The effect of caffeine on the absorption of 3H-dihydroergocryptine (DHEC) in the rat.

1. Following single oral doses of 3H-dihydroergocryptine (DHEC) to rats, most of the absorbed radioactivity was excreted in the bile, 18.5% +/- 3.2 SD after dosing with 3H-DHEC (0.1 mg/kg) and caffeine (1 mg/kg), and 15.1 +/- 4.6 SD after dosing with 3H-DHEC (0.1 mg/kg) alone. The exception data indicated that about 25% of a single oral dose of 3H-DHEC was absorbed. 2. During 7 h after the last of daily oral doses for 7 days, plasma concentrations of radioactivity were consistently significantly greater (P < 0.001 to < 0.01) in rats dosed with 3H-DHEC (0.1 mg/kg) and caffeine (1 mg/kg) than in those dosed with 3H-DHEC (0.1 mg/kg) alone. The extent of bioavailability of radioactivity was also signficantly greater during this time (P < 0.01) and during 24 h (P < 0.05) after the last of repeated oral doses of 3H-DHEC and caffeine than after 3H-DHEC alone.