AJP - Regulatory, Integrative and Comparative Physiology, Vol 262, Issue 6 981-R985, Copyright © 1992 by American Physiological Society
Exercise-induced sympathetic FFA mobilization in VMH-lesioned rats is normalized by fasting
B. Balkan, G. Van Dijk, J. H. Strubbe, J. E. Bruggink and A. B. Steffens
Department of Animal Physiology, University of Groningen, Haren, The Netherlands.
This study investigates whether reduced sympathetic responses during
physical exercise in ventromedial hypothalamus (VMH)-lesioned obese rats
are the direct result of damage to hypothalamic circuits or a secondary
effect of the altered metabolism in obesity. Obese, VMH-lesioned rats and
lean controls were deprived of food for 48 h and submitted to 15 min of
swimming. Food-deprived lean and obese rats displayed increased free fatty
acid mobilization and utilization, whereas blood glucose concentrations
were decreased. Basal plasma insulin levels were reduced by fasting in both
groups, when compared with the ad libitum situation, but remained higher in
the obese animals. Fasting augmented the norepinephrine response of the
obese rats, resulting in equal profiles in lean and obese animals. These
results indicate that VMH-lesioned animals are able to increase the
sympathetic activation of adipose tissue during exercise to overcome an
energy deficiency. Therefore, the function of the VMH in the regulation of
the sympathetic nervous system controlling metabolism can be taken over by
redundant mechanisms. The reduced sympathetic activity in ad libitum fed
VMH-lesioned animals is therefore likely to be the result of the altered
metabolism.
