AJP - Regulatory, Integrative and Comparative Physiology, Vol 242, Issue 5 441-R446, Copyright © 1982 by American Physiological Society
Reduction of cerebrovascular reactivity during hypercapnia
A. L. Lopez de Pablo, M. C. Gonzalez, G. Dieguez, B. Gomez and S. Lluch
The effects on cerebral blood flow of alpha- or beta-adrenergic receptor
stimulation of cerebral vessels were examined in 13 unanesthetized goats
before and during hypercapnia produced by inhalation of 10% CO2 in air.
This procedure increased the PCO2 from 34 to 52 and was accompanied by a
fall in pH from 7.39 to 7.26. Electrical stimulation of the cervical
sympathetic nerve and injections of norepinephrine and tyramine into the
internal maxillary artery produced reductions in cerebral blood flow that
were abolished or reduced in hypercapnia. The increase in cerebral blood
flow in response to beta-adrenergic stimulation with isoproterenol was also
reduced. Hypercapnia caused a similar depression of the constrictor and
dilatory effects of the nonadrenergic drugs vasopressin and diazoxide. The
results show a decreased response of cerebral vessels to adrenergic and
nonadrenergic stimuli in hypercapnia. The findings do not suggest any
difference between the refractoriness of cerebral vessels in hypercapnia
and that described in other vascular beds.
