Temporal variation in endotoxin‐induced vascular hyporeactivity in a rat mesenteric artery organ culture model

Endotoxin‐induced vascular hyporeactivity to phenylephrine (PE) is well described in rodent aorta, but has not been investigated in smaller vessels in vitro . Segments of rat superior mesenteric artery were incubated in culture medium with or without foetal bovine serum (10%) for 6, 20 or 46 h in the presence or absence of bacterial lipopolysaccharide (LPS; 1 – 100 μg ml −1 ). Contractions to PE were measured with or without nitric oxide synthase (NOS) inhibitors: L ‐NAME (300 μ M ), aminoguanidine (AMG; 400 μ M ) 1400W (10 μ M ) and GW273629 (10 μ M ); the guanylyl cyclase inhibitor, ODQ (3 μ M ); the COX‐2 inhibitor, NS‐398 (10 μ M ). Contractile responses to the thromboxane A 2 mimetic, U46619 were also assessed. In the presence of serum, LPS induced hyporeactivity at all time points. In its absence, hyporeactivity only occurred at 6 and 20 h.L ‐NAME and AMG fully reversed hyporeactivity at 6 h, whereas they were only partially effective at 20 h and not at all at 46 h. In contrast partial reversal of peak contraction was observed with 1400W (62% at 46 h), GW273629 (57% at 46 h) and ODQ (75% at 46 h). COX‐2 inhibition produced no reversal. In contrast to PE, contractions to U46619 were substantially less affected by LPS. We describe a well‐characterized reproducible model of LPS‐induced hyporeactivity, which is largely mediated by the NO‐cyclic GMP‐dependent pathway. Importantly, long‐term (2‐day) production of NO via iNOS is demonstrated. Moreover, conventional doses of L ‐NAME and AMG became increasingly ineffective over time. Thus, the choice of inhibitor merits careful consideration in long‐term models.British Journal of Pharmacology (2001) 133 , 351–360; doi: 10.1038/sj.bjp.0704079