In the conscious rat, 6-hydroxydopamine, or reserpine (5 mg/kg) pretreatment produced a marked fall in the mean systolic blood pressure whilst immunosympathectomized rats had resting blood pressures just below that of control animals. In pithed preparations, 6-hydroxydopamine treatment or immunosympathectomy potentiated the pressor responses to injected noradrenaline; reserpine pretreatment did not potentiate the noradrenaline response to the same degree. Tyramine responses were abolished after 6-hydroxydopamine or reserpine pretreatment but were unaffected by immunosympathectomy. Stimulation of the sympathetic outflow by the Gillespie & Muir (1967) preparation was abolished after 6-hydroxydopamine and reserpine pretreatment, and reduced after immunosympathectomy. It is concluded that 6-hydroxydopamine produces a destruction of the sympathetic nerve endings, abolishing the physiological uptake process and, therefore, producing supersensitivity to injected noradrenaline. Immunosympathectomy, although showing a marked reduction in sympathetic nerve supply leaves a functional uptake process. Reserpine (5 mg/kg), given 6 h previously, depletes endogenous catecholamines without significantly altering the sensitivity to injected noradrenaline, the uptake process remaining functional.
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Finch et al. (1970) studied this question.
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