Changes in adrenoreceptor density in brown adipose tissue from hyperthyroid rats.

Treatment of rats with triiodothyronine (T3 10 micrograms/100 g per day, 20 days) increased the mass of brown adipose tissue (BAT) and heart ventricle and stimulated beta-adrenoreceptor number (assessed from radioligand binding) by 43% in isolated BAT and heart membranes. alpha-Receptor number was slightly increased in BAT membranes (42%) but reduced in heart from T3-treated rats. The ratio of alpha-receptors/beta-receptors was unaffected by T3 treatment in BAT membranes (control and hyperthyroid = 1.54) but reduced in heart (control = 2.8, T3 = 1.04).