PDGF-β receptor expression and ventilatory acclimatization to hypoxia in the rat

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Abstract
Activation of platelet-derived growth factor-β (PDGF-β) receptors in the nucleus of the solitary tract (nTS) modulates the late phase of the acute hypoxic ventilatory response (HVR) in the rat. We hypothesized that temporal changes in PDGF-β receptor expression could underlie the ventilatory acclimatization to hypoxia (VAH). Normoxic ventilation was examined in adult Sprague-Dawley rats chronically exposed to 10% O2, and at 0, 1, 2, 7, and 14 days, Northern and Western blots of the dorsocaudal brain stem were performed for assessment of PDGF-β receptor expression. Although no significant changes in PDGF-β receptor mRNA occurred over time, marked attenuation of PDGF-β receptor protein became apparent after day 7 of hypoxic exposure. Such changes were significantly correlated with concomitant increases in normoxic ventilation, i.e., with VAH ( r: −0.56, P < 0.005). In addition, long-term administration of PDGF-BB in the nTS via osmotic pumps loaded with either PDGF-BB ( n = 8) or vehicle (Veh; n = 8) showed that although no significant changes in the magnitude of acute HVR occurred in Veh over time, the typical attenuation of HVR by PDGF-BB decreased over time. Furthermore, PDGF-BB microinjections did not attenuate HVR in acclimatized rats at 7 and 14 days of hypoxia ( n = 10). We conclude that decreased expression of PDGF-β receptors in the dorsocaudal brain stem correlates with the magnitude of VAH. We speculate that the decreased expression of PDGF-β receptors is mediated via internalization and degradation of the receptor rather than by transcriptional regulation.