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1 Centre for Respiratory Adaptation, Institute of Biology, University of Southern Denmark, Main Campus: Odense University, DK-5230 Odense M, Denmark; and 2 School of Biological Sciences, The University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
Massive feeding in ectothermic
vertebrates causes changes in metabolism and acid-base and respiratory
parameters. Most investigations have focused on only one aspect of
these complex changes, and different species have been used, making
comparison among studies difficult. The purpose of the present study
was, therefore, to provide an integrative study of the multiple
physiological changes taking place after feeding. Bullfrogs (Rana
catesbeiana) partly submerged in water were fed meals (mice or
rats) amounting to ~
of their body weight. Oxygen
consumption increased and peaked at a value three times the
predigestive level 72-96 h after feeding. Arterial
PO2 decreased slightly during
digestion, whereas hemoglobin-bound oxygen saturation was unaffected.
Yet, arterial blood oxygen content was pronouncedly elevated because of
a 60% increase in hematocrit, which appeared mediated via release of
red blood cells from the spleen. Gastric acid secretion was associated
with a 60% increase in plasma HCO
3 concentration
([HCO
3]) 48 h
after feeding. Arterial pH only increased from 7.86 to 7.94, because
the metabolic alkalosis was countered by an increase in
PCO2 from 10.8 to 13.7 mmHg. Feeding
also induced a small intracellular alkalosis in the sartorius muscle.
Arterial pH and HCO
3 returned to
control values 96-120 h after feeding. There was no sign of
anaerobic energy production during digestion as plasma and tissue
lactate levels remained low and intracellular ATP concentration stayed
high. However, phosphocreatine was reduced in the sartorius muscle and
ventricle 48 h after feeding.
specific dynamic action; O2 transport; alkaline tide; metabolites; high-energy phosphates
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