Lacrimal protein secretion: comparison of young and old rats

The in vitro protein secretory response of lacrimal glands from healthy 4- and 24-month-old F344 rats was measured. Tissue fragments were incubated in a 0.2 ml perifusion chamber and stimulated to secrete protein by a 4-min bolus of 0.01 mM carbachol. Fractions of the perifusate were collected and assayed for protein concentration and peroxidase activity. The response to carbachol was a well-defined peak of secreted protein that included peroxidase. The response was inhibited by 1.0 microM atropine. No differences were found between the responses of male and female glands. The peak of protein secretion by the young glands contained 263.9 +/- 71.8 micrograms g tissue-1 compared to 175.4 +/- 56.5 micrograms g tissue-1 for the old glands (P less than 0.005). While the mean activity of the secreted peroxidase was similar in the two age groups, the aged glands were significantly more variable in their response. The F344 rat may provide a useful model for studying the normal age-dependent changes that occur in lacrimal gland.