Structural and functional changes in rat portal veins after experimental portal hypertension

Stretch-dependent smooth muscle differentiation in the portal vein-role of actin polymerization, calcium signaling, and microRNAs

The mechanical forces acting on SMC in the vascular wall are known to regulate processes such as vascular remodeling and contractile differentiation. However, investigations to elucidate the underlying mechanisms of mechanotransduction in smooth muscle have been hampered by technical limitations associated with mechanical studies on pressurized small arteries, due primarily to the small amount of available tissue. The murine portal vein is a relatively large vessel showing myogenic tone that in many respects recapitulates the properties of small resistance vessels. Studies on stretched portal veins to elucidate mechanisms of mechanotransduction in the vascular wall have shown that stretch-sensitive regulation of contractile differentiation is mediated via Rho-activation and actin polymerization, while stretch-induced growth is regulated by the MAPK pathway. In this review, we have summarized findings on mechanotransduction in the portal vein with focus on stretch-induced contractile differentiation and the role of calcium, actin polymerization and miRNAs in this response.

Distinct effects of voltage- and store-dependent calcium influx on stretch-induced differentiation and growth in vascular smooth muscle

Stretch of the vascular wall stimulates smooth muscle hypertrophy by activating the MAPK and Rho/Rho kinase (ROK) pathways. We investigated the role of calcium in this response. Stretch-stimulated expression of contractile and cytoskeletal proteins in mouse portal vein was inhibited at mRNA and protein levels by blockade of voltage-dependent Ca(2+) entry (VDCE). In contrast, blockade of store-operated Ca(2+) entry (SOCE) did not affect smooth muscle marker expression but decreased global protein synthesis. Activation of VDCE caused membrane translocation of RhoA followed by phosphorylation of its downstream effectors LIMK-2 and cofilin-2. Stretch-activated cofilin-2 phosphorylation depended on VDCE but not on SOCE. VDCE was associated with increased mRNA expression of myocardin, myocyte enhancer factor (MEF) -2A and -2D, and smooth muscle marker genes, all of which depended on ROK activity. SOCE increased ERK1/2 phosphorylation and c-Fos expression but had no effect on phosphorylation of LIMK-2 and cofilin-2 or on myocardin and MEF2 expression. Knockdown of MEF2A or -2D eliminated the VDCE-induced activation of myocardin expression and increased basal c-Jun and c-Fos mRNA levels. These results indicate that MEF2 mediates VDCE-dependent stimulation of myocardin expression via the Rho/ROK pathway. In addition, SOCE activates the expression of immediate-early genes, known to be regulated by MEF2 via Ca(2+)-dependent phosphorylation of histone deacetylases, but this mode of Ca(2+) entry does not affect the Rho/ROK pathway. Compartmentation of Ca(2+) entry pathways appears as one mechanism whereby extracellular and membrane signals influence smooth muscle phenotype regulation, with MEF2 as a focal point.

Evolutive phases of experimental prehepatic portal hypertension

Partial portal vein ligation is the experimental model most frequently used to study prehepatic portal hypertension. Different systemic and splanchnic biochemical and histological alterations in short-term (28-45 days) and long-term (12-14 months) evolutive phases which has been described in this experimental model suggest the existence of different pathophysiological mechanisms involved in their production. The enteropathy produced could develop in three phases: an early or acute phase with vasomotor hemodynamic alterations (ischemia-reperfusion associated with intestinal hyperemia, edema and oxidative stress); an intermediate phase with immunological alterations (mesenteric lymphadenopathy, increased mucosal infiltration by mast cells and the hepato-intestinal release of pro- and anti-inflammatory mediators); and a late or chronic phase with intestinal remodeling (vascular and epithelial). The alterations which are produced in these three evolutive phases make it possible to propose an inflammatory etiopathogeny for hypertensive portal enteropathy.

Stretch-dependent growth and differentiation in vascular smooth muscle: role of the actin cytoskeleton

The smooth muscle cells in the vascular wall are constantly exposed to distending forces from the intraluminal pressure. A rise in blood pressure triggers growth of the vessel wall, which is characterized primarily by hypertrophy of smooth muscle cells with maintained differentiation in a contractile phenotype. Growth factor stimulation of dissociated smooth muscle cells, on the other hand, causes proliferative growth with loss of contractility. This type of response is also found in neointima development following angioplasty and in atherosclerotic lesions. An intact tissue environment is therefore critical for preserved differentiation. Recent advances point to a role of actin polymerization in the expression of smooth muscle differentiation marker genes, in concert with serum response factor (SRF) and cofactors, such as myocardin. Stretch of intact venous smooth muscle activates Rho and inhibits the actin filament severing factor cofilin, resulting in increased actin polymerization. Concomitantly, the rates of synthesis of SRF-regulated differentiation markers, such as SM22α, calponin, and α-actin, are increased. This increase in differentiation signals is parallel with activation of the mitogen-activated protein (MAP) kinase pathway. Thus stretch-induced growth in a maintained contractile phenotype occurs by dual activation of signal pathways regulating both growth and differentiation. A current challenge is to identify sites of crosstalk between these pathways in intact smooth muscle tissue.Key words: stretch, hypertension, ERK, Rho, caveolae.

Stretch-induced contractile differentiation of vascular smooth muscle: sensitivity to actin polymerization inhibitors

Signaling mechanisms for stretch-dependent growth and differentiation of vascular smooth muscle were investigated in mechanically loaded rat portal veins in organ culture. Stretch-dependent protein synthesis was found to depend on endogenous release of angiotensin II. Autoradiography after [(35)S]methionine incorporation revealed stretch-dependent synthesis of several proteins, of which SM22 and actin were particularly prominent. Inhibition of RhoA activity by cell-permeant C3 toxin increased tissue mechanical compliance and reduced stretch-dependent extracellular signal-regulated kinase (ERK)1/2 activation, growth, and synthesis of actin and SM22, suggesting a role of the actin cytoskeleton. In contrast, inhibition of Rho-associated kinase by Y-27632 did not reduce ERK1/2 phosphorylation or actin and SM22 synthesis and did not affect tissue mechanical compliance but still inhibited overall growth. The actin polymerization inhibitors latrunculin B and cytochalasin D both inhibited growth and caused increased tissue compliance. Whereas latrunculin B concentration-dependently reduced actin and SM22 synthesis, cytochalasin D did so at low (10(-8) M) but not at high (10(-6) M) concentration. The results show that stretch stabilizes the contractile smooth muscle phenotype. Stretch-dependent differentiation marker expression requires an intact cytoskeleton for stretch sensing, control of protein expression via the level of unpolymerized G-actin, or both.

Cirrhosis of the liver and receptor-mediated function in vascular smooth muscle

Altered regulation of receptors on the vascular smooth muscle has been proposed as one of the mechanisms that may account for the vascular abnormalities in patients with cirrhosis of the liver. Impaired contractility and down-regulation of contractile receptors have been demonstrated in cirrhotic patients and animal models, although interpretation of the literature is hampered by methodological variation and conflicting results. There is little evidence, however, that receptor down-regulation is the cause of contractile dysfunction in either patients or animal models. Receptor desensitisation may contribute to impaired contraction in human arteries, but further investigation is required to confirm this possibility.

Altered adrenergic responsiveness of endothelium-denuded hepatic arteries and portal veins in patients with cirrhosis

BACKGROUND & AIMS

Patients with cirrhosis are characterized by a reduced splanchnic vascular resistance and a hyporeactivity to adrenergic vasoconstrictors. So far, their adrenergic splanchnic vascular responsiveness has not been evaluated in vitro. We compared responses to alpha1- and beta2-adrenoceptor stimulation of hepatic arteries and portal veins of patients with cirrhosis undergoing transplantation with those of organ donors.

METHODS

Isometric contractions of endothelium-denuded vessel rings were induced cumulatively by methoxamine and relaxations by isoproterenol. Results are expressed as percentage of the contraction obtained by 85 mmol/L KCl or of the relaxation obtained by 100 micromol/L papaverine, respectively.

RESULTS

Maximal methoxamine-induced contractions were reduced in cirrhotic hepatic arteries (cirrhosis, 51.8% +/- 6.8%; donor, 89.9% +/- 6.6%; P < 0.01) and portal veins (cirrhosis, 49.2% +/- 6.4%; donor, 94.0% +/- 5.3%; P < 0.01). In cirrhosis, isoproterenol induced a less marked relaxation of hepatic arteries (cirrhosis, 46.6% +/- 3.2%; donor, 100.3% +/- 4.4%; P < 0. 01) but an increased relaxation of portal veins (cirrhosis, 41.9% +/- 6.2%; donor, 26.2% +/- 2.8%; P < 0.01).

CONCLUSIONS

In cirrhosis, endothelium-free hepatic arteries are hyporeactive to alpha1- and beta2-adrenoceptor agonists, and portal veins are hyporeactive to alpha1- but hyperreactive to beta2-adrenoceptor agonists. These findings support the in vivo findings of a hyporesponsiveness to adrenergic vasoconstrictors in patients with cirrhosis.

Increased endothelial nitric oxide synthase activity in the hyperemic vessels of portal hypertensive rats

BACKGROUND/AIM

Portal hypertension is characterized by splanchnic hyperemia due to a reduction in mesenteric vascular resistance. Mediators of this hyperemia include nitric oxide. This is based on several reports indicating a marked splanchnic hyporesponsiveness in portal hypertension to vasoconstrictor stimuli both in vitro and in vivo, and a subsequent reversal using specific inhibitors of nitric oxide synthase. The objective of this study was to determine firstly whether the functional activity and/or expression of nitric oxide synthase is altered in portal hypertensive vasculature and secondly which isoenzyme form was responsible for the preferential response to nitric oxide blockade in these animals.

METHODS

We compared nitric oxide synthase functional activity in the hyperemic vasculature of sham and portal hypertensive rats (following partial portal vein ligation). Nitric oxide synthase activities were determined by measuring the conversion of L-arginine to citrulline using ion-exchange chromatography and the amount of immunodetectable nitric oxide synthase in sham and portal hypertensive vessels was determined by Western blot.

RESULTS

Ca(2+)-dependent nitric oxide synthase activity was significantly elevated (p < 0.05) in portal hypertensive particulate fractions from the superior mesenteric artery, thoracic aorta and portal vein. Vascular tissue cGMP levels and plasma nitrite levels were both significantly elevated in portal hypertension. Immunodetection with specific antisera raised against the inducible nitric oxide synthase demonstrated a lack of induction within the hyperemic vasculature. Immunodetection with antisera against endothelial nitric oxide synthase showed a significant increase in portal hypertensive portal vein only. These results demonstrate enhanced calcium-dependent nitric oxide synthase activity in portal hypertension hyperemic vessels concurrent with elevated tissue cGMP levels.

CONCLUSION

We conclude that enhanced endothelial nitric oxide synthesis may in part contribute to the hyperdynamic circulation of portal hypertension.

Cytoskeletal features in longitudinal and circular smooth muscles during development of the rat portal vein

Immunohistochemistry of alpha-smooth muscle actin and desmin, two markers of smooth muscle cell differentiation, and electron-microscopic observation of thick filaments of myosin were performed on the media of the developing rat hepatic portal vein to gain insights into the chronology of differentiation of its longitudinal and circular smooth muscles. In accordance with the ultrastructural distribution of thin filaments, staining of alpha-smooth muscle actin is lightly positive in the myoblasts at postnatal day 1 and then extends in probably all muscle cells of the developing vessel. Desmin, which appears later than alpha-smooth muscle actin in the two muscles, is distributed throughout the longitudinal layer at day 8, whereas the first arrangements of thick filaments are detectable in most longitudinal muscle cells; at this stage, desmin and thick filaments are absent from the poorly differentiated circular muscle cells. The longitudinal muscle cells differentiate in a strikingly synchronized way from day 8 onwards, conferring a homogeneous structure to the developing and mature longitudinal layer. Several desmin-positive cells and a heterogeneous distribution of thick filaments occur in the circular muscle at day 14; the subsequent extension of these filaments in this layer results in a persisting heterogeneous distribution in the young 7-week-old adult. Many features of the mature smooth muscle cells are established within the third week in the longitudinal muscle, approximately one week before those of the circular layer. These results are consistent with the function of the longitudinal muscle as a spontaneously contractile smooth muscle unit, and emphasize the need for its fast maturation to fulfil its major role in the control of portal blood flow.

Altered adenylyl cyclase activities and G-protein abnormalities in portal hypertensive rabbits

Portal hypertension (PHT) is characterized by splanchnic hyperemia due to a reduction in mesenteric vascular resistance. We hypothesized that alterations in the activity of a guanine-nucleotide regulatory protein (G-protein) might be partially responsible for the marked circulatory disturbances observed in PHT. We, therefore, determined alterations in adenylyl cyclase/cAMP system in prehepatic portal hypertensive rabbits and correlated these changes to the activity of a G-protein. Basal and G-protein-stimulated adenylyl cyclase activities were lower in the PHT superior mesenteric artery (22-26%) and thoracic aorta (31-46%) membranes, but higher (178-321%) in portal vein. The functional activity of Gi alpha proteins (pertussis toxin-catalyzed ADP-dependent ribosylation) increased in the PHT superior mesenteric artery and thoracic aorta, but decreased in portal vein. Immunodetection revealed an increase in the Gi alpha protein subunits (Gi alpha 1/Gi alpha 2 and Gi alpha 3/Go alpha) in PHT thoracic aorta, without any change in Gs alpha proteins; and a decrease in the amount of Gi alpha proteins in PHT portal vein. There was no change in the amount of Gs alpha/Gi alpha in the PHT superior mesenteric artery. We conclude the hemodynamic alterations of PHT are associated with intrinsic alterations in G-protein-enzyme effector systems. These alterations are vessels specific and suggest a possible unique global derangement underlying the vasculopathy of PHT.

Effects of long-term portal hypertension on structure, active force and content of contractile and structural proteins in smooth muscle of the rat portal vein

Growth of the smooth muscle cells in the rat portal vein was induced by a partial ligation of the vessel. The ligation caused an increase in the transmural pressure and segments of the portal vein were investigated 6 weeks after the ligation. The spontaneous contractile activity of the ligated veins was similar to that of the control veins. In the ligated vessels the active force at optimal length for force development was doubled, 22.8 +/- 1.3 compared with 12.5 +/- 1.4 mN for the controls. The cross-sectional area of the media in the ligated veins, determined on transverse sections, increased from the control value of 0.10 +/- 0.01 to 0.19 +/- 0.01 mm2. Electron microscopy revealed that the mean cross-sectional area of the smooth muscle cells in the ligated portal vein was doubled (controls: 6.4 +/- 0.6, hypertrophic: 13.6 +/- 1.8 microns2). This suggests hypertrophy of the smooth muscle cells in the vessel wall as the cause for the increase in cross-sectional area of the ligated veins. An increase in the number of intermediate filaments was observed in the hypertrophied smooth muscle. The relative contents of contractile (myosin and actin) and structural (desmin and vimentin) proteins were determined with SDS-polyacrylamide gel electrophoresis. The actin/myosin and vimentin/actin ratios were unaltered by hypertrophy. The hypertrophied veins showed an increase in the desmin/actin ratio (control: 0.20 +/- 0.01, hypertrophied: 0.27 +/- 0.03). The increased amounts of desmin correlates with the increased number of intermediate filaments observed by electron microscopy.(ABSTRACT TRUNCATED AT 250 WORDS)

Increase in insulin-like growth factor I in hypertrophying smooth muscle

The present study focuses on the role of the insulin-like growth factor (IGF) system in the development of smooth muscle hypertrophy. Hypertrophy was initiated by partial ligation of portal vein or urethra in female Sprague-Dawley rats weighing approximately 220 g. Levels of mRNA were analyzed by solution hybridization. Seven days after ligation, the wet weight of the portal vein was increased about threefold and the concentration of IGF-I mRNA was increased fourfold. The bladder wet weight was increased twofold 3 days after ligation and fourfold 10 days after ligation. IGF-I mRNA in the bladder was elevated 3-fold after 3 days and 2.5-fold after 10 days, whereas IGF binding protein 2 mRNA was increased approximately 2-fold after 3 days and 5-fold after 10 days. IGF-I receptor mRNA in the hypertrophying bladder remained unchanged. Increased levels of IGF-I were demonstrated with immunohistochemistry in both hypertrophying portal vein and urinary bladder. The results show a specific increase in IGF-I mRNA as well as an increased IGF-I immunoreactivity during hypertrophy of smooth muscle, which suggests that the local IGF-system may play a role in smooth muscle hypertrophy.

Lactate dehydrogenase activity and isoform distribution in the rat urinary bladder: effects of outlet obstruction and its removal

The rat urinary bladder responded to infravesical obstruction by an increased weight. The weight began to increase after 3 days of obstruction. After 10 days the weight gain had become significant, but increased further with time. At 90 days the bladders weighed 12 times the initial weight. Lactate dehydrogenase (LDH) activity per unit bladder weight increased with the duration of the obstruction. The increase was significant in the 90 day group. The isoform pattern of LDH was determined. For the control group the M3H form was dominant, with M4 second; M4 became the dominant isoform after 3 days of obstruction. The relative amount of M4 had increased by 80% after 90 days. In one group, which was first obstructed for 10 days and then had the obstruction removed for 4 weeks, bladder weight and LDH isoform pattern were normal. We suggest that the changes in isoform pattern in the obstructed bladder reflect a metabolic adaptation to the prolonged voiding time and the increased detrusor pressure, with a consequently compromised oxygen supply, and that the changes are reversible if the outlet conditions are normalized.

Postnatal development of the rat portal vein: correlation with occurrence of peptidergic innervation

The portal vein of the rat is immature at birth, and is composed of an endothelium surrounded by undifferentiated cells of mesenchymal origin. Three days after birth, these cells have begun to differentiate and aggregate around the lumen to form two separate layers of perpendicularly oriented myoblasts, while a rich calcitonin gene-related peptide (CGRP) innervation is present around the vessel. In the internal circular muscle layer of the media myofibrils first develop on the endothelial side of the myoblasts, and then progressively reach the other side. In the longitudinal muscular layer of the media, which is separated from the circular layer by a connective lamina as early as 3 days after birth, myofibrils develop randomly in the cells. At the time of the enlargement of the longitudinal layer, long close contacts and intermediate junctions between external myoblasts and adventitial fibroblast-like cells were noted, suggesting that recruitment of this cell type is necessary for the maturation of the vessel wall. At about 28 days, the vein has reached its final structure and the smooth muscle cells are fully differentiated. The dense CGRP perivascular innervation already present at birth persists for the first 14 days of postnatal life when most of the cells have not yet acquired their complete contractile differentiation and are still capable of division. This innervation decreases transiently between 15-17 days, when the vessel acquires its spontaneous contractile activity, then rises to a peak between 20 and 25 days, and falls again. CGRP innervation, which is very scarce at 28 days, slowly increases during the peripubescent stage, by which time the adult structure of the vessel is established. Similar fluctuations in the density of peptidergic innervation were observed for substance P and neuropeptide Y, although these peptides were not yet present at birth and occurred only after 5 days. Vasoactive intestinal polypeptide- and bombesin-immunoreactive fibres were not found at any stage investigated. In addition to a description of the different cell-to-cell contacts which could play a role in the maturation of the vessel wall, we discuss the possible implication of the different peptides in the differentiation, maturation or maintenance of the vessel wall.

Fetal ductus arteriosus ligation. Pulmonary vascular smooth muscle biochemical and mechanical changes

To evaluate the smooth muscle mechanical and biochemical changes associated with persistent pulmonary hypertension syndrome of the newborn, we studied 31 fetal sheep in which the ductus arteriosus was ligated at 125 days of gestation. Sixty-one noninstrumented and six sham-operated fetuses served as controls. All animals were delivered by cesarean section at 137-140 days of gestation, and the experimental group had the ductus arteriosus ligated for 12 +/- 3 days. The ligated group demonstrated a higher mean (+/- SEM) pulmonary artery pressure (72.3 +/- 3.8 versus 54.1 +/- 2 mm Hg, p < 0.01) and right ventricular mean free wall weight (12.5 +/- 0.7 versus 6.8 +/- 0.3 g, p < 0.01) as compared with the sham-operated group. Significant changes in the pulmonary vascular smooth muscle of the ligated group were observed. The myosin content of vessels from the second through fifth generation demonstrated a significant increase in actin and myosin content (p < 0.01), but given their disproportional changes, the noninstrumented group demonstrated a lower actin/myosin ratio than the experimental group (p < 0.01). Changes in the myosin heavy chain isoform stoichiometry, characterized by an increase in both the mean high/low myosin heavy chain isoform ratio (1.8 +/- 0.3 versus 1.0 +/- 0.1, p < 0.05) and the nonmuscle isoform as a percentage of the total myosin heavy chain (12.4 +/- 0.7% versus 2.7 +/- 0.9%, p < 0.01), were also observed in the ligated as compared with the noninstrumented animals. In addition, the muscle Mg-ATPase activity was significantly (p < 0.05) reduced in the experimental group.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypertrophic smooth muscle in the partially obstructed opossum esophagus. Excitability and electrophysiological properties

Partial obstruction of the opossum esophagus leads to thickening of the circular muscle, hypertrophy of smooth muscle cells, and diminution of the extracellular space. The pharmacological and electrophysiological properties of this hypertrophied muscle were studied. Carbachol produced phasic and tonic contractions of the circular muscle. The EC50 for tonic contractions was greater for hypertrophied than for normal muscle (21.1 +/- 3.9 mumol/L vs. 4.8 +/- 2.2 mumol/L; P less than 0.05). The resting membrane potential difference of hypertrophied muscle (-50.8 +/- 0.2 mV) was similar to that of normal muscle (-50.0 +/- 0.2 mV). Electrical stimulation of intrinsic nerves in the normal muscle produced a hyperpolarization followed by a depolarization of smooth muscle membrane potential. Hypertrophied muscle responded either with an attenuated hyperpolarization or no hyperpolarization, both of which were followed by a depolarization. The space constant in the long axes of the hypertrophied circular muscle cells was greater than normal (4.4 +/- 0.2 mm vs. 3.4 +/- 0.1 mm; P less than 0.001). The threshold potential for initiation of action potentials was more negative for hypertrophied (-43.2 +/- 0.4 mV) than for normal circular muscle (-41.6 +/- 0.2 mV; P less than 0.005). These data indicate that alterations in neuromuscular function accompany the hypertrophy of esophageal smooth muscle.

Contractile and cytoskeletal proteins in smooth muscle during hypertrophy and its reversal

Hypertrophy of rat urinary bladder smooth muscle was induced by partial urethral obstruction. Bladder weight increased from 70 to 240 mg after 10 days and to 700 mg after 7 wk. Removal of the obstruction after 10 days caused a regression of bladder weight to 130 mg. The relative volume of smooth muscle in the bladder wall increased during hypertrophy. The concentration of myosin in the smooth muscle cells decreased in 10-day hypertrophied bladders, whereas the concentration of actin was unchanged. The actin-myosin ratio was 2.3 in controls, 3.3 in 10-day obstructed bladders, and 2.9 in 7-wk obstructed bladders. After removal of obstruction, the ratio was normalized. Two isoforms of myosin heavy chains were identified (SM1 and SM2). The relative amount of SM2 decreased during hypertrophy. The relative proportion of actin isoforms (alpha, beta, and gamma) was altered toward more gamma and less alpha. These changes were reversible upon removal of the obstruction. Desmin was the dominating intermediate filament protein. The concentration of desmin and filamin increased in the hypertrophic bladders. The increased desmin-actin and filamin-actin ratios in obstructed bladders were normalized after removal of the obstruction. The results suggest that the turnover of contractile and cytoskeletal proteins is fast and can be regulated in response to changes in the functional demands in smooth muscle.

Hypertrophy of visceral smooth muscle

Smooth muscles of viscera undergo a large increase in volume when there is a chronic, partial obstruction impairing the flow of lumenal contents. Hypertrophy of smooth muscle occurs in various medical conditions and several methods are available for inducing it experimentally in laboratory animals, especially in urinary bladder, small intestine and ureter. The hypertrophic response differs somewhat with the type of organ, the animal species, the age of the subject, and the experimental procedure. Ten- to fifteen-fold increases in muscle volume develop within a few weeks in the urinary bladder or the ileum of adult animals, a growth that would not have occurred in the lifespan of the animal without the experimental intervention. The general architecture of the muscle and the boundaries with adjacent tissues are well preserved. In intestinal hypertrophy, muscle cells increase in number: mitoses are found in mature, fully differentiated muscle cells. Cell division by full longitudinal splitting of muscle cells may also occur. Enlargement of muscle cells accounts for most of the muscle hypertrophy. The hypertrophic muscle cell has an irregular profile with deep indentations of the cell membrane, bearing caveolae and dense bands; however, the cell surface grows less than the cell volume (reduction of surface-to-volume ratio). The nucleus is crenated and is much less enlarged than the cell (reduction of the nucleo-plasmatic ratio). Mitochondria grow in number but in some muscles their spatial density decreases; intermediate filaments increase more than myofilaments. The spatial density of sarcoplasmic reticulum is generally increased. In the hypertrophic intestine, gap junctions increase in number and size; in the bladder, gap junctions are absent both in control and in hypertrophy. Thus the hypertrophic muscle cell is not only larger than a control cell, but has a different pattern of its structural components. Extensive neo-angiogenesis maintains a good blood supply to the hypertrophic muscle. The density of innervation is much decreased in the hypertrophic intestine, whereas it appears well maintained in the bladder. Neuronal enlargement is found in the intramural ganglia of the intestine and in the pelvic ganglion. The mechanisms involved in hypertrophic growth are unknown. Three possible factors, mechanical factors, especially stretch, altered nerve discharge, and trophic factors are discussed.

Isoform distribution and tissue contents of contractile and cytoskeletal proteins in hypertrophied smooth muscle from rat portal vein

Growth of the smooth muscle in the rat portal vein was initiated by an increased transmural pressure. After 7 days, the cross-sectional area of the vessel wall and the maximal active force of the longitudinal muscle layer had increased twofold. Electron microscopy showed that the cell cross-sectional area was increased, suggesting cellular hypertrophy. Increased amounts of intermediate (10 nm) filaments were observed in the hypertrophied cells. The hypertrophied vessels had decreased DNA content per unit wet weight compared with the control vessels (hypertrophied, 1.5 +/- 0.1; control, 1.9 +/- 0.1 micrograms/mg; p less than 0.01). Protein composition was studied with electrophoretic methods. Compared with control preparations the hypertrophied veins had similar myosin and actin contents per unit wet weight (myosin: hypertrophied, 4.4 +/- 0.8; control, 5.9 +/- 0.9; actin: hypertrophied 12.2 +/- 0.6; control, 11.8 +/- 1.0 mg/g). Two different forms of the myosin heavy chain were detected with 5% sodium dodecyl sulfate-polyacrylamide gels. The proportion of the lower molecular weight heavy chain relative to total heavy chain content was about 30% and similar in both preparations. The relation filamin/myosin was increased in the hypertrophied vessels. Pyrophosphate gel electrophoresis revealed two protein bands, with an increase in the slower migrating band in the hypertrophied vessels possibly reflecting an increase in filamin content in the extracts. In the control portal vein alpha-actin is the dominating isoform constituting about 55% of total actin. In hypertrophied vessels, alpha-actin decreased (by 15%) and gamma-actin increased (by 20%). The portal vein contained desmin and vimentin in a ratio of about 6:1. The hypertrophied vessels showed a marked increase in the amount of these proteins (desmin/actin: hypertrophied, 0.32; control, 0.14). In conclusion, during pressure-induced growth of the portal vein, contractile protein contents increase in proportion to the increase in weight. A change in isoforms of actin occurs but no evidence for a change in myosin isoforms was found. The structural proteins increase relative to tissue weight, possibly associated with the increased number of intermediate filaments demonstrated with electron microscopy.

Electrical and mechanical properties of spontaneous contraction in hypertensive rat portal vein

Contractile and electrical activities of longitudinal smooth muscle of portal vein from normotensive Wistar Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP) were compared. Amplitude and duration of spontaneous contraction of SHRSP portal vein were greater than those of WKY portal vein. No significant differences were observed in the resting membrane potentials between these preparations. Spontaneous spike activity appeared as a form of bursts. Duration of the burst and the number of spikes in each burst was greater in the portal vein of SHRSP than that of WKY. The amplitude of phasic and tonic components of K-contracture was also greater in SHRSP portal vein. Adrenergic and cholinergic nerves were not involved in the differences in contractions of the portal vein of these animal strains. Cross-sectional area of the longitudinal muscle layer was greater in SHRSP portal vein. These results suggest that the differences in spontaneous electrical activity are the cause of the differences in force and duration of the spontaneous contraction of portal vein from WKY and SHRSP, although the difference in excitation-contraction coupling of smooth muscle may be involved in much less extent.

Contractile properties during development of hypertrophy of the smooth muscle in the rat portal vein

Structural and mechanical alterations during hypertrophy of the rat portal vein were investigated. Growth of the vessel was induced by a partial ligature of the vessel causing an increased transmural pressure. Vessel segments from animals kept with ligature for 1, 3, 5 and 7 days, were compared with vessels from sham-operated animals. Maximal active force and vessel cross-sectional area increased with time in the ligated group. On day 7, force and cross-sectional area at the optimal length, were markedly increased in the ligated group (21.1 +/- 1.0 mN, 0.55 +/- 0.04 mm2, n = 9) compared with the control vessels (11.7 +/- 1.0 mN, 0.30 +/- 0.02 mm2, n = 7). Light and electron microscopy of preparations fixed at optimal length showed that the amount of smooth muscle and the cross-sectional area of cell profiles were almost doubled in the ligated group on day 7, consistent with hypertrophy of the smooth muscle. The force per smooth muscle cell area was similar in the two groups (ligated: 132 +/- 15; control: 145 +/- 16 mN mm-2, n = 4-5). The maximal shortening velocity was significantly lower in the hypertrophied group (ligated: 0.28 +/- 0.02; control: 0.41 +/- 0.01 optimal length s-1, n = 6). In chemically skinned preparations, activated by maximal thiophosphorylation of the myosin light chains, force was higher in the ligated group compared to the controls but no difference in maximal shortening velocity was observed. In conclusion, the increased transmural pressure is associated with a rapid increase in the amount of smooth muscle in the portal vein. The mechanical data show that after 7 days the force generating ability of the contractile system has increased in proportion to the smooth muscle cell mass. The unaltered maximal shortening velocity in the skinned hypertrophied preparations suggests that the kinetic properties of the maximally activated contractile system are unaltered. The decreased maximal shortening velocity in the intact hypertrophied preparations may reflect alterations in the excitation-contraction coupling.

Chronic papaverine treatment: the effect of repeated injections on the simian erectile response and penile tissue

To investigate the effect of chronic papaverine treatment, seven monkeys underwent repeated intracavernous injections for one year. One monkey died after 56 injections; the others received a total of 100 each. The strength and duration of erection were recorded after each injection, and the erectile tissue was examined histologically at the end of the study. Over the long term, papaverine maintains its erection-inducing capability, but it does cause pathologic changes in the erectile tissue: minimal to marked fibrosis at the injection site and hypertrophy of smooth muscle in the non-injected area of the corpus.

Evidence for increased media thickness, increased neuronal amine uptake, and depressed excitation--contraction coupling in isolated resistance vessels from essential hypertensives

The functional and morphologic characteristics of isolated subcutaneous resistance vessels (about 170 micron i.d.) from 15 untreated subjects with essential hypertension and 15 matched controls were examined. The vessels from the hypertensives had a 29% increase in the media-thickness-to-lumen-diameter ratio. The maximal force development to noradrenaline (NA) expressed as active pressure (an estimate of the pressure the vessels could have contracted against in vivo) was 30% higher in vessels from the hypertensives, while active media stress (force per square unit of smooth muscle) and sensitivity to NA was not significantly different. Increased active pressure, as well as unaltered active media stress and sensitivity, was seen for vasopressin, serotonin, angiotensin II, and K+. There was, however, an enhanced leftward shift of the NA sensitivity with cocaine (an inhibitor of the neuronal amine pump) in vessels from the hypertensives [pD2(+cocaine) and pD2(-cocaine) were 0.185 +/- 0.53) and 0.040 +/- 0.044, hypertensives and normotensives, respectively, p less than 0.05] suggesting an abnormality of presynaptic function in essential hypertension. Furthermore, the calcium sensitivity was depressed (pD2 was 4.197 +/- 0.050 and 4.381 +/- 0.068, hypertensives and normotensives, respectively, p less than 0.05), and the rate of relaxation was faster (p less than 0.05) in vessels from hypertensives, suggesting that excitation-contraction coupling might be depressed. The results suggest that the increased pressor response in essential hypertension can, to a large extent, be explained by altered vascular structure, while smooth muscle function is either unchanged or possibly depressed.

Hypersensitivity of mesenteric veins to 5-hydroxytryptamine- and ketanserin-induced reduction of portal pressure in portal hypertensive rats

Isolated superior mesenteric veins from portal hypertensive rats were 3 to 10 times more sensitive to 5-hydroxytryptamine (5-HT) and 3 times less sensitive to (-)-noradrenaline than veins from sham-operated rats. The sensitivity to vasopressin did not differ in the 2 groups. Ketanserin competitively antagonized the effects of 5-HT in superior mesenteric veins and portal veins with high affinity (KB values 0.1-0.3 nM), as expected for 5-HT2-receptors. The affinity of ketanserin for 5-HT2-receptors was similar in veins from normal, sham-operated or portal-hypertensive rats. Intraportal injections of low doses of 5-HT caused increases in portal pressure which were more pronounced in portal hypertensive rats than in sham-operated rats and were blocked by 0.3 mg kg-1 ketanserin in both groups. Ketanserin 0.3 mg kg-1 did not block the portal pressor response to (-)-noradrenaline in either group of rats. In portal hypertensive rats but not in sham-operated rats, 0.3 mg kg-1 ketanserin caused decreases in portal pressure, portal flow and cardiac output, as estimated by radioactive microspheres. The reduction in portal pressure caused by ketanserin was due mainly to a decrease in portal venous inflow secondary to a decreased cardiac output. The reduction in cardiac output, which was observed only in the portal hypertensive rats but not in sham-operated rats, is consistent with venous dilatation and pooling of blood in the portal venous system. The venous pooling could be secondary to the blockade of 5-HT2-receptors in the portal venous system. It is proposed that ketanserin should be explored for the treatment of patients with portal hypertension.

Splanchnic and systemic hemodynamics in portal hypertensive rats during hemorrhage and blood volume restitution

In portal hypertension the hemodynamic events after episodes of bleeding and blood transfusions may have important pathophysiological and therapeutic implications. The present study was designed to evaluate the effect of hemorrhage and blood restitution on splanchnic and systemic hemodynamics in a rat model of portal hypertension induced by portal vein constriction. In 16 portal hypertensive rats, sequential measurements of arterial and portal pressure were obtained during withdrawal and reinfusion of 15 ml X kg-1 body wt of blood. At the completion of the hemorrhage, a decrease of 16.9% +/- 2.6% in arterial pressure and 27.3% +/- 2.2% in portal pressure was observed. After blood reinfusion, arterial pressure returned to baseline values while portal pressure increased by 20.4% +/- 3.2% (p less than 0.01). This increase in portal pressure was not observed in 5 normal rats that were subjected to the same blood volume changes. Hemodynamic studies using a radioactive microsphere technique revealed that the withdrawal of 15 ml X kg-1 body wt of blood is followed by a decrease in portal venous inflow (6.4 +/- 0.4 vs. 10.4 +/- 0.6 ml X min-1 X 100 g-1 body wt in the control group, p less than 0.01). After blood volume restitution, the portal venous inflow returned to control values while the portal-collateral resistance increased significantly (2.06 +/- 0.13 vs. 1.67 +/- 0.07 mmHg X min X ml-1. 100 g, p less than 0.05). These results indicate that during hypovolemia there is a marked reduction in portal pressure because of a reduction in portal venous inflow. Blood volume restitution returns the portal venous inflow to control values. However, the portal pressure increases beyond control values because of an increase in portal-collateral resistance.

Hemodynamic studies in long- and short-term portal hypertensive rats: the relation to systemic glucagon levels

It is not known whether the hyperdynamic state which has been observed in several experimental models and in patients with portal hypertension reflects a temporary phase during the evolution of the portal hypertensive syndrome or is an expression of a permanent steady state. A hemodynamic study was performed in a group of rats with long-standing portal hypertension induced by portal vein constriction performed 6.2 +/- 0.1 months earlier. A group of rats matched by age and weight with short-term (20.7 +/- 0.9 days) portal hypertension and a group of long-term (6.2 +/- 0.1 months) sham-operated rats were used as controls. Cardiac output and regional blood flows were measured using a radioactive microsphere technique. Arterial blood levels of glucagon, a known vasodilator that was implicated in the etiology of the hyperdynamic circulation, were also measured. Portal pressure in long- and short-term portal hypertensive groups (12.3 +/- 0.4 and 13.7 +/- 0.4 mm Hg; not statistically significant) was higher than in the sham group (9.0 +/- 0.3 mm Hg; p less than 0.01). Cardiac output in the long-term portal hypertensive rats was similar to the sham-operated group and lower than in the short-term portal hypertensive group (19.4 +/- 1.0 and 20.6 +/- 1.5 vs. 32.7 +/- 2.0 ml X min-1 X 100 gm body weight-1; p less than 0.01). Portal venous inflow in the long-term portal hypertensive group was also similar to the sham group and lower than in the short-term portal hypertensive group (4.51 +/- 0.36 and 4.58 +/- 0.39 vs. 6.72 +/- 0.48 ml X min-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac mass and peripheral vascular structure in hydralazine-treated spontaneously hypertensive rats

We have examined the effect of antihypertensive treatment on heart weight and on structural and functional characteristics of isolated mesenteric resistance vessels (internal diameter 170-220 micron) in spontaneously hypertensive rats (SHR) and in Wistar-Kyoto rats (WKY). The SHR and WKY were treated with hydralazine from the age of 4 weeks and were examined at ages 12 to 14 weeks and 23 to 27 weeks. Treated SHR had a mean blood pressure as much as 29% below that of control WKY, which in turn was 25 to 40% less than that of control SHR. In 12- to 14-week-old rats the heart to body weight ratio (which in control SHR was 13% greater than of WKY) was unaffected by treatment. Thereafter, the heart to body weight ratio of treated SHR did not increase as much as usual. At both ages, the media thickness and contractile response of the resistance vessels of the SHR (which were, respectively, 37% and 30% greater than those of vessels of WKY) were unaffected by treatment. However, because treatment caused a small (8%) increase in the lumen diameter of the vessels of the SHR, treatment did cause small, but possibly physiologically important, decreases both in the media to lumen ratio (11%) and in the pressure against which these vessels would have been able to contract (10%). Treatment had little effect on the pharmacological characteristics of vessels of either SHR or WKY. The results suggest that the increased heart weight, media thickness, and contractile response in mesenteric resistance vessels of SHR up to ages 23 to 27 weeks are due primarily to factors other than increased pressure.

Effects of Ca2+ on force-velocity characteristics of normal and hypertrophic smooth muscle of the rat portal vein

Portal hypertension was induced in rats by partial ligation of the hepatic branches of the portal vein. After 5 days of hypertension the portal veins were taken out and mounted for isometric and quick-release experiments. Portal veins from sham-operated normal rats served as controls. The ligated veins had an increased cross-sectional area, indicating smooth-muscle hypertrophy. Although the absolute magnitude of active force of these veins was increased, the active force per cross-sectional area was decreased, indicating an alteration in the properties of the contractile system. No difference in the Ca2+ concentration-response relations to K+-activated intact control and hypertrophic veins was found. In chemically skinned preparations, devoid of functional plasma membranes, the hypertrophic veins had similar Ca2+ sensitivity (in the presence of I microM calmodulin) but a lower force per cross-sectional area. Force-velocity relations were determined in K+-activated intact preparations. In control veins a reduction in extracellular Ca2+ was associated with a significant reduction in both isometric force and maximal shortening velocity (Vmax). In hypertrophic veins the decreased isometric force at maximal activation was associated with a low Vmax. A comparison between hypertrophic and submaximally stimulated control vessels showed corresponding Vmax and isometric force values. We conclude that the low isometric force of hypertrophic veins is associated with a lower rate of cross-bridge turnover. This could be an effect of alterations in the activation mechanisms or in the intrinsic properties of the contractile system itself.

Pathogenesis of portal sclerosis in the liver with idiopathic portal hypertension. Observations of 19 autopsy cases and animal experiments

The pathomorphological changes of intrahepatic portal veins were studied in 19 autopsy cases of idiopathic portal hypertension (IPH), and the pathogenesis of portal sclerosis was discussed by the observations on the human and experimental materials. The degree and morphological appearance of intimal lesions vary from vessel to vessel. Fibro-cellular proliferation of subendothelial tissue and incorporation of organized mural thrombi were suggested as the cause of intimal thickening in the portal veins. Animal experiment showed that injury of portal vein wall was followed by intimal hyperplasia and/or incorporation of mural thrombi, and resulted in portal sclerosis similar to that of IPH liver. The cause of portal phlebosclerosis in IPH can not be explained by passive congestion alone. There might be a certain possibility of direct injurious effect in the vessel wall in the pathogenesis of portal lesions of IPH. The following pathogenesis of portal sclerosis in IPH is postulated: phlebo-sclerotic changes of the portal veins are initiated by injury to the vessel wall due to unknown cause(s) and accelerated by secondary thrombosis and/or mechanical injury due to increased portal pressure.

Electron probe analysis of sodium and other elements in hypertrophied and sodium-loaded smooth muscle

The composition of normal, hypertrophied, or sodium-loaded rabbit portal anterior mesenteric vein and of normal and sodium-loaded guinea pig taenia coli smooth muscle was measured in cryosections with electron probe analysis, and the effects of wash with cold sodium-free (Lithium) solutions were determined. There was no significant difference in the cytoplasmic, nuclear, or mitochondrial concentrations of any of the measured elements (sodium, potassium, chloride, magnesium, calcium, phosphorus, sulfur) between hypertrophied, sham-operated, or control veins. The cytoplasmic potassium:sodium:chloride ratio in rabbit portal anterior mesenteric vein was 1:0.26:0.46, and the average sodium concentration (198 mmol/kg dry cytoplasmic weight) was nearly twice as high as estimated from ion flux measurements. The cytoplasmic sodium concentration of normal guinea pig taenia coli was 61 mmol/kg dry weight. The existence of a rapidly exchanging, relatively low affinity, and temperature-insensitive component of cytoplasmic sodium efflux was indicated by the reduction in cytoplasmic sodium after washout in cold, sodium-free (lithium or Tris-substituted) solutions. This reduction, by 62% in normal, 71% in sodium-loaded portal anterior mesenteric vein, and 36% in sodium-loaded guinea pig taenia coli smooth muscle, suggests that the lithium wash method can underestimate cell sodium. In sodium-loaded guinea pig taenia coli and portal anterior mesenteric vein smooth muscles, the cytoplasmic sodium analyzed in individual cells showed a bimodal distribution; in cryosections, the cells having the highest sodium and lowest potassium and phosphorus content also had a more electronlucent (light cell) appearance.

Membrane potential in smooth muscle cells from hypertrophic rat portal vein

Portal hypertension was induced in rats by partial ligation of the hepatic branches of the portal vein. After 5 days the vein was removed and mounted in vitro. In contrast to control (C) veins, hypertensive (H) vessels were almost devoid of spontaneous contractions. Microelectrode recordings showed that the smooth muscle cells of H vessels were hyperpolarized. If [K+]o was increased, or if Ba2+ was added spontaneous activity could be initiated in H vessels. A relation in H cells between hyperpolarization and increased aerobic glycolysis (suggesting an increased electrogenic Na+-K+-pumping) is proposed.

Vascular smooth muscle cell hypertrophy and hyperploidy in the Goldblatt hypertensive rat

Our major objective in this study was to examine the hypothesis that the aortic smooth muscle cell hypertrophy and hyperploidy observed in previous studies of spontaneously hypertensive rats is not peculiar to that model, but also occurs in Sprague-Dawley rats made hypertensive by a Goldblatt procedure (two-kidney, one-clip model). Flow microfluorometric and microdensitometric analysis of smooth muscle cell DNA content showed a significant increase in the frequency of tetraploid smooth muscle cells from 5.6 +/- 0.9% in controls to 14.6 +/- 1.94% in hypertensives 1 month after Goldblatt surgery. Neither differences in ploidy nor elevation in blood pressure were apparent 2 weeks after surgery. The frequency of polyploid smooth muscle cells increased with age, duration of hypertension, and level of blood pressure. Analysis of the interrelationship between smooth muscle cell ploidy and hypertrophy in 5-month post-surgery Goldblatts by cytospectrophotometric measurements of the protein and DNA content of individual smooth muscle cells showed that tetraploid and octaploid cells from Goldblatt rats had 64% and 129% greater protein mass, respectively, than diploid cells. In addition, the mean protein mass of smooth muscle cells from Goldblatts was approximately 100% greater than that of normotensive controls, with each of the ploidy classes in Goldblatts having a higher frequency and mass than the corresponding cells in controls. Estimates of cell number per centimeter aortic length, based on measurements of average DNA/cell and total aortic medial DNA, showed no difference between hypertensives and controls. Furthermore, the rate of accumulation of polyploid cells could account for the increased frequency of cells undergoing DNA synthesis as measured by [3H]thymidine autoradiography. Thus, smooth muscle cell hypertrophy, not hyperplasia, was responsible for the increased mass of smooth muscle in aortas of Goldblatt hypertensive rats compared with normotensive controls, and this smooth muscle cell hypertrophy was accompanied by an increase in DNA ploidy.

Length-tension relations of smooth muscle from normal and denervated rat urinary bladders

Urinary bladders of rats were denervated by bilateral excision of the pelvic ganglion and removed 10 days after the operation. They were filled with 0.75 ml saline and a longitudinal muscle strip was marked out, measured and dissected out. Strips from normal bladders filled with the same volume were used as controls. Denervated bladders were 4-5 times heavier than control bladders. Muscle strips from denervated bladders showed, in contrast to controls, marked phasic spontaneous contractions which were unaffected by tetrodotoxin, indicating a myogenic origin. Active tension in response to AC stimulation was measured at different lengths. In relation to the in situ length (Lin situ) at 0.75 ml the denervated strips had to be stretched to much greater extent than controls in order to reach optimum length (L0) for force development. Furthermore, the denervated strips shortened less in relation to Lin situ than the controls. If active length-tension relations were expressed in relation to L0, the difference between denervated and control strips was abolished. Maximal active force was the same for denervated and control strips. Water content increased significantly in denervated bladders. The results suggest a remodelling of the smooth muscle structure in denervated bladders; the characteristics of the contractile machinery seem, however, to be unaltered.

Structural and mechanical alterations in hypertrophic venous smooth muscle

Portal hypertension was induced in rats by partial ligation of the hepatic branches of the portal vein. After 5 days the transluminal pressure of the portal vein was measured, and the vessel was fixed in situ for electron-microscopy, or dissected out and mounted in an apparatus recording force and shortening. Portal veins from sham-operated animals were used as controls. Portal venous pressure had increased about twofold after the partial ligation and the cross-sectional area of the longitudinal muscle layer about twofold. Number of muscle cells per mm2 cross-sectional area decreased to half of the control value, whereas extracellular space in the muscle layer and the dry weight of the preparations were unaltered. Number of cells was unchanged suggesting that no hyperplasia had occurred. Length-passive force relations were shifted towards higher force values in the hypertrophic vessels, whereas passive stress-strain characteristics were similar. The structures that carry passive tension have thus increased in proportion to the vessel as a whole. Length-active tension curves obtained by stimulation with AC current or high K+ solutions indicated that the hypertrophic vessels could not, in relation to optimal length for active force, shorten to the same extent as control vessels. Maximum active tension per vessel was unaltered whereas force per unit muscle area and force per cell had decreased. As the preparations were supramaximally stimulated and had optimal extracellular Ca2+ concentrations we suggest that the amount of functional contractile proteins has not increased in proportion to the increase in size of the muscle cells.

Hypertrophy-induced increase of intermediate filaments in vascular smooth muscle

The distribution of filaments was studied in hypertrophied rabbit vascular smooth muscle. Hypertrophy was induced by partial ligation of the portal-anterior mesenteric vein. 14 d after ligation, there was an approximately threefold increase in the number of intermediate filaments per cross-sectional area, as compared to control values. The actin:intermediate:myosin filament ratio was 15:1.1:1 in control and 15:3.5:0.5 in hypertrophied portal-anterior mesentric vein vascular smooth muscle. Comparison of the filament ratios with the increase in volume density of the hypertrophied cells suggests that the number of myosin filaments per cell profile remained approximately the same as in controls, whereas the number of actin filaments increased in proportion to the increase in cell volume.

Experimental portal hypertension in the rat

Previous attempts to produce sustained portal hypertension in experimental animals by portal venous obstruction have not been successful. Experiments were designed to study the effects of gradual portal venous occlusion plus hepatic lymphatic ligation in the rat. Adult male Lewis rats were divided into three groups: (A) nonoperated or sham-operated; (B) operated, with hepatic lymphatic ligation only; and (C) operated, with placement of a portal vein ameroid constrictor and hepatic lymphatic ligation. There were no differences noted in portal venous pressures (control 9.6 +/- 0.4 cm H2O) and portovenograms between groups A and B throughout the study. In group C there was greater than doubling of portal venous pressure by 1 wk which remained for 2 mo. Portal pressure then fell but remained elevated at greater than 30% above control values for 1 yr. Three systems of collateral circulation developed rapidly in response to this extrahepatic portal venous occlusion: (A) veins directly bridging across the occluding ameroid reestablishing hepatopetal flow which steadily increased; (B) spontaneous portosystemic shunts at the splenorenal area that occur early and then regress; and (C) retroperitoneal, paraesophageal and submucosal esophageal veins that develop late and remain stable. Quantitative assessment of the lumen size of the submucosal esophageal veins revealed a twofold increase in these veins in group B when compared to controls by 4 wk and a fivefold increase in these veins in group C by 8 wk that persisted for 1 yr. This model appears useful for studying the course and effects of extrahepatic portal hypertension and its gradual alteration by the spontaneous development of portosystemic collaterals in the rat. This model may have enough similarities to the extrahepatic portal hypertension seen in children that its use for future studies may be fruitful.

Cellular thin filament protein contents and force generation in porcine arteries and veins

We estimated the cellular myosin, actin, and tropomyosin contents of vascular smooth muscle from (1) seven major arteries, (2) seven large veins, and (3) the first through third order branches of the uterine vasculature to determine whether variations in the contractile apparatus contribute to the functional diversity of vascular smooth muscle. We obtained the estimates by quantitative densitometry of stained polyacrylamide gels after electrophoresis of sodium dodecyl sulfate-treated tissue homogenates. No differences in cellular myosin content were found (18.7 +/- 1.0 mg/g cell wet weight in arteries vs. 17.2 +/- 0.7 in veins). However, the actin and tropomyosin contents were higher in arteries (49.7 +/- 2.9 and 13.1 +/- 0.8 mg/g cell, respectively) than in veins (25.5 +/- 1.4 and 7.0 +/- 0.3 mg/g cell). These differences persisted in the smaller uterine vessels. The higher contents of thin filament proteins in arteries, compared with veins and several other smooth muscle tissues previously studied, may underlie the high force generating capacity of arterial smooth muscle.

Hypertrophic smooth muscle. IV. Myofilaments, intermediate filaments and some mechanical properties

The ultrastructure of filaments is studied in the hypertrophic musculature of the small intestine of the guinea pig oral to an experimental stenosis. No structural change is observed in the thin and the thick myofilaments. However, there is a remarkable and consistent increase in the number of intermediate (10 nm) filaments; they are the predominant type of filament in many hypertrophic muscle cells. Experiments, in which the force developed in vitro by strips of control and hypertrophic musculature upon stimulation with carbachol, indicate that the force per unit sectional area is slightly less in the hypertrophic muscle than in the control tissue.

Hypertrophic smooth muscle. I. Size and shape of cells, occurrence of mitoses

An extensive hypertrophy of the muscle coat develops in the small intestine of the guinea pig oral to an experimental stenosis. The profiles of smooth muscle cells become larger and irregular in shape. From the analysis of serial sections the arrangement of the muscle cells is less orderly than in control muscles. Many muscle cells are split into two or more branches over part of their length. The average cell volume is 3--4 times that of control muscle cells; the cell surface increases less dramatically and, in spite of the appearance of deep invaginations of the cell membrane, the surface-to-volume ratio falls from 1.4 to 0.8. The average cell length is only slightly increased compared with controls. Smooth muscle cells in mitosis are observed in all the hypertrophic muscles examined, in both muscle layers; in the circular musculature they occur mainly found in the middle part of the layer.

Myogenic microvascular responses to change of transmural pressure. A mathematical approach

The recently described static and dynamic myogenic responses in the sympathectomized skeletal muscle microvessels to a given transmural pressure (PT) change applied at different rates (dPT/dt) (Grände & Mellander 1978), were further analysed in this study with a mathematical approach. The hypothesis that myogenic reactions are triggered by and related to wall tension was also tested. The mathematical model was based on a force-equilibrium in the microvessel wall including passive forces related to vascular transmural pressure, elasticity, and wall-viscosity, and active myogenic forces related to wall tension and its rate of change. Great resemblance was demonstrated between microvascular resistance curves obtained with the model and corresponding curves observed in vivo, indicating that the model quite adequately can describe myogenic microvascular resistance responses to transmural pressure stimuli. The results support the myogenic hypothesis in general and, in particular, the concept of an important rate-sensitivity in myogenic microvascular control and are compatible with the view that myogenic reactions are triggered by and related to change of wall tension. The model, in addition, provided data for certain microvascular variables which are difficult to assess by in vivo observations, e.g. Young's modulus of elasticity, wall tension, its rate of change, and internal vessel radius, and it offered a means to define more precisely the role of physical factors like effects of Poiseuille's and Laplace's laws in vascular resistance regulation.

Influence of muscle length on the force-velocity relation of K+-contractures in smooth muscle from rabbit urinary bladder

Force-velocity relations of K+-contractures of longitudinal smooth muscle from rabbit urinary bladder were studied by isotonic quick release at 37 degrees C. In order to minimize the influence of parallel elasticity the study was limited to the rising part of the length-tension curve. The force-velocity data fitted well with Hill's equation. The in situ length of the strip at a bladder volume of 10 ml is called L10. This length is 50% of that at which maximum active tension is developed. At L10 Vmax was 0.29 muscle lengths per second and it was estimated to be 0.36 lengths/s at optimum length. Constant b in Hill's equation had a value of 0.052 L10/s and it was unaffected by length changes over the interval 0.69 L10-1.44L10. At L10 a/Po was 0.17. In the interval given above, a/Po decreased with increasing length in proportion to the increase in Po, indicating that a was also length independent. According to Hill's equation [V = b(Po - P)/(P + a)], V should increase in proportion to (Po - P) when the muscle length is increased if a and b are constants. Such a linear relation was found at shorter lengths but at lengths close to or at the length for maximum active tension, V increased more than (Po - P). Two possible explanations were considered; firstly that b/(P + a) increased, and secondly that the load on the contractile element could be less that P due to an influence of the considerable tension in the parallel elastic element at these lengths. The series elastic recoil of the active muscle amounted to 3-4% of the muscle length when released to zero tension.