Adrenergic changes due to pertussis: insulin, glucose and free fatty acids

Probing cell type-specific functions of Gi in vivo identifies GPCR regulators of insulin secretion

The in vivo roles of the hundreds of mammalian G protein-coupled receptors (GPCRs) are incompletely understood. To explore these roles, we generated mice expressing the S1 subunit of pertussis toxin, a known inhibitor of G(i/o) signaling, under the control of the ROSA26 locus in a Cre recombinase-dependent manner (ROSA26(PTX)). Crossing ROSA26(PTX) mice to mice expressing Cre in pancreatic beta cells produced offspring with constitutive hyperinsulinemia, increased insulin secretion in response to glucose, and resistance to diet-induced hyperglycemia. This phenotype underscored the known importance of G(i/o) and hence of GPCRs for regulating insulin secretion. Accordingly, we quantified mRNA for each of the approximately 373 nonodorant GPCRs in mouse to identify receptors highly expressed in islets and examined the role of several. We report that 3-iodothyronamine, a thyroid hormone metabolite, could negatively and positively regulate insulin secretion via the G(i)-coupled alpha(2A)-adrenergic receptor and the G(s)-coupled receptor Taar1, respectively, and protease-activated receptor-2 could negatively regulate insulin secretion and may contribute to physiological regulation of glucose metabolism. The ROSA26(PTX) system used in this study represents a new genetic tool to achieve tissue-specific signaling pathway modulation in vivo that can be applied to investigate the role of G(i/o)-coupled GPCRs in multiple cell types and processes.

Pancreatic beta-cell receptors and G proteins coupled to adenylyl cyclase

Glucagon and tGLP-1 receptors can be either coexpressed or selectively expressed in beta-cell models. Our results indicate that both these peptides can regulate insulin secretion from beta-cells through their own specific receptors. The finding of a selective expression of G proteins in insulin and glucagon cells indicates a clear difference in their transduction pathways. A key role of the G alpha s family in beta-cell function is further supported by its conserved cell distribution between different species. In conclusion, one could postulate that in the human beta-cells, tGLP-1 and glucagon receptors could mediate their action through different G protein alpha-subunits of the G alpha s family.

A biphasic serum glucose response in mice to inoculation with pertussis vaccine

The effect of B. pertussis vaccine on the serum glucose level of mice was investigated. The results show that at least two components in the vaccine interfere with glucose metabolism. A heat-stable component which is assumed to be LPS induced hypoglycemia 3-5.5 h after inoculation, especially in LPS-sensitized mice. A heat-labile component which is possibly equivalent with the LPF/HSF/IAP complex, is responsible for persistence of the hypoglycaemia for at least 6 days. If hypoglycaemia contributes to the neurological side effects after pertussis vaccination both components have to be considered as being responsible for these effects.

Glycerol-releasing activity of histamine-sensitizing factor of Bordetella pertussis for rat adipocytes in vitro

Histamine-sensitizing factor (HSF) purified from Bordetella pertussis induced specifically the release of glycerol from rat epididymal adipocytes in vitro. The most sensitive and reproducible results were obtained by using 1 to 2 x 10(5) adipocytes/tube from rats weighing 150 to 200 g, and by incubation at 37 C for 180 min. After a lag period of about 60 min, HSF-treated adipocytes released glycerol in increasing amounts between 60 and 240 min, depending on the dose of HSF. A close correlation between the glycerol-releasing (GR) activity of HSF for adipocytes and histamine-sensitizing or leukocytosis-promoting activity in mice was observed. The GR activity was inactivated by heating at 56 C for 60 min, 63 C for 30 min or 96 C for 10 min. The adipocytes washed out with a Krebs-Ringer bicarbonate buffer immediately after being exposed to HSF for 1 to 3 min manifested about 75% of the total GR activity induced by HSF, and those washed out after being exposed for 30 min or longer had full activity. Anti-HSF serum neutralized the activity when it was added to adipocytes simultaneously with HSF, but did not when it was added 30 min after being exposed to HSF. By using both native and 125 I-labeled HSF, the ratio of binding of HSF to adipocytes was estimated to be 10 to 15% of the total HSF per 2 x 10(5) cells/tube, and to be about 1,000 molecules of HSF per cell to induce the release of glycerol. The GR activity induced with 10 ng of HSF was inhibited by addition of insulin at a dose of over 1 micro IU/tube, but not by concanavalin A.

Islet activating protein (IAP) derived from the culture supernatant fluid of Bordetella pertussis: effect on spontaneous diabetic rats

The early phase of insulin secretion to an oral glucose load was blunted in spontaneous diabetic rats. The blunted insulin secretion was associated with markedly impaired glucose tolerance. A single injection of the islet activating protein (IAP), a protein derived from the culture medium of Bordetella pertussis, into the spontaneous diabetic rats normalised glucose tolerance. The increase in insulin response to glucose was an important contributing factor to the improvement of glucose tolerance. This curative effect of the IAP on the diabetic state was of long duration; glucose tolerance remained virtually normal over a period of one month in the diabetic rats. Perfusion of the isolated pancreas of the diabetic rats pretreated with IAP showed an increase in insulin response to glucose and loss of suppression of glucagon secretion by noradrenaline.