(A) Insulin levels in conditioned medium from β cell–like MIN6 cells. Cells were incubated in low (3 mM) or high (15 mM) glucose in the presence or absence of the Par2 agonist SLIGRL. SLIGRL (100 μM) inhibited GSIS (n = 4; **P = 0.0055, control versus 100 μM), and this was prevented by pretreatment with pertussis toxin (50 ng/ml for 16 hours). (B) Plasma insulin levels were measured at time 0 and again at 3 minutes following administration of vehicle or SLIGRL (10 μmol/kg, i.p.). Note the larger SLIGRL-induced decrease in plasma insulin levels in control relative to Par2^–/– mice (n = 12; *P = 0.012). (C) Par2^–/– and littermate control mice were fasted for 2 hours then dosed with SLIGRL (10 μmol/kg, i.p.); blood glucose levels were measured at the indicated times after SLIGRL administration. Data are expressed relative to glucose levels at time 0 for each genotype (123 ± 10 mg/dl, control; 118 ± 13 mg/dl, Par2^–/–). Littermate control mice became hyperglycemic relative to Par2^–/– mice (n = 12–13; **P < 0.01). (D) RIP-PTX and littermate control mice were treated as in C. Basal glucose levels were 124 ± 14 mg/dl in littermate control mice and 86 ± 13 mg/dl in RIP-PTX mice. RIP-PTX mice failed to show glucose elevations in response to SLIGRL (n = 7–9; **P < 0.001). (E) Blood glucose levels in Par2^–/– and littermate controls after i.p. glucose administration (IPGTT). Increases in blood glucose levels were blunted in Par2^–/– mice compared with controls (n = 29–35; P = 0.0006 for difference between genotypes, 2-way ANOVA; **P = 0.001, *P = 0.01, difference in glucose levels at individual time points, unpaired Student’s t test).