CARDIORESPIRATORY RESPONSES OF NORMOTENSI VE (WKY) AND SPONTANEOUSLY HYPERTENSIVE (SHR) RATS TO HYPEROXIA AND NONHYPOTENSIVE HEMORRHAGE COMBINED

In 17 normotensive Wistar-Kyoto-rats (WKY) and in 18 spontaneously hyp ertensive rats (SHR) of the Okamoto-Aoki-strain in chloralose-urethan anesthesia the parameters of the arterial acid-base balance and extern al ventilation as well as heart rate and mean systemic arterial pressu re were measured in normoxia and during breathing 60% O-2 in N-2. An i ncrease of mean arterial pressure in response to hyperoxia was prevent ed by removing blood from the animals circulation. Both groups respond ed to the combined hyperoxia and blood loss with a rise in arterial pO (2) and pCO(2). Hyperoxia depressed external ventilation only initiall y and transiently. To prevent a rise in mean arterial blood pressure i n response to oxygen breathing in the SHR maximally 0.31 +/- 0.05 ml a nd in the WKY 0.57 +/- 0.11 mi blood per 100 g body weight had to be r emoved. The data suggest that the benefit effects of breathing oxygen during and/or after hemorrhage result, at least partly, from both arte riolar vasoconstriction and an increase of the overall tone of the ven ous or capacitance vessels, respectively. The reasons for the weaker r esponse of the venous wall of the SHR to oxygen are unknown.