Effect of interferon gamma on intrahepatic haemodynamics of the cirrhotic rat liver.

Sublethal injury of the liver with carbon tetrachloride (CCl4) induces the modulation of hepatic stellate cells to their myofibroblast (MFB) phenotype. Pretreatment or concomitant treatment with interferon gamma (IFNgamma) has been shown to inhibit this phenomenon. The aim of this study was to investigate the influence of IFNgamma treatment (50000 IU s.c. each day for 5 days) in rats with an established cirrhosis. Cirrhosis was induced with nine doses of CCl4. Comparison of biopsies before and after treatment with IFNgamma showed that the number of MFB present, identified by their alpha-smooth muscle actin immunoreactivity, was markedly reduced. Pressure-flow curves were constructed in isolated perfused liver preparations from IFNgamma-treated and saline-treated cirrhotic rats and analysed to obtain the extrapolated zero-flow intercept (Po, an index of hepatic vascular distensibility) and the vasodilator-induced change in resistance at a flow rate of 1 mL/min per g (deltaR1, an indication of the level of intrinsic vascular tone). In IFNgamma-treated rats, portal venous pressure measured in vivo was significantly reduced compared with controls (11.9+/-1.2 vs 16.0+/-0.5 mmHg, P< 0.05), Po was lower (2.03+/-0.18 vs 2.87+/-0.32 mmHg, P<0.05) and deltaR1 was decreased (0.39+/-0.15 vs 1.02+/-0.19 mmHg/mL per min per g, P< 0.05). The findings indicate that treatment with IFNgamma is effective in reducing MFB density in established CCl4-cirrhosis in the rat and results in a marked improvement in intrahepatic haemodynamics.

The effect of hepatocyte enlargement on the hemodynamic characteristics of the isolated perfused rat liver preparation.

The influence of hepatocyte enlargement on intrahepatic hemodynamics was assessed in the isolated perfused rat liver preparation (IPRL) using two experimental models: hypotonic liver cell swelling and phenobarbitone-induced hepatocyte hypertrophy. The analysis of pressure-flow data obtained from the portal vascular bed over a flow range of 0 to 70 mL/min in the presence of a maximally-effective concentration of the vasodilator agent papaverine hydrochloride (6 x 10(-4) mol/L) enabled the calculation of P0, an estimate of the pressure required to passively distend the intrahepatic vasculature, and Gmax, the maximal portal vascular conductance. By comparison with an isotonic perfusion medium (Krebs-Henseleit buffer [KH] containing 2.5% bovine serum albumin [BSA]), perfusion with a hypotonic medium induced a significant increase in mean hepatocyte cross-sectional area (H(A)) (590 +/- 21 vs. 324 +/- 23 microm(-2), p < .05), a fall in Gmax (0.39 +/- 0.08 vs. 2.02 +/- 0.18 mL/min/g/mm hg, P < .001), and an increase in P0 (2.96 +/- 0.38 vs. 1.58 +/- 0.07 mm hg, P < .001). Phenobarbitone administered in drinking water (0.5 g/L) over a period of 60 days also induced a significant degree of hepatocyte enlargement (HA, 510 +/- 29 microm2, P < .05). On day 7, portal pressure measured in vivo in this group was significantly elevated compared with untreated controls (10.5 +/- 0.3 vs. 8.4 +/- 0.2 mm hg, P < .001), while in the IPRL Gmax was reduced (0.48 +/- 0.01 mL/min/g/mm hg, P < .001), and P0 was increased (2.23 +/- 0.17 mm hg, P < .05). However, with continued phenobarbitone treatment portal pressure, Gmax and P0 returned toward control values. The results confirm that hepatocyte enlargement is associated with a significant disturbance of intrahepatic hemodynamics but also that some adaptation occurs if hepatocyte enlargement is sustained over a prolonged period of time.

Endothelin-induced vasoconstriction in isolated perfused liver preparations from normal and cirrhotic rats.

Isolated, perfused rat liver preparations (IPRL), obtained from rats with carbon tetrachloride-induced cirrhosis and normal controls, were used to investigate responses to the vasoactive peptide endothelin-1 (ET-1). The mean perfusion resistance (R) of cirrhotic IPRL was significantly greater than that of controls (2.63 +/- 0.24 vs 1.54 +/- 0.14 mmHg/mL per min per g; P < 0.01). Both control and cirrhotic IPRL demonstrated a concentration-related increase in resistance (delta R) in response to ET-1, with a minimum effective concentration of approximately 3 x 10(-11) mol/L. The EC50 (-log of the 50% effective concentration) was not significantly different between cirrhotic and control IPRL (8.48 +/- 0.19 and 8.79 +/- 0.11, respectively); however, the maximum response to ET-1 was significantly greater in cirrhotic preparations (R: 10.4 +/- 2.2 vs 4.4 +/- 0.5 mmHg/mL per min per g, P < 0.01; DR, 7.8 +/- 2.1 vs 2.8 +/- 0.4 mmHg/mL per min per g, P < 0.01). Following maximal stimulation by ET-1, the mean portal-hepatic venous pressure gradient at a physiological flow rate of 1 mL/min per g was approximately 90% greater across cirrhotic IPRL than that across normal IPRL (11.2 +/- 2.0 vs 5.9 +/- 0.9 mmHg, respectively; P < 0.05). These results support the hypothesis that endogenously released ET-1 has a significant influence on the portal vascular resistance of cirrhotic liver in vivo and has an important role in the pathogenesis of portal hypertension.

Predictors of mortality in children with severe mental retardation: the effect of placement.

OBJECTIVES: This study was undertaken to assess the predictors of mortality in severely disabled children with mental retardation, and to compare risk-adjusted mortality rates for those living in institutions with rates for those living in the community. METHODS: Statistical analysis was performed on a set of 24,469 person-years, derived from a population of all children with severe mental retardation and a fragile medical condition who are registered with the California Department of Developmental Services. Variables included age, several measures of mobility, the presence or absence of tube feeding, the level of retardation, and certain adaptive skills. RESULTS: Reduced mobility and the use of tube feeding were associated with a large increase in mortality risk. Own home residence and community care facilities have an estimated 25% higher risk-adjusted odds on mortality than institutions and health facilities. CONCLUSIONS: The differential mortality in the placements points to a possible effect of quality of care. One consequence of the current trend toward deinstitutionalization may be an increased mortality rate in children with severe developmental disability.

Effect of changes in vascular tone on the haemodynamic characteristics of the portal vascular bed of the isolated perfused rat liver.

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.

Hemodynamic characteristics of the intrahepatic portal vascular bed over an extended flow range: a study in the isolated perfused rat liver.

The relationship between the perfusion pressure (P) and resistance (R) of the intrahepatic portal vascular bed was determined in isolated rat liver preparations perfused with fresh, heparinized rat blood (hematocrit 30%), with rat blood containing a vasodilator agent (sodium nitroprusside, 1 X 10(-3) mol/L), or with 2.5% bovine serum albumin in Krebs-Henseleit buffer (BSA-KH). Pressure-flow curves were constructed over an extended range of portal venous inflow (0 to 70 mL.min-1, corresponding to a flow rate per gram liver wet weight, Q, of approximately 0 to 7 mL.min-1.g-1). Subsequent analysis showed that two mathematical expressions adequately described the data over the full range of flow. Thus, the pressure-flow curve could be represented by (a) the sum of a linear plus a hyperbolic function, i.e., P = Q.R' + Pmax.Q/(Q + Km), where R', Pmax, and Km are constants, or (b) by the simple equation G = C.P, where G is the conductance (Q/P), and C is a conductivity constant. The values of R', Pmax, Km, and C were significantly different under each of the circumstances investigated, but the form of the curve was not altered. Hence, it is proposed that these parameters can be used to describe the fundamental hemodynamic properties of the portal vascular bed of the isolated rat liver. The results are discussed in terms of the microvascular recruitment and distensible resistance vessel models of the hepatic microcirculation.

Survival of profoundly disabled people with severe mental retardation.

OBJECTIVE: To define further the association between survival and clinical disabilities in profoundly disabled people with mental retardation in an 11-year period. RESEARCH DESIGN: An 11-year follow-up study of the survival of six mutually exclusive subgroups. The presence of severe, profound, or suspected mental retardation and incontinence were considered in all individuals when forming the subgroups. Varying combinations of abilities in mobility, rolling, feeding, and arm-hand use were also considered. PARTICIPANTS: Six subgroups of severely disabled subjects. Included were 128,248 of 155,851 persons who received services from the California Department of Developmental Services between January 1980 and March 1991. MEASUREMENTS/MAIN RESULTS: Survival estimates for individuals who were immobile and could not roll over were short regardless of arm-hand use or feeding status, as were estimates for people who were tube fed. For individuals who could roll over, but were otherwise immobile, survival was relatively improved. CONCLUSION: Individuals who are unable to move their extremities or bodies voluntarily or who require tube feeding have very shortened life expectancies.

Mortality and the acquisition of basic skills by children and adults with severe disabilities.

OBJECTIVE: To determine normative data on age-related probabilities of children with severe disabilities acquiring mobility or self-feeding skills, or dying during a 5-year follow-up period. RESEARCH DESIGN: A 5-year follow-up study of three mutually exclusive subgroups formed on the basis of severe, profound, or suspected levels of retardation and incontinence and the following combinations of feeding and mobility skills. PARTICIPANTS: The sample was made up of 7836 children and adults distributed among the three subgroups being served in California between January 1981 and December 1985. MEASUREMENTS/MAIN RESULTS: Subjects who were tube-fed and immobile showed very little likelihood of becoming mobile or feeding themselves and had a high probability of death. Individuals who had some mobility experienced a better outcome. CONCLUSIONS: After age 6 years, the most probable outcome for children who are immobile and cannot feed themselves is death or no improvement in self-help skills.

Enhanced vasoconstrictor response of the isolated perfused cirrhotic rat liver to humoral vasoconstrictor substances found in portal venous blood.

Humoral vasoconstrictor factors in portal venous blood have an important influence on hepatic vascular tone. The aim of this study was to determine whether there is altered reactivity of the intrahepatic portal vascular bed of cirrhotic livers to such factors. Isolated perfused rat liver preparations (IPRLP) obtained from rats with carbon tetrachloride-induced cirrhosis and from normal controls were treated with small aliquots of fresh, heparinized venous blood (4% vol/vol) added to a synthetic perfusate composed of 2.5% bovine serum albumin in Krebs-Henseleit buffer. Compared with blood from the inferior vena cava, portal venous blood produced a greater increase in perfusion resistance of normal IPRLP (2.8 +/- 0.7 vs 15 +/- 3%, P less than 0.05). There was no significant difference in the response of normal IPRLP to portal venous blood obtained from cirrhotic animals compared with portal blood from normal controls (10 +/- 4 vs 15 +/- 3%). However, cirrhotic IPRLP were significantly (P less than 0.05) more responsive to portal venous blood than were control livers, regardless of whether the blood was obtained from control (28 +/- 6%) or cirrhotic (24 +/- 6%) rats. The response of both control and cirrhotic IPRLP to portal blood could be partially inhibited by the alpha-adrenoceptor antagonist phentolamine (5 x 10(-6) mol/L) and cirrhotic IPRLP were more responsive than controls to exogenous noradrenaline (518 +/- 27 vs 363 +/- 21%, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

The life expectancy of profoundly handicapped people with mental retardation.

BACKGROUND: The life expectancy of people with mental retardation is shorter than that of the general population. Exact estimates of the length of survival for mentally retarded persons at especially high risk are not available, however. METHODS: We collected data on mortality and other factors for 99,543 persons with developmental disabilities, including mental retardation, who received services from the California Department of Developmental Services between March 1984 and October 1987. Three subgroups were selected on the basis of the four characteristics identified in previous studies as the best predictors of mortality among mentally retarded people (deficits in cognitive function, limitations on mobility, incontinence, and inability to eat without assistance). In all three subgroups, the subjects had severe deficits in cognitive function and were incontinent; the subjects in subgroup 1 (n = 1550) were immobile and required tube feeding; those in subgroup 2 (n = 4513) were immobile but could eat with assistance; those in subgroup 3 (n = 997) were mobile (but not ambulatory) and could eat with assistance. Life tables were generated for each of the three subgroups. RESULTS: Immobile subjects were found to have a much shorter life expectancy than those who could move about. Those who also required tube feeding (subgroup 1) had a very short life expectancy (i.e., four to five additional years). Those who could eat if fed by others (subgroup 2) had an average life expectancy of approximately eight additional years. In contrast, those who were mobile though not ambulatory (subgroup 3) had a life expectancy of about 23 additional years. CONCLUSIONS: Severe mental retardation is associated with a decrease in life expectancy, particularly for those who were immobile.

Leucocyte-induced endothelium-dependent vasodilatation and post-ischaemic vasospasm in the isolated rat superior mesenteric artery.

The purpose of this study was to investigate the possible role of leucocytes in the pathogenesis of reperfusion-induced vasospasm of ischaemic mesenteric arteries. Scanning electron microscopy of the rat superior mesenteric artery (SMA) after 30 min of ischaemia in vivo revealed adherence of leucocytes to the vessel wall. Isolated SMA preparations were perfused with Krebs-Henseleit buffer containing noradrenaline. Infusion of homologous leucocytes resuspended in perfusate (3 x 10(6) cells/ml) into these preconstricted preparations caused a fall in resistance of 29 +/- 2%. Removal of the endothelium by collagenase treatment abolished this response. Indeed, leucocyte infusion caused an increase in resistance of 39 +/- 8% under these circumstances. Following 30 min of normothermic ischaemia, leucocyte infusion caused a transient vasodilatation of 31 +/- 4% followed by an increase of 38 +/- 11% in the perfusion resistance of isolated SMA preparations. In each case, a similar response was obtained to infusion of the cell-free supernatant. These results suggest that leucocyte activation occurs in vivo during reperfusion of the SMA after as little as 30 min of ischaemia, and that activated leucocytes can release humoral vasoactive factors which evoke an endothelium-dependent vasodilator response in normal vessels but a predominantly vasoconstrictor response following brief intervals of ischaemia.

Effect of ischaemia on endothelium-dependent vasodilatation in the isolated rat superior mesenteric artery.

The isolated perfused rat superior mesenteric artery preparation was used to determine whether endothelium-dependent vasodilatation occurs in this vessel, and to test whether impairment of this function may contribute to post-ischaemic mesenteric vasospasm. It was found that vessels preconstricted with noradrenaline responded to optimal concentrations of acetylcholine (3 X 10(-5) M), ADP (2 X 10(-5) M) and to isolated homologous platelets (500,000/mm3) with an 84%, 85% and 37% decrease in mean perfusion resistance, respectively. In preparations treated with collagenase to denude the vessels of endothelium there was a significantly diminished response to acetylcholine and ADP (24% & 23% decrease in resistance, respectively). Platelets, on the other hand, caused a further 34% increase in resistance. A model of mesenteric ischaemia was produced by interrupting perfusate flow through the preparation for intervals of 1 to 4 h. This was associated with morphological evidence of endothelial cell damage and with a progressive decline in the responsiveness to acetylcholine and ADP. After 1 h there was also a significant reduction in the response to platelets. With intervals of ischaemia longer than 2 h platelets caused only further constriction which could be inhibited by the serotonin antagonist, methysergide. This study suggests that an altered response of the endothelium to platelet-derived vasoactive substances may contribute to the post-ischaemic vasospasm encountered during reperfusion.

Reduction of the increased portal vascular resistance of the isolated perfused cirrhotic rat liver by vasodilators.

This study was undertaken to compare the in vitro responses of the portal vascular bed of normal and cirrhotic rat livers to a variety of vasodilator agents. Using carbon tetrachloride-induced cirrhosis in the rat as a model, isolated liver preparations were perfused via the portal vein with a synthetic medium (2.5% bovine serum albumin in Krebs-Henseleit buffer) to eliminate extrahepatic neural and humoral influences. Under these experimental conditions the mean perfusion resistance of the cirrhotic livers was approximately 117% higher than in controls (P less than 0.001). The vascular tone of the normal liver was minimal as assessed by the response to a variety of vasodilator agents, including sodium nitroprusside (3.0 X 10(-3) M), magnesium sulphate (6.0 X 10(-2) M), papaverine hydrochloride (6.4 X 10(-4) M), and cytochalasin B (6.3 X 10(-5) M). In contrast, these agents reduced the perfusion resistance of the cirrhotic livers by approximately 15%. Prostaglandin E1 (3.0 X 10(-6) M) and isoprenaline hydrochloride (2.4 X 10(-6) M) produced a lesser fall in resistance which nevertheless was greater in cirrhotic livers than controls. Cirrhotic livers, unlike the controls, were found to contain large numbers of myofibroblasts in perivenous and perisinusoidal locations. Previous studies have shown that myofibroblasts are capable of sustaining a high level of intrinsic tone and relax in response to vasodilator agents. It is concluded that part of the increased resistance to flow through the portal vascular bed of the cirrhotic rat liver in vitro is due to an increase in intrinsic vascular tone, possibly mediated via myofibroblasts, and can be reversed by pharmacological agents.

Application of the isolated perfused rat liver preparation to pharmacological studies of the intrahepatic portal vascular bed.

A method is described for the perfusion of the isolated rat liver preparation which is particularly suited to a selective pharmacological study of the portal vascular bed of the liver. A synthetic medium free of vasoactive substances and composed of 2.5% bovine serum albumin in Krebs-Henseleit buffer is pumped into the portal vein at a controlled rate while the perfusion pressure is recorded electronically. The advantages of this technique are that while the viability of the isolated organ is preserved, the preparation remains haemodynamically stable and the response to vasoactive agents can be accurately and reproducibly determined. The constant perfusate flow also allows cumulative dose-response curves to be constructed, even for powerful vasoconstrictor agents. The present perfusion method has also been validated by comparing the responses obtained from a variety of vasoactive substances with those reported in other in vivo studies.