Evaluation of the permanent sympathectomy produced by the administration of guanethidine to adult rats.

The administration of guanethidine to adult rats has been shown by morphological criteria to destroy sympathetic neurons. The objective of this study was to evaluate by biochemical and functional criteria the degree and permanence of this sympathectomy. Young adult male rats (260-300 g) were injected with saline (controls) or with guanethidine for 5 weeks. The status of the sympathetic nervous system in the animals was evaluated 1, 3 and 6 to 7 months after cessation of treatment. Seven months after cessation of treatment; the activity of tyrosine hydroxylase in the superior cervical ganglia of treated animals was greatly reduced, as were the norepinephrine levels in peripheral tissues. The concentration of epinephrine and the activity of tyrosine hydroxylase in adrenals were not different from controls at any of the times studied. Norepinephrine concentrations in several areas of the central nervous system were unchanged. Increases in blood pressure in response to stimulation of the sympathetic vasomotor outflow in the pithed rat preparation were markedly and permanently reduced in guanethidine-treated animals. Isolated intestinal nerve-muscle preparations from guanethidine-treated animals usually contracted in response to nerve stimulation, rather than relaxing as in controls. The response to stimulation of the hypogastric nerve in vas deferens preparations was reduced 1 month after cessation of treatment. The responses of the vas deferens from guanethidine-treated and control animals were the same 7 months after treatment despite a 93% reduction in norepinephrine concentration. The data demonstrate that the administration of guanethidine to adult rats produces a marked and permanent destruction of the peripheral sympathetic nervous system.