Components of the hemodynamic response to elevated cerebrospinal fluid pressure

The cardiovascular effects of elevated cerebrospinal fluid (CSF) pressure were studied in adrenalectomized dogs with and without ganglionic blockade. A significant increase in vascular pressures and cardiac output occurred in those without ganglionic blockade but was absent or markedly blunted in those with ganglionic blockade. This indicated that an intact sympathetic nervous system was required for the pressor response to elevated cerebrospinal fluid pressure but the adrenals were not required. A betaadrenergic effect was noted in dogs with ganglionic blockade and adrenalectomy. The effects of elevated CSF pressure were also studied using a perfused gracilis muscle preparation in 12 animals with beta-adrenergic blockade, with and without adrenalectomy. Animals with intact adrenals and denervated gracilis muscle showed an increase in aortic pressure and gracilis muscle resistance. Adrenalectomized animals with innervated gracilis muscle demonstrated an increase in aortic pressure and gracilis muscle resistance. Elevated CSF pressure with intact adrenals and alpha-adrenergic blockade demonstrated a decrease in aortic pressure but no change in gracilis muscle resistance. The presence of a nonadrenal circulating beta agonist that increases cardiac output and decrease peripheral vascular resistance is indicated by these studies. Also, the Cushing reflex involves an adrenal alpha-adrenergic component affecting skeletal muscle resistance and another alpha-adrenergic component dependent on an intact sympathetic nervous system.