Thyroid hormone-induced up-regulation of β1- and β2-adrenergic receptors during aging

Strong experimental evidence suggests that thyroid hormones influence β-adrenoceptor regulation. The question arises whether in tissues like mouse brain cortex bearing both β1- and β2-subpopulations, these receptor subtypes may be regulated independently, as demonstrated after some drug stimulations. An eventual influence of aging on triiodothyronine (T₃)-induced subpopulation response is also worth studying, because of the decrease of receptor density in old animals observed only in the β1-type. These points have been addressed in the present paper, performing experiments on young and old mice stimulated with a single injection of T₃. The response has been assayed as rapidly as 15 min after T₃ treatment. Results on untreated control mice confirm previous findings showing that the decrease of receptor density is in charge only of the β1-subtype. T₃ stimulation induces up-regulation of both β1- and β2-adrenoceptors in young animals. The response shows no impairment with aging, as in both receptor subtypes a significant increase can be demonstrate. Due to the very short time of response, and unmasking mechanism can be hypothesized for receptor up-regulation, though an increase of protein synthesis cannot be excluded.