This study showed that arterial blood pressure of chemically sympathectomized rats (SR) was decreased, whereas heart rate was increased relative to controls. The cardiac output in SR was higher than that in intact animals (by 36% under urethane anaesthesia and by 80% without anaesthesia). The total peripheral resistance of SR was 1.7 times less than normal, although the magnitude of the structural component of resistance was increased. The half-time clearance of 133Xe from skeletal muscle during motor nerve stimulation was greater in SR than in intact rats by a factor of 2. It is concluded that the number of small resistance vessels in SR is low, while the lumen of individual vessels is greater than in controls, thus giving rise to an insufficient "vasodilator reserve".

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Partial sympathectomy of neonatal rats was produced by treatment with guanethidine. The number of neurons of the superior cervical ganglion decreased to 15% of control values and remained constant throughout the subsequent observation period of 4 months. The volume of the remaining neuronal perikarya increased faster than that of control animals during the observation period, and the density of adrenergic innervation of the iris and the noradrenaline content of the heart were found to partially recover after the initial decrease produced by the guanethidine treatment, reaching 33% and 30% of control values, respectively, after 4 months. The noradrenaline content of the duct of the vas deferens was greatly reduced by guanethidine treatment, but almost recovered after 4 months. The frequency of sympathetic preganglionic impulses was elevated throughout the 4 months observation period, and it is suggested that this increase is responsible for the compensatory changes in cell volume, terminal density and terminal noradrenaline content of the remaining neurons.

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