[Influence of temperature, basic tension and propranolol on the effect of noradrenaline in the isolated vascular strip of rat aorta]

Hypothermia-induced potentiation of histamine H2-receptor-mediated relaxation and cyclic AMP increase in the isolated mesenteric artery of the rabbit

On helically cut strips of the rabbit's mesenteric artery, a temperature decrease from 42 degrees C to 25 degrees C reduced the contractile responses to histamine. Metiamide shifted the dose-response curve of the histamine-induced contraction towards higher values at 25 degrees C, but not at 42 degrees C. Furthermore, on arterial strips contracted by phenylephrine histamine evoked a dose-dependent relaxation at 25 degrees C whereas at 42 degrees C only slight relaxing responses to histamine occurred. Metiamide was capable of preventing the relaxation induced by histamine in a competitive manner. At 25 degrees C the relaxation as produced by histamine was accompanied by increases in cyclic AMP which occurred prior to the relaxing effects. Metiamide abolished the cyclic AMP increase in response to histamine. At 42 degrees C histamine was unable to elevate the cyclic AMP content. Thus, it is concluded that a cyclic AMP-mediated relaxation due to stimulation of H2-receptors counteracts the histamine-induced contraction and reduces the contractile responses to histamine at low temperatures. In addition, clear-cut evidence exists from the present study that also on artery smooth muscle the H2-receptor-mediated responses are closely associated to cyclic AMP.

Effects of temperature on the responses to noradrenaline, isoprenaline and histamine on isolated rabbit mesenteric artery

On the rabbit mesenteric artery, the elevation of temperature from 25 degrees up to 42 degrees diminished the affinity of histamine, whereas that of noradrenaline to the alpha-adrenoceptors remained unchanged. The presence of beta-adrenoceptors could not be demonstrated.

The influence of temperature and calcium on the degree of stretch-activation in isolated K-depolarized vascular smooth muscle strips

Stretching of K-depolarized contracted helically cut strips of pig coronary arteries produced a delayed increase in tension. The influence of temperature and extracellular calcium on this active response to stretch was investigated. Reference for all tension values was the amplitude of contraction (induced by K-depolarization) starting from the high resting tension. 1. The mean amplitude of the delayed tension increase after stretch amounted to 27.5 plus or minus 4.8% (x plus or minus SEM, n equals 9); lowering the bath temperature from 37 degrees C to 27 degrees C caused a drop to 10.8 plus or minus 1.5% (n equals 9; P smaller than 0.0025); increasing the calcium concentration of the bath solution from 2.7 to 6.9 mM produced negligible effects on both the amplitude of the delayed tension increase (24.6 plus or minus 1.0%; n equals 9), and the amplitude of contraction after depolarization. 2. The peak tension time of the active response to stretch was not changed by the 6.9 mM calcium, but prolonged from 27.9 plus or minus 4.0 to 40.7 plus or minus 4.4 minutes (P smaller than 0.025) by lowering the bath temperature to 27 degrees C. At the high calcium level the preparation contracted faster after depolarization than at the normal calcium level. 3. The experimental results correspond with the conception of the sliding filament mechanism as the basic process of contraction also in vascular smooth muscle preparations. The delayed tension increase after stretch may be caused by a recruitment of interaction sites between contractile proteins.