Vascular nitric oxide production during the development of two experimental models of portal hypertension

BACKGROUND/AIMS

The aim of this study was to determine the relative roles of constitutive NOS (NOS3) and inducible NOS (NOS2) isoforms during the development of two models of portal hypertension in rats.

METHODS

Vascular reactivity of aortic rings for norepinephrine was performed in control, sham-operated, portal-vein-stenosed and secondary biliary cirrhotic rats 1, 4, 7, 14 and 28 days after surgery. NOS activity and nitrate plasma levels were also measured.

RESULTS

An impaired response to norepinephrine observed in sham-operated, portal-vein-stenosed and cirrhotic rats at days 1 and 4 compared with controls was reversed after L-NNA and aminoguanidine. Portal hypertensive rats remained hyporeactive at days 7, 14 and 28 compared with sham-operated rats. At days 7 and 14 in portal-vein-stenosed rats, vascular hyporeactivity was reversed by L-NNA and W7. At days 14 and 28 in cirrhotic rats, vascular hyporeactivity was reversed by L-NNA and W7. Nitrate levels increased at day 1 in the 3 groups, and increased at days 14 and 28 in portal hypertensive rats. Total NOS-activity increased in cirrhotic rats at day 28, in portal-vein-stenosed rats at day 14, and in sham-operated rats at day 1 compared to controls. NOS2 activity increased only in sham-operated rats at day 1.

CONCLUSIONS

This study shows that for two models of portal hypertension, increased NO production in the first days is related to NOS2 induction secondary to surgery. On the other hand, when portal hypertension has fully developed, the NOS3 isoform appears to play the major role.

Seminal plasma choline phospholipid-binding proteins stimulate cellular cholesterol and phospholipid efflux

Bovine seminal plasma (BSP) contains a family of phospholipid-binding proteins (BSP-A1/-A2, BSP-A3 and BSP-30-kDa, collectively called BSP proteins) that potentiate sperm capacitation induced by high-density lipoproteins. We showed recently that BSP proteins stimulate cholesterol efflux from epididymal spermatozoa and play a role in capacitation. Here, we investigated whether or not BSP proteins could stimulate cholesterol and phospholipid efflux from fibroblasts. Cells were radiolabeled ([3H]cholesterol or [3H]choline) and the appearance of radioactivity in the medium was determined in the presence of BSP proteins. Alcohol precipitates of bovine seminal plasma (designated crude BSP, cBSP), purified BSP-A1/-A2, BSP-A3 and BSP-30-kDa proteins stimulated cellular cholesterol and choline phospholipid efflux from fibroblasts. Efflux mechanistic differences were observed between BSP proteins and other cholesterol acceptors. Preincubation of BSP-A1/-A2 proteins with choline prevented cholesterol efflux, an effect not observed with apolipoprotein A-I. Also, the rate of BSP-induced efflux was rapid during the first 20 min, but leveled off thereafter in contrast to a relatively slow, but constant, rate of cholesterol efflux mediated by apolipoprotein A-I, apolipoprotein A-I-containing reconstituted lipoproteins (LpA-I) and high-density lipoproteins. These results indicate that fibroblasts are a good cell model to study the mechanism of lipid efflux mediated by BSP proteins.

Elevated circulating cardiac troponin I in patients with cirrhosis

It has been shown that certain patients with cirrhosis have asymptomatic cardiac abnormalities that have not yet been explained. Thus, cardiac troponin I, a specific marker of myocardial injury, has been measured in patients with cirrhosis without previous cardiac disease. Thirty-two consecutive patients (age 49 +/- 11) with cirrhosis and normal ECG were selected, 22 of which were alcoholic. Hemodynamic investigations were performed. Left ventricular function and mass were evaluated by echocardiography. Serum creatine kinase MB mass, myoglobin, and cardiac troponin I concentrations were measured. Cardiac troponin I concentrations were elevated in 10 patients (32%) (range 0.06-0.25 microg/L) whereas creatine kinase MB mass and myoglobin were normal in all patients. Abnormal troponin I values were not related to the severity of cirrhosis, to the degree of portal hypertension, or to other hemodynamic values. In contrast, elevated serum cardiac troponin I concentrations were related to a decreased stroke-volume index (P <. 05) and a decreased left ventricular mass (P <.05). These results show a high prevalence of slightly elevated serum cardiac troponin I in patients with cirrhosis, especially in those with alcoholic cirrhosis. Elevated troponin I is associated with subclinical left ventricular myocardial damage. These findings may be linked to a lack of left ventricular adaptation in certain patients with cirrhosis and alcoholic cardiomyopathy.

Heparin and high-density lipoprotein mediate bovine sperm capacitation by different mechanisms

Capacitation is an important process in bovine sperm maturation and is an obligatory step prior to fertilization. Two capacitating agents, namely heparin and high-density lipoprotein (HDL), have been shown to induce sperm capacitation. A family of major proteins of bovine seminal plasma designated BSP-A1/A2, BSP-A3, and BSP-30 kDa (collectively called BSP proteins) bind to the sperm surface upon ejaculation via their membrane choline phospholipids. Our previous studies with bovine epididymal sperm showed that BSP proteins potentiate sperm capacitation induced by heparin and HDL. This study was undertaken to clarify the mechanism of capacitation induced by heparin and HDL in the presence of BSP proteins. Washed bovine ejaculated sperm were incubated with heparin (12 microg/ml) or HDL (10-160 microg/ml) in the presence of polyclonal antibodies against purified BSP proteins (anti-BSP proteins). The percentage of capacitated sperm was evaluated after the induction of the acrosome reaction (AR) with lysophosphatidylcholine. When sperm were incubated for 5 h with heparin and anti-BSP proteins (40 microg/ml), the AR level was not significantly different from control levels (16. 8 +/- 0.9% vs. 12.9 +/- 0.9%). In contrast, incubation of sperm for 8 h with HDL and anti-BSP proteins did not inhibit the AR (42.4 +/- 1.1% vs. 17.1 +/- 1.6 for the control samples). We also investigated the effect of heparin and HDL on protein tyrosine phosphorylation associated with capacitation. The tyrosine phosphorylation of a group of proteins was increased in the presence of heparin. However, HDL did not significantly stimulate protein phosphorylation. The increase in phosphorylation was correlated with an increase in the AR after the incubation with heparin but not with HDL. These results indicate that heparin and HDL mediate capacitation via different mechanisms.

Endothelium-dependent blunted membrane potential responses to ATP-sensitive K+ channel modulators in aortae from rats with cirrhosis

BACKGROUND/AIMS

In vivo studies have shown that arterial vasodilation induced by synthetic openers of ATP-sensitive K+ (K(ATP)) channels is decreased in rats with cirrhosis. Since vasodilation induced by these substances is mediated by membrane potential hyperpolarization in arterial smooth muscle cells, membrane potential hyperpolarization in response to K(ATP) channel openers may be altered in cirrhotic smooth muscle cells. The aim of the present study was to investigate the effects of K(ATP) channel modulators (i.e. openers and blockers of these channels) on the membrane potential in smooth muscle cells in isolated aortae from cirrhotic and normal rats. The influence of endothelin-1 production by endothelial cells on smooth muscle cells membrane potential responses to K(ATP) channel modulators was also studied.

METHODS

Cells were impaled in situ (in intact and endothelium-denuded aortae) with a microelectrode that was used to measure membrane potentials. K(ATP) channel openers were diazoxide or cromakalim; blockers were glibenclamide or tolbutamide. Bosentan (a mixed endothelin receptor antagonist) and exogenous endothelin-1 were also used. Preproendothelin-1 mRNA was assayed in aortae by RNase protection assay. Aortic wall endothelin-1 concentration was measured by double antibody radioimmunoassay technique.

RESULTS

As expected, in smooth muscle cells in intact normal aortae, K(ATP) channel openers induced membrane potential hyperpolarization and K(ATP) channel blockers membrane potential depolarization. In smooth muscle cells in intact cirrhotic aortae, K(ATP) channel openers and blockers did not significantly change the membrane potential. Endothelium removal or exposure of intact aortae to bosentan restored normal membrane potential responses to K(ATP) channel modulators in cirrhotic smooth muscle cells and did not alter the effects of these substances in normal smooth muscle cells. In endothelium-denuded aortae, exposure to exogenous endothelin-1 suppressed membrane potential responses to K(ATP) channel modulators. In intact aortae, the abundance of preproendothelin-1 mRNA and endothelin-1 did not significantly differ between normal and cirrhotic rats.

CONCLUSIONS

K(ATP) channel opener-induced membrane hyperpolarization and K(ATP) channel blocker-elicited membrane depolarization are blunted in smooth muscle cells in intact cirrhotic aortae. This blunting is due to the activation of the endothelin-1 pathway in the aortic wall, downstream to the endothelial production of endothelin-1.

Vascular properties of isoflurane: comparison between normal and cirrhotic rats

Isoflurane is known to dilate blood vessels and to modulate nitric oxide production. Because cirrhosis is characterized by over production of endothelial nitric oxide, isoflurane-induced vasodilatation may be altered in this situation. We have compared the vasodilator effects of isoflurane in normal rats and rats with secondary biliary cirrhosis. Aortic rings (intact or endothelium denuded) from normal and cirrhotic rats were suspended in HEPES solution and preconstricted with KCl 40 mmol litre-1. Isoflurane dose-dependently relaxed vessels in both groups. Maximal relaxation was comparable between normal and cirrhotic rats in intact (mean 80 (SEM 4) vs 81 (6)%; ns) and in denuded (100 (4) vs 95 (5)%; ns) vessels. Intact vessels relaxed more than denuded vessels in both groups (100 (4) vs 80 (4)% (P = 0.0008) in normal rats and 95 (5) vs 80 (6)% (P = 0.0008) in cirrhotic rats). We conclude that cirrhosis did not modify isoflurane-induced vasodilatation and that the modulator effect of endothelium was conserved.

Cl- absorption across the thick ascending limb is not altered in cystic fibrosis mice. A role for a pseudo-CFTR Cl- channel

The cortical thick ascending limb (CTAL) absorbs Cl- via a Na+-K+-Cl- cotransport at the apical membrane and several Cl- channels at the basolateral membrane, including a 9-pS channel having several properties of the cystic fibrosis transmembrane conductance regulator (CFTR). Having checked that CFTR mRNA is present in the mouse CTAL, we investigated whether this channel is a CFTR molecule by applying the patch-clamp technique to CTALs microdissected from CFTR knockout mice (cftrm1Unc). The 9-pS channel was active in cell-attached patches from tubules of mice homozygous for the disrupted cftr gene [CFTR (-/-)] at the same frequency and with the same activity (NPo) as in normal [CFTR (+/+)] or heterozygous [CFTR (+/-)] mice. The conductive properties of the channel, studied on inside-out patches, were identical in CFTR (-/-), CFTR (+/+), and CFTR (+/-) tubules, as were the sensitivities to internal pH and internal ATP, two typical features of this channel. In addition, the Cl- absorption in isolated, microperfused CTALs and the Na+-K+-Cl- cotransport activity were identical in CFTR (-/-), CFTR (+/+), and CFTR (+/-) mice. These results show that the 9-pS Cl- channel is distinct from CFTR, and that the CFTR protein has no influence on the Cl- absorption in this part of the renal tubule.

In vitro and in vivo vascular responses to the L-type calcium channel activator, Bay K 8644, in rats with cirrhosis

A substance which increases the entry of extracellular calcium into arterial smooth muscle may decrease cirrhosis-induced vasodilation. The aim of the present study was to measure the effects of the L-type Ca2+ channel activator, Bay K 8644, on the haemodynamics of rats with cirrhosis. Vascular reactivity to this substance was also investigated. Splanchnic and systemic haemodynamic responses to Bay K 8644 (50 microg/kg) were measured in cirrhotic and normal rats. Contraction induced by 0.1 micromol/L Bay K 8644 was measured in arterial rings (aorta and superior mesenteric artery) from cirrhotic and normal rats. In cirrhotic rats, Bay K 8644 significantly decreased portal pressure (15%) and portal tributary blood flow (24%), significantly increased portal territory vascular resistance (54%) and did not significantly change hepatocollateral vascular resistance. Bay K 8644 significantly increased arterial pressure (7%) and systemic vascular resistance (24%) and did not change the cardiac index. In normal rats, Bay K 8644 significantly increased vascular resistance (150%) in portal, hepatocollateral and systemic territories and significantly decreased the cardiac index (44%). Changes in portal territory, hepatocollateral and systemic vascular resistances were significantly less marked in cirrhotic than in normal rats. In rings from the aorta and superior mesenteric artery, Bay K 8644-induced contraction was significantly lower in cirrhotic than in normal rats. In conclusion, in rats with cirrhosis, Bay K 8644 administration reduced vasodilation in splanchnic and systemic arteries and did not affect hepatocollateral vascular resistance. The Bay K 8644-induced reduction in splanchnic vasodilation caused a decrease in portal hypertension. This study also shows that Bay K 8644-induced vascular contraction was less marked in cirrhotic than in normal rats, in systemic and splanchnic vascular beds.

Major proteins of bovine seminal plasma and high-density lipoprotein induce cholesterol efflux from epididymal sperm

One of the hypotheses to explain the mechanism of capacitation involves the loss of sperm membrane cholesterol. Here, we studied whether or not the major proteins of bovine seminal plasma designated as BSP-A1, -A2, -A3, and -30-kDa (collectively called BSP proteins), which are implicated in sperm capacitation, induce cholesterol efflux. When epididymal sperm were labeled with [3H]cholesterol and incubated with bovine seminal plasma (0.05-2%) or BSP proteins (20-120 microg/ml) for 8 h, the sperm lost [3H]cholesterol (3.6-fold and 3-fold, respectively). The same results in the presence of BSP-A1/-A2 were obtained (3.5-fold) by direct determination of cholesterol on unlabeled epididymal sperm. Analysis of efflux particles by ultracentrifugation on a sucrose gradient revealed a single symmetrical peak of radioactivity at 1.14 g/ml. Immunoblotting of the fractions obtained from size-exclusion chromatography of the efflux particles showed that a portion of the BSP proteins were associated with [3H]cholesterol. Heparin (12 microg/ml) alone did not stimulate cholesterol efflux. In contrast, high-density lipoprotein (HDL, 100 microg/ml) alone stimulated cholesterol efflux up to 3.1-fold after 8 h. When labeled epididymal sperm were preincubated for 20 min with BSP-A1/-A2 (120 microg/ml), washed, and incubated with HDL (100 microg/ml) for 8 h, the total cholesterol efflux of the sperm suspension was 51.8 +/- 5.0% compared to 39.3 +/- 1.2% when HDL alone was used. These results indicate that BSP proteins and HDL play an important role in the sperm sterol efflux that occurs during capacitation. Furthermore, the heparin-induced sperm capacitation did not involve the efflux of sperm membrane cholesterol.

Beneficial effects of the 2-day administration of terlipressin in patients with cirrhosis and hepatorenal syndrome

BACKGROUND/AIMS

A treatment to induce a sustained increase in glomerular filtration rate in patients with hepatorenal syndrome has not yet been identified. Thus, the aim of the present study was to investigate the effects of terlipressin for 2 days on the glomerular filtration rate in patients with cirrhosis and hepatorenal syndrome.

METHODS

A double-blind, cross-over randomized study was performed in nine patients. Patients received terlipressin (2 mg/day for 2 days) and a placebo for 2 days in a randomized order.

RESULTS

Terlipressin administration significantly increased creatinine clearance (from 15+/-2 ml/min to 27+/-4 ml/min) and urine output (from 628+/-67 ml/day to 811+/-76 ml/day), but did not significantly change urinary sodium concentrations. Urinary sodium excretion was not significantly different after placebo administration (0.6+/-0.1 mmol/24 h) and terlipressin administration (9.3+/-7.2 mmol/24 h). Terlipressin administration significantly decreased plasma concentrations of renin and aldosterone but not atrial natriuretic peptide levels. Placebo elicited no significant effects.

CONCLUSIONS

This study shows that 2-day terlipressin administration increases the glomerular filtration rate in patients with cirrhosis and hepatorenal syndrome.

Beneficial hemodynamic effects of bosentan, a mixed ET(A) and ET(B) receptor antagonist, in portal hypertensive rats

In patients with cirrhosis, the plasma level of endothelin, a potent vasoconstrictor peptide, is elevated, and endothelin plays a role in increased intrahepatic vascular resistance. Thus, the aim of this study was to evaluate the hemodynamic effects of bosentan, a mixed ET(A) and ET(B) endothelin receptor antagonist in three models of portal hypertension. In all groups of rats, endothelin (2 microg/kg intravenously) administration significantly increased intrahepatic vascular resistance. In rats with secondary biliary cirrhosis, bosentan (30 mg/kg) significantly reduced portal pressure from 14.6 +/- 1.2 to 12.1 +/- 0.6 mm Hg, while portal blood flow and cardiac output increased by 45% and 57%, respectively. Thus, hepatocollateral vascular resistance decreased significantly from 177 +/- 19 to 101 +/- 9 dyn x s x cm(-5) x 10(-3). Similar results were observed in rats with CCl4-induced cirrhosis. In isolated perfused cirrhotic rat livers, bosentan (1 to 100 micromol/L) had no significant effect on hepatic vascular resistance. In portal vein-stenosed rats, bosentan administration significantly decreased portal pressure from 13.1 +/- 0.6 to 11.4 +/- 0.5 mm Hg by reducing portosystemic vascular resistance, because bosentan had no effect on vascular resistance of normal rat liver. In conclusion, bosentan administration decreased portal pressure in vivo by reducing hepatocollateral vascular resistance in rats with cirrhosis. Thus, mixed endothelin receptor antagonists might be a new approach in the pharmacological treatment of portal hypertension.

Effects of protein kinase C modulators on Na+/K+ adenosine triphosphatase activity and phosphorylation in aortae from rats with cirrhosis

Protein kinase C (PKC) modulates the activity and phosphorylation of the catalytic alpha-subunit of sodium-potassium-adenosine triphosphatase (Na+/K+ ATPase) in normal arteries. Because PKC is altered in cirrhotic aortae, Na+/K+ ATPase may also be altered in these arteries. The aim of the present study was to investigate alpha-subunit activity and phosphorylation in aortae from normal and cirrhotic rats, under baseline conditions and during exposure to PKC modulators. Alpha-subunit activity was assessed by measuring the amount of 32P released by hydrolysis of [gamma-32P]ATP in freshly isolated cell membranes (in the absence of PKC modulators only) and membrane depolarization caused by ouabain-induced alpha-subunit inhibition in isolated aortae (in the absence and presence of PKC modulators). Alpha-subunit phosphorylation was assessed by incorporation of 32P into alpha-subunits. Staurosporine, a PKC inhibitor, and phorbol 12,13-dibutyrate (PDBU), a PKC activator, were used. In addition, alpha-subunit expression was studied by Western blot analysis. In the absence of PKC modulators, the amount of 32P released by hydrolysis of [gamma-32P]ATP and ouabain-induced membrane depolarization were significantly lower in cirrhotic than in normal aortae. Staurosporine suppressed ouabain-induced membrane depolarization in cirrhotic and normal arteries. Ouabain-induced membrane depolarization was similar in cirrhotic aortae exposed to PDBU and in normal arteries studied under baseline conditions. Alpha-subunit phosphorylation was significantly lower in cirrhotic than in normal aortae, in aortae under baseline conditions, and in arteries exposed to staurosporine. Phosphorylation of the alpha-subunit was similar in cirrhotic aortae exposed to PDBU and in normal arteries under baseline conditions. Western blot analysis showed that the amount of alpha-subunit did not significantly differ between cirrhotic and normal aortae. In conclusion, a decrease in baseline Na+/K+ ATPase alpha-subunit activity occurs in aortae from cirrhotic rats as a result of reduced basal PKC activity. This PKC-dependent decreased alpha-subunit activity may be caused by a reduction in PKC-induced alpha-subunit phosphorylation.

Body pool and synthesis of ascorbic acid in adult sea lamprey (Petromyzon marinus): an agnathan fish with gulonolactone oxidase activity

Although many vertebrates can synthesize ascorbic acid (vitamin C), it is still unclear from the evolutionary perspective when the ability to synthesize the vitamin first appeared in the animal kingdom and how frequently the trait has been lost. We report here ascorbic acid biosynthesis ability in sea lamprey (Petromyzon marinus) which represent the most ancient vertebrate lineage examined thus far for presence of gulonolactone oxidase, the enzyme catalyzing the terminal step in biosynthesis of vitamin C. This finding supports the view that the ancestors of living vertebrates were not scurvy prone and that the loss of gulonolactone oxidase activity subsequently occurred several times in vertebrate phylogeny. Adult sea lamprey allocate significant amounts of ascorbic acid to the gonads to guaranty high-quality gametes. Tissue stores of ascorbate were maintained by de novo synthesis (1.2-1.3 mg of ascorbic acid/300-g sea lamprey per day at 15 degrees C) while sea lamprey fast during spawning migration. We estimate that the in vivo daily renewal rate of ascorbate is 4-5% of the whole-body ascorbate pool based on measurement of its biosynthesis and concentration in the whole animal.

Influence of transjugular intrahepatic portosystemic shunts (TIPS) on tissue oxygenation in patients with cirrhosis

AIMS/BACKGROUNDS: The aim of this prospective study was to evaluate the influence of transjugular portosystemic intrahepatic shunts (TIPS) on tissue oxygenation in patients with cirrhosis and refractory ascites.

METHODS

Five shunted patients were included in the study. The blood and tissue oxygenation values were analyzed 12 days and 4 months after TIPS procedure. The results were compared with those observed in patients treated by paracentesis.

RESULTS

Unlike patients treated by paracentesis, PaO2 values remained unchanged throughout follow-up in shunted patients. After the TIPS procedure, there was a transient increase in systemic O2 transport and O2 uptake and a transient decrease in O2 saturation of hepatic oxyhemoglobin. After 4 months, TIPS resulted in an increase in PCO2 values and bicarbonate concentrations.

CONCLUSIONS

The TIPS procedure seems to prevent the decrease in PaO2 observed in patients treated by paracentesis and may improve the respiratory alkalosis of cirrhosis.

Influence of aluminum on the regulation of PTH- and 1,25(OH)2D3-dependent pathways in the rat osteosarcoma cell line ROS 17/2.8

The role of hormonal status in the development of aluminum (Al)-dependent renal osteodystrophy, which is characterized by reduced bone matrix deposition, still remains largely unknown. To address this question, we used the osteoblast-like osteosarcoma cell line ROS 17/2.8 to evaluate the role of Al on parathyroid hormone (PTH)- and 1,25-dihydroxyvitamin D3 (1,25(OH)2D3)-dependent activities in these cells. Al (1 microM) caused an inhibition of basal and 1,25(OH)2D3-induced alkaline phosphatase, but only at low doses (< 1 nM) of the steroid. Al partly inhibited basal osteocalcin (OC) secretion in ROS cells (p < 0.001), and the dose-dependent increase in 1,25(OH)2D3-induced OC release by these cells was also reduced by 1 microM Al at low concentrations of the steroid (< or = 1 nM), whereas high doses of 1,25(OH)2D3 (> or = 5 nM) totally prevented the inhibiting effects of Al. Al also had strong inhibitory actions on PTH-dependent cAMP production by ROS cells over the concentration range tested (0.5-50 nM). This inhibitory action of Al was also observed for PTH-related peptide- (PTHrp, 50 nM) but not for Isoproterenol-dependent (100 nM) cAMP formation. To evaluate more fully the mechanism of this inhibition of cAMP formation, we investigated the effect of Al on toxin-modulated, G protein-dependent regulation of cAMP formation and on the activation of adenylate cyclase by Forskolin. Cholera toxin (CT, 10 micrograms/ml), applied to cells for 4 h prior to PTH challenge, enhanced cAMP production about 2-fold above PTH alone (p < 0.001), a process that was further stimulated by Al. Pertussis toxin (PT, 1 microgram/ml, 4 h) did not modify basal PTH-dependent cAMP formation by ROS cells. However, PT treatment prevented the inhibitory effect of Al on cAMP formation by these cells (p < 0.025). The stimulation of adenylate cyclase by Forskolin (0.1 and 1 microM), which bypasses G protein regulation, was not modified by Al, indicating that Al does not affect adenylate cyclase directly. Northern blot analysis of PTH receptor mRNA levels showed that Al did not modify PTH receptor message in ROS cells. Likewise, Western blot analyses of G protein subunits showed that Al did not significantly alter Gs alpha subunit levels, in accordance with the results obtained for cAMP-dependent formation in response to CT. In contrast, Gi alpha-1 and Gi alpha-2 subunits were decreased by Al treatment, consistent with PT-restricted increases in cAMP formation in Al-treated ROS cells. Taken together, these results suggest that Al has multiple actions in osteoblast-like ROS cells. The effects of Al are modulated by hormonal control of the pathways investigated. Al affects 1,25(OH)2D3-regulated functions only when this steroid is low. Al has large inhibitory effects on PTH- and PTHrp-dependent cAMP formation. This last feature is related to the ability of Al to alter the G protein transducing pathway for PTH/PTHrp-dependent formation of cAMP since it does not affect adenylate cyclase activity directly and does not affect the PTH receptor message level. Thus, Al has stronger deleterious effects in osteoblast-like cells with an already compromised 1,25(OH)2D3 status and can modulate specifically PTH/PTHrp-mediated cAMP formation at the postreceptor level.

Type II domains of BSP-A1/-A2 proteins: binding properties, lipid efflux, and sperm capacitation potential

Bovine seminal plasma contains a family of major proteins (collectively called 1BSP proteins) that potentiate sperm capacitation by binding to capacitation factors such as heparin and by stimulating sperm membrane cholesterol efflux. Here, we investigated the structure-function relationship of type II domains of BSP proteins. We isolated from a tryptic digest of citraconylated BSP-A1/-A2 proteins the intact second type II domain (domain b or Db). Similar to native protein, Db bound to heparin-Sepharose, p-aminophenylphosphorylcholine-Agarose and liposomes containing phosphatidylcholine. When assessed for biological function, Db did not stimulate cholesterol efflux from human fibroblasts, a cell model for lipid efflux studies, and from bovine spermatozoa, or potentiate bovine sperm capacitation induced by heparin and high-density lipoproteins. Therefore, type II motifs of BSP proteins represent binding units for sperm membrane choline phospholipids and heparin but the second type II domain of BSP-A1/-A2 alone is not sufficient to stimulate lipid efflux nor is sufficient to potentiate bovine sperm capacitation. Thus, the presence of both type II domains in BSP proteins is essential for the expression of functional properties, namely lipid efflux and sperm capacitation.

Protein kinase C alterations in aortic vascular smooth muscle cells from rats with cirrhosis

BACKGROUND/AIMS

Alterations in signal transduction in vascular smooth muscle cells may contribute to vascular hyporeactivity in cirrhosis. Protein kinase C plays a role in vascular cell contraction by modifying contractile proteins and intracellular [Ca2+] homeostasis. The aim of this study was to examine the vascular reactivity and expression of protein kinase Calpha in aortae from rats with cirrhosis.

METHODS

The contractile response to phorbol ester, a protein kinase C activator, was evaluated in endothelium-denuded aortic rings from normal and cirrhotic rats. Protein kinase Calpha expression was determined by Western blot analysis.

RESULTS

Maximal contraction was significantly less marked in cirrhotic (1.24+/-0.24 g) than in control (3.43+/-0.27 g) aortae. Phorbol myristate-acetate-induced contraction was dependent on extracellular [Ca2+] concentrations, as shown by a reduction in maximal contraction when control and cirrhotic aortic rings were exposed to a Ca2+-free medium. Increasing the intracellular [Ca2+], by incubation with a Ca2+ ionophore, significantly increased the maximal contraction induced by phorbol myristate-acetate in cirrhotic but not in control rat aortae. Protein kinase Calpha expression was significantly lower in aortae in cirrhotic than in control rats.

CONCLUSION

These results confirm alterations in protein kinase C in aortae from cirrhotic rats.

Acute and chronic haemodynamic effects of naftazone in portal hypertensive rats

It has been demonstrated that hyperproduction of nitric oxide (NO) plays a major role in the vasodilatation of cirrhosis; thus, the vasodilatation might be reversed by an inhibition of NO production. Experimental studies in isolated aortic rings showed that naftazone inhibits the effects of NO production. The aim of this study was to evaluate the haemodynamic effects of acute and chronic administration of naftazone in rats with portal hypertension. Haemodynamic values were measured either before and 10 min after intravenous administration of 432 microg/kg of naftazone or after 4 days of oral administration of 10 mg/kg per day. Acute administration of naftazone significantly reduced portal pressure in portal vein-stenosed and cirrhotic rats. This reduction was related to a decrease in the resistance of the liver and collateral circulation and it was associated with an increased cardiac output. Oral administration of naftazone significantly decreased portal pressure in rats with portal vein stenosis; this decrease depended on a significant reduction of portal blood flow. In both groups, arterial pressure did not change significantly. These haemodynamic effects differed from those observed following prazosin or propranolol administration. However, these effects were similar but less marked than those observed following N-nitro-L-arginine administration in systemic and splanchnic arterial territories. In conclusion, acute and oral administration of naftazone significantly reduces portal pressure by two different mechanisms in portal hypertensive rats. The exact mechanism has, however, to be elucidated.

Pharmacological and biochemical evidence for the regulation of osteocalcin secretion by potassium channels in human osteoblast-like MG-63 cells

Previous reports have suggested the involvement of voltage-activated calcium (Ca2+) channels in bone metabolism and in particular on the secretion of osteocalcin by osteoblast-like cells. We now report that potassium (K+) channels can also modulate the secretion of osteocalcin by MG-63 cells, a human osteosarcoma cell line. When 1,25-dihydroxyvitamin D3(1,25(OH)2D3)-treated MG-63 cells were depolarized by step increases of the extracellular K+ concentration ([K+]out) from 5-30 mM, osteocalcin (OC) secretion increased from a control value of 218 +/- 13 to 369 +/- 18 ng/mg of protein/48 h (p < 0.005 by analysis of variance). In contrast, in the absence of 1,25(OH)2D3, there is no osteocalcin secretion nor any effect of cell depolarization on this activity. The depolarization-induced increase in 1,25(OH)2D3-dependent osteocalcin secretion was totally inhibited in the presence of 10 microM Nitrendipine (a Ca2+ channel blocker, p < 0.005) without affecting cellular alkaline phosphatase nor cell growth. Charybdotoxin, a selective blocker of Ca2+-dependent K+ channels (maxi-K) present in MG-63 cells, stimulated 1,25(OH)2D3-induced osteocalcin synthesis about 2-fold (p < 0.005) after either 30, 60, or 120 minutes of treatment. However, Charybdotoxin was without effect on basal release of osteocalcin in the absence of 1,25(OH)2D3 pretreatment. Using patch clamp technique, we occasionally observed the presence of a small conductance K+ channel, compatible with an ATP-dependent K+ channel (GK[ATP]) in nonstimulated cells, whereas multiple channel openings were observed when cells were treated with Diazoxide, a sulfonamide derivative which opens GK(ATP). Western blot analysis revealed the presence of the N-terminal peptide of GK(ATP) in MG-63 cells, and its expression was regulated with the proliferation rate of these cells, maximal detection by Western blots being observed during the logarithmic phase of the cycle. Glipizide and Glybenclamide, selective sulfonylureas which can block GK(ATP), dose-dependently enhanced 1,25(OH)2D3-induced OC secretion (p < 0.005). Reducing the extracellular calcium concentration with EGTA (microM range) totally inhibited the effect of Glipizide and Glybenclamide on osteocalcin secretion (p < 0.005), which remained at the same levels as controls. Diazoxide totally prevented the effect of these sulfonylureas. These results suggest that voltage-activated Ca2+ channels triggered via cell depolarization can enhance 1,25(OH)2D3-induced OC release by MG-63 cells. In addition, OC secretion is increased by blocking two types of K+ channels: maxi-K channels, which normally hyperpolarize cells and close Ca2+ channels, and GK(ATP) channels. The role of these channels is closely linked to the extracellular Ca2+ concentration.