GCC-mediated bioassay responses of colonic tissue isolated from rats maintained on low-, normal-, or high-salt diets. Each bar shows the fold-increase in cGMP levels when tissue explants are challenged with STa. Responses are significantly reduced in rats from the low-salt group (*P < 0.04 compared with control). The basal levels of cGMP were 6.8 ± 0.42, 7.39 ± 0.45, and 7.37 ± 0.39 pmol/mg protein in the low-, normal-, and high-salt groups, respectively. Although the average basal level in the low-salt group was less than that of either of the other two treatment groups, the difference was not statistically significant (P = 0.25).