Johnnie B. Andersen

Physiology: postprandial cardiac hypertrophy in pythons.

Oxygen consumption by carnivorous reptiles increases enormously after they have eaten a large meal in order to meet metabolic demands, and this places an extra load on the cardiovascular system. Here we show that there is an extraordinarily rapid 40% increase in ventricular muscle mass in Burmese pythons (Python molurus) a mere 48 hours after feeding, which results from increased gene expression of muscle-contractile proteins. As this fully reversible hypertrophy occurs naturally, it could provide a useful model for investigating the mechanisms that lead to cardiac growth in other animals.

The Effects of Fasting Duration on the Metabolic Response to Feeding in Python molurus: An Evaluation of the Energetic Costs Associated with Gastrointestinal Growth and Upregulation

The oxygen uptake of Python molurus increases enormously following feeding, and the elevated metabolism coincides with rapid growth of the gastrointestinal organs. There are opposing views regarding the energetic costs of the gastrointestinal hypertrophy, and this study concerns the metabolic response to feeding after fasting periods of different duration. Since mass and function of the gastrointestinal organs remain elevated for several days after feeding, the metabolic increment following a second meal given soon after the first can reveal whether the metabolic costs relate to the upregulation of gastrointestinal organs or merely the metabolic cost of processing a meal. Eight juvenile pythons were kept on a regular feeding regime for 6 mo after hatching. At the beginning of the metabolic measurements, they were fed mice (20% of body mass), and the metabolic response to similarly sized meals was determined following 3, 5, 7, 14, 21, 30, and 60 d of fasting. Our data show that the metabolic response following feeding was large, ranging from 21% to 35% of ingested energy ( \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

Cardiorespiratory effects of forced activity and digestion in toads.

\mathrm{mean}\,=27\%

Cardiovascular responses to hypoxia and anaemia in the toad Bufo marinus.

\end{document} ), but the metabolic response seems independent of fasting duration. Hence, the extraordinarily large cost of digestion in P. molurus does not appear to correlate with increased function and growth of gastrointestinal organs but must be associated with other physiological processes.

Normal right ventricular three-dimensional architecture, as assessed with diffusion tensor magnetic resonance imaging, is preserved during experimentally induced right ventricular hypertrophy.

Although myocardial architecture has been investigated extensively, as yet no evidence exists for the anatomic segregation of discrete myocardial pathways. We performed post‐mortem diffusion tensor imaging on 14 pig hearts. Pathway tracking was done from 22 standardized voxel groups from within the left ventricle, the left ventricular papillary muscles, and the right ventricular outflow tract. We generated pathways with comparable patterns in the different hearts when tracking from all chosen voxels. We were unable to demonstrate discrete circular or longitudinal pathways, nor to trace any solitary tract of myocardial cells extending throughout the ventricular mass. Instead, each pathway possessed endocardial, midwall, and epicardial components, merging one into another in consistent fashion. Endocardial tracks, when followed towards the basal or apical parts of the left ventricle, changed smoothly their helical and transmural angulations, becoming continuous with circular pathways in the midwall, these circular tracks further transforming into epicardial tracks, again by smooth change of the helical and transmural angles. Tracks originating from voxels in the papillary muscles behaved similarly to endocardial tracks. This is the first study to show myocardial pathways that run through the mammalian left and right ventricles in a highly reproducible manner according to varying local helical and transmural intrusion angles. The patterns generated are an inherent feature of the three‐dimensional arrangement of the individual myocytes aggregated within the walls, differing according to the regional orientation and branching of individual myocytes. We found no evidence to support the existence of individual muscles or bands. Anat Rec, 2009.

Effects of anaesthesia on blood gases, acid–base status and ions in the toad Bufo marinus

Digestion and physical activity are associated with large and sometimes opposite changes in several physiological parameters. Gastric acid secretion during digestion causes increased levels of plasma bicarbonate ([ \( \mathrm{HCO}\,^{-}_{3} \) ]pl), whereas activity leads to a metabolic acidosis with increased lactate and decrease in plasma bicarbonate. Here we describe the combined effects of feeding and activity in the toad Bufo marinus to investigate whether the increased bicarbonate buffering capacity during digestion (the so‐called alkaline tide) protects the acid‐base disturbance during activity and enhances the subsequent recovery. In addition, we describe the changes in arterial oxygen levels and plasma ion composition, as well as rates of gas exchange, heart rates, and blood pressures. Toads were equipped with catheters in the femoral artery and divided into four experimental regimes: control, digestion, forced activity, and forced activity during the postprandial period (N = 6 in each). Digestion induced a significant metabolic alkalosis with increased [ \( \mathrm{HCO}\,^{-}_{3} \) ]pl that was completely balanced by a respiratory acidosis; that is, increased arterial Pco2 (Paco2), so that arterial pH (pHa) did not change. Forced activity led to a substantial reduction in pHa by 0.43 units, an increase in plasma lactate concentration by 12.5 mmol L−1, and a reduction in [ \( \mathrm{HCO}\,^{-}_{3} \) ]pl of similar magnitude. While digesting animals had higher Paco2 and [ \( \mathrm{HCO}\,^{-}_{3} \) ]pl at rest, the magnitude and duration of the changes in arterial acid‐base parameters were similar to those of fasting animals, although the reduction in pHa was somewhat lower (0.32 units). In conclusion, while recovery from the acidosis following exercise did not seem to be affected by digestion, the alkaline tide did slightly dampen the reduction in pHa during activity.

Improving efficiency in stereology: a study applying the proportionator and the autodisector on virtual slides

This study describes and exemplifies generally applicable design‐based stereological methods for obtaining quantitative estimates of the numbers and sizes of capillaries, cardiomyocytes, and cardiomyocyte nuclei in immersion‐fixed human left ventricles (N = 6). The design‐based stereological methods are valid in all cardiac investigations onto quantifying changes in structure and function as seen under various conditions such as during development, aging, hypertrophy, and following ischemia/reperfusion. The applied principles of unbiased stereology were as follows: 1) uniform random sampling was taken at all levels, also in respect to orientations, for estimates of length and mean sizes. 2) All global structural quantities were estimated as total quantity = density × volume of the left ventricle. As an example, the left ventricle contains 1.5 × 109 capillaries with a total length of just below 200 km. 3) Stereological methods were used for estimating the volume density, surface area density, and length density of capillaries and cardiomyocytes. The numerical density of cardiomyocyte nuclei and capillaries was estimated, using the optical and physical disector, respectively. 4) In all local quantities, “size” was estimated either directly, using unbiased estimators to obtain the average individual size and size distribution parameters, or indirectly, using the relationship that: average size = total quantity/total number. In the six hearts constituting this study, we observed the anticipated correlation between left ventricular volume and global estimates such as total number of capillaries. There were no correlation between local quantities and total left ventricular volume (e.g., average star volume of individual cardiomyocytes). Anat Rec, 2009.

Effects of temperature and oxygen availability on circulating catecholamines in the toad Bufo marinus.

SUMMARY Amphibians exhibit cardiorespiratory responses to hypoxia and, although several oxygen-sensitive chemoreceptor sites have been identified, the specific oxygen stimulus that triggers these responses remains controversial. This study investigates whether the cardiovascular response to oxygen shortage correlates with decreased oxygen partial pressure of arterial blood (PaO2) or reduced oxygen concentration ([O2]) in toads. Toads, equipped with blood flow probes and an arterial catheter, were exposed to graded hypoxia [fraction of oxygen in the inspired air (FIO2)=0.21, 0.15, 0.10, 0.07 and 0.05] before and after reductions in arterial [O2] by isovolemic anaemia that reduced haematocrit by approximately 50%. Toads responded to hypoxia by increasing heart rate (fH) and pulmocutaneous blood flow (Q̇pc) and reducing the net cardiac right-to-left-shunt. When arterial [O2] was reduced by anaemia, the toads exhibited a similar cardiovascular response to that observed in hypoxia. While arterial CO2 partial pressure (PaCO2) decreased significantly during hypoxia, indicative of increased alveolar ventilation, anaemia did not alter PaCO2). This suggests that reductions in [O2] mediate cardiovascular adjustments, while ventilatory responses are caused by reduced PaO2.