Influence of Hypo- and Hyperthyroidism on Noradrenaline Metabolism in Brown Adipose Tissue of the Developing Rat

Abstract

We studied the noradrenaline content, and monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT) activities in brown adipose tissue (BAT) of normal, hypothyroid, and hyperthyroid developing rat. In the newborn, thyroid hormones are necessary for the increase in noradrenaline content which occurs between 0 and 5 days. Hypothyroidism increases both MAO and COMT activities. Hyperthyroidism decreases MAO activity but not noradrenaline content or COMT activity. In the full-term fetus, hypothyroidism decreases noradrenaline content as in the newborn, and also decreases MAO and COMT activities. It is suggested that thyroid hormones could modulate BAT nonshivering thermogenesis by regulating the level of noradrenaline, the direct mediator of heat production.

Uptake and Turnover Rate of Norepinephrine in Interscapular Brown Adipose Tissue of the Young Rat

“…In this respect, the decrease we have found in the intensity of this uptake in the young hypothyroid animals could be fol lowed by a lessening in the entrance rate of the transmitter in the tissue, and this could, then, partially explain why the norepineph rine content is lower in ISBAT of these hypo thyroid rats [11].…”

“…In a previous report [11], we described an inhibition of the neonatal increase in ISBAT norepinephrine content after chemical thy roidectomy. In the same animals, the activi ties of the two major enzymes of norepineph rine catabolism, monoamine oxidase and catechol-O-methyltransferase were increased as compared to control animals.…”

“…For both groups, the slope of the last part of the curve (k) is given in table I, together with the norepinephrine content of the tissue [11], and the TR of nor epinephrine. Finally, the TR of norepineph rine per pad or per unit of ISBAT weight is shown in figure 4.…”

The Thermoregulation of the Nude Mouse

“…Because of hypothyroidism or independent of this the BAT mass with its thermogenic capacity is poorly developed [2]. It is concluded that promising measures to improve the health and life expectancy of nude mice -apart from con trolling infectious diseases -would be to pro vide a warmer environment (Ta 30-32 °C) and thyroid hormone substitution.…”