Hypoglycemia overrides amylin-mediated regulation of gastric emptying in rats

Amylin, a 37-amino acid peptide hormone co-secreted with insulin, potently governs the rate of gastric emptying. Hypoglycemia, in the absence of agents such as amylin, is reported to accelerate gastric emptying. We asked whether hypoglycemia had a similar action on gastric emptying in the presence of amylin. In preliminary experiments using a phenol red gavage technique in fasted SD rats, we showed that insulin administration accelerated gastric emptying in a dosage-dependent manner. This acceleration was totally prevented by coadministration of glucose in dosages that prevented a change in plasma glucose, indicating that insulin per se did not affect gastric emptying. The effect on gastric emptying of hypoglycemia induced by a 5 mU/min insulin infusion (t = 5-90 min) was assessed in conscious rats continuously infused with amylin (50 pmol x kg-1 x min-1; t = -30 to 90 min). Gastric emptying was indicated by the appearance in plasma of label from 3-O-methyl-[3H]glucose gavaged at t = 0 min. Label appearance was markedly inhibited in rats preinfused with amylin (84% reduced vs. saline controls at t = 30 min), indicating amylin inhibition of gastric emptying. In amylin-treated rats that were subsequently infused with insulin, gavaged label abruptly appeared in plasma when plasma glucose had fallen to 2.1 +/- 0.1 mmol/l (at t approximately 45 min), consistent with a reversal by hypoglycemia of amylin's inhibition of gastric emptying. These data support the idea of a central "fail-safe" mechanism whereby hypoglycemia can override the slowing of gastric emptying by amylin.