Nutrient induced insulin release from an insulinoma derived B-cell line

A Synthetic Polymer, Poly(2-methacryloyloxyethyl phosphorylcholine-co-n-stearyl methacrylate), Stimulates Insulin Release from RINm5F Insulinoma Cells

A water-soluble phospholipid-like polymer, poly(2-methacryloyloxyethyl phosphorylcholine-co-n-stearyl methacrylate) (PMC(18), average molecular weight = 4.3 x 10(4)), at a concentration (0.5-5 mg/ml) showing no inhibition of cell proliferation, stimulated insulin release from RINm5F rat insulinoma cells in a concentration- and time-related manner. But poly(2-methacryloyloxyethyl phosphorylcholine) and other synthetic phospholipid-like polymers failed to stimulate insulin release.

Angiotensin I-converting enzyme inhibitory activity and insulin secretion stimulative activity of fermented fish sauce

Angiotensin I-converting enzyme (ACE) inhibitory peptides, Ala-Pro, Lys-Pro, and Arg-Pro, were isolated from fermented fish sauce. Five other proline-containing dipeptides having weak ACE inhibitory activity were also isolated from the fermented fish sauce. Orally administered Lys-Pro showed a tendency to lower the blood pressure of spontaneously hypertensive rats. As fermented anchovy sauce also stimulated insulin secretion by cultured RINm5F insulinoma cells, the sauce may be useful as a source of biologically active substances.

Role of polyamines in the regulation of proliferation and hormone production by insulin-secreting cells

This paper focuses on the mechanisms regulating proliferation and insulin production by normal and tumoral pancreatic beta-cells. In particular, the evidence for involvement of polyamines is reviewed. Pancreatic islet cells contain high levels of polyamines, and based on findings obtained using enzyme-directed inhibitors, it appears that putrescine and spermidine are necessary for proinsulin biosynthesis, whereas spermine may exert a stimulatory or permissive role in RNA transcription-stabilization and long-term insulin release. Islet polyamine content is not altered by short-term secretory stimulation, nor is the acute secretory response impeded by polyamine synthesis inhibitors, making it unlikely that these amines play any major role in short-term insulin release. Various mitogens increase islet polyamine contents and DNA synthesis, but increases in cytosolic polyamines do not seem to mediate their mitogenicity. Nuclear polyamine content is not altered by the inhibitors, suggesting that maintenance of polyamines within this organelle may be sufficient to sustain elevated DNA synthesis. In tumoral RINm5F cells, polyamine depletion results in decreased proliferation and increased cellular content of insulin and insulin secretory granules without affecting insulin mRNA levels or translation. Moreover, polyamine-depleted RINm5F cells display improved substrate metabolism and sensitivity of the stimulus-secretion coupling. Possible levels of polyamine interaction with Ca2+ metabolism are discussed.

The effects of amylin on insulin secretion from Rin m5F cells and glycogen synthesis and lipogenesis in rat primary cultured hepatocytes

The purpose of the study was to determine the physiological actions of amylin, a novel 37-amino acid peptide isolated from pancreatic islet amyloid deposits. Our results showed that an infusion of amylin reduced fasting plasma insulin levels and impaired glucose tolerance in mice. Amylin significantly reduced insulin secretion in rat insulinoma cell lines (Rin m5F cells) that were stimulated by either isoproterenol and forskolin, but it did not affect insulin secretion stimulated by isobutyl-methylxanthine (IBMX) or dibutyryl cyclic-adenosine monophosphate (db-cAMP). Amylin also reduced cAMP levels in Rin m5F cells in response to isoproterenol, but did not affect cAMP levels in cells pretreated with pertussis toxin. These results suggest that the reduction of cAMP by amylin may be mediated through pertussis toxin-sensitive Gi proteins. Amylin significantly reduced basal and insulin-stimulated glycogen synthesis in rat primary cultured hepatocytes. Amylin stimulated basal and insulin-stimulated lipogenesis in hepatocytes. Amylin did not affect DNA synthesis in hepatocytes. These results suggest that amylin conducts dispersion actions on in vivo glucose metabolism in rat, and in vitro insulin secretion from Rin m5F cells and metabolism in rat hepatocytes.

Increased glucose oxidation and contents of insulin and ATP in polyamine-depleted rat insulinoma cells (RINm5F)

In order to elucidate the role of polyamines in the replication and insulin production of insulin-secreting cells, we have investigated the impact of partial polyamine depletion on the proliferation, metabolism, insulin synthesis and ultrastructure of clonal rat insulinoma cells (RINm5F). For this purpose RINm5F cells were exposed for 4 days to the specific ornithine decarboxylase (ODC) inhibitor difluoromethylornithine (DFMO). This resulted in a profound decrease in ODC activity and cytoplasmic polyamine contents. The polyamine content of cell nuclei was, however, not altered by DFMO. Addition of small amounts of putrescine during culture elevated the intracellular content of this diamine and suppressed ODC activity. The decrease in polyamine contents was accompanied by a pronounced inhibition of the cellular proliferative activity. The rates of glucose utilization, oxygen uptake and activity of the pentose cycle were decreased in DFMO-treated cells, whereas the glucose oxidation rate, oxidation/utilization ratio, ATP content and ATP/ADP ratio were increased. Insulin mRNA content and synthesis of proinsulin, insulin and total protein were not altered by DFMO. In contrast, there was a sizeable increase in the cellular insulin content, despite a lowered total protein content. Electron-microscopic analysis revealed an accumulation of insulin-secretion granules in the DFMO-treated cells. In addition, short-term insulin release was increased after DFMO exposure, but was not rendered glucose-sensitive. It is concluded that polyamines are necessary for the maintenance of rapid insulinoma-cell replication and that DFMO-treated RINm5F cells acquire an enhanced substrate oxidation and increased content of insulin and ATP.

Cholinergic stimulation of insulin release from cloned B-cell lines HIT-T15 and RINm5F

Acetylcholine stimulated the release of insulin from cultured HIT-T15 and RINm5F cells in the absence of glucose confirming that the insulin response to cholinergic stimulation is preserved in these two cloned B-cell lines. In addition acetylcholine potentiated glucose stimulated insulin release from HIT-T15 but not from RINm5F cells. Perifused HIT-T15 cells responded to square wave acetylcholine challenge with a monophasic release of insulin while the release profile for RINm5F cells was irregular and reduced. Acetylcholine stimulated insulin release from both cell lines was reduced by atropine but unaffected by hexamethonium confirming a mechanism of action involving muscarinic receptor activation.