Pressure-flow autoregulation, although weak, was seen in the hepatic artery (HA) of every cat that also showed dilation to infused adenosine. Several means of quantitating autoregulation are described and evaluated, and all indices showed that the selective adenosine antagonists, 8-phenyltheophylline and 8-(p-sulfophenyl)theophylline, inhibited autoregulation as well as the vasodilator response to exogenous adenosine and the hepatic arterial buffer response (HABR; vasodilation of HA in response to reduced portal flow). The mechanism of HABR is proposed to be dependent on washout of locally produced adenosine into portal blood; reduced portal flow causes adenosine accumulation and dilation of HA. The present data suggest that local levels of adenosine can also be washed into HA blood so that reduced arterial flow will also lead to raised adenosine levels and arterial vasodilation. Thus the mechanisms of the HABR and HA pressure-flow autoregulation are suggested to be the same, i.e., washout of locally produced adenosine, probably from the space of Mall just prior to entry of the vessels into sinusoids.
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