EFFECT OF CHANGES IN VASCULAR TONE ON THE HEMODYNAMIC CHARACTERISTICSOF THE PORTAL VASCULAR BED OF THE ISOLATED-PERFUSED RAT-LIVER

The effect of altered vascular tone on the haemodynamic characteristic s 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 pr esence of a maximally effective concentration of a vasoconstrictor age nt (noradrenaline, NA(max), 3 x 10(-5)mol/L), an intermediate concentr ation (NA(max), 1x10(-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 (P-0) of 6.8 +/- 0.9 mmHg for NA(max), 4.5 +/- 0.5 mmHg for NA(med), 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. Thu s, G = C.P, where C is a constant (mean values for NA(max), NA(med) an d PAP-treated preparations were 0.0090 +/- 0.0020, 0.023 +/- 0.005, an d 0.26 +/- 0.02 mL/min per g per mmHg(2), respectively). It is conclud ed that both C and P-0 may be useful indices of tone in the isolated p erfused rat liver, and that analysis of hepatic portal haemodynamics i n this manner may have considerable practical value in studies of the action of vasoactive agents.