronounced (p less than 0.01). However, continuation of barbital treatment beyond puberty resulted in mean serum TSH titers declining to twice the mean control values so that only the variances between the data were different(p less than 0.05). This group of young adults showed endocrine profiles which resembled those of more mature rats. The latter group included the mothers of these young adults and of the neonates. In contrast to the action of barbital, feeding rats 0.05% propylthiouracil (PTU) in the drinking water caused substantial increases in mean serum levels of TSH (p less than 0.001) and goiter size (p less than 0.001). Moreover, the precipitous declines in serum T4 elicited by PTU were of far greater magnitude than that caused by barbital (p less than 0.001).