Paradoxical effects of temperature on vascular tone

Temperature may have significant influence on vascular tone in such cases a s organ preservation, coronary bypass surgery, and extracorporeal circulati on. The aim of this research was to study the direct effect of temperature variation on vascular tone in an attempt to elucidate the mechanisms involv ed. In a first series of experiments, the isometric tension of two differen t vessels (rat thoracic aorta and pig renal branch artery) was studied at d ifferent temperatures. To study the role of calcium in this response, a sec ond series of experiments was performed. In this the vessels were incubated with the intracellular chelator BAPTA/AM. Further experiments were perform ed to Lest the effect of cold storage. Our results show that changes in tem perature lead to different results in pig renal artery and rat aorta. A dec rease 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 r at aorta, it did not provoke cooling-induced contraction in pig renal arter y. 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 aor ta may be due to structural factors. This hypothesis is supported by the re sult of histological studies which demonstrate a higher proportion of elast in fibres in rat aorta than in pig renal artery. (C) 2000 Academic Press.