Alkaline Tide of the Alligator

SUMMARY 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°C. Following a meal of approximately 10% of body mass, V̇O2 and V̇CO2 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), V̇O2 and V̇CO2 increased to approximately threefold fasting values(V̇O2, 0.95–2.57 ml min–1 kg–1; V̇CO2 0.53–1.63 ml min–1 kg–1) while respiratory exchange ratio(R) remained constant (0.62–0.73). During digestion, arterial PCO2 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.

Section: Discussionmentioning

confidence: 61%

Section: Introductionmentioning

confidence: 99%

Section: Metabolic Response: Fasted Vs Fedmentioning

confidence: 99%

See 1 more Smart Citation

Metabolic and blood gas dependence on digestive state in the Savannah monitor lizardVaranus exanthematicus: an assessment of the alkaline tide

Hartzler

Munns

Bennett

et al. 2006

“…Coulson et al, 1950;Wang et al, 2001a;Andrade et al, 2004) results in only very modest increases in pHa, as a result of respiratory compensation [i.e. an increase in Pa CO 2 (Wang et al, 1995;Wang et al, 2001a;Overgaard et al, 1999;Busk et al, 2000a;Busk et al, 2000b;Andersen and Wang, 2003)] that appears to be caused by hypoventilation Secor et al, 2000;Wang et al, 2001b).…”

Section: Discussionmentioning

confidence: 99%

The alkaline tide and ammonia excretion after voluntary feeding in freshwater rainbow trout

Bucking

Wood

2008

SUMMARYWe investigated the potential acid-base and nitrogenous waste excretion challenges created by voluntary feeding in freshwater rainbow trout, with particular focus on the possible occurrence of an alkaline tide (a metabolic alkalosis created by gastric HCl secretion during digestion). Plasma metabolites (glucose, urea and ammonia) were measured at various time points before and after voluntary feeding to satiation (approximately 5% body mass meal of dry commercial pellets), as was the net flux of ammonia and titratable alkalinity to the water from unfed and fed fish. Arterial blood, sampled by indwelling catheter, was examined for post-prandial effects on pH, plasma bicarbonate and plasma CO 2 tension. There was no significant change in plasma glucose or urea concentrations following feeding, whereas plasma ammonia transiently increased, peaking at threefold above resting values at 12 h after the meal and remaining elevated for 24 h. The increased plasma ammonia was correlated with an increase in net ammonia excretion to the water, with fed fish significantly elevating their net ammonia excretion two-to threefold between 12 and 48 h post feeding. These parameters did not change in unfed control fish. Fed fish likewise increased the net titratable base flux to the water by approximately threefold, which resulted in a transition from a small net acid flux seen in unfed fish to a large net base flux in fed fish. Over 48 h, this resulted in a net excretion of 13·867·μmol·kg -1 more base to the external water than in unfed fish. The arterial blood exhibited a corresponding rise in pH (between 6 and 12 h) and plasma bicarbonate (between 3 and 12 h) following feeding; however, no respiratory compensation was observed, as Pa CO 2 remained constant. Overall, there was evidence of numerous challenges created by feeding in a freshwater teleost fish, including the occurrence of an alkaline tide, and its compensation by excretion of base to the external water. The possible influence of feeding ecology and environmental salinity on these challenges, as well as discrepancies in the literature, are discussed.

“…Similarly, following ingestion of a frog meal, gastric pH of N. natrix decreases from 7.2 to 3.3 within 4·h, a response noticeably faster than that of P. molurus (Skoczylas, 1970b). For turtles, lizards, alligators and other snake species, gastric pH of fasting individuals ranges between 7 and 8 and declines to a range of 1.5-4 during digestion (Blain and Campbell, 1942;Coulson et al, 1950;Wright et al, 1957;Fox and Musacchia, 1959).…”

Section: Gastric Phmentioning

confidence: 99%

Gastric function and its contribution to the postprandial metabolic response of the Burmese pythonPython molurus

Secor

2003

139

141

SUMMARY The large intact prey ingested by Burmese pythons require considerable processing by the stomach before passage into the small intestine. To investigate the function and cost of gastric digestion and its contribution to postprandial metabolic response for the Burmese python, I examined the rate of gastric digestion, the postprandial profile of gastric pH and the effects of decreasing gastric workload on the metabolic cost of digestion, referred to as specific dynamic action (SDA). Ingested meal mass (equivalent to 25% of snake body mass) was reduced by 18% within 1 day postfeeding, by which time intragastric pH had decreased from 7.5 to 2. Gastric pH was maintained at 1.5 for the next 5–7 days, after which it returned to 7.5. The SDA generated by digesting an intact rat meal was reduced by 9.1%, 26.0%, 56.5% and 66.8%,respectively, when pythons were fed steak, ground rat, liquid diet or ground rat directly infused into the small intestine. The production of HCl and enzymes and other gastric functions represent an estimated 55% of the python's SDA generated from the digestion of an intact rodent meal. Additional contributors to SDA include protein synthesis (estimated 26%),gastrointestinal upregulation (estimated 5%) and the activities of the pancreas, gallbladder, liver, kidneys and intestines during digestion(estimated 14%). Operating on a `pay before pumping' principle, pythons must expend endogenous energy in order to initiate acid production and other digestive processes before ingested nutrients can be absorbed and channeled into metabolic pathways.