The effect of angiotensin and vasopressin blockade separately and in combination with cerebellectomy on recovery from hemorrhagic hypotension

We demonstrated previously that cerebellectomy or ablation of the fastigial nuclei (FN) in the dog impairs markedly the restoration of blood pressure and increases the death rate after severe hypotension. Angiotensin (AII) and vasopressin (AVP) participate in the pressor response to hypotension, and plasma levels of both are increased by electrical stimulation of the FN. The present studies examined the importance of the FN in mediating the secretion of AII and AVP after hemorrhage to 50 mm Hg. Cerebellectomy reduced significantly both the rate of recovery and level of maintenance of blood pressure after hemorrhage. Blockade of conversion of AI to AII with captopril produced a similar deficit, and combination of both treatments produced a greater impairment than either alone. Treatment with an AVP antagonist decreased the level of maintenance of blood pressure but not the initial rate of recovery. The AVP antagonist in combination with cerebellectomy did not produce a greater deficit than cerebellectomy alone. This would suggest that although the cerebellum mediates some activation of the renin-angiotensin system during severe hypotension, it may mediate most of the AVP secretion under these conditions.