A series of experiments was conducted to assess the physiological effects of dietary PCB (Aroclor 1254) ingestion in white mice (Mus musculus) and in laboratory-reared white-footed mice (Peromyscus leucopus), and to determine if these effects were aggravated by group-caging or feed restriction. The underlying hypothesis was that PCBs may have different physiological effects, dependent on the nutritional status of the animal and the density of the population of which it is a member. The physiological characteristics examined were various organ weights, plasma corticoid levels, testicular spermatozoan reserves (right testis only) and hepatic microsomal enzyme activity. Pentobarbital- induced sleeping times were used as an index of enzyme activity. A competitive protein binding assay was used for determining plasma corticoid levels.

PCBs (200 and 1000 ppm) in the diet of male white mice for 2 weeks significantly increased liver weights and decreased pentobarbital-induced sleeping times, whereas 100 ppm or below had no such effect in either male or female white mice. Male white-footed mice fed PCBs (100, 200 or 400 ppm) for 2 weeks and female white-footed mice fed PCBs (25, 36, 100 or 143 ppm) for 3 weeks exhibited greater liver weights and shorter sleeping times than control mice at all PCB levels. A significant PCB x Diet interaction effect was observed on liver weights and sleeping times in white mice. PCB feeding resulted in a greater increase in liver weights and a greater reduction in sleep times in feed-restricted than ad libitum fed mice.

Plasma corticoid levels of white mice were significantly elevated by PCB-ingestion, group-caging and restrictive-feeding. In addition, significant PCB x Diet and PCB x Caging interaction effects were observed on corticoid levels. The PCB-induced increase in plasma corticoid levels was greater in grouped than in singly caged mice and in feed-restricted than ad libitum fed mice. Conversely, plasma corticoid levels were reduced in PCB-fed white-footed mice. PCB feeding did not significantly affect body weights, feed consumption or female reproductive organ weights. In addition, the proportion of white-footed mice exhibiting estrus as judged by vaginal smears was not altered by PCB feeding. In general the weight of the male reproductive organs were not affected by PCB ingestion. Testicular spermatozoa were significantly reduced by PCBs and grouping, whereas feed restriction did not affect spermatozoan counts. It was hypothesized that PCBs disrupted the spermatogenic cycle via reduction in androgen and/or gonadotrophin levels. No interactions were observed between PCBs and Diet or PCBs and Caging on any of the reproductive characteristics examined in either species.

In summary, PCB ingestion resulted in the induction of hepatic microsomal enzymes of both white mice and white-footed mice, and in the mobilization of corticosteroids from the adrenals of white mice. These effects were intensified in white mice subjected simultaneously to either increased density or feed restriction. It was concluded that animals subjected to overcrowding or inanition are more susceptible to the toxicological effects of PCBs than are normal, healthy animals.