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This Article Full Text Full Text (PDF) All Versions of this Article: 289/5/E768    most recent 00469.2004v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (5) Citing Articles via Google Scholar Google Scholar Articles by Cunha, D. A. Articles by Rocha, E. M. Search for Related Content PubMed PubMed Citation Articles by Cunha, D. A. Articles by Rocha, E. M.

Insulin secretion by rat lachrymal glands: effects of systemic and local variables

¹Institute of Biology and ²School of Medical Sciences, State University of Campinas, Campinas; and ³School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, Sao Paulo, Brazil

Submitted 5 October 2004 ; accepted in final form 20 June 2005

To understand the secretory mechanisms and physiological role of insulin in the tear film, the present study examined 1) the time course of insulin secretion in the tear film under glucose intravenous stimulation, 2) the glucose- and carbachol-induced insulin secretion from isolated lachrymal gland (LG), 3) the effect of insulin on glucose consumption by the cornea, and 4) the expression of insulin, pancreatic duodenal homeobox-1 (PDX-1), and glucose transport proteins (GLUTs) in LG tissue. The insulin level in the tear film of 8-wk-old male Wistar rats increased from 0.6 ± 0.45 to 3.7 ± 1.3 ng/ml in the initial minutes after glucose stimulation. In vitro assays demonstrated that higher glucose concentrations from 2.8 to 16.7 mM, 200 µM carbachol, or 40 mM KCl significantly increased insulin secretion from lacrimal glands compared with controls, but did not detect C-peptide as measured by RIA. Glucose consumption by corneal tissue, evaluated by radiolabeled D-[U-¹⁴C]glucose uptake, was 24.07 ± 0.61 and was enhanced to 31.63 ± 3.15 nmol·cornea^–1·2 h^–1 in the presence of 6 nM insulin (P = 0.033) and to 37.5 ± 3.7 nmol·cornea^–1·2 h^–1 in the presence of 11.2 mM glucose (P = 0.015). Insulin and PDX-1 mRNA was detected in LG. Insulin was located in the apical areas of acinar cells by immunoperoxidase and the expression of GLUT-1, but not PDX-1, was confirmed by Western blot. These findings suggest that insulin secretion in the tear film is influenced by local stimuli such as nutrient and neural inputs and that this hormone plays a metabolic role in ocular surface tissues. These data also indicate that under normal conditions the insulin secreted by LG is stored, but it is not clear that is locally produced in the LG.

glucose transporter; tear film; ocular surface

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