Cutaneous blood flow during heating and cooling in the American alligator

Seven freshwater turtles Trachemys scripta were instrumented with flow probes and cannulated for blood pressure measurements. The turtles were warmed from 24 to 34°C, and cooled down to 24°C, with and without atropine. Animals exhibited a hysteresis of heart rate and blood flow to both the pulmonary and systemic circulations, which was not cholinergically mediated. Blood pressure remained constant during both warming and cooling, while systemic resistance decreased during heating and increased during cooling, indicating a barostatic response. There was a large right-to-left (R-L) shunt during warming and cooling in untreated animals, which remained relatively constant. Atropinisation resulted in a large L-R shunt, which decreased during warming and increased during cooling. Nevertheless, heating rates were the same in untreated and atropinised animals, and cooling rates were significantly longer in atropinised animals, indicating that shunt patterns contribute little to heat exchange.

supporting

confidence: 90%

Section: Rates Of Heating and Coolingmentioning

confidence: 99%

The cardiovascular responses of the freshwater turtleTrachemys scriptato warming and cooling

Galli

Taylor

Wang

2004

“…Prostaglandins are a possible mechanism that may control cardiac response during heating and cooling (Robleto and Herman, 1988) via the baroreflex, by contraction or dilation of capillary beds, and/or by directly stimulating the heart. The baroreflex is likely to play a role in modulating heart rate, particularly in crocodiles (Altimiras et al, 1998); it has been demonstrated that peripheral blood flow changes in response to heat (Grigg and Alchin, 1976;Smith et al, 1978), and this response in blood flow may precede the response in heart rate (Morgareidge and White, 1972). The difference between heat lamp and hot water treatments indicates, however, that there may be additional control mechanisms operating.…”

Section: Discussionmentioning

confidence: 99%

The effect of heat transfer mode on heart rate responses and hysteresis during heating and cooling in the estuarine crocodileCrocodylus porosus

Franklin

Seebacher

2003

SUMMARYThe effect of heating and cooling on heart rate in the estuarine crocodile Crocodylus porosus was studied in response to different heat transfer mechanisms and heat loads. Three heating treatments were investigated. C. porosus were: (1) exposed to a radiant heat source under dry conditions;(2) heated via radiant energy while half-submerged in flowing water at 23°C and (3) heated via convective transfer by increasing water temperature from 23°C to 35°C. Cooling was achieved in all treatments by removing the heat source and with C. porosushalf-submerged in flowing water at 23°C. In all treatments, the heart rate of C. porosus increased markedly in response to heating and decreased rapidly with the removal of the heat source. Heart rate during heating was significantly faster than during cooling at any given body temperature, i.e. there was a significant heart rate hysteresis. There were two identifiable responses to heating and cooling. During the initial stages of applying or removing the heat source, there was a dramatic increase or decrease in heart rate (`rapid response'), respectively, indicating a possible cardiac reflex. This rapid change in heart rate with only a small change or no change in body temperature (<0.5°C) resulted in Q10 values greater than 4000, calling into question the usefulness of this measure on heart rate during the initial stages of heating and cooling. In the later phases of heating and cooling, heart rate changed with body temperature, with Q10 values of 2–3. The magnitude of the heart rate response differed between treatments, with radiant heating during submergence eliciting the smallest response. The heart rate of C. porosus outside of the`rapid response' periods was found to be a function of the heat load experienced at the animal surface, as well as on the mode of heat transfer. Heart rate increased or decreased rapidly when C. porosus experienced large positive (above 25 W) or negative (below –15 W) heat loads,respectively, in all treatments. For heat loads between –15 W and 20 W,the increase in heart rate was smaller for the `unnatural' heating by convection in water compared with either treatment using radiant heating. Our data indicate that changes in heart rate constitute a thermoregulatory mechanism that is modulated in response to the thermal environment occupied by the animal, but that heart rate during heating and cooling is, in part,controlled independently of body temperature.

“…A number of laboratory-and field-based studies of reptiles have reported values of fH for a given T b that are higher during heating than during cooling, and the associated changes in peripheral blood flow are thought to facilitate faster rates of heating and slower rates of cooling in order to maximize the period of time spent at the preferred T b (Bartholomew and Tucker, 1963;Smith et al, 1978;Grigg and Seebacher, 1999;Seebacher and Grigg, 2001). Similarly, V. rosenbergi in the present study displayed a hysteresis in fH over a broad range of T b , where values were higher during heating than during the subsequent cooling period.…”

Section: Hysteresis Of Cardio-metabolic Variablesmentioning

confidence: 99%

Digestive state influences the heart rate hysteresis and rates of heat exchange in the varanid lizardVaranus rosenbergi

Butler

Frappell

2005

SUMMARY To maximize the period where body temperature (Tb)exceeds ambient temperature (Ta), many reptiles have been reported to regulate heart rate (fh) and peripheral blood flow so that the rate of heat gain in a warming environment occurs more rapidly than the rate of heat loss in a cooling environment. It may be hypothesized that the rate of cooling, particularly at relatively cool Tbs, would be further reduced during postprandial periods when specific dynamic action (SDA) increases endogenous heat production (i.e. the heat increment of feeding). Furthermore, it may also be hypothesized that the increased perfusion of the gastrointestinal organs that occurs during digestion may limit peripheral blood flow and thus compromise the rate of heating. Finally, if the changes in fh are solely for the purpose of thermoregulation, there should be no associated changes in energy demand and, consequently, no hysteresis in the rate of oxygen consumption(V̇O2). To test these hypotheses, seven individual Varanus rosenbergi were heated and cooled between 19°C and 35°C following at least 8 days fasting and then approximately 25 h after consumption of a meal (mean 10% of fasted body mass). For a given Tb between the range of 19-35°C, fh of fasting lizards was higher during heating than during cooling. Postprandial lizards also displayed a hysteresis in fh, although the magnitude was reduced in comparison with that of fasting lizards as a result of a higher fh during cooling in postprandial animals. Both for fasting and postprandial lizards,there was no hysteresis in V̇O2 at any Tb throughout the range although, as a result of SDA,postprandial animals displayed a significantly higher V̇O2 than fasting animals both during heating and during cooling at Tbs above 24°C. The values of fh during heating at a given Tb were the same for fasting and postprandial animals,which, in combination with a slower rate of heating in postprandial animals,suggests that a prioritization of blood flow to the gastrointestinal organs during digestion is occurring at the expense of higher rates of heating. Additionally, postprandial lizards took longer to cool at Tbs below 23°C, suggesting that the endogenous heat produced during digestion temporarily enhances thermoregulatory ability at lower temperatures, which would presumably assist V. rosenbergiduring cooler periods in the natural environment by augmenting temperature-dependent physiological processes.