Relationship between cAMP production and protein secretion in rat submandibular acini: evidence for loss of reserve capacity with age.

We assessed isoproterenol and forskolin-stimulated cAMP production and protein secretion in submandibular salivary glands from young (4-7 mo) and old (25 mo) male F-344 rats. In senescent acini, the maximum amount of cAMP produced was three-fold less and the protein secreted was one-third less in response to the highest dose of isoproterenol (100 microM). Following isoproterenol stimulation, the young acini were more sensitive than the old for protein secretion than for cAMP production. Post-receptor stimulation (by forskolin) of cAMP production and protein secretion were less in the senescent rats. This report demonstrates the validity of an in vitro model for simultaneous assessment of biochemical and functional correlates. Furthermore, the observations suggest that both receptor and post-receptor stimulation of cAMP production and protein secretion diminish with age. Moreover, there is a reserve capacity for cAMP production with respect to protein secretion in the young that is diminished or even absent in the old rats.