Table 1.

Examples of GPCRs in the pancreatic islet for receiving circulatory inputs.

GPCR	Family	Ligands	Transduction mechanism	Functions	References
GHSR1a	Rhodopsin	Ghrelin	Gq/11; Gi/o; G12/13	• Inhibit insulin secretionb	(12)
GPR40	Rhodopsin	Long-chain carboxylic acid	Gq/11; Gs; Gi/o	• Stimulate glucagon secretionc • Enhance insulin secretiona	(13, 14)
GPR119	Rhodopsin	N-oleoylethanolamide	Gs	• Enhance insulin secretionc • Stimulate β-cell replicationc	(15, 16)
ChemR23	Rhodopsin	Chemerin	Gi/o	• Stimulate glucagon secretionc • Enhance insulin secretiona	(17)
MT1	Rhodopsin	Melatonin	Gi/o; Gq/11	• Stimulate glucagon secretiona • Enhance insulin secretionb	(18)
MT2	Rhodopsin	Melatonin	Gi/o	• Stimulate glucagon secretiona • Enhance insulin secretionb	(18)
α2AAR	Rhodopsin	Adrenaline; Noradrenaline	Gi/o; Gs	• Inhibit insulin secretionb	(19)
β1AR	Rhodopsin	Adrenaline; Noradrenaline	Gs; Gi/o; β-arrestin $\frac{1}{2}$	• Stimulate glucagon secretiona • Stimulate somatostatin secretiona	(19, 20)
β2AR	Rhodopsin	Adrenaline; Noradrenaline	Gs; Gi/o; β-arrestin 1	• Stimulate glucagon secretiona • Stimulate somatostatin secretiona	(19, 20)
β3AR	Rhodopsin	Adrenaline; Noradrenaline	Gs; Gi/o	• Enhance insulin secretionb	(21)
PAC1	Secretin	PACAP	Gs; Gq/11	• Enhance insulin secretionb • Stimulate glucagon secretiona	(22, 23)
GLP1R	Secretin	GLP1	Gs	• Inhibit cytokine-induced apoptosis of β-cellsc • Inhibit glucagon secretionb	(14)
GIPR	Secretin	GIP	Gs	• Inhibit cytokine-induced apoptosisc • Induce insulin production regulated by inflammationb	(14, 24)

The GCPRs expressed in the pancreatic islet receive circulatory signals and exert their functions on hormone-secreting cells, initiating the autocrine and/or paracrine regulations between pancreatic cells. The primary transduction mechanisms are listed at the first row followed by secondary transduction mechanisms (if any).

^aInitiate both autocrine and paracrine regulations.

^bInitiate paracrine regulations.

^cInitiate autocrine regulations.