Dopamine signalling in pancreatic islet cells and role in adaptations to metabolic stress.

OBJECTIVES Dopamine and related receptors are evidenced in pancreatic endocrine tissue, but the impact on islet β-cell stimulus-secretion as well as (patho)physiological role are unclear. METHODS The present study has evaluated islet cell signalling pathways and biological effects of dopamine, as well as alterations of islet dopamine in rodent models of diabetes of different aetiology. KEY FINDINGS The dopamine precursor L-DOPA partially impaired glucose tolerance in mice and attenuated glucose-, exendin-4, and alanine-induced insulin secretion. The latter effect was echoed by the attenuation of glucose-induced [Ca2+]i dynamics and elevation of ATP levels in individual mouse islet cells. L-DOPA significantly decreased β-cell proliferation rates, acting predominantly via the D2 receptor, which was most abundant at the mRNA level. The administration of streptozotocin (STZ) or high-fat diet (HFD) in mice significantly elevated numbers of dopamine-positive islet cells, with HFD also increasing colocalization of dopamine with insulin. At the same time, colocalization of dopamine with glucagon was increased in STZ-treated and pregnant mice, but unaffected by HFD. CONCLUSION These findings highlight a role for dopamine receptor signalling in islet cell biology adaptations to various forms of metabolic stress.