Effect of phencyclidine (PCP) on adrenergic responses to spinal cord stimulation in pithed rats.

The effect of PCP (1 mg/kg i.a.) on sympathetic and cardiovascular responses were studied in conscious rats and pithed intact and adrenalmedullectomized rats (MEDX). Also, we examined the effect of Phencyclidine (PCP) (3 mg/kg s.c.) on the uptake and disposition of [3H]norepinephrine [3H]NE in rat heart and plasma. In conscious rats, PCP significantly increased blood pressure (PB), heart rate (HR) and plasma catecholamine (CA). Sympathetic stimulation in pithed intact and MEDX rats elicited increases in PB, HR and plasma CA. Administration of PCP (1 mg/kg i.v.) prior to stimulation potentiated the pressor responses to stimulation in both intact and MEDX rats. The HR response to stimulation was reduced significantly in MEDX rats, suggesting it was largely related to epinephrine release. PCP (3 mg/kg s.c.) failed to alter significantly [3H]NE uptake by the heart after i.v. administration of labelled catecholamine nor prolong the presence in plasma of infused [3H]NE. These results suggest that, in conscious rats, PCP enhances sympathetic outflow from the central nervous system. The enhancement by PCP of stimulation-induced NE release in pithed rats suggests that the drug also has a presynaptic effect which enhances NE release from the sympathetic nerve endings. The enhancement by PCP of stimulation-induced increases in plasma NE cannot be attributed to differences in sympathetic outflow nor inhibition of uptake, suggesting a presynaptic effect leading to enhanced NE release.