THYROID HORMONE-INDUCED UP-REGULATION OF BETA-1-ADRENERGIC AND BETA-2-ADRENERGIC RECEPTORS DURING AGING

Strong experimental evidence suggests that thyroid hormones influence beta-adrenoceptor regulation. The question arises whether in tissues like mouse brain cortex bearing both beta-1- and beta-2-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 beta-1-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 beta-1-subtype. T3 stimulation induces up-regulation of both beta-1- and beta-2-adrenoceptors in young animals. The response shows no impairment with aging, as in both receptor subtypes a significant increase can be demonstrated. Due to the very short time of response, an unmasking mechanism can be hypothesized for receptor up-regulation, though an increase of protein synthesis cannot be excluded.