Norikazu Kitano

Effects of environmental tobacco smoke on urinary cotinine excretion in nonsmokers. Evidence for passive smoking.

Abstract Despite recognition of the deleterious effects of passive smoking, quantitative information on the intake of environmental tobacco smoke is still lacking. Cotinine is the major metabolite ...

Characteristic features of insulin secretion in the streptozotocin-induced NIDDM rat model

Male Wistar neonatal rats at age 1.5 days (Streptozotocin [STZ] group 1) and 5 days (STZ group 2) received a subcutaneous injection of 90 mg/kg STZ. After 10 weeks, the rats were subjected to an oral glucose tolerance test (OGTT) (2 g/kg) in a conscious state. The pancreas perfusion experiments were conducted 2 weeks after the OGTT. There was no statistical difference in insulin response between the STZ group 1 and the control group. On the contrary, in the STZ group 2, the plasma glucose response to OGTT showed a typical diabetic pattern, and the plasma insulin response was markedly blunted. In the isolated perfused rat pancreas, the infusion of glucose evoked a biphasic insulin secretion, but the peak insulin levels induced by 16.7 mmol/L glucose in the STZ group 1 were significantly lower than in the controls. We further investigated characteristics of insulin secretion in response to different secretagogues in these animal models using isolated islets. The insulin content of the islets of the STZ group 1 were about one half that of the control group. Insulin secretion in the STZ group 1 was impaired in response to glucose stimulation, but remained normal in response to arginine and forskolin. These results suggest that insulin secretion of non-insulin-dependent diabetes mellitus (NIDDM) rat model is selectively impaired in response to glucose stimulation, possibly due to a disorder of signaling mechanism other than adenylate cyclase.

Mutations in the Hepatocyte Nuclear Factor-1α Gene (MODY3) Are Not a Major Cause of Late-Onset NIDDM in Japanese Subjects

Maturity-onset diabetes of the young (MODY) is a monogenic form of NIDDM characterized by an early age of onset, often in childhood or adolescence and usually <25 years of age, and autosomal dominant inheritance. Clinical studies of subjects with one form of MODY (M0DY3), the gene for which has been localized to chromosome 12, have suggested that impaired insulin secretion is the primary defect responsible for hyperglycemia in these subjects (1,2). Recently, Mahtani et al. (3), studying Finnish families with late-onset NIDDM, has mapped a gene affecting the susceptibility to NIDDM associated with low insulin secretion, designated NIDDM2, to the region of the M0DY3 locus on chromosome 12 (3). They suggest that NIDDM2 and M0DY3 may be different alleles of the same gene, which with severe mutations causes MODY and with milder mutations causes late-onset NIDDM with low insulin secretion. Recently, it has been shown that mutations in the gene encoding hepatocyte nuclear factor-la (HNF-la), a homeodomain-containing transcription factor originally identified in liver, are the cause of M0DY3 (4), but the molecular mechanism by which mutations in this gene cause MODY is still unclear. The possibility that mutations in the HNF-la gene might also cause late-onset NIDDM prompted us to screen this gene for mutations in Japanese subjects with late-onset NIDDM, a group characterized by primary pancreatic (3-ceD dysfunction rather than insulin resistance (5). We studied 103 Japanese subjects with late-onset NIDDM (mean age at diagnosis, 62.0 ± 10.2 years) from two diabetes care centers in Hyogo and Gunma prefectures, 68 of which had at least one relative with NIDDM (48 in a first-degree relative). The subjects involved were not diabetic by annual health examination before 40 years of age. NIDDM was diag-

Effects of naloxone on basal and vagus nerve-induced secretions of GRP, gastrin, and somatostatin from the isolated perfused rat stomach

The effects of naloxone, an opiate antagonist, on basal and vagus nerve-induced secretions of GRP, gastrin, and somatostatin were examined using the isolated perfused rat stomach prepared with vagal innervation. Naloxone (10(-6) M) significantly inhibited basal somatostatin secretion in the presence and absence of atropine and of hexamethonium, whereas basal GRP and gastrin secretion was not affected by naloxone. Electrical stimulation (10 Hz, lms duration, 10V) of the distal end of the subdiaphragmatic vagal trunks elicited a significant increase in both GRP and gastrin but a decrease in somatostatin. Naloxone (10(-6) M) failed to affect these responses in the presence or absence of atropine. On the other hand, when hexamethonium was infused, naloxone significantly inhibited both the GRP and gastrin responses to electrical vagal stimulation. Somatostatin secretion was unchanged by vagal stimulation during the infusion of hexamethonium with or without naloxone. These findings suggest that basal somatostatin secretion is under the control of an opiate neuron and that opioid peptides might be involved in vagal regulation of GRP and gastrin secretion.

Effects of oral glucose administration on preproinsulin mRNA in rats in vivo.

An experiment was performed to examine whether the acute increase in insulin release induced by oral glucose ingestion is associated with alterations in pancreatic preproinsulin mRNA (PImRNA) levels. Rats either fed ad libitum or after overnight fast were used. Fasted rats were administered glucose orally in a conscious, unrestrained state. Pancreatic RNA was extracted and the relative level of PImRNA was determined by dot blot analysis with a cloned rat preproinsulin I cDNA probe. In fasted animals PImRNA levels decreased compared with those of fed animals and showed no significant changes after acute glucose administration, while blood glucose and plasma insulin increased rapidly to maximum values at 15 min after glucose administration. Although the transcription rate was not directly measured in this experiment, it is possible that the rapid increase in insulin release from the beta cell under physiological conditions is controlled by post-transcriptional regulations.

Comparative effect of somatostatin-14 and somatostatin-28 on glucagon-induced glycogenolysis from the perfused rat liver

The effect of somatostatin (SS)-14 and SS-28 on glycogenolysis was studied, using a rat liver perfusion technique. Livers from nonfasted rats were perfused with 5.5 mmol/L glucose or perfusate without the glucose addition. Glucagon-induced glucose output was lower in the presence of 5.5 mmol/L glucose than in glucose free perfusate at every concentration of glucagon. Under glucose free conditions, SS-14 given at five minutes prior to the glucagon addition reduced the glucagon-induced glucose output dose-dependently. SS-14 given 15 minutes after glucagon addition also inhibited glucagon-induced glucose output significantly. However, various concentrations of SS-28 failed to affect glucose output. On the other hand, in the presence of 5.5 mmol/L glucose, neither SS-14 nor SS-28 affected glucagon-induced glucose output. It is suggested, therefore, that glycogenolysis induced by glucagon from the liver is reduced by SS-14, but not by SS-28, only under glucose free conditions.

Effect of vitamin D on gastrin and gastric somatostatin secretion from the isolated perfused rat stomach

We have studied the role of vitamin D in the regulation of gastrin and gastric somatostatin secretion from the isolated perfused rat stomach. In Ca-deficient vitamin D-deficient rats (Ca(-)D(-) group), the basal and bombesin-stimulated gastrin and gastric somatostatin release (basal IRGa, basal IRS, sigma delta IRGa, and sigma delta IRS) all were significantly lower than in Ca-replete vitamin D-replete rats (Ca(+)D(+) group), and also lower than in Ca-replete vitamin D-deficient rats (Ca(+)D(-) group) except for the basal IRGa. In the Ca(+)D(-) group, the basal IRGa and IRS, and sigma delta IRS were not significantly lower than in the Ca(+)D(+) group. Although there was no significant impairment in basal IRGa, sigma delta IRGa in the Ca(+)D(-) group was significantly lower than in the Ca(+)D(+) control group. Thus, the gastrin and gastric somatostatin secretion from the Ca-deficient vitamin D-deficient rats were impaired. In addition, the impaired gastrin and gastric somatostatin secretions seem to be caused not only by a decrease in serum Ca but also by the reduced effect of the vitamin D on the G and gastric D cells.

Effect of antithyroid autoantibodies on pancreatic islet-cell function

SummaryInsulin-dependent diabetes mellitus is frequently associated with organ-specific autoimmune diseases and/or high titers of organ-specific autoantibodies. The effects of thyroid autoantibodies on islet-cell function were examined in the present study. Islet cell surface antibody (ICSAb) was detected in sera from 6 of 40 patients with autoimmune thyroid disease (AITD) who were positive for thyroid microsomal autoantibodies (TMA). Furthermore, all of the ICSAb-positive patients had high TMA titers.In vitro study using isolated rat pancreatic islets revealed that TMA positive sera significantly suppressed glucose-induced insulin release. Only one of 19 (5%) AITD patients showed complement-dependent antibody-mediated cytotoxicity and only one of 6 AITD patients (17%) was positive for antibody-dependent cellular cytotoxicity. These results suggest that TMA has an effect on an antigen of the islet cell membrane in which insulin releasing mechanism might be involved.

Detection of Antibodies against Wheat Germ Agglutinin Bound Glycoproteins on the Islet-cell Membrane

An attempt was made to detect islet cell surface antibodies (ICSAb) using solubilized islet‐cell glycoproteins as antigens. Isolated rat islets were labelled with 125l‐wheat germ agglutinin (WGA) and solubilized by Nonidet P‐40 with sonication. 125l‐WGA‐bound islet‐cell proteins were incubated with test sera, and bound antibodies were precipitated with anti‐human IgG or IgM immunobeads. Serum which had a bound percent beyond the mean plus 2SD of control sera was defined as antibody‐positive. Results obtained by this method correlated well with those by the immunofluorescence method of detecting ICSAb. Prevalences of antibodies were 21/114 (18%) for IgG antibodies and 9/114 (8%) for IgM antibodies in patients with insulin‐dependent diabetes mellitus (IDDM). The prevalence was highest for both IgG and IgM antibodies in patients within a year of the onset of disease (38 and 25%, respectively), and decreased thereafter. The prevalence of IgM antibodies was lower than that of IgG antibodies at all stages. In NIDDM patients, the prevalence of antibodies was 5/72 (7%) for both IgG and IgM antibodies. If these preliminary results are confirmed, this radioassay may be developed to detect antibodies against islet cell membrane proteins on a large scale.