Suzanne L. Munns

Regenerating lizard tails: a new model for investigating lymphangiogenesis

Impaired lymphatic drainage in human limbs causes the debilitating swelling termed lymphoedema. In mammals, known growth factors involved in the control of lymphangiogenesis (growth of new lymph vessels) are vascular endothelial growth factors‐C and –D (VEGF‐C/D). Here we characterize a model of lymphangiogenesis in which the tail of lizards is regenerated without becoming oedematous. Three weeks after the tail is shed (autotomy), there are a small number of large diameter lymphatic vessels in the regenerated tail. Thereafter, the number increases and the diameter decreases. A functional lymphatic network, as determined by lymphoscintigraphy, is established 6 wk after autotomy. The new network differs morphologically and functionally from that in original tails. This lymphatic regeneration is associated with an up‐regulation of a reptilian homologue of the VEGF‐C/D protein family (rVEGF‐C/D), as determined by Western blot analysis using a human reactive VEGF‐C polyclonal antibody. Regenerating lizard tails are potentially useful models for studying the molecular basis of lymphangiogenesis with a view to developing possible treatments for human lymphoedema.

Terrestrial Locomotion does not Constrain Venous Return in the American Alligator, Alligator mississippiensis .

SUMMARY The effects of treadmill exercise on components of the cardiovascular (heart rate, mean arterial blood pressure, central venous pressure, venous return) and respiratory (minute ventilation, tidal volume, breathing frequency, rate of oxygen consumption, rate of carbon dioxide production) systems and on intra-abdominal pressure were measured in the American alligator, Alligator mississippiensis, at 30°C. Alligators show speed-dependent increases in tidal volume and minute ventilation, demonstrating that the inhibition of ventilation during locomotion that is present in some varanid and iguanid lizards was not present in alligators. Exercise significantly increases intra-abdominal pressure; however, concomitant elevations in central venous pressure acted to increase the transmural pressure of the post caval vein and thus increased venous return. Therefore, despite elevated intra-abdominal pressure, venous return was not limited during exercise in alligators, as was the case in Varanus exanthematicus and Iguana iguana. Respiratory cycle variations in intra-abdominal pressure, central venous pressure and venous return indicate that, at high tidal volumes, inspiration causes a net reduction in venous return during active ventilation and thus may act to limit venous return during exercise. These results suggest that, while tonically elevated intra-abdominal pressure induced by exercise does not inhibit venous return, phasic fluctuations during each breath cycle may contribute to venous flow limitation during exercise.

Elevated Intra-Abdominal Pressure Limits Venous Return during Exercise in Varanus exanthematicus

SUMMARY The effects of treadmill exercise on components of the cardiovascular (venous return, heart rate, arterial blood pressure) and respiratory systems (minute ventilation, tidal volume, breathing frequency, oxygen consumption, carbon dioxide production) and intra-abdominal pressure were investigated in the Savannah monitor lizard, Varanus exanthematicus B., at 35°C. Compared with resting conditions, treadmill exercise significantly increased lung ventilation, gular pumping, intra-abdominal pressure, mean arterial blood pressure and venous return (blood flow in the post caval vein). However, venous return declines at high levels of activity, and mean arterial pressure and venous return did not attain peak values until the recovery period, immediately following activity. Elevating intra-abdominal pressure in resting lizards (via saline infusion) resulted in significant reductions in venous return when the transmural pressure of the post caval vein became negative (i.e. when intra-abdominal pressure exceeded central venous pressure). Together these results suggest that increments in intra-abdominal pressure compress the large abdominal veins and inhibit venous return. During locomotion, the physical compression of the large abdominal veins may represent a significant limitation to cardiac output and maximal oxygen consumption in lizards.

The effects of environmental temperature, hypoxia, and hypercapnia on the breathing pattern of saltwater crocodiles (Crocodylus porosus).

This study aimed to describe the effects of change in environmental temperature, hypoxia, and hypercapnia on the breathing pattern of Crocodylus porosus. Increased environmental temperature, hypoxia, and hypercapnia each caused an increase in minute ventilation and changes in breathing pattern. Breathing frequency increased and the duration of the nonventilatory period decreased in response to all three conditions. Under hypercapnia tidal volume also increased, with no change in rate of inspiration. The number of breaths per breathing burst decreased with increased temperature but remained unaltered under hypoxia. Hypercapnia reduced the number of breaths per burst at 20°C, but the number did not decrease further at 30°C. The results support the idea that the responses to increased temperature, hypoxia, and hypercapnia are under separate control but that some effects of hypercapnia and temperature may involve a common regulatory pathway.

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

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.

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

SUMMARY Crocodilians 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.

Breathing with Big Babies: Ventilation and Oxygen Consumption during Pregnancy in the Lizard Tiliqua rugosa

We determined the effects of high gestational loads on ventilation and the rate of oxygen consumption (V̇o2) in the scincid lizard Tiliqua rugosa. Tiliqua rugosa is a large viviparous lizard that gives birth to one to four young after 6–7 mo gestation. Pregnant females gave birth to large young, weighing \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Calibration of the HemoCue point-of-care analyser for determining haemoglobin concentration in a lizard and a fish

89.5\pm 5.9