Sympathetic activation following central vasopressin receptor stimulation in conscious rats

Vasopressin (AVP)-containing pathways from hypothalamic neurons have been shown to project to blood pressure controlling brain centres. This suggests that AVP neurons may be involved in central blood pressure regulation. The effects of central AVP receptor stimulation on blood pressure, heart rate and directly recorded efferent sympathetic nerve activity in the splanchnic nerve (SNA) were investigated in conscious chronically instrumented rats. Intracerebroventricular (i.c.v.) injections of AVP (1-100 ng) caused dose-dependent blood pressure increases (maximum 26.9 +/- 3.5 mmHg) together with marked rises in heart rate and SNA. More pre-treatment with the AVP receptor antagonist d(CH2)5AVP (3/micrograms i.c.v.) completely prevented the central responses to AVP. Intracarotid injection of the same AVP doses produced rises in blood pressure accompanied by drastic falls in heart rate and SNA, similar to those seen after i.v. AVP injection. Thus, stimulation of specific neuronal AVP receptors produces a characteristic haemodynamic and sympathetic response pattern with marked sympathetic nerve activation, which is clearly distinct from the responses to vascular AVP receptor stimulation. It is concluded that AVP pathways in the brain can contribute to central blood pressure control via regulation of sympathetic outflow to the periphery.