Abstract
Cerebral hypocapnic vasoconstriction is limited such that CBF no longer decreases when PaCO2 falls below 20-25 torr, presumably because tissue hypoxia resulting from hypoperfusion counteracts the CO2 induced vasoconstriction. This study examines the effect of theophylline (T), an adenosine receptor antagonist, on the CBF response to hypocapnia in newborn piglets. Twelve piglets (2-5) days, ventilated under 30% N2O anesthesia, were divided into two groups; one received T, 10 me/kg i.v. (n=5) while controls received saline (n=7). CBF (microspheres), blood gases, pH, and blood pressure were measured during baseline (PaCO2=40) and following sequential hyperventilation for 10 min, to PaCO2's of 31 (HV1), 23 (HV2), and 14 torr (HV3). In control pigs, CBF decreased from baseline (55±7) to 47±6 and 38±5 ml/min/100g during HV1 and HV2 with no further decrease at HV3, 38±5 ml/min/100g (mean±SEM). In T pigs, CBF decreased from 54±4 to 41±5 and 36±5 during HV1 and HV2 and decreased further to 28±4 ml/min/100g during HV3, p <0.01. T enhanced vasoconstriction at low PaCO2 in all brain regions. Additional studies in 6 piglets (α-chloralose), with a cranial window implanted over the left parietal lobe, examined the response of pial vessels to topical adenosine before and after T. Adenosine (10−5 M) caused 31% increase in pial vessel caliber, 151±21 μm (12 vessels) to 199±26 μm. T caused pial vasoconstriction (135±18 μm) but had no effect on adenosine-induced vasodilation (176±20 μn, 30%). These data show that T enhanced hypocapnic vasoconstriction at doses where cerebral vessel response to adenosine was not inhibited, suggesting that T acts by a mechanism other than adenosine receptor inhibition.
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Wagerle, L., Lawson, B. & Delivoria-Papadopoulos, M. 1714 EFFECT OF THEOPHYLLINE ON THE CEREBRAL BLOOD FLOW RESPONSE TO HYPOCAPNIA IN NEWBORN PIGLETS. Pediatr Res 19, 396 (1985). https://doi.org/10.1203/00006450-198504000-01732
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DOI: https://doi.org/10.1203/00006450-198504000-01732