AJP - Endocrinology and Metabolism, Vol 257, Issue 3 E336-E339, Copyright © 1989 by American Physiological Society
Increased ACTH response to corticotropin-releasing factor in cold-adapted rats in vivo
A. Uehara, Y. Habara, A. Kuroshima, C. Sekiya, Y. Takasugi and M. Namiki
Department of Internal Medicine III, Asahikawa Medical College, Hokkaido, Japan.
We have recently reported that chronically repeated restraint stress
results in improved cold tolerance in rats via an increased activity of
nonshivering thermogenesis, a characteristic metabolic change observed
during cold adaptation, suggesting the presence of cross-adaptation between
cold and stress. It is well established that the
hypothalamic-pituitary-adrenal (HPA) axis is activated in various stress
responses. In the present study, therefore, we examined whether cold
adaptation would alter the adrenocorticotropic hormone (ACTH)-releasing
state in vivo using freely moving, conscious rats chronically implanted
with intra-atrial cannulas. There was no difference in the basal levels of
plasma ACTH between warm control and cold-adapted rats. On the other hand,
the ACTH response to the intravenous administration of
corticotropin-releasing factor (CRF; 2 micrograms/animal) was significantly
elevated in cold-adapted rats. However, the injection of 10 micrograms of
CRF, which was considered as a dose to elicit the maximal ACTH response,
resulted in similar ACTH release patterns between the two groups. These
changes in the responsiveness of ACTH secretion have been observed in rats
chronically exposed to stressful conditions. The results demonstrated in
the present study, therefore, provide further evidence for our hypothesis
that there may exist cross-adaptation between cold and nonthermal stress.
