Effect of temperature on osmotic regulation in Larval Ambystoma gracile

Temperature effects on osmoregulation were studied in larval Ambystoma gracile. There was a pronounced effect on the osmotic uptake of water through the skin. The rates at 5°C, 15°C and 25°C were respectively 0.03 ml/hr., 0.1 ml/hr. and 0.2 ml/hr. for a 10g animal. The Q₁₀'s for these changes in rate are larger than would be expected for simple diffusion, which indicates that an active regulation is causing an increase in the permeability of the skin with a temperature increase. There was no gross change in the body weight at any temperature studied, indicating that the water loss was closely regulated. A possible mechanism for water regulation is discussed as well as the possibility of hormonal control over this mechanism. Temperature also has an effect on net potassium loss. The losses at 5°C, 15°C and 25°C were 0.09 μeq/10g hr., 0.23 μeq/10g hr. and 0.48 μeq/10g hr. These changes are comparable to the change in the rate of uptake of water. This indicates that there is a general change in the permeability of the skin to both salts and water with a change in temperature. Sodium and chloride were fully regulated at all temperatures studied. Sodium fluxes were obtained using radioactive sodium. There was no difference in the flux values obtained from animals acclimated at 15°C and 25°C, the rates were 1.7 μeq/10g hr. At 5°C the flux values dropped to 0.7 μeq/10g hr. Reasons are given indicating that a temperature increase causes: (1) a decrease in the activity of the sodium uptake across the skin and gills and (2) an increase in the activity of the sodium uptake across the tubular epithelium. Possible hormonal control of these responses is also discussed

Studies on temperature acclimation in the freshwater pulmonate mollusc Lymnaea stagnalis (L.)

PhDThis work is concerned with processes of thermal acclimation in the freshwater pulmonate, Lymnaea stagnalis. Three physiological functions were studied: heart rate, rate of oxygen consumption and assimilation efficiency, Seasonal changes in rate-temperature curves of the first two processes were investigated and compared with alterations induced by exposure to constant temperatures in the laboratory. Simple comparisons were made to determine whether season affected assimilation efficiency. The aims of the investigation were to show whether the measured physiological functions exhibited acclimatory responses to determine the precise nature and interrelationship of any such adaptations, and to suggest possible mechanisms responsible for the changes. It was found that changes in the heart rate-temperature relation were induced both by season and by laboratory acclimation. Results of the seasonal study showed apparent capacity adaptations, so that winter animals had a higher heart rate than summer animals at temperatures between 15 and 25 degrees C, and also resistance adaptations, which gave summer animals increased resistance to heat and winter animals greater tolerance of cold. Laboratory acclimation induced resistance adaptations at both temperature extremes but capacity adaptation was absent. Observed bimodality in heart rate-temperature curves of both studies indicated that control of heart rate is complex. These results are discussed further with reference to changes in physiological mechanisms. Seasonal changes occurred in the size-rate regression for oxygen consumption and in the general shape of the rate temporature curves. There was evidence for a 'reverse acclimation' in response to seasonal changes in temperature. These seasonal responses were not produced, however, by exposure to constant temperature in the laboratory. It is proposed that the observed changes resulted essentially from reproductive activity and seasonal changes in dietary conditions. Hormonal influences are thought to be most important in mediating these changes. No significant differences were found in the assimilation efficiencies of winter and summer snails. Results of this and other studies suggest that the assimilation function does not show acclimatory changes in response to either temperature or season. The results are discussed in relation to the known biology of Lymnaea stagnalis and with reference to fundamental temperature acclimation

Sympathomimetic Activity in the Isolated Frog's Heart (<i>Rana Temporaria</i>)

1. It was found that addition of ascorbic acid or an extract of frog's liver to the medium perfusing hearts showing a linear, low Q10, temperature-pulse rate curve (type E) led to an increased frequency response at the higher temperatures. By such treatment curves of types A, B or D were obtained (Smith, 1951). 2. In nearly all cases it was necessary to add adrenaline (1 in 107) to the perfusate to obtain an early response of this nature. In the absence of external adrenaline a similar change was observed after longer treatment with ascorbic acid or liver extract (up to 20 hr.). The possible action of adrenaline in this respect is discussed, and it is suggested that it may afford protection to sympathomimetic substances in the heart tissues. 3. The occurrence of a decreasing acceleration of pulse rate at higher temperatures in certain types of hearts was observed. This phenomenon was reversible on lowering the temperature again, but there was a marked time lag before equilibrium was re-established. When such hearts were treated with ascorbic acid or liver extract, and type A or B curves produced, the direction of this delayed pulse rate change was reversed. The significance of this behaviour in relation to the hypothesis that sympathomimetic substances are synthesized by the isolated heart is discussed. 4. It is suggested that the observed modifications of the type E curve produced by treatment with anterior pituitary extract, liver extract, or ascorbic acid were due to their action in promoting synthesis of adrenergic material by the heart. In the case of ascorbic acid there was evidence for an additional protective action. 5. It was found that treatment of types A or B hearts with ergotoxine and iodoacetic acid caused a definite change of the temperature-pulse rate curve towards the type E form. 6. Temperature-amplitude curves were constructed for numerous hearts of various types, and it was found that distinct forms occurred in correlation with the different types of temperature-pulse rate curves. It has been shown that the frequency and amplitude changes are related in such a way that they can both be attributed to production or inactivation of sympathomimetic substances. 7. The action of thyroxine in modifying the form of the temperature-pulse rate curve is attributed to its protective action on adrenergically active compounds. 8. An analysis of the various forms of temperature-pulse rate curve has been made on the basis of the action of temperature on three independent systems: (i) the pacemaker mechanism of the heart, (ii) the synthesis of sympathomimetic material, and (iii) the rate of inactivation of such material. In the summer heart (type C) synthesis is active and the material formed is protected by the relatively high level of circulating thyroid hormone. In the winter (type A) form, owing to the lower activity of the thyroid, the effects of inactivation lead to an exponential relation between pulse rate and frequency. Prior to the breeding season and in female frogs in the autumn there is apparently defective synthesis of adrenergic material and the type E relation appears. In January and February this type is often further modified, owing to thyroid inactivity, so that a constant acceleration is not maintained over the whole temperature range.</jats:p