Metabolic control of estrous cycles in syrian hamsters: i. central
versus peripheral neural signals mediating effects of
lipoprivation.
Schneider, Jill E., Angela J. Hall, and George N. Wade.
Department of Biological Sciences, Lehigh University, Bethlehem,
Pennsylvania 18015, Department of Psychology and Neuroscience and
Behavior Program, University of Massachusetts, Amherst, Massachusetts
01003
APStracts 3:0237R, 1996.
Metabolic energy availability has profound effects on reproduction in
a wide variety of species. We have been studying the effects of
fasting on estrous cycles in Syrian hamsters as a model system for
metabolic control of reproduction. In previous experiments, a 48 h
period of fasting inhibited estrous cycles in lean, but not fat
hamsters. In fat hamsters, the effects of fasting may have been
offset by the presence of high circulating levels of free fatty acids
mobilized from lipids in adipose tissue. Consistent with this idea,
fat hamsters treated with the inhibitor of fatty acid oxidation,
methyl palmoxirate (MP), showed fasting-induced anestrus. Experiment
1 was designed to examine whether vagally-transmitted signals are
critical for the inhibitory effects of fasting and MP treatment. Lean
or fat hamsters that had received either bilateral, subdiaphragmatic
vagotomy or sham surgery were fasted and treated with either MP or
vehicle. In both vagotomized and sham-operated hamsters, estrous
cycles were inhibited in lean, fasted hamsters, and in fat, fasted
hamsters treated with MP, but not in fat, fasted hamsters treated
with vehicle. Thus, the results of experiment 1 indicated that
vagally-transmitted signals about peripheral fatty acid availability
are not critical for the effects of these particular metabolic
challenges on estrous cycles in Syrian hamsters. In experiment 2,
hamsters without food were allowed to ingest pure glucose or fructose
solutions, or vegetable shortening. Half of each group was treated
with an inhibitor of glucose utilization, 2-deoxy-D-glucose (2DG), or
vehicle. If ingestion of fructose or shortening, but not glucose, had
protected hamsters from 2DG-induced anestrus, this would have
indicated that decreased peripheral fuel availability is critical for
anestrus. To the contrary, 2DG treatment induced anestrus regardless
of the type of fuel ingested. Neither experiment yielded results that
implicated changes in peripheral fatty acid oxidation as a critical
signal in metabolic control of estrous cycles. Metabolic control of
estrous cycles may differ in important ways from metabolic control of
food intake, but may be similar to metabolic control of the
compensatory sympathoadrenal response.
Received 6 October 1995; accepted in final form 20 May 1996.
APS Manuscript Number R632-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 4 July 96