AJP - Regulatory, Integrative and Comparative Physiology, Vol 252, Issue 4 737-R742, Copyright © 1987 by American Physiological Society
Enhancement of cold-stimulated thermogenesis in the corpulent rat (LA/N cp) by aminophylline
T. F. Lee, L. C. Wang and J. C. Russell
Previous studies on obese strains of rats (e.g., Zucker and LA/N cp) have
shown that they are deficient in nonshivering thermogenesis and poor in
cold tolerance. Our earlier studies have established that aminophylline
(AMPY; 85% theophylline-15% ethylenediamine) is effective in significantly
improving cold tolerance in the lean Sprague-Dawley rat regardless of age
or thermogenic capacity. The present study tested whether AMPY may be also
effective in improving cold tolerance in both young (12-18 wk) and older
(36-42 wk) lean and corpulent LA/N cp rats. Contrary to previous reports,
however, the norepinephrine (NE)-stimulated nonshivering thermogenesis was
not only present but also equal in magnitude in the corpulent rats to that
of their lean controls. Further, no difference in cold tolerance was
observed between the two groups regardless of age. Similarly, AMPY (18.7
mg/kg ip) significantly improved thermogenesis and cold tolerance in both
lean and corpulent rats, again without any age-related difference in
response. These results indicate that, despite the existence of obesity, no
difference in thermogenic capacity to either NE or cold stimulation is
evident in the LA/N cp rats. Thus the ontogeny of obesity in this strain
may be caused by factors other than deficiency in NE- or cold-stimulated
thermogenesis at the end-organ level.
