AJP - Regulatory, Integrative and Comparative Physiology, Vol 268, Issue 2 389-R394, Copyright © 1995 by American Physiological Society
Reduced norepinephrine turnover in organs and brains of obesity-prone rats
B. E. Levin
Department of Veterans Affairs Medical Center, East Orange, New Jersey 07018.
One-half of the adult male Sprague-Dawley rats fed a diet relatively high
in fat, sucrose, and energy content (HE diet) develop diet-induced obesity
(DIO). The rest are diet resistant (DR). The role of peripheral and central
norepinephrine (NE) activity in predisposing them to these weight gain
patterns was assessed before HE diet exposure. Chow-fed male 3-mo-old
Sprague-Dawley rats were separated as being prone to become DIO or DR by
their high (3.06 +/- 0.14 micrograms) vs. low (1.17 +/- 0.10 micrograms; P
= 0.001) 24-h urine NE output, respectively. Turnover of NE, an index of
sympathetic activity, was assessed by synthesis inhibition with
alpha-methyl-p-tyrosine. DIO-prone rats had significant 53 and 18%
reductions in heart and pancreas NE turnover, with interscapular brown
adipose tissue turnover comparable to that of DR-prone rats. Hypothalamic
NE turnover was significantly decreased by 85 and 60% in the ventromedial
nucleus and lateral area vs. DR-prone rats. Although present in DR-prone
rats, no turnover was found in the dorsomedial nucleus of DIO-prone rats.
Endogenous NE was reduced by 28% in the paraventricular nucleus, whereas
arcuate/median eminence turnover was increased by 100% in DIO-prone rats.
Amygdalar NE turnover was similar between phenotypes. These intrinsic
differences in NE metabolism may play an important role in the development
of DIO on HE diets.
