The purpose of this study was to determine whether 4 days of resistance exercise facilitated insulin secretory adaptations at the level of the pancreatic islets. Eighteen male 400-g Sprague-Dawley rats were randomly assigned to two groups. All animals were operantly conditioned to engage in a resistance exercise protocol that required full extension of the hindlimbs. Resistance was applied to the animals via a leather-and-Velcro vest to which weighted pouches were attached. The acute (Acute, n = 9) group engaged in four exercise sessions (50 reps each) with increased resistance for each session (70-->120-->120-->190 g). Sessions were separated by 48 h of rest. The nonexercised (Nonex, n = 9) group engaged in the same protocol without resistance. Islets were dispersed 16 h postexercise, incubated for 48 h, and perifused (17-20 islets/rat) with a medium containing 10 mM L-arginine or 16 mM glucose as the insulin secretagogue. Basal insulin secretion from the islets before the introduction of L-arginine or 16 mM glucose was the same for the Acute and Nonex groups (P > 0.05). The total insulin response to 10 mM arginine was significantly higher for the Acute than for the Nonex group (1.16 +/- 0.30 and 0.31 +/- 0.10 ng insulin.islet-1.25 min-1, respectively, P < 0.05). There were no differences between groups for the overall insulin response to glucose (P > 0.05). However, the late-phase insulin response to glucose was higher for the Acute group (P < 0.05). These data suggest that insulin secretory adaptations occur at the level of the pancreatic islets after 4 days of resistance exercise.