Python Regius Research Articles

Functional morphology and patterns of blood flow in the heart of Python regius

Brightness-modulated ultrasonography, continuous-wave Doppler, and pulsed-wave Doppler-echocardiography were used to analyze the functional morphology of the undisturbed heart of ball pythons. In particular, the action of the muscular ridge and the atrio-ventricular valves are key features to understand how patterns of blood flow emerge from structures directing blood into the various chambers of the heart. A step-by-step image analysis of echocardiographs shows that during ventricular diastole, the atrio-ventricular valves block the interventricular canals so that blood from the right atrium first fills the cavum venosum, and blood from the left atrium fills the cavum arteriosum. During diastole, blood from the cavum venosum crosses the muscular ridge into the cavum pulmonale. During middle to late systole the muscular ridge closes, thus prohibiting further blood flow into the cavum pulmonale. At the same time, the atrio-ventricular valves open the interventricular canal and allow blood from the cavum arteriosum to flow into the cavum venosum. In the late phase of ventricular systole, all blood from the cavum pulmonale is pressed into the pulmonary trunk; all blood from the cavum venosum is pressed into both aortas. Quantitative measures of blood flow volume showed that resting snakes bypass the pulmonary circulation and shunt about twice the blood volume into the systemic circulation as into the pulmonary circulation. When digesting, the oxygen demand of snakes increased tremendously. This is associated with shunting more blood into the pulmonary circulation. The results of this study allow the presentation of a detailed functional model of the python heart. They are also the basis for a functional hypothesis of how shunting is achieved. Further, it was shown that shunting is an active regulation process in response to changing demands of the organism (here, oxygen demand). Finally, the results of this study support earlier reports about a dual pressure circulation in Python regius.

Histamine induces postprandial tachycardia through a direct effect on cardiac H2-receptors in pythons

The intrinsic heart rate of most vertebrates studied, including humans, is elevated during digestion, suggesting that a nonadrenergic-noncholinergic factor contributes to the postprandial tachycardia. The regulating factor, however, remains elusive and difficult to identify. Pythons can ingest very large meals, and digestion is associated with a marked rise in metabolism that is sustained for several days. The metabolic rise causes more than a doubling of heart rate and a fourfold rise in cardiac output. This makes the python an interesting model to investigate the postprandial tachycardia. We measured blood pressure and heart rate in fasting Python regius, and at 24 and 48 h after ingestion of a meal amounting to 25% of body wt. Digestion caused heart rate to increase from 25 to 56 min, whereas blood pressure was unchanged. The postprandial rise in heart rate was partially due to a doubling of intrinsic heart rate. The H(2)-antagonist did not affect heart rate of fasting snakes but decreased heart rate by 15-20 min at 24 h into digestion, whereas it had no effects at 48 h. Thus, the histaminergic tone on the heart rose from none to 30% at 24 h but vanished after 48 h. In anesthetized snakes, histamine caused a systemic vasodilatation and a marked increase in heart rate and cardiac output mediated through a direct effect on H(2)- receptors. Our study strongly indicates that histamine regulates heart rate during the initial phase of digestion in pythons. This study describes a novel regulation of the vertebrate heart.

Effects of preoperative administration of butorphanol or meloxicam on physiologic responses to surgery in ball pythons

To characterize physiologic responses of ball pythons (Python regius) following a minor surgical procedure and investigate the effects of 2 commonly used analgesics on this response. 15 healthy ball pythons. Snakes were randomly assigned to receive 1 of 3 treatments: meloxicam (0.3 mg/kg [0.14 mg/lb]; n = 5), butorphanol (5 mg/kg [2.3 mg/lb]; 5), or saline (0.9% NaCl) solution (5) before catheterization of the vertebral artery. Plasma concentrations of catecholamines and cortisol, blood pressure, heart rate, and blood gas values were measured at various times for 72.5 hours after catheterization. The 72.5-hour point was defined as baseline. Heart rate of ball pythons increased significantly during the first hour following surgery. Mean plasma epinephrine concentration increased slightly at 2.5 hours after surgery, whereas mean plasma cortisol concentration increased beginning at 1.5 hours, reaching a maximum at 6.5 hours. Mean blood pressure increased within the first hour but returned to the baseline value at 2.5 hours after surgery. After 24.5 hours, blood pressure, heart rate, and plasma hormone concentrations remained stable at baseline values. There were no significant differences in values for physiologic variables between snakes that received saline solution and those that received meloxicam or butorphanol. Measurement of physiologic variables provides a means of assessing postoperative pain in snakes. Meloxicam and butorphanol at the dosages used did not decrease the physiologic stress response and did not appear to provide analgesic effects in ball pythons.

Evaluation of transcutaneous pulmonoscopy for examination and biopsy of the lungs of ball pythons and determination of preferred biopsy specimen handling and fixation procedures

To establish a safe and effective technique for the endoscopic examination and biopsy of snake lungs by use of a 2.7-mm rigid endoscope system. Clinical trial. 17 adult ball pythons (Python regius). The right lung of each anesthetized snake was transcutaneously penetrated at a predetermined site. Endoscopic lung examination was objectively scored, and 3 lung biopsies were performed. Tissue samples were evaluated histologically for diagnostic quality. One year later, 11 of the 17 snakes again underwent pulmonoscopy and biopsy; specimens were placed in various fixatives to compare preservation quality. All 17 snakes were euthanatized and necropsied. No major anesthetic, surgical, or biopsy-associated complications were detected in any snake. In 16 of 17 pythons, ease of right lung entry was satisfactory to excellent, and views of the distal portion of the trachea; primary bronchus; intrapulmonary bronchus; cranial lung lobe; and faveolar, semisaccular, and saccular lung regions were considered excellent. In 1 snake, mild hemorrhage caused minor procedural difficulties. After 1 year, pulmonoscopy revealed healing of the previous transcutaneous lung entry and biopsy sites. Important procedure-induced abnormalities were not detected at necropsy. Diagnostic quality of specimens that were shaken from biopsy forceps into physiologic saline (0.9% NaCl) solution before fixation in 2% glutaraldehyde or neutral-buffered 10% formalin was considered good to excellent. By use of a 2.7-mm rigid endoscope, lung examination and biopsy can be performed safely, swiftly, and with ease in ball pythons. Biopsy specimens obtained during this procedure are suitable for histologic examination.

Stable isotopes may provide evidence for starvation in reptiles

Previous studies have attempted to correlate stable isotope signatures of tissues with the nutritional condition of birds, mammals, fishes, and invertebrates. Unfortunately, very little is known about the relationship between food limitation and the isotopic composition of reptiles. We examined the effects that starvation has on delta13C and delta15N signatures in the tissues (excreta, carcass, scales, and claws) of six, distantly related squamate reptiles (gaboon vipers, Bitis gabonica; ball pythons, Python regius; ratsnakes, Elaphe obsoleta; boa constrictors, Boa constrictor; western diamondback rattlesnakes, Crotalus atrox, and savannah monitor lizards, Varanus exanthematicus). Analyses revealed that the isotopic composition of reptile carcasses did not change significantly in response to bouts of starvation lasting up to 168 days. In contrast, the isotopic signatures of reptile excreta became significantly enriched in 15N and depleted in 13C during starvation. The isotopic signatures of reptile scales and lizard claws were less indicative of starvation time than those of excreta. We discuss the physiological mechanisms that might be responsible for the starvation-induced changes in 13C and 15N signatures in the excreta, and present a mixing model to describe the shift in excreted nitrogen source pools (i.e. from a labile source pool to a nonlabile source pool) that apparently occurs during starvation in these animals. The results of this study suggest that naturally occurring stable isotopes might ultimately have some utility for characterizing nitrogen and carbon stress among free-living reptiles.

Fatty acid analyses may provide insight into the progression of starvation among squamate reptiles

Fasting-induced changes in fatty acid composition have been reported to occur within the body lipids of several types of animals; however, little is known about the changes in fatty acid profiles exhibited by reptiles subjected to prolonged fasting. This study characterizes the fatty acid profiles of six reptile species subjected to sublethal periods of fasting lasting 0, 56, 112, and 168 days. Analyses of fatty acid methyl esters (FAMEs) conducted on the total body lipids of rattlesnakes ( Crotalus atrox), ratsnakes ( Elaphe obsoleta), pythons ( Python regius), boas ( Boa constrictor), true vipers ( Bitis gabonica), and monitor lizards ( Varanus exanthematicus) revealed that all of the species exhibited similar characteristic changes in their fatty acid profiles during starvation stress. According to ANOVAs, the four most effective indicators of the onset of starvation were significant increases in the [1] fatty acid unsaturation index as well as ratios of [2] linoleic to palmitoleic acid, [3] oleic to palmitic, and [4] arachidonic to total fatty acid concentrations. The results of this study suggest that FAME analyses might be useful for identifying nutritional stress and/or starvation among squamate reptiles; however, forthcoming studies will be required to validate the generality of these responses. I also review the potential limitations of this approach, and suggest experiments that will be important for future applications of FAME analyses. Ultimately, it is hoped that FAME analyses can be used in conjunction with current practices as an additional tool to characterize the prevalence of starvation experienced by free-living reptiles.

Initiation and patterning of the snake dentition are dependent on Sonic Hedgehog signaling

Here we take the first look at cellular dynamics and molecular signaling in the developing snake dentition. We found that tooth formation differs from rodents in several respects. The majority of snake teeth bud off of a deep, ribbon-like dental lamina rather than as separate tooth germs. Prior to and after dental lamina ingrowth, we observe asymmetries in cell proliferation and extracellular matrix distribution suggesting that localized signaling by a secreted protein is involved. We cloned Sonic hedgehog from the African rock python Python sebae and traced its expression in the species as well as in two other snakes, the closely-related Python regius and the more derived corn snake Elaphe guttata (Colubridae). We found that expression of Shh is first confined to the odontogenic band and defines the position of the future dental lamina. Shh transcripts in pythons are progressively restricted to the oral epithelium on one side of the dental lamina and remain in this position throughout the prehatching period. Shh is expressed in the inner enamel epithelium and the stellate reticulum of the tooth anlagen, but is absent from the outer enamel epithelium and its derivative, the successional lamina. This suggests that signals other than Shh are responsible for replacement tooth formation. Functional studies using cyclopamine to block Hh signaling during odontogenesis prevented initiation and extension of the dental lamina into the mesenchyme, and also affected the directionality of this process. Further, blocking Hh signaling led to disruptions of the inner enamel epithelium. To explore the role of Shh in lamina extension, we looked at its expression in the premaxillary teeth, which form closer to the oral surface than elsewhere in the mouth. Oral ectodermal Shh expression in premaxillary teeth is lost soon after the teeth form reinforcing the idea that Shh is controlling the depth of the dental lamina. In summary, we have found diverse roles for Shh in patterning the snake dentition but, have excluded the participation of this signal in replacement tooth formation.

Minimal volume regulation after shrinkage of red blood cells from five species of reptiles

Red blood cells (RBCs) from most vertebrates restore volume upon hypertonic shrinkage and the mechanisms underlying this regulatory volume increase (RVI) have been studied extensively in these cells. Despite the phylogenetically interesting position of reptiles, very little is known about their red cell function. The present study demonstrates that oxygenated RBCs in all major groups of reptiles exhibit no or a very reduced RVI upon ~ 25% calculated hyperosmotic shrinkage. Thus, RBCs from the snakes Crotalus durissus and Python regius, the turtle Trachemys scripta and the alligator Alligator mississippiensis showed no statistically significant RVI within 120 min after shrinkage, while the lizard Tupinambis merianae showed 22% volume recovery after 120 min. Amiloride (10 − 4 M) and bumetanide (10 − 5 M) had no effect on the RVI in T. merianae, indicating no involvement of the Na +/H + exchanger (NHE) or the Na +/K +/2Cl − co-transporter (NKCC) or insentive transporters. Deoxygenation of RBCs from A. mississippiensis and T. merianae did not significantly affect RVI upon shrinkage. Deoxygenation per se of red blood cells from T. merianae elicited a slow volume increase, but the mechanism was not characterized. It seems, therefore, that the RVI response based on NHE activation was lost among the early sauropsids that gave rise to modern reptiles and birds, while it was retained in mammals. An RVI response has then reappeared in birds, but based on activation of the NKCC. Alternatively, the absence of the RVI response may represent the most ancient condition, and could have evolved several times within vertebrates.

Rodents as intermediate hosts of Hepatozoon ayorgbor (Apicomplexa: Adeleina: Hepatozoidae) from the African ball python, Python regius?

Two experimental trials were performed to elucidate the role of rodents in the life cycle of Hepatozoon species using snakes as intermediate hosts. In one trial, two ball pythons, Python regius Shaw, 1802 were force fed livers of laboratory mice previously inoculated with sporocysts of Hepatozoon ayorgbor Sloboda, Kamler, Bulantová, Votýpka et Modrý, 2007. Transmission was successful in these experimentally infected snakes as evidenced by the appearance of intraerythrocytic gamonts, which persisted until the end of trial, 12 months after inoculation. Developmental stages of haemogregarines were not observed in histological sections from mice. In another experimental trial, a presence of haemogregarine DNA in mice inoculated with H. ayorgbor was demonstrated by PCR in the liver, lungs and spleen.

Histamine regulates heart rate during digestion in pythons

The intrinsic heart rate of most vertebrates, including humans, is elevated during digestion, suggesting that a non‐adrenergic‐non‐cholinergic (NANC) factor contributes to the postprandial tachycardia. The NANC factor(s) may be released from the digestive organs, but the regulating factors remain elusive and difficult to identify. Pythons can ingest very large whole meals and digestion is associated with a marked rise in metabolism that is sustained for several days. The metabolic rise causes more than a doubling of heart rate and a four‐fold rise in cardiac output. This makes the python an interesting animal to investigate the postprandial tachycardia. We measured blood pressure and heart rate in fasting Python regius and at 24 and 48h after ingestion of a meal amounting to 25% of body weight. Digestion caused heart rate to increase from 25 to 56 min−1, while blood pressure was unchanged. The postprandial rise in heart rate was partially due to a doubling of the intrinsic heart rate (from 28 to 55 min−1), revealed after double autonomic block. The H2‐antagonist did not affect heart rate of fasting snakes, but decreased heart rate by 15–20 min−1 at 24h into digestion, while it had no effects at 48h. Thus, the histaminergic tone on the heart rose from none to 30% at 24h, but vanished after 48h. Bolus injection of histamine exerted a positive chronotropic effect in fasting snakes, but the effect was abolished during digestion. Our study strongly indicates that histamine regulates heart rate during the initial phase of digestion in pythons.Supported by the Danish Research Council.

Comparison of ophthalmic measurements obtained via high-frequency ultrasound imaging in four species of snakes

To measure the dimensions of the eyes of living snakes by use of high-frequency ultrasound imaging and correlate those measurements with age, length, and weight. Animals-14 clinically normal snakes. Species, age, length, weight, and horizontal spectacle diameter were recorded, and each snake underwent physical and ophthalmic examinations; ultrasonographic examination of both eyes was performed by use of a commercially available ultrasound unit and a 50-MHz transducer. Ultrasonographic measurements included spectacle thickness, subspectacular space depth, corneal thickness, anterior chamber depth, lens thickness, vitreous cavity depth, and globe length. All measurements were made along the visual axis. 2 corn snakes, 5 California king snakes, 1 gopher snake, and 6 ball pythons were examined. There were no significant differences within or between the species with regard to mean spectacle thickness, corneal thickness, or subspectacular space depth. However, mean horizontal spectacle diameter, anterior chamber depth, and axial globe length differed among the 4 species; for each measurement, ball pythons had significantly larger values than California king snakes. Spectacle thickness, subspectacular space depth, and corneal thickness were similar among the species of snake examined and did not vary significantly with age, length, or weight. Measurements of these dimensions can potentially serve as baseline values to evaluate snakes of these species with a retained spectacle, subspectacular abscess, or subspectacular fluid accumulation. Anterior chamber depth and axial length appeared variable among species, but axial length did not vary with age, length, or weight in the species studied.

A NEW SPECIES OF HEPATOZOON (APICOMPLEXA: ADELEORINA) FROM PYTHON REGIUS (SERPENTES: PYTHONIDAE) AND ITS EXPERIMENTAL TRANSMISSION BY A MOSQUITO VECTOR

Hepatozoon ayorgbor n. sp. is described from specimens of Python regius imported from Ghana. Gametocytes were found in the peripheral blood of 43 of 55 snakes examined. Localization of gametocytes was mainly inside the erythrocytes; free gametocytes were found in 15 (34.9%) positive specimens. Infections of laboratory-reared Culex quinquefasciatus feeding on infected snakes, as well as experimental infection of juvenile Python regius by ingestion of infected mosquitoes, were performed to complete the life cycle. Similarly, transmission to different snake species (Boa constrictor and Lamprophis fuliginosus) and lizards (Lepidodactylus lugubris) was performed to assess the host specificity. Isolates were compared with Hepatozoon species from sub-Saharan reptiles and described as a new species based on the morphology, phylogenetic analysis, and a complete life cycle.

Snakes survive starvation by employing supply- and demand-side economic strategies

Animals vary widely in their abilities to tolerate extended periods of food limitation. Although some snakes are known for their unique ability to survive periods of inanition that last up to 2 years, very little is known about the biological mechanisms that allow them to do this. Consequently, the present study examined physiological, compositional, and morphological responses to 168 days of starvation among three distantly related snake species (i.e., ball python, Python regius; ratsnake, Elaphe obsoleta; and western diamondback rattlesnake, Crotalus atrox). Results revealed that each of these species was able to successfully tolerate starvation by adaptively utilizing supply- and demand-side regulatory strategies. Effective demand-side strategies included the ability of snakes to depress their resting metabolic demands by up to 72%. Moreover, supply-side regulation of resources was evidenced by the ability of snakes to spare their structurally critical protein stores at the expense of lipid catabolism. Such physiological strategies for minimizing endogenous mass and energy flux during periods of resource limitation might help explain the evolutionary persistence of snakes over the past 100 million years, as well as the repeated radiation of snake lineages into relatively low-energy environments. The final section of this study outlines a novel modeling approach developed to characterize material and chemical flux through animals during complete inanition. This approach was used to make comparisons about the efficacy of various supply- and demand-side starvation strategies among the three species examined, but could also be used to make similar comparisons among other types of animals.

Evidence that neurotensin mediates postprandial intestinal hyperemia in the python,Python regius

Digestion of large meals in pythons produces substantial increases in heart rate and cardiac output, as well as a dilation of the mesenteric vascular bed leading to intestinal hyperemia, but the mediators of these effects are unknown. Bolus intra-arterial injections of python neurotensin ([His(3), Val(4), Ala(7)]NT) (1 - 1,000 pmol/kg) into the anesthetized ball python Python regius (n = 7) produced a dose-dependent vasodilation that was associated with a decrease in systemic pressure (P(sys)) and increase in systemic blood flow (Q(sys)). There was no effect on pulmonary pressure and conductance. A significant (P < 0.05) increase in heart rate (f(H)) and total cardiac output (Q(tot)) was seen only at high doses (>30 pmol/kg). The systemic vasodilation and increase in Q(tot) persisted after beta-adrenergic blockade with propranolol, but the rise in f(H) was abolished. Also, the systemic vasodilation persisted after histamine H(2)-receptor blockade. In unanesthetized pythons (n = 4), bolus injection of python NT in a dose as low as 1 pmol/kg produced a significant increase in blood flow to the mesenteric artery (177% +/- 54%; mean +/- SE) and mesenteric conductance (219% +/- 74%) without any increase in Q(sys), systemic conductance, P(sys), and f(H). The data provide evidence that NT is an important hormonal mediator of postprandial intestinal hyperemia in the python, but its involvement in mediating the cardiac responses to digestion may be relatively minor.

Behavioural examination of the infrared sensitivity of ball pythons

AbstractThe ability to detect infrared (IR) radiation is a characteristic trait in boids and pitvipers. These snakes possess highly sensitive IR receptors, which enable them to perceive IR sources and assess their direction and distance independently of visual cues. Electrophysiological studies have been conducted to determine IR detection thresholds in boids and pitvipers. This, however, is the first behavioural study that focuses on the detection threshold of a boid snake to IR stimuli. Blindfolded ball pythons Python regius were exposed to a moving IR stimulus of constant size and temperature at various distances (10–100 cm). Distinct behavioural changes during stimulus presentation (S‐form posture, freeze and fix, follow and fix) allowed quantification of the behavioural responses. The threshold to elicit behavioural responses was used to assess the IR detection threshold. The results revealed that P. regius can detect a moving IR stimulus resembling a mouse in temperature and size up to a distance of 30 cm, which corresponds to an irradiance contrast of 38.83 × 10−6 W cm−2. This irradiance contrast detection threshold value is about one‐third lower (reveals a 1.5 times higher sensitivity) than the results from earlier electrophysiological studies.

Identification and comparison of marbofloxacin metabolites from the plasma of ball pythons (Python regius) and blue and gold macaws (Ara ararauna)

Marbofloxacin is a veterinary only, synthetic, broad spectrum fluoroquinolone antimicrobial agent. In mammals, approximately 40% of the oral dose of marbofloxacin is excreted unchanged in the urine; the remaining is excreted via the bile as unchanged drug in the feces. The Vd ranges from 1.1 (cattle) to 1.3 (dog, goat, swine) L/kg. Because of extra-label use of marbofloxacin in birds and reptiles, this study was designed to determine the profile of metabolites in plasma and compare the circulating metabolite profile between a reptile and an avian species. Six adult ball pythons (Python regius) and 10 blue and gold macaws (Ara ararauna) were used in this study. The macaws were dosed both i.v. and p.o. with a single 2.5 mg/kg administration where as the pythons received a single 10 mg/kg dose both i.v. and p.o. The metabolite profiles of marbofloxacin in the plasma of these species were determined using a high performance liquid chromatography system with a mass spectrometer for detection (LC/MS/MS). Mass spectra data generated from the snake and bird plasma samples were compared with previously reported LC/MS/MS mass spectral data. Evidence does not suggest differences due to route of administration (i.v. vs. p.o.) in either species. Four chromatographic peaks with resulting daughter spectrum were identified and represent 12 possible metabolite structures. All of the proposed metabolites, except for the N-oxide, appear to be unique to macaws. The potential metabolites identified in macaws appear to be very different than those reported for chickens.

Contractile properties of the functionally divided python heart: Two sides of the same matter

The heart of Python regius is functionally divided so that systemic blood pressure is much higher than pulmonary pressure (6.6+/-1.0 and 0.7+/-0.1 kPa, respectively). The present study shows that force production of cardiac strips from the cavum arteriosum and cavum pulmonale exhibits similar force production when stimulated in vitro. The high systemic blood pressure is caused, therefore, by a thicker ventricular wall surrounding the cavum arteriosum rather than differences in the intrinsic properties of the cardiac tissues. Similarly, there were no differences between the contractile properties of right and left atria. Force production was similar in atria and ventricle but the atria contracted and relaxed much faster than the ventricle. Graded hypoxia markedly reduced twitch force of all four cardiac tissues, and this was most pronounced when PO(2) was below 40 kPa. In contrast, the four cardiac tissues were insensitive to acidosis during normoxia although acidosis increased the sensitivity to hypoxia. Adrenergic stimulation increased twitch force of all cardiac tissues, while cholinergic stimulation only affected the atria and reduced twitch force markedly. In spite of the different oxygen availability of the two sides of the heart, the biochemical and functional properties are alike and the differences may instead be overcome by the coronary blood supply.

Using Direct Calorimetry to Test the Accuracy of Indirect Calorimetry in an Ectotherm

We previously demonstrated that the relationship between respiratory gas exchange and metabolic heat production is unexpectedly variable and that conventional approaches to estimating energy expenditure by indirect calorimetry can incorporate large errors. Prior studies, however, comparing direct and indirect calorimetry of animals focused only on endothermic organisms. Given that endothermy and ectothermy represent a fundamental dichotomy of animal energetics, in this analysis we explore how these contrasting physiologies correlate with the relationship between heat production and respiratory gas exchange. Simultaneous indirect and direct calorimetry in an ectotherm, the ball python (Python regius Shaw), revealed that the relationships between gas exchange and heat production were within 1% of those expected when analyses using indirect calorimetry were based on the assumption that the fasting animal catabolized only protein. This accuracy of indirect calorimetry contrasts sharply with our previous conclusions for three species of birds and mammals.

The role of the sarcoplasmic reticulum in the generation of high heart rates and blood pressures in reptiles

The functional significance of the sarcoplasmic reticulum (SR) in the generation of high heart rates and blood pressures was investigated in four species of reptile; the turtle, Trachemys scripta; the python, Python regius, the tegu lizard, Tupinanvis merianae, and the varanid lizard, Varanus exanthematicus. Force-frequency trials and imposed pauses were performed on ventricular and atrial tissue from each species with and without the SR inhibitor ryanodine, and in the absence and presence of adrenaline. In all species, an imposed pause of 1 or 5 min caused a post-rest decay of force, and a negative force-frequency response was observed in all species within their in vivo frequency range of heart rates. These relationships were not affected by either ryanodine or adrenaline. In ventricular strips from varanid lizards and pythons, ryanodine caused significant reductions in twitch force within their physiologically relevant frequency range. In atrial tissue from the tegu and varanid lizards, SR inhibition reduced twitch force across the whole of their physiological frequency range. In contrast, in the more sedentary species, the turtle and the python, SR inhibition only decreased twitch force at stimulation frequencies above maximal in vivo heart rates. Adrenaline caused an increase in twitch force in all species studied. In ventricular tissue, this positive inotropic effect was sufficient to overcome the negative effects of ryanodine. In atrial tissue however, adrenaline could only ameliorate the negative effects of ryanodine at the lower pacing frequencies. Our results indicate that reptiles recruit Ca2+ from the SR for force development in a frequency and tissue dependent manner. This is discussed in the context of the development of high reptilian heart rates and blood pressures.

Endoscopic examination of snakes by access through an air sac

Sixteen boa constrictors (Boa constrictor), three royal pythons (Python regius) and 15 Burmese pythons (Python molurus bivittatus) were examined endoscopically by access through the air sac. The snakes were immobilised...