Effect of chronic crowding and cold on the pituitary-adrenal system: Responsiveness to an acute stimulus during chronic stress

The effects of chronic exposure to crowding or cold stress were assessed in male rats over a period of 8 weeks. Body growth was inhibited by both conditions. Anterior pituitary weights decreased after 2 weeks of either treatment, but by 8 weeks the glands of cold exposed rats had hypertrophied. Cold resulted in a sustained adrenal and testicular hypertrophy, whereas crowding had no such effect. Plasma and adrenal corticosterone levels were elevated after 1 week of cold or crowding, followed by a marked reduction after 8 weeks in cold-exposed animals only. Plasma ACTH remained unchanged until 8 weeks when it started rising in both groups of animals. The data obtained in these experiments indicate that the pituitary-adrenal system responds to chronic stress neither by stabilization at a new steady state nor by a return to a period of normalcy, at least within the 8 weeks of exposure studied. The responsiveness of these chronically stressed animals to an additional acute stressful stimulus (1 min of ether) was also evaluated. Crowding depressed both the plasma and adrenal corticosterone response to ether anesthesia at 1 week. Cold exposure enhanced the plasma corticosterone response at all intervals (1–8 weeks) studied and enhanced the ACTH response at 1 and 2 weeks.