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Constance S. Kaufman Pediatric Pulmonary Research Laboratory, Departments of Pediatrics and Physiology, Interdepartmental Neuroscience and Molecular and Cellular Biology Training Programs, Tulane University School of Medicine, New Orleans, Louisiana 70112
Platelet-activating factor receptor (PAFR) activation is
associated with increases in neuronal excitability. We hypothesized that PAF may play a role in cardiorespiratory control. Ventilatory responses to microinjection of a long-acting PAF analog
(mc-PAF, 1 µg in 1 µl) within the
dorsocaudal brain stem were measured in unrestrained adult rats.
mc-PAF elicited significant minute ventilation (
E) enhancements that were
primarily due to tidal volume increases and were accompanied by
respiratory alkalosis, heart rate increase, and reduction of arterial
blood pressure. Such cardiovascular and respiratory effects did not
occur after administration of either vehicle or the inactive analog
lyso-PAF. The effect was blocked when animals were coadministered the
presynaptic PAFR antagonist BN-52021 or recombinant PAF acetyl
hydrolase. To determine the relative contribution of PAF to hypercapnic
and hypoxic ventilation, microinjections were performed in additional animals with either vehicle (CO, 1 µl) or with 5 µg in 1 µl of BN-52021. Hypercapnic challenges with 5%
CO2 were unaffected by BN-52021.
In contrast, although 10% O2
breathing increased
E from
120.4 ± 7.5 to 204.6 ± 11.4 ml/min in CO, after
BN-52021,
E increased only from 118.7 ± 6.9 to 137.3 ± 8.9 ml/min (CO vs. BN-52021,
P < 0.001). We conclude that PAFR
activation in the dorsocaudal brain stem exerts significant
cardioventilatory effects during normoxia and appears to play an
important modulatory role in the
E
response to hypoxia in conscious rats.
respiratory control; brain stem; hypoxia; hypercapnia; blood pressure; heart rate
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