Abstract
The effect of altered vascular tone on the haemodynamic characteristics of the intrahepatic portal vascular bed was studied in the isolated perfused rat liver preparation. The relationship between portal venous inflow (Q) and portal perfusion pressure (P) was determined in the presence of a maximally effective concentration of a vasoconstrictor agent (noradrenaline, NAmax, 3 x 10(-5)mol/L), an intermediate concentration (NAmed, 1 x 10(-6)mol/L) or a vasodilator agent (papaverine, PAP, 6 x 10(-4)mol/L). At flow rates greater than 20 mL/min, the pressure-flow relationship could be regarded as linear (P < 0.001), with mean values for the extrapolated intercept with the pressure axis (Po) of 6.8 +/- 0.9 mmHg for NAmax, 4.5 +/- 0.5 mmHg for NAmed, and 1.65 +/- 0.05 mmHg for PAP-treated preparations. Over the full flow range (0-70 mL/min), in both NA- and PAP-treated preparations, portal vascular conductance (G = Q/P) was related directly to perfusion pressure. Thus, G = C.P, where C is a constant (mean values for NAmax, NAmed, and PAP-treated preparations were 0.0090 +/- 0.0020, 0.023 +/- 0.005, and 0.26 +/- 0.02 mL/min per g per mmHg2, respectively). It is concluded that both C and Po may be useful indices of tone in the isolated perfused rat liver, and that analysis of hepatic portal haemodynamics in this manner may have considerable practical value in studies of the action of vasoactive agents.
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