Immunomodulatory screening test of corn oil administered orally to female mice: effect of timing of dosing within 24 hours

The effect of varying the dose-delivery time within a 24 h period (12:12 light-dark cycle) on the immunomodulatory properties of corn oil administered by gavage to 120 B6C3F1 female mice was investigated. Mice, housed in six separate boxes equipped with timers to regulate light onset and offset (staggered by 4 h increments), were treated for 5 consecutive days by intragastric (i.g.), administration of 5 mL/kg corn oil. Negative and positive control mice were given sham injections (needle inserted, but no injection). Sheep red blood cells (SRBCs) were injected intraperitoneally (i.p.) on the fifth day. Three days later, positive control mice were given cyclophosphamide intraperitoneally (80 mg/kg). Four days after SRBC injection, mice were weighed and killed, and spleens and thymuses were removed and weighed. Spleens were brought to single-cell suspensions and tested for an antibody response to the SRBC. Plaque-forming cells (PFCs), as measured per spleen, per 10(6) viable spleen cells or per 10(6) total spleen cells, exhibited significant circadian rhythms for mice given corn oil, but not for sham-gavage- and cyclophosphamide-treated mice. The peak response (acrophase, phi) occurred at 21 h, 22 h, and 23 h after lights on (HALO), respectively, with PFC values significantly different between the different time points. Corn oil and sham gavage affected the circadian pattern of antibody production; there was a high-amplitude (21-27%) rhythm observed when mice were treated with corn oil and no rhythm when mice received the sham-gavage treatment. In addition to testing mice near the end of the daily dark span and/or early light span to obtain a maximum immune response, this finding points to the importance of including as controls a group of animals that are not treated at all and a group given vehicle alone, rather than only sham-treated animals, for comparison with experimentally treated animals.