Changes in dopamine D(2)-receptor modulation of the hypoxic ventilatory response with chronic hypoxia.

Modulation of the hypoxic ventilatory response (HVR) by dopamine D(2)-receptors (D(2)-R) in the carotid body (CB) and central nervous system (CNS) are hypothesized to contribute to ventilatory acclimatization to hypoxia. We tested this with blockade of D(2)-R in the CB or CNS in conscious rats after 0, 2 and 8 days of hypoxia. On day 0, CB D(2)-R blockade significantly increased VI and frequency (fR) in hyperoxia (FI(O(2))=0.30), but not hypoxia (FI(O(2))=0.10). CNS D(2)-R blockade significantly decreased fR in hypoxia only. On day 2, neither CB nor CNS D(2)-R blockade affected VI or fR. On day 8, CB D(2)-R blockade significantly increased hypoxic VI and fR. CNS D(2)-R blockade significantly decreased hypoxic VI and fR. CB and CNS D(2)-R modulation of the HVR decreased after 2 days of hypoxia, but reappeared after 8 days. Changes in the opposing effects of CB and CNS D(2)-R on the HVR during chronic hypoxia cannot completely explain ventilatory acclimatization in rats.