- It was hypothesized that alterations in plasma concentrations of
corticosterone (CS) and prolactin (PRL) may be at least partially responsible
for polychlorinated biphenyl (PCB)-induced immunosuppression.
A 2 by 2 factorial experiment examined the interactions of PCB and P815,
an allogeneic tumor, on plasma concentrations of CS and PRL, and on body,
spleen, and thymus weights. The PCB dosage used (10 mg/kg) was
previously shown to suppress immune response to the tumor. The four study
groups were: Group A (vehicle control), Group B (tumor only), Group C (PCB
only), and Group D (tumor plus PCB). Mice received one dose of PCB
(Groups C and D) or carrier (Groups A and B) on day -1; tumor (Groups B
and D) or carrier (Groups A and C) was injected intraperitoneally on day 0. In
Experiment 1, animals were killed on days -1, -0.6, 0 through 10, 21, 42, and
84. Body, spleen, and thymus weights were measured. Plasma samples were
obtained for CS and PRL measurements. In Experiment 2, the study was
repeated with samples obtained only on days 3 and 10.
Group A body weights increased steadily throughout Experiment 1.
Relative to Group A, the weight gain in Group B was significantly (p < 0.05)
higher. Group C lost weight on days 0 through 6, and gained significantly (p
< 0.05) less weight than Group A. Group D gained significantly (p < 0.05)
less weight than Groups A, B, and C.
As a percent of body weight, spleen weight remained constant over 21
days in Experiment 1 in both Groups A and D. Compared to Group A, Group
B showed significantly (p < 0.05) increased spleen percent body weight while
Group C showed significantly (p < 0.05) decreased spleen percent body
As a percent of body weight, thymus weight remained constant for 21
days in Experiment 1 in Group A. Groups Band C were similar (p > 0.05)
and showed a decreased thymus percent body weight compared to Group A.
Group D showed significantly (p < 0.05) decreased thymus percent body
weight relative to the other three groups.
Mean CS concentrations in Experiment 1 in Groups A and B were similar
(p < 0.05). Relative to Groups A and B, Group C CS concentrations were
elevated, with a peak of 126.1 ng/ml on day 4. Group D CS concentrations
were higher than the other three groups, peaking at 294.1 ng/ml on day 10.
There was no significant difference in PRL concentrations in Groups A, B,
and C in Experiment 1 (p > 0.05). Mean PRL concentration in Group D was
significantly (p < 0.05) lower than in the other three groups.
The results of Experiment 2 validated those of Experiment 1. Although
absolute values differed, the pattern of changes seen in body and organ
weights and in CS and PRL concentrations was similar.
An acute exposure to PCB and tumor resulted in an increase in
circulating CS concentration and a decrease in circulating PRL concentrations.
These changes may contribute to PCB-induced immunosuppressioin.