Blood pressure, the renin-angiotensin system and neurogenic vasoconstriction in pithed rats

The influence of changing baseline blood pressure by various means, both related or unrelated to the renin-angiotensin system, on the pressor responses to spinal cord stimulation has been examined in the pithed rat. Mean arterial pressure and neurogenic vasoconstriction were higher in pithed rats with intact kidneys (2-kidney rats) than in nephrectomized pithed rats. Increasing blood pressure by infusion of vasopressin increased the pressor response to nerve stimulation in both 2-kidney and nephrectomized pithed rats. Decreasing blood pressure produced by administration of enalaprilat or hydralazine in 2-kidney pithed rats or by administration of hydralazine in nephrectomized pithed rats, decreased the pressor responses to nerve stimulation. Our results showed a positive correlation between the mean arterial blood pressure and the response to nerve stimulation in pithed rats. Therefore, we conclude that the pithed rat is an animal model which should be used with caution to study the interaction between the sympathetic nervous system and drugs which change baseline blood pressure.