Failure of ergotamine to act as an amplifier of sulfonylurea-stimulated insulin secretion.

Normal dogs were injected i.v. with 0.25 mg/kg sodium salt of HB 419 (glibenclamide) and plasma insulin concentrations were measured over a period of 2 hrs. When the animals were given a single i.v. injection of 0.2 mg/kg dihydroergotamine tartrate (DHE) 30 min prior to the administration of HB 419, the insulinogenic effect of the sulfonylurea was considerably amplified (192 muU/ml vs 34 muU/ml at 45 min). No augmentation of the insulinogenic effect of HB 419 was observed when the same experiments were conducted with 0.05, 0.025 or 0.01 mg/kg ergotamine tartrate. At the dose level of 0.1 mg/kg the insulinogenic effect of HB 419 was suppressed. Since the structural difference between these two ergot alkaloids consists of the presence or absence of the double bond at C9 and C10 of the lysergic acid moiety, it appears that saturation of this double bond is an essential structural requirement for DHE to function as an amplifier of sulfonylurea-stimulated insulin release.