Intrahepatic portal occlusion by microspheres: a new model of portal hypertension in the rat.

Abstract

.4 mm Hg increase from basal), which declined gradually to a steady state pressure of 13-3-15*1 mm Hg (4-0-5.0 mm Hg increase). There was no significant difference between pressure increases produced by microspheres of differing sizes. It is concluded that portal hypertension can be produced acutely by blocking portal radicles with microspheres. The maximum pressure achieved, however, is substantially less than that obtained by total portal vein occlusion (mean: 57 6 mm Hg). This suggests the existence of functional intrahepatic portal systemic shunts not previously described in the normal liver.

Hepatic arterial perfusion regulates portal venous flow between hepatic sinusoids and intrahepatic shunts in the normal rat liver in vitro

“…In all instances, a rapid, dramatic increase in hepatic arterial perfusion pressure was observed that exceeded the venous pressure elicited by intraportal injections of latex microspheres [18,22]. The failure of the portal venous pressure to rise, following portal venous microsphere injections, to values comparable to those achieved by total extrahepatic portal venous occlusion is also attributable to intrahepatic shunting [18]. The data from the present study corroborate our earlier studies and further suggest that sustained increases in transhepatic portal resistance, induced either by portal venous injection of microspheres or diversion of hepatic arterial flow, may be the driving stimulus for the opening of intrahepatic shunts.…”

“…To ascertain whether the hepatic arterial circulation also possessed intrahepatic shunts, the identical number of 15-µm latex microspheres was injected into the cannula entering the hepatic arterial vasculature in three separate experiments. In all instances, a rapid, dramatic increase in hepatic arterial perfusion pressure was observed that exceeded the venous pressure elicited by intraportal injections of latex microspheres [18,22]. The failure of the portal venous pressure to rise, following portal venous microsphere injections, to values comparable to those achieved by total extrahepatic portal venous occlusion is also attributable to intrahepatic shunting [18].…”

“…Latex microspheres were suspended in Krebs' buffer at 37°C and numbers per sample counted using an electronic counter (model ZBI, Coulter) prior to injection, having previously been accurately confirmed for size (15-µm diameter) using a Coulter Channelizer as described previously [18,22]. The stock solution was diluted in Krebs' buffer to yield 2.5×10 7 microspheres/100 µl.…”

“…However, intrahepatic shunting of portal venous blood is also a complication of portal hypertension and is characterised by entry of essentially unprocessed portal venous blood into the systemic circulation via intrahepatic routes [20,23,24]. The existence of intrahepatic shunts in the cirrhotic human or rat [26], and to a lesser degree in the normal rat [17,18,22] liver is now recognised. It is uncertain whether portal hypertension is due to increased portal resistance, or to a hyperdynamic splanchnic circulation [1].…”

“…It is uncertain whether portal hypertension is due to increased portal resistance, or to a hyperdynamic splanchnic circulation [1]. In both cases, intrahepatic shunts are presumed to play an important role in alleviating raised portal pressure [18,22]; yet the shunting process fails to relieve or compensate the underlying condition. The reasons for this failure to compensate are unknown and, consequently, the conditions under which these shunts become operative remain to be fully elucidated.…”