AJP - Heart and Circulatory Physiology, Vol 248, Issue 1 98-108, Copyright © 1985 by American Physiological Society
Regional blood flow distribution during the Cushing response: alterations with adrenergic blockade
D. G. van Wylen and L. G. D'Alecy
Regional blood flow distribution (microspheres) and cardiac output (CO,
thermal dilution) were measured during the Cushing response in unblocked
(UB), beta-receptor-blocked (BB, 2 mg/kg propranolol iv), or alpha-receptor
blocked (AB, 0.5 mg/kg + 0.5 mg X kg-1 X min-1 phentolamine iv)
chloralose-anesthetized dogs. Intracranial pressure was increased to 150
mmHg by infusion of temperature-controlled artificial cerebrospinal fluid
into the cisterna magna. Similar increases in mean arterial pressure were
seen in UB and BB, but in AB a Cushing response could not be sustained. In
UB, cerebral blood flow (CBF) decreased 50%, coronary blood flow (CoBF)
increased 120%, and peripheral tissue blood flow was reduced only in the
kidneys (18%) and the intestines (small 22%, large 35%). Blood flow to the
other viscera, skin, and skeletal muscle was unchanged. CO (16%) and heart
rate (HR, 38%) decreased, and total peripheral resistance (TPR, 68%) and
stroke volume (SV, 38%) increased. In BB, CBF decreased 50%, CoBF decreased
20%, and blood flow was reduced 40-80% in all peripheral tissues. CO (69%)
and HR (62%) decreased, TPR increased 366%, and SV was unchanged. We
conclude that the Cushing response in UB animals combines an
alpha-receptor-mediated vasoconstriction with a beta-receptor cardiac
stimulation. The beta-mechanism is neither necessary nor sufficient for the
hypertension. However, the combination of alpha- and beta-adrenergic
mechanisms maintains cardiac output and peripheral tissue blood flow
relatively constant while producing a systemic hypertension.
