REGULATION OF MUCOUS ACINAR EXOCRINE SECRETION WITH AGE

Denny and co-workers (Navazesh et al., 1992) recently reported decreas ed concentrations of MG1 and MG2 mucins in resting and stimulated whol e human saliva with age. The current study was therefore conducted to examine whether there is a corresponding attenuation with age in stimu lus-secretion coupling regulating mucous cell exocrine secretion. We u tilized an in vitro model system, isolated rat sublingual acini, to ev aluate the regulation of mucous cell exocrine secretion. Rat sublingua l glands are similar to human sublingual and minor mucous glands, both histologically and in terms of their pattern of innervation, which is predominantly parasympathetic. Mucin secretion is thus activated prim arily by muscarinic cholinergic agonist and to a lesser extent by vaso active intestinal peptide (VIP), which is co-localized with acetylchol ine in parasympathetic nerve terminals. We isolated sublingual mucous acini from five-month-old and 24-month-old rats and compared the conce ntration responses for mucin secretion induced by VIP and the muscarin ic agonist, arecaidine propargyl ester (APE). Concentration-response c urves for VIP were nearly identical for mucous acini from the five-mon th-old and 24-month-old animals. Values for basal secretion, maximal s ecretion, and EC(50) (approximate to 200 nmol/L VIP) were statisticall y equivalent between both age groups. Concentration-response curves fo r APE were also very similar between age groups, with no statistically significant difference in basal secretion or EC(50) values (approxima te to 50 nmol/L APE). Maximal secretion was slightly less but statisti cally different for 24-month-old vs. five-month-old animals, 158% vs. 169% above basal secretion, respectively. Collectively, we found no su bstantial age-related changes in the secretory responsiveness of saliv ary mucous cells.