ANDROGRAPHOLIDE SUPPRESSES THE EXPRESSION OF INDUCIBLE NITRIC-OXIDE SYNTHASE IN MACROPHAGE AND RESTORES THE VASOCONSTRICTION IN RAT AORTA TREATED WITH LIPOPOLYSACCHARIDE

1 We investigated whether andrographolide, a diterpenoid lactone found at Andrographis paniculata, influences the induction of the inducible nitric oxide synthase (iNOS) in RAW264.7 cells activated by bacterial endotoxin (LPS), as well as in the rats with endotoxic shock and in a ortic rings treated with LPS. 2 Incubation of RAW264.7 cells with andr ographolide (1 to 50 mu M) inhibited the LPS (1 mu g ml(-1))-induced n itrite accumulation in concentration- and time-dependent manners. Maxi mum inhibition was observed when andrographolide was added together wi th LPS and decreased progressively as the interval between andrographo lide and LPS was increased to 20 h. 3 Western blot analysis demonstrat ed that iNOS expression was markedly attenuated in the presence of and rographolide for 6-24 h, suggesting that andrographolide inhibited iNO S protein induction. 4 Thoracic aorta incubation with LPS (300 ng ml(- 1)) for 5 h in vitro exhibited a significant decrease in the maximal c ontractile response to phenylephrine (10(-9)-10(-5) M). Andrographolid e (30 mu M) restored the contractile response to control level. 5 In a naesthetized rats, LPS (10 mg kg(-1), i.v.) caused a fall in mean arte rial blood pressure (MAP) from 116 +/- 4 to 77 +/- 5 mmHg. The presser effect of phenylephrine (10 mu g ml(-1), i.v.) was also significantly reduced at 30, 60, 120 and 180 min after LPS injection. In contrast, animals pretreated with andrographolide (1 mg kg(-1), i.v., 20 min pri or to LPS) maintained a significantly higher MAP when compared to LPS- rats given with vehicle. Administration of andrographolide 60 min afte r LPS caused a increase in MAP and significantly reversed the reductio n of the presser response to phenylephrine. 6 Our results indicated th at andrographolide inhibits nitrite synthesis by suppressing expressio n of iNOS protein in vitro. And, this inhibition of iNOS synthesis may contribute to the beneficial haemodynamic effects of andrographolide in endotoxic shock.