Free fatty acids play an important role in regulating animal insulin secretion response. Acute elevated free fatty acids increased animal insulin secretion and glucose-stimulated insulin secretion. In the present study, we perfused the rat pancreas to explore the effect of unsaturated fatty acids on insulin secretion. The results showed that linoleic acid, γ-linolenic acid and arachidonic acid significantly stimulated insulin secretion. Glucose (10 mM) alone induced a biphasic insulin secretion response. The peak effluent insulin concentrations increased by 444% and 800% compared with the baseline in the first and second insulin secretion phases, respectively. Based on comparison of the percentage increases, arachidonic acid, γ-linolenic acid or linoleic acid increased glucose-induced insulin release by 555% and 934%, 522% and 995% and 463% and 1,105% in the first and second insulin secretion phases, respectively. However, the percentage increases of insulin secretion decreased significantly to 402% and 564% in the first and second phases in the rats fed a high-fat diet for 13 weeks. Linoleic acid alone stimulated a 391% increase in the peak insulin concentration compared with the baseline in the rats fed a normal diet. The peak insulin concentration decreased significantly to183% in the rats fed a long-term high-fat diet. All the results suggested that unsaturated fatty acids stimulated insulin secretion and additively increased glucose-induced insulin secretion in the perfused rat pancreas. However, the rats fed a high-fat diet had a decreased linoleic acid-induced insulin secretion response.

A small nonpeptidyl compoud extracted from Pseudomassaria sp. was found to induce the activity of human insulin receptor tyrosine kinase in vitro. The compound was identified as demethylasterriquinone B-1 (DMAQ-B1). DMAQ-B1 also induced an increase in [Ca2+]i and insulin secretion in mice pancreatic beta-cells at low glucose (3 mM) concentration via insulin receptor substrate-1/phosphatidylinositol-3-kinase (PI3 kinase) pathway. By using rat pancreatic perfusion technique, we found that 10 μM DMAQ-B1 directly stimulated insulin secretion up to 240% in normal rat pancreas. In the dosage from 1 to 20 μM, DMAQ-B1 stimulated insulin secretion in a dose dependent manner. Furthermore, DMAQ-B1 enhanced glucose-induced insulin secretion by 17.6% (first stage) and 19.0% (second stage), respectively. The PI3 kinase inhibitors, LY 294002 (3.9 μM) or wortmannin (100 nM), inhibited DMAQ-B1-induced insulin secretion by 46.3% and 57.4%, respectively. LY 294002 or wortmannin also inhibited DMAQ-B1 with 10 mM glucose-induced insulin secretion by 70.3% and 79.0%, respectively. All the results suggested that DMAQ-B1 directly stimulated insulin secretion and enhanced glucose-induced insulin secretion. The effect of DMAQ-B1 may mediate through the activation of PI3 kinase pathway to stimulate insulin secretion in normal rat pancreas.

Human and animal diabetes mellitus were controlled by a dietary treatment supplemented with either a sulfonylurea drug or insulin injection. Insulin injections were inconvenient and the hypoglycemia induced by insulin-overdose could be fatal. Sulfonylurea drugs were administered orally, however, do not typically provide satisfactory control of blood glucose as a starting treatment in 25%-30% patients. Therefore, it was imperative to develop a method for the control of human and animal diabetes mellitus. Recently, insulin gene transferred and expressed in non-pancreatic cells as a means for the treatment of diabetes was developed rapidly in the expanding gene therapy. Retrovirus, lentivirus, adenovirus, adenoassociated virus and herpes simplex had been used as viral vectors, and the constructed viral-insulin gene was successfully transferred into diabetic rat cells. A gene, containing promoter, enhancer and rat type I insulin gene (a-chain, b-chain and signal peptide), was constructed into a retrovirus vector in the study. The constructed viral-insulin gene was transferred into mouse fibroblast cell. The insulin concentration in 3day cultured mouse fibroblast cells was 4806.35 ± 53.72 pg/ml. The insulin concentration for the viral vector containing enhancer and promoter of rat insulin gene was higher than the vector containing only insulin gene by a 61% increase in the cultured mouse fibroblast cells. The enhancer and promoter activity of rat insulin gene would be an important determinant for the expression of insulin gene. The secreted amount of insulin by retrovirus vector contained enhancer/promoter gene in this study could achieve as high concentrations (4806.35 ± 53.72 pg/ml) as the insulin injection therapy. Blood glouse decreased significantly for at last 10 days demonstrated that transfection, direction injection of viral-insulin gene into pancreas of diabetic rat, was successful. These studies suggest that the retrovirus vector might be used to transfer the insulin gene in vitro and in vivo.

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