AGE-RELATED-CHANGES IN MORPHOLOGY AND SECRETORY RESPONSES OF MALE-RATLACRIMAL GLAND

This study investigates the differences in the outward appearance and morphology of lacrimal glands, the morphology within the lacrimal acin ar cells and the secretion of protein from acinar cells of young (3-5 months) and aged (20 and 24 months) male rats. The appearance of the g lands, as seen by the naked eye, differed between the three age-groups . The lacrimal gland of young animals was a smooth pink tissue, while the tissue from aged animals appeared lobular and white in colour, tho ught to result from infiltration of fatty/connective tissue. Glands fr om 24 month old animals had a more pronounced lobular appearance than the glands from 20 month old animals. Light microscopy studies reveale d that as the animals aged there was evidence of progressive morpholog ical changes. These changes included thickening of the connective tiss ue sheath. chronic inflammation with increased infiltration by mast ce lls, patchy destruction of ductal and vascular tissues, enlargement of lacrimal ducts, luminal swelling of the acini, and changes in acinar type. Electron microscopy (EM) studies revealed the presence of 3 type s of acini in the rat lacrimal gland: acini which contained only prote in secretory granules (serous acini), acini which contained protein an d mucous secretory granules (seromucous acini), and acini which contai ned only mucous secretory granules (mucous acini), In young glands the !majority of acini were serous with a few seromucous acini and even fe wer mucous acini. In aged glands there were significant reductions in serous acini (ANOVA; P < 0.01) when compared to the young, glands. In 20-month-old glands, there were marked increases in the percentage occ urrence of seromucous acini, while in 24 month old glands, there were large increases in the relative number of mucous acini.Qualitative EM studies demonstrated that the typical acini from young glands containe d numerous protein secretory granules, Ageing was associated with a pr ogressive loss of protein (serous) secretory granules. Furthermore, ma rked changes and patchy destruction of the endoplasmic reticulum and G olgi apparatus were observed in acini of glands from aged rats when co mpared to acini of glands from young rats. Measurement of total protei n output from acini revealed a significant (Student's t-test, P < 0.05 ) decrease in protein secretion from aged glands compared to glands fr om young animals. These results suggest that not only is there conside rable structural damage, chronic inflammation and mast cell infiltrati on to the lacrimal gland with ageing, but also possible redifferentiat ion of acini from serous to seromucous and then to mucous acini. Furth ermore, the results also suggest a reduction or an inability of the ac ini to synthesise and to secrete protein from glands of aged animals c ompared to glands of young rats. All of these changes appear to occur more rapidly as the rats mature between 20 and 24 months. These findin gs provide a morphological basis to explain the phenomenon of reduced tear/protein secretion with ageing. (C) 1998 Elsevier Science B.V. All rights reserved.