Table 1. VIP increases cGMP levels in WT and nNOS^-/-, but not HO2^-/- or DKO, animals.

	cGMP, fmol/mg
Treatment	WT	nNOS-/-	HO2-/-	DKO
Unstimulated	960 ± 45	802 ± 61	652 ± 18*	724 ± 33*
VIP-stimulated	1,643 ± 102†	1,731 ± 97†	747 ± 54*	805 ± 27*
ODQ + VIP	489 ± 23	393 ± 32	415 ± 29	450 ± 36
DDA + VIP	1,509 ± 51†	1,617 ± 125†	633 ± 44*	761 ± 48*

Anal sphincter muscle strips equilibrated in the organ bath were treated with VIP (250 nm) for 30 s and instantaneously frozen. cGMP content was determined by radioimmunoassay and expressed as fmol/mg. Where indicated, tissues were preincubated for 30 minutes with the cGMP inhibitor ODQ or the cAMP inhibitor DDA prior to simulation with 250 μM VIP. Data represent mean ± SEM. ODQ, 1H-[1,2,4]-oxadiazolo-[4,3-a]-quinoxaline-1-one; DDA, 2′,5′-dideoxyadenosine. ^*, P < 0.05, compared with WT. ^†, Significant increase by VIP, P < 0.05.