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Z Li, FA Karlsson and S Sandler

The aim of this study was to investigate the alpha cell population during the development of type 1 diabetes following multiple low-dose streptozotocin administration in mice. For this purpose C57BL/Ks male mice were injected with streptozotocin (40 mg/kg body weight for 5 days). Development of hyperglycemia was monitored over 28 days and a morphometric analysis of islet endocrine cells was performed. A reduction of islet cell area was observed after two injections of streptozotocin. The subsequent decrease of the area throughout the study period averaged 35%. Insulin-positive beta cells gradually disappeared from the identified islets. Hyperglycemia was present from day 7 onwards and in parallel with hyperglycemia, insulitis developed. An analysis of the alpha cell number per islet area revealed a 2- to 3-fold increase in this cell population, with the highest value on day 21. Confocal microscopy analysis of the ICA 512 protein tyrosine phosphatase revealed strong expression in the alpha cells at day 21, suggesting high secretory activity in the diabetic state. It is concluded that multiple low-dose streptozotocin treatment of C57BL/Ks male mice causes the disappearance of a fraction of the islets of Langerhans. In the remaining islet tissue an expansion of alpha cells occurs, reflecting a loss of intraislet beta cells as well as a regeneration of alpha cells.

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Y. D. Li, Z. W. Zhang and W. X. Li

ABSTRACT

The effect of transferrin on basal and FSH-stimulated aromatase activity of granulosa cells from immature female rats treated with diethylstilboestrol (DES) was examined in vitro by a radiometric method. The basal activity of the enzyme was very low after 3 days of incubation. Treatment with FSH (20 ng/ml) resulted in a 9·6-fold increase in activity, whereas coincubation with increasing doses of transferrin (3–300 μg/ml) produced a dose-dependent inhibition of FSH-stimulated aromatase activity with a projected minimal effective dose of < 2 μg/ml. A time-course study showed that the inhibitory effect of transferrin on aromatase activity has become significant at 48 h of incubation.

The inhibitory action of transferrin on the enzyme complex was further confirmed by showing that the FSH dose–response curve was significantly suppressed by concomitant treatment with 100 μg transferrin/ml with a maximum suppression of 54·1 % at a dose of 30 ng FSH/ml.

The possibility that transferrin may act through a non-specific inhibitory effect seems unlikely, as no changes in cell number and DNA content per well were observed. In fact, protein synthesis was enhanced after treatment with transferrin. Aromatase activity, stimulated by several promoters of cyclic AMP (cAMP), such as prostaglandin E2 (PGE2), forskolin and 8-bromo-cAMP, was significantly suppressed by 100 μg transferrin/ml (36·6, 47·4 and 23·4% inhibition respectively), suggesting that the effect of transferrin on FSH action may involve a site(s) distal to cAMP generation.

These findings indicated that transferrin, present in follicular fluid, may play an important role in the regulation of granulosa cell differentiation.

Journal of Endocrinology (1991) 131, 245–250

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L Zhao, Z Li, M Kullin, L A H Borg and F A Karlsson

The pancreatic B-cell GLUT2 transporter and glucose metabolism were examined in isolated rat islets subjected to treatments affecting insulin secretion. Diazoxide was used to inhibit, while glipizide or depolarization of the plasma membrane with a high extracellular K+ concentration were used to stimulate insulin release in short-term experiments. Islet GLUT2 and insulin were determined by quantitative immunohistochemistry and GLUT2 was also determined by Western blot analysis. Islet net glucose uptake and glucose oxidation were measured using radioactively labelled glucose. Exposure of the islets to diazoxide was associated with a marked increase in the B-cell plasma membrane staining for GLUT2 and increased net glucose uptake. Glucose oxidation was not changed, which may reflect a lowered energy requirement. Conversely, islets subjected to a stimulated insulin secretion with glipizide or a high extracellular K+ concentration showed a reduced staining of the GLUT2 transporter. The net glucose uptake and glucose oxidation were also reduced. In islets exposed to the high K+ concentration no change in the molecular weight or phosphorylation of GLUT2 was observed but a lesser amount of the transporter was found by Western blot analysis. Thus, GLUT2 and glucose uptake in the pancreatic B-cell are modified by the secretory process, which suggests that changes in the glucose transporter have a functional role in normal B-cell physiology.

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J L Környei, X Li, Z M Lei and Ch V Rao

Abstract

The present study investigated the mechanisms involved in the mitogenic action of epidermal growth factor (EGF) in cultured human myometrial smooth muscle cells. The cells contained EGF/transforming growth factor-α (TGF-α) receptors as well as EGF and TGF-α mRNA transcripts and the corresponding proteins. Culturing with human EGF resulted in concentration- and time-dependent increases in cell density. The maximal increase was seen at 1 nm followed by a decrease to control levels at 100 nm EGF. The EGF increased cell density from 4 to 8 days followed by a plateau coinciding with the cells reaching confluence. EGF treatment concomitantly decreased the average size of cells. TGF-α mimicked EGF and there was no synergism between the two, suggesting a common mechanism of action. Although the presence of 10% fetal bovine serum enhanced overall cell growth, it was not required for EGF and TGF-α action. The receptor antibody, which is directed against the extracellular domain and can inhibit ligand binding to the receptors, dramatically inhibited the basal cell growth and exogenous EGF reversed the antibody effect. While TGF-α antibody was only marginally effective, EGF antibody had no effect on basal cell growth. Lavendustin (a tyrosine kinase inhibitor), calphostin (a protein kinase C inhibitor), but not H-89 (a protein kinase A inhibitor), inhibited EGF action. Indomethacin, a cyclo-oxygenase inhibitor, completely inhibited, whereas nordihydroguaiaretic acid, a lipoxygenase inhibitor, slightly inhibited EGF action. While estradiol-17β modestly inhibited basal as well as EGF-stimulated myometrial smooth muscle cell density, progesterone had no effect.

In summary, mitogenic action of EGF in human myometrial smooth muscle cells does not require serum components and it involves tyrosine kinase and protein kinase C signaling and eicosanoids from the cyclo-oxygenase pathway of arachidonic acid metabolism.

Journal of Endocrinology (1995) 146, 261–270

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Yu Wu, Tingting Wu, Jun Wu, Lei Zhao, Qing Li, Zac Varghese, John F Moorhead, Stephen H Powis, Yaxi Chen and Xiong Z Ruan

Inflammatory stress is closely related to metabolic disease and insulin resistance. The precise cellular mechanism linking obesity and diabetes is largely unknown, but about 14–20% of obese individuals develop diabetes. In this study, we investigated whether chronic inflammation exacerbated glucose metabolism disorder by impairing β cell function in high-fat diet (HFD)-fed C57BL/6J mice. We used s.c. casein injection to induce chronic inflammation in HFD-fed C57BL/6J mice; 14 weeks on a HFD resulted in weight gain, hyperlipidemia, and low insulin sensitivity in these mice which nevertheless had normal blood glucose and serum inflammatory cytokines levels. Casein injection in the background of HFD elevated serum tumor necrosis factor α (TNFα) and serum amyloid A levels and increased TNFα and MCP1 expression in the adipose tissue, liver, and muscle of HFD-fed mice. Chronic inflammation induced by casein injection further decreased insulin sensitivity and insulin signaling, resulting in insulin deficiency and hyperglycemia in these mice. Islet mass and insulin content were markedly increased in HFD mice. However, in contrast with HFD-fed alone, chronic inflammation in HFD-fed mice decreased both islet mass and insulin content, reduced the genetic expression of insulin synthesis and secretion, and increased β cell apoptosis. We conclude that chronic inflammation exacerbated glucose metabolism disorders by impairing β cell function in HFD-fed C57BL/6J mice, suggesting that this mechanism may operate in obese individuals with chronic inflammation, making them prone to hyperglycemia.