Insulin secretion by rat lacrimal glands: effects of systemic and local variables.
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 lacrimal 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 microM 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 x cornea(-1) x 2 h(-1) in the presence of 6 nM insulin (P = 0.033) and to 37.5 +/- 3.7 nmol x cornea(-1) x 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.
Cunha
Daniel Andrade
DA
Institute of Biology, State University of Campinas, Brazil.
Carneiro
Everardo M
EM
Alves
Mônica de C
Mde C
Jorge
Angélica Gobbi
AG
de Sousa
Sylvia Morais
SM
Boschero
Antonio C
AC
Saad
Mário J A
MJ
Velloso
Lício A
LA
Rocha
Eduardo M
EM
D000818:Animals; D015153:Blotting, Western; D002217:Carbachol / Q000494:pharmacology; D005947:Glucose / Q000008:administration & dosage; D018398:Homeodomain Proteins / Q000096:biosynthesis / Q000235:genetics; D007328:Insulin / Q000096:biosynthesis / Q000097:blood / Q000235:genetics / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000378:metabolism; D007765:Lacrimal Apparatus / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008916:Miotics / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013666:Tears / Q000187:drug effects / Q000378:metabolism; D015534:Trans-Activators / Q000096:biosynthesis / Q000235:genetics
D018398:Homeodomain Proteins; D007328:Insulin; D008916:Miotics; D012333:RNA, Messenger; D015534:Trans-Activators; C084010:pancreatic and duodenal homeobox 1 protein; D011189:Potassium Chloride; D002217:Carbachol; D005947:Glucose