Effects of thyroidectomy and L-thyroxine on adrenaline and noradrenaline concentrations in the adrenal glands and plasma of rats during the pro-oestrous phase of the oestrous cycle and pregnancy.

1 The influence of thyroidectomy upon the adrenaline and noraddrenaline content of adrenal glands and plasma in mature female rats in pro-oestrus and in pregnant rats was studied. 2 Adrenal adrenaline and noradrenaline declined significantly after thyroidectomy in pro-oestrous and pregnant females but the effects were more marked in pregnant females. 3 Plasma adrenaline increased by 160% after thyroidectomy in pro-oestrous females but similar treatment resulted in 85% decrease in plasma adrenaline of pregnant rats. The loss of thyroid increased plasma noradrenaline significaantly in both groups of females. 4 The administration of L-thyroxine of thyroidectomized females increased adrenal noradrenaline stores of both the groups. The effects of L-thyroxine in pro-oestrous females resulted in decreased adrenaline stores of the adrenals but the pregnant group showed an increase. Plasma noradrenaline increased after treatment of pro-oestrous and pregnant-thyroidectomized females with L-thyroxine. 5 The thyroidectomized females in pro-oestrous phase receiving L-thyroxine showed a return to the control values for plasma adrenaline but in pregnant females whose plasma adrenaline had declined after thyroidectomy no such change occurred. 6 Considering the variations in total catecholamines in plasma and adrenals, it was observed that the loss of thyroid hormones results in an increase in total catecholamine storyage and output in the blood. The results provide evidence that the thyroid-catecholamine interrelation is significantly affected by pregnancy.