Aims/hypothesis: To study the role of the human alpha2A-adrenoceptor in the regulation of insulin secretion and the maintenance of glucose homeostasis in transgenic mice overexpressing this receptor in pancreatic beta cells.
Methods: A human insulin promoter/human alpha2C10-adrenoceptor chimeric gene was microinjected into mouse embryos and transgenic mice were obtained.
Results: Analysis by RT-PCR showed that the expression of the transgene was restricted to pancreatic islets. Study of the binding of the alpha2-antagonist [3H]RX821002 to membrane preparations showed that islets from transgenic mice had ninefold higher alpha2-adrenoceptor density than those from controls. Immunohistological analysis showed, however, no change in the number or size of islets between control and transgenic mice. Transgenic animals had normal glycaemia and insulinaemia in basal conditions but greater hyperglycaemic and hypoinsulinaemic responses after injection of the alpha2-agonist, UK14304. The lower blood insulin concentration detected in transgenic mice was a reflection of a stronger inhibitory effect of the alpha2-agonist on glucose-stimulated insulin secretion in transgenic islets than in controls. Furthermore, transgenic mice did not have lower glycaemia to basal values after an intraperitoneal glucose tolerance test. This defect was abolished by treatment with the alpha2-adrenoceptor antagonist, RX821002.
Conclusion/interpretation: These results provide evidence in vivo that overexpression of alpha2-adrenoceptors in beta cells can lead to impaired insulin secretion and glucose intolerance.