Unresponsiveness of Pial Precapillary Vessels to Catecholamines and Sympathetic Nerve Stimulation

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Abstract
A systematic analysis of the possible existence of neurogenic control of precapillary pial vessels was made in three species (cat, dog, and rabbit). In all of these animals, pial vessels failed to respond to externally applied isoproterenol or norepinephrine in high concentrations (up to 100 µg/ml), although the vessels did dilate in response to externally applied histamine. Adrenergic nerve endings on the pial vessels were demonstrated by fluorescent histochemical techniques specific for catecholamines. However, in the absence of changes in arterial blood pressure and arterial blood carbon dioxide tension, pial precapillary vessels showed no change in caliber in response to stimulation of the ipsilateral superior cervical ganglion. These results show that pial precapillary vessels are not subject to vasoconstriction probably because they lack sufficient receptors for the catecholamine neurotransmitter.