We evaluated the effect of HCL-31D. a novel cAMP-specific phosphodiesterase
inhibitor, on the induction of inducible nitric oxide synthase (iNOS) in l
ipopolysaccharide (LPS) and interferon-gamma (IFN-gamma)-treated rat aortic
smooth muscle cells (RASMC) and on survival in a murine model of severe en
dotoxaemia. Treatment of cultured RASMC with LPS and IFN-gamma resulted in
an increase of nitrite, tumour necrosis factor (TNF-alpha) production and i
nduction of iNOS mRNA. However, incubation with HCL-31 D (1 similar to 50 m
uM) for 24 It caused significant attenuation of nitrite and TNF-alpha forma
tion as well as iNOS mRNA induction in a dose-dependent manner but no effec
t on iNOS activity in RASMC. In addition, administration of HCL-31D (5 mg/k
g, i.p.) resulted in that the increase of both plasma nitrate and TNF-alpha
levels induced by LPS in vivo was significantly reduced in LPS-treated rat
s. Treatment of conscious mice with a high dose of LPS (60 mg/kg, i.P.) to
ICR mice resulted in a 24-h survival rate of only 10%. However, administrat
ion of HCL-31D (5 mg/kg, i.p. at 0 h and 6 h after LPS) improved the 24-h s
urvival to 50%. indicating that HCL-3 I D has a beneficial effect in murine
model endotoxaemia. These effects may be mainly due to inhibition of TNF-a
lpha formation and of the induction of iNOS. We proposed that the elevation
of cAMP levels by HCL-31D may be involved in the prevention of TNF-alpha.
formation and iNOS induction.