Mechanism of adrenergic stimulation of mammalian arteries and its failure at low temperatures

These experiments are an attempt to identify the main events by which noradrenaline causes contraction of mammalian arteries and to discover which events fail at low temperature. The effect of low temperature was of interest because there is evidence both from in vitro experiments (Keatinge, 1958) and from work on intact man (Keatinge, 1961) and cats (Folkow, Fox, Krog, Odelram & Thoren, 1963) that failure of vascular smooth muscle to respond to constrictor agents is a cause of the vasodilatation produced by severe local cooling. In the present experiments, electrical and mechnical responses of sheep carotid arteries to constrictor hormones and potassium-rich solutions were measured at normal and low temperatures by a sucrose-gap technique. The mechanical response to strong electrical stimulation was also tested at different temperatures. Since the results suggested that one of the temperature-sensitive processes might be the adenosine triphosphateactomyosin system, which is more temperature-sensitive at low than at normal pH (Brown, 1957), the effect of abrupt temperature change during active contraction was compared at normal and low pH. Brief reports of these experiments have been published (Keatinge, 1963 a, b).