Effects of chronic isoproterenol administration on beta 1-adrenoceptors and growth of pancreas of young and adult rats.

[3H]Dihydroalprenolol (DHA) binding of membranes of adult pancreas differed from that of pancreas of young rats, and the DHA binding in the presence of atenolol or butoxamine also was different in the two age groups. The adult pancreas had 93% beta 2- and 7% beta 1-adrenoceptors and did not exhibit an increased incorporation of [3H]thymidine into deoxyribonucleic acid (DNA) following 2 days of DL-isoproterenol (ISO) administration; in contrast, pancreas of the 20-day-old rat had 71% beta 2-adrenoceptors and 27% beta 1-adrenoceptors and exhibited a 34-fold increase over that of adult, and a 6-fold increase over that of the control 20-day-old pancreas. Acinar cell differentiation was also accelerated by a 7-day regimen of ISO administration from 13 to 20 days of age. These growth responses to ISO appear to be beta 1 mediated. The lack of beta 1-adrenoceptors in the adult may account for the failure of the adult pancreas to exhibit a growth response to ISO.