[Noradrenaline is involved in cardiovascular responses induced by intracerebroventricular injection substance P in rabbits].

Aim: To investigate the role of intracerebroventricular (icv) injection substance P(SP) in cardiovascular regulation and the relationship with noradrenergic system.
Methods: Rabbits anesthetized with urethane were intracerebroventricularly given SP in presence or absence of phentolamine, prazosin, yohimbine. Cardiovascular responses including heart rate (HR), mean arterial blood pressure (MAP), left ventricular systolic pressure (LVSP), left ventricular end diastolic pressure (LVEDP), the maximum velocity of ascending or descending in intraventricular pressure (+/- dp/dt(max)) and the maximum shortening velocity(Vpm) of myocardial contractile element were recorded, and changes of NA content in cerebrospinal fluid (CSF) were determined in rabbits with icy injection of SP.
Results: (1) icv SP elicited significant increased of HR, MAP, LVSP, LVEDP, + dp/dt(max), -dp/dt(max), Vpm and the levels of NA in intracisternal CSF 30 min after injection. (2) Pretreatment with phentolamine, prazosin, but not yohimbine, attenuated icv SP-induced cardiovascular responses compared with controls (P < 0.05).
Conclusion: (1) icv SP can produce positive inotropic and chronic response in myocardium and pressor response in intact rabbits. (2) alpha1 adrenoceptors may be involved in the cardiovascular responses to icy SP. (3) Central administration of SP can increase the release of NA or inhibit reuptake of NA, which may be responsible for an important mechanism of SP-potentiated cardiovascular responses in brain.