Neural effects of systemic hypoxia on hindlimb vascular resistance in sinoaortic-denervated cats.
The effects of systemic hypoxia on the neurogenic component of hindlimb vascular resistance were studied in six sinoaortic-denervated, anesthetized cats with intact central nervous system. Hindlimb perfusion pressure (PP) was measured under conditions of constant flow of normoxic blood from a donor cat. The neural component of the PP was estimated from the change in PP upon administration of hexamethonium (10 mg/kg i.v.). Ventilation of the recipient cat with 12.5% and 10% O2 was associated with an average 35 +/- 15% (SEM) and 13 +/- 10% decrease, respectively, of the estimated neural component of the PP. In contrast ventilation with 7.5% and 5% O2 produced increases of 27 +/- 7% and 58 +/- 10%, respectively, of the estimated neural component of the PP. Both the vasodilator and vasoconstrictor responses were abolished by hexamethonium (10 mg/kg i.v.). The vasodilator response appeared to be due to withdrawal of alpha-adrenergic tone since it was eliminated by constant infusion of phentolamine to the hindlimb (45 micrograms/ml blood/min). We conclude that, in addition to the already known sympatho-excitation seen in the sinoaortic-denervated cat during severe systemic hypoxia, there is also a sympatho-depressant effect which dominates at more moderate levels of systemic hypoxia.
D000818:Animals; D001011:Aorta / Q000294:innervation*; D002346:Carotid Sinus / Q000294:innervation*; D002415:Cats; D003714:Denervation; D005260:Female; D006614:Hindlimb / Q000098:blood supply*; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D009420:Nervous System / Q000503:physiopathology*; D014630:Vagus Nerve / Q000503:physiopathology; D014655:Vascular Resistance; D014661:Vasoconstriction; D014664:Vasodilation