The role of nitric oxide in aloe-induced diarrhoea in the rat

The role of nitric oxide (NO) on aloe-induced diarrhoea was studied in the rat. Nine hours after oral administration, aloe produced diarrhoea at doses of 5 g kg(-1) (20% rats with diarrhoea) and 20 g kg(-1) (100% of rats with diarrhoea). Lower doses of aloe (0.1 and 1 g kg(-1)) did not produce a dia rrhoeal response. Pre-treatment (i.p.) of rats with the NO synthase inhibit or N-G-nitro-L-arginine methyl ester (L-NAME 2.5-25 mg kg(-1)) reduced the diarrhoea induced by aloe (20 g kg(-1)) 9 h after its oral administration. L-NAME (25 mg kg(-1)) also reduced the increase in faecal water excretion p roduced by aloe (20 g kg(-1)). L-arginine (1500 mg kg(-1), i.p.), administe red to rats pre-treated with L-NAME (25 mg kg(-1)), drastically reduced the effect of L-NAME on diarrhoea and increase in faecal water excretion induc ed by aloe (20 g kg(-1)). Given alone, L-arginine did not modify aloe-induc ed diarrhoea. Basal Ca2+-dependent NO synthase activity in the rat colon wa s dose-dependently inhibited by aloe (0.1-20 g kg(-1)) and by aloin (0.1-1 g kg(-1)), the active ingredient of aloe. These results suggest that endoge nous NO modulates the diarrhoeal effect of aloe. (C) 1999 Elsevier Science B.V. All rights reserved.