IgG subclasses and IgM in rats: immunoregulatory effects of cimetidine on serum levels

Previous studies have demonstrated an immunomodulatory role for cimetidine on antibody production. In these experiments we measured IgG subclasses and IgM in rats and also examined the effects of cimetidine on serum levels. Four week-old Sprague-Dawley rats were given cimetidine in three different treatment regimens. IgG subclasses and IgM determinations were carried out by radial immunodiffusion method on sera when animals were 6 and 8 weeks old. IgG1 levels in 6 week-old animals who received intraperitoneal cimetidine on days 1, 2, 3, 4, 5, 6, 8, 9, 15 and 16 were significantly higher (305 +/- 12 mg/l vs 236 +/- 53 in control animals). By 8 weeks of age in control animals, IgG1 levels had fallen to 78 mg/l and were statistically lower than the levels in all cimetidine treatment groups. Eight week-old control animals also demonstrated a four-fold fall in IgG2b levels (613 +/- 310 mg/l) when compared to in 6 week-old control (2295 +/- 1057 mg/l) animals, or 8 week-old animals who had received cimetidine. Animals receiving intravenous cimetidine on days 4, 11 and 18 had significantly lower (133 +/- 3 mg/l) serum levels of IgG2c, at 6 weeks of age, as compared to control animals (177 +/- 16); however, no statistically significant differences in IgG2c levels were observed in 8 week-old animals. No statistically significant differences in the levels of IgG2a or IgM were observed in either 6 or 8 week-old control and experimental animals. It appears that cimetidine does influence certain IgG subclasses, however, route and timing of cimetidine administration are critical in modulating these effects.