Keiji Murakami

Physiologic Role of Somatostatin Insulin Release from Rat Islets Treated by Somatostatin Antiserum

In order to clarify the physiologic role of somatostatin in insulin release, rat pancreatic islets treated by somatostatin antiserum were incubated in media containing various concentrations of glucose. Insulin release from antiserum-treated islets was significantly elevated above that from nontreated ones at 3.3 and 8.3 mM glucose, while the former was not different from the latter at 16.7 mM glucose. It is suggested that somatostatin plays an important role in the regulation of insulin release in the physiologic range of glucose concentration.

Presence of insulin-like immunoreactivity and its biosynthesis in rat and human parotid gland.

SummaryExtracts from homogenates of rat and human parotid glands contained insulin-like immunoreactivity. The values were 5.6±2.8 ng/g wet tissue in six groups of rat parotid glands and 23.8 and 39.7 ng/g wet tissue in two human extracts. Upon gel filtration immunoreactive insulin of rat origin was eluted in a peak corresponding to the elution volume of isotopically labelled insulin. The material obtained from the two peak fractions showed an immunoassay dilution curve identical with that of rat insulin. Furthermore, biosynthesis of insulin-like immunoreactivity in rat and human parotid glands was confirmed in vitro by a specific separation method using anti-insulin antibody. These findings suggest that the parotid gland may be a further extrapancreatic source of insulin, and that insulin biosynthesis does occur in extrapancreatic tissues.

Effects of tris(hydroxymethyl)aminomethane on biosynthesis and release of insulin in the pancreatic Langerhans islets

Tris(hydroxymethyl)aminomethane (Tris) has been shown to inhibit selectively the Golgi apparatus and Golgi-endoplasmic reticulum-lysosomal system (GERL system) of several kinds of cells including pancreatic B cells. This study was designed to assess the effect of Tris on insulin, glucagon and somatostatin release and insulin synthesis in pancreatic B cells by using isolated rat pancreatic islets. Tris suppressed glucose-induced insulin release, whereas it did not affect the glucagon and somatostatin release. Furthermore, the incorporation of [3H]leucine into the insulin fraction was suppressed by 10 mM Tris, but the sum of the radioactivity of both proinsulin and insulin fraction were not influenced. The present study suggests that the Golgi apparatus and GERL system may play a role in insulin secretion and biosynthesis in pancreatic B cells.

A multicenter study on HLA and autoimmunity in Japanese patients with early-onset insulin-dependent diabetes mellitus (IDDM): the JDS Study.

The Japan Diabetes Society (JDS) conducted a multicenter study on HLA and autoimmunity in Japanese patients with early-onset insulin-dependent diabetes mellitus (IDDM). HLA, immunoglobulin heavy-chain complex (Gm), properdin factor B (BF), and glyoxalase of erythrocytes (GLO) were typed, and organ-specific autoantibodies including islet cell antibodies (ICA) were assayed in 159 IDDM patients and their relatives and in 258 healthy Japanese subjects. The HLA-DRw9 phenotype and HLA-Bw61/DRw9 haplotype were significantly increased among the patients with autoantibodies other than ICA, whereas the DR4 phenotype and Bw54/DR4 haplotype were significantly increased in those without the autoantibodies. The DR4 phenotype was significantly increased in the patients with autoimmune thyroid diseases. The relative risk of the HLA-DRw9/DR4 genotype was highest among all DR genotypes. The Gm phenotype of g and gft were significantly increased in the patients with the autoantibodies. The BF-F phenotype was significantly decreased in the patients either with or without the autoantibodies. There was no association of GLO types with IDDM. The prevalence of ICA among IDDM patients was decreased with duration of IDDM. No significant association was found between the prevalence of ICA and sex, age at onset, or HLA type. On the other hand, the prevalence of the autoantibodies was not significantly changed with duration of the disease, and was significantly higher in females than in males.

Evaluation of cryopreservation techniques of pancreatic fragments and islets in vitro and in vivo

We evaluated cryopreservation techniques for pancreatic fragments and islets using rat tissue. After equilibration in 10% dimethyl sulfoxide (Me2SO), the tissue was frozen in a programmable freezer at 1 degree C/min down to -40 degrees C and at 3 degrees C/min down to -71 degrees C. The islets, when thawed, released abundant insulin in the presence of as little as 3.3 mM glucose, much more so than non-frozen islets did. Three additional procedures, prefreezing and post-thawing culture and the stepwise dilution of the Me2SO, lowered the non-specific insulin release of the thawed islets and improved their insulin response to 16.7 mM glucose. Thawed pancreatic fragments subjected to these additional procedures, transplanted into the peritoneal cavity of streptozotocin-induced diabetic rats, reduced their hyperglycemia significantly. The thawed fragments and islets did not differ from their corresponding non-frozen controls in 3H-leucine incorporation. The maintenance of tissue function was not satisfactory. However, our observations indicate that culturing pancreatic tissue before freezing and after thawing and the stepwise dilution of the cryoprotective agent reduce the damage induced by freezing the tissue.

The Maintenance of Insulin Secretory Response of Long-Term Cultured Pancreatic Islets to Glucose, Acetylcholine and Epinephrine

The present study was performed to investigate whether long-term cultured rat pancreatic islets possess a postcultural insulin secretory response to hormones and neurotransmitters in spite of their lack of stimulation during the culture period. We also investigated the method of maintaining the insulin secretory response of islets cultured in a physiological concentration of glucose. The tissue culture media were TCM 199 supplemented with 5.5 mM glucose (A medium), 5.5 mM glucose plus 1 mM adenosine (B medium), 16.7 mM glucose (C medium), and 16.7 mM glucose plus 1 mM adenosine (D medium). Short-term incubation after the culture period of 14 days showed that the islets cultured in B, C and D media maintained the same insulin secretory responsiveness to 8.3 mM glucose and/or 5 microM acetylcholine and also to 1 microM epinephrine as did non-cultured islets. A similar response was found among the islets maintained in B, C and D media. An insulin secretory response to epinephrine and phentolamine was deficient in islets cultured in A medium, whereas it was maintained in those cultured in C medium. The responsiveness of the islets cultured in C medium to the concomitant stimulation by epinephrine and phentolamine was not different from that of the non-cultured islets. It was thus concluded that the addition of adenosine in the culture medium containing the physiological concentration of glucose was as effective in amintaining the insulin secretory ability of the islets as was the culture medium containing a high concentration of glucose, and it was suggested that even the pancreatic islets cultured in these media, though separated from the innervation might preserve acetylcholine and adrenergic receptors similar to freshly isolated islets. Considering the action of adenosine, the necessity of enhancing ATP and C-AMP concentrations in B cells was also suggested in order to maintain the insulin secretory ability of cultured pancreatic islets.