Beta-adrenergic regulation of insulin secretion: evidence of tissue heterogeneity of beta-adrenergic responsiveness in the elderly.

Aging is associated with reduced beta-adrenergic receptor (beta-AR) function in several tissues. If this age effect on beta-ARs also applies to the pancreatic B-cell, it would result in relatively unopposed alpha-adrenergic inhibition of insulin secretion with adrenergic stimulation during stress states. This study compared insulin secretory responses to beta-AR stimulation (multiple IV doses of isoproterenol) with cardiac and circulating mononuclear lymphocyte (MNL) beta-AR responses in 9 healthy, non-obese young subjects, and 9 healthy, non-obese old subjects. We found no age-related decrease in the relationship between isoproterenol dose and insulin response. In contrast, the old subjects had significantly reduced heart rate responses to isoproterenol and generally lower MNL beta-AR function. We conclude that pancreatic B-cell beta-AR mediated function is not impaired in the elderly, suggesting that heterogeneity of tissue beta-AR mediated function exists in this population. Diminished pancreatic islet beta-AR mediated function does not appear to be a mechanism that predisposes healthy older individuals to the development of stress hyperglycemia.