Effects of insulin and beta-adrenergic blockade on the migrating motor complex in humans.

BACKGROUND

Interdigestive small-intestinal motility is suppressed by hyperglycemia and also by hyperinsulinemia per se. Since hyperinsulinemia may increase sympathetic activity, the present study was undertaken to ascertain to what extent insulin affects phase III of the migrating motor complex (MMC) and MMC-related duodenal retroperistalsis and whether beta-adrenergic receptors may mediate the effects of insulin.

METHODS

Fasting motility was studied in eight healthy volunteers on three occasions with an eight-lumen perfused pressure catheter, with closely spaced recording points in the proximal duodenum. On the control day 5-h antroduodenojejunal manometry was performed. On another study day euglycemic hyperinsulinemic clamping was performed for 2 h after an initial basal recording. On a 3rd day motility was recorded during propranolol infusion, combined with a period of euglycemic hyperinsulinemia.

RESULTS

During hyperinsulinemia complete absence of phase III of the MMC in the gastric antrum was observed, whereas 55% of the MMC had a gastric phase-III component on the control day. The duration of phase III in the proximal duodenum was decreased during hyperinsulinemia compared with the control period (p < 0.05). This inhibitory effect of insulin on the activity front was not prevented by beta blockade. Under control conditions the proportion of retroperistaltic pressure waves in the proximal duodenum was 13 +/- 8% in early phase III, increasing in late phase III to 79 +/- 15% (p < 0.01). Duodenal phase III during hyperinsulinemia showed a similar increase in retroperistalsis, from 4 +/- 4% in early phase III to 67 +/- 21% in late phase III (p < 0.01). The corresponding proportions during beta blockade were 16 +/- 10% and 86 +/- 14%, respectively.

CONCLUSIONS

Hyperinsulinemia per se abolishes antral phase III and makes the duodenal phase III shorter but does not interrupt the distinct pattern of retroperistalsis in late phase III. Beta-adrenergic receptors seem not to be important for these effects of insulin or for the retroperistalsis in duodenal phase III.