Paradoxical effects of temperature on vascular tone.

Temperature may have significant influence on vascular tone in such cases as organ preservation, coronary bypass surgery, and extracorporeal circulation. The aim of this research was to study the direct effect of temperature variation on vascular tone in an attempt to elucidate the mechanisms involved. In a first series of experiments, the isometric tension of two different vessels (rat thoracic aorta and pig renal branch artery) was studied at different temperatures. To study the role of calcium in this response, a second series of experiments was performed. In this the vessels were incubated with the intracellular chelator BAPTA/AM. Further experiments were performed to test the effect of cold storage. Our results show that changes in temperature lead to different results in pig renal artery and rat aorta. A decrease in temperature induced a highly reproducible relaxation in rat aorta, whereas pig renal artery presented cooling-induced contraction. Moreover, whereas calcium depletion failed to inhibit cooling-induced relaxation in rat aorta, it did not provoke cooling-induced contraction in pig renal artery. Similar responses were obtained with cold storage and calcium depletion. We intend to demonstrate that, just as the effect of temperature variation on pig renal artery is due to a metabolic mechanism, its effect on rat aorta may be due to structural factors. This hypothesis is supported by the result of histological studies which demonstrate a higher proportion of elastin fibres in rat aorta than in pig renal artery.