Calculated and actual changes in beta-adrenoceptor number associated with increases in rat and guinea-pig cardiac sensitivity.

Chronic catecholamine depletion induced by reserpine pretreatment of rats, or 6-hydroxydopamine pretreatment of guinea-pigs, resulted in an enhanced sensitivity of isolated papillary muscles to isoprenaline. This hypersensitivity was accompanied by 1.41-(rats) and 1.52-fold (guinea-pigs) increases in the number of [3H]dihydroalprenolol binding sites, without changes in binding affinity. An equation was derived for calculation of increases in receptor number. Application of this showed that substantially greater increases in receptor number were required (2.32- to 4.04-fold) to account for the degree of supersensitivity observed.