The effect of the migraine drugs ergotamine and sumatriptan on the cerebral blood flow (CBF) autoregulation was studied in halothane/nitrous oxide-anesthetized normotensive Wistar Kyoto rats. Ergotamine, an ergot alkaloid affecting 5HT, norepinephrine, and dopamine receptors, was administered intravenously as a single dose of 25 microg/kg. Sumatriptan, a selective 5HT1-like receptor agonist, was administered by intravenous infusion of 300 microg/kg/h. CBF was measured with the intracarotid 133Xe-injection method. The blood pressure limits of CBF autoregulation were determined by computerized least sum of square analysis. CBF autoregulation was preserved after both ergotamine and sumatriptan. Ergotamine shifted the lower blood pressure limit of CBF autoregulation towards higher blood pressures from 60 +/- 3 mmHg to 82 +/- 4 mmHg (p<0.01), but did not significantly affect the upper blood pressure limit of CBF autoregulation. Sumatriptan had no significant effects on the blood pressure limits of CBF autoregulation.