Hindquarters vascular responses in chronically hypoxic rats.

AOKI, VINCENT S., AND SUMNER M. ROBINSON. Hindquarters vascular responses in chronically hypoxic rats. Am. J. Physiol. 217(3) : 661-665. 1969.-Following 6 weeks exposure to a hypoxic environment, vascular responsiveness of the rat to lumbar sympathetic nerve stimulation (NS) and intra-arterial injections of norepinephrine (NE), epinephrine (E), and tyramine (T) was studied by autoperfusion of the hindquarters. The erythrocytosis of chronically hypoxic rats necessitated exchange transfusion with normal rat plasma to reduce blood viscosity and, consequently, perfusion pressure to levels comparable to that of controls. Under these conditions, chronically hypoxic rats showed normal responses to NS and T and increased responses to NE and E, when compared to control rats. Norepinephrine content in gastrocnemius muscles was not appreciably lowered in hypoxic rats. It is suggested that newly opened vascular channels and possibly increased availability of adrenergic receptor sites may account for the heightened response to intraarterial norepinephrine and epinephrine in chronically hypoxic rats.