Metabolic and blood gas dependence on digestive state in the Savannah monitor lizard Varanus exanthematicus: an assessment of the alkaline tide.
A large alkaline tide (up to 20 mmol l(-1) increase in bicarbonate concentration [HCO3-] with an accompanied increase in blood pH) has previously been reported for some carnivorous reptiles within 24 h after ingesting a large meal. This phenomenon has been attributed to the secretion of large amounts of H+ ions into the stomach, which is required for digestion of large prey items. To test the generality of this phenomenon in carnivorous reptiles, this study quantified the metabolic and acid-base status of the Savannah monitor lizard, Varanus exanthematicus, during digestion at 35 degrees C. Following a meal of approximately 10% of body mass, V(O2) and V(CO2) were measured continuously and arterial pH, blood gases and strong ions were measured every 8 h for 5 days. During peak digestion (24 h post feeding), V(O2) and V(CO2) increased to approximately threefold fasting values (V(O2), 0.95-2.57 ml min(-1) kg(-1); V(CO2) 0.53-1.63 ml min(-1) kg(-1)) while respiratory exchange ratio (R) remained constant (0.62-0.73). During digestion, arterial P(CO2) increased (from 4.6 kPa to 5.8 kPa), and [HCO3-] also increased (from 24.1 mmol l(-1) to 40.3 mmol l(-1)). In contrast to early studies on crocodilians, arterial pH in V. exanthematicus remained relatively stable during digestion (7.43-7.56). Strong ions contributed little to the acid-base compensation during the alkalosis. Collectively the data indicate that the metabolic alkalosis associated with H+ secretion (as indicated by increased plasma bicarbonate) is partially compensated by a respiratory acidosis.
Hartzler
L K
LK
Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697-2525, USA. lynn.hartzler@wright.edu
Munns
S L
SL
Bennett
A F
AF
Hicks
J W
JW
D000821:Animal Feed; D000818:Animals; D001784:Blood Gas Analysis / Q000379:methods; D004063:Digestion / Q000502:physiology*; D004435:Eating / Q000502:physiology; D005215:Fasting / Q000502:physiology; D005740:Gases / Q000097:blood*; D006863:Hydrogen-Ion Concentration; D008116:Lizards / Q000502:physiology*; D019518:Postprandial Period; D013696:Temperature
D005740:Gases