Metabolic and blood gas dependence on digestive state in the Savannah monitor lizard<i>Varanus exanthematicus</i>: an assessment of the alkaline tide

SUMMARYCrocodilians use a combination of three muscular mechanisms to effect lung ventilation: the intercostal muscles producing thoracic movement, the abdominal muscles producing pelvic rotation and gastralial translation, and the diaphragmaticus muscle producing visceral displacement. Earlier studies suggested that the diaphragmaticus is a primary muscle of inspiration in crocodilians, but direct measurements of the diaphragmatic contribution to lung ventilation and gas exchange have not been made to date. In this study, ventilation, metabolic rate and arterial blood gases were measured from juvenile estuarine crocodiles under three conditions: (i) while resting at 30°C and 20°C; (ii) while breathing hypercapnic gases; and (iii) during immediate recovery from treadmill exercise. The relative contribution of the diaphragmaticus was then determined by obtaining measurements before and after transection of the muscle. The diaphragmaticus was found to make only a limited contribution to lung ventilation while crocodiles were resting at 30°C and 20°C, and during increased respiratory drive induced by hypercapnic gas. However, the diaphragmaticus muscle was found to play a significant role in facilitating a higher rate of inspiratory airflow in response to exercise. Transection of the diaphragmaticus decreased the exercise-induced increase in the rate of inspiration (with no compensatory increases in the duration of inspiration), thus compromising the exercise-induced increases in tidal volume and minute ventilation. These results suggest that, in C. porosus, costal ventilation alone is able to support metabolic demands at rest, and the diaphragmaticus is largely an accessory muscle used at times of elevated metabolic demand.

Section: Discussionsupporting

confidence: 80%

The accessory role of the diaphragmaticus muscle in lung ventilation in the estuarine crocodile Crocodylus porosus

Munns

Owerkowicz

Andrewartha

et al. 2012

“…However, body temperature as well as the size, composition and frequency of meals can alter the metabolic response to feeding in reptiles (Beaupre, 2005;Bennett and Hicks, 2001;Hartzler et al, 2006;Hicks et al, 2000;Secor et al, 2000;Toledo et al, 2003;Wang et al, 2012). Pilot data from lizards in the present study, voluntarily fed their captive (relatively low protein) diet at 30°C, demonstrated that the duration of metabolic rate elevation caused by feeding is ~48h.…”

Section: Experimental Protocolmentioning

confidence: 50%

Gestation increases the energetic cost of breathing in the lizard, Tiliqua rugosa

Munns

2012

SUMMARYHigh gestational loads result in fetuses that occupy a large proportion of the body cavity and may compress maternal organs. Compression of the lungs results in alterations in breathing patterns during gestation, which may affect the energetic cost of breathing. In this study, the energetic cost of breathing during gestation was determined in the viviparous skink Tiliqua rugosa. Radiographic imaging showed progressive lung compression during gestation and a 30% reduction in the lung inflation index (rib number at which the caudal margin of the lung was imaged divided by total rib number). Pneumotachography and open flow respirometry were used to measure breathing patterns and metabolic rates. Gestation induced a twofold increase in minute ventilation via increases in breathing frequency, but no change in inspired tidal volume. The rates of O 2 consumption and CO 2 production did not change significantly during gestation. Together, these results suggest that a relative hyperventilation occurs during gestation in T. rugosa, which in turn suggests that diffusion and/or perfusion limitations may exist at the lung during gestation. The energetic cost of breathing was estimated as a percentage of resting metabolic rate using hypercapnia to stimulate ventilation at different stages of pregnancy. The energetic cost of breathing in non-pregnant lizards was 19.96±3.85% of resting metabolic rate and increased threefold to 62.80±10.11% during late gestation. This significant increase in the energetic cost of breathing may have significant consequences for energy budgets during gestation.

“…2A). A number of studies have shown that plasma Cl -levels drop following a meal in some ectotherms (Busk et al, 2000a;Hartzler et al, 2006), whereas it remains stable in others (Overgaard et al, 1999;Busk et al, 2000b). Studies have also shown that HCO 3 -/Cl -exchange is 1:1 (for a review, see Grosell, 2006), which would not explain why there is such a substantial difference between the large drop in plasma Cl -(17 mmol l -1 ) and the moderate rise in plasma HCO 3 -(4 mmol l -1 ) in catheter-fed fish after 6 h ( Fig.…”

Section: Role Of the Gills And Kidney In Recovery From The Alkaline Tidementioning

confidence: 99%

“…There are now many examples in the literature of post-prandial alkaline tides occurring in reptiles and mammals (Regev et al, 2001;Ozaki et al, 2000;Arvedsen et al, 2005;Hartzler et al, 2006;Weber and White, 1986). Comparative information of a post-prandial alkaline tide in fish (i.e.…”

Section: Introductionmentioning

confidence: 99%

Post-prandial alkaline tide in freshwater rainbow trout: effects of meal anticipation on recovery from acid–base and ion regulatory disturbances

Cooper

Wilson

2008

SUMMARYThe post-feeding alkaline tide (elevated blood pH and HCO 3 -) has been well characterised in air-breathing animals, but to date this phenomenon has only been demonstrated in one piscine species, a marine elasmobranch. We have investigated the acid-base and ion regulatory responses of a freshwater teleost to voluntary feeding as well as to involuntary filling of the stomach via an indwelling gastric intubation tube. One group of rainbow trout (Oncorhynchus mykiss) were fed a 1% body mass ration of homogenised food via the gastric intubation tube. Another group fed voluntarily on a 1% body mass ration. Blood samples were taken via dorsal aortic catheters from fish in both groups before feeding and over the subsequent 72 h. Trout fed via the gastric intubation tube exhibited post-prandial metabolic alkalosis of the blood (pH and plasma HCO 3 -increases of up to ~0.2 pH units and 3 mmol l -1 , respectively), that was more than twofold greater than the voluntary feeding fish, and took three times as long to recover (72 versus 24 h). Arterial P CO 2 was unchanged in both groups indicating that freshwater trout do not retain CO 2 to compensate for a post-prandial alkaline tide. Although excretion of HCO 3 -to the water increased post-prandially, NH 4 + excretion followed a similar pattern, such that net acid equivalent fluxes were unaffected. Thus, sites other than the gills or kidney must be responsible for recovery of blood acid-base status, with intestinal HCO 3 -secretion being a likely candidate. In addition, fish fed via the gastric intubation tube experienced a large (17 mmol l -1 ) but acute (6 h) drop in plasma chloride and a very large (53%) and long lasting decline in plasma magnesium concentration, that were absent in voluntarily feeding fish. These results further indicate a potentially important role for neuro-endocrine mediated mechanisms when fish feed voluntarily, in promoting the earlier initiation of compensatory responses that regulate blood ion levels and acid-base status. This aspect should also be considered when interpreting studies on other aspects of post-prandial physiology, where force feeding by gavage is commonly used in preference to voluntary feeding.