Role of renal nerve activity, plasma catecholamines and plasma vasopressin in cardiovascular responses to intracisternal neurotoxins in the rabbit

We have examined the acute (0-3 h) effect of intracisternally administered 5,7-dihydroxytryptamine (DHT) and 6-hydroxydopamine (6-OHDA) on blood pressure, heart rate, renal nerve activity, plasma adrenaline, plasma noradrenaline and plasma vasopressin in conscious rabbits. The increase in blood pressure seen following 5,7-DHT treatment was associated with increases in adrenaline and vasopressin levels and renal nerve activity throughout the response. The increase in blood pressure which followed 6-OHDA administration was associated with an increase in renal nerve activity alone. These findings indicate that the rise in blood pressure elicited by these drugs involves an increase in sympathetic nerve activity. The absence of a rise in vasopressin levels during the response to 6-OHDA suggests that the rise in blood pressure seen in these animals is due entirely to a bulbospinal sympathoexcitatory pathway.