Hypercholesterolaemia severely impairs EDRF-dependent collateral perfusion following acute arterial occlusion in rabbit isolated ear.

1. We have used a rabbit isolated buffer-perfused ear as a model of acute arterial occlusion to investigate the effects of dietary-induced hypercholesterolaemia on EDRF-dependent collateral perfusion. The effects of hypercholesterolaemia on endothelium-dependent relaxations to acetylcholine were also investigated in the unligated isolated buffer-perfused ear of the rabbit. 2. In rabbits receiving a high cholesterol diet (1%) for 4 weeks, blood cholesterol levels were significantly (P < 0.001) increased (26.0 +/- 3.6 vs. 2.6 +/- 0.6 mmol l-1), EDRF-dependent collateral perfusion was similar to that in age-matched controls for the first 15 min after occlusion but then decreased and was significantly (P < 0.01) less than control during the maintenance phase of collateral perfusion. 3. Cholesterol feeding for 8 weeks (blood cholesterol = 56.2 +/- 3.8 vs. 1.3 +/- 0.1 mmol l-1) was associated with almost complete impairment of collateral perfusion, an effect previously observed following inhibition of EDRF synthesis. 4. Endothelium-dependent relaxations to acetylcholine in isolated perfused ears were impaired in the rabbits fed the diet for 8 weeks but not those fed for 4 weeks. In the 8 week group, the maximum relaxation of tone was 32.6 +/- 11.6% and was significantly (P < 0.01) less than that in the controls (77.9 +/- 5.7%). 5. We conclude that EDRF-dependent collateral perfusion is severely impaired in hypercholesterolaemia and that the level of impairment is related to the duration of feeding.     

Mechanotransduction through the endothelial cytoskeleton: mediation of flow- but not agonist-induced EDRF release.

1. We have used a cascade bioassay system and isolated arterial ring preparations to investigate the contribution of the endothelial microfilament and microtubule cytoskeleton to EDRF release evoked by time-averaged shear stress and by acetylcholine in rabbit abdominal aorta. 2. Cytochalasin B (1 microM) and phalloidin (100 nM) were used to depolymerize and stabilize, respectively, F-actin microfilaments. Colchicine (500 nM) was used to inhibit tubulin dimerization and thus disrupt the microtubule network. Experiments were performed before or 1 h after administration of agents to the donor perfusate or organ bath. 3. In cascade bioassay studies, time-averaged shear stress was manipulated with dextran (1-4% w/v, 80,000 MW), to increase perfusate viscosity. EDRF release induced by increased perfusate viscosity was significantly (P < 0.01) attenuated by cytochalasin B, phalloidin and colchicine. 4. Endothelium-dependent relaxations to acetylcholine (0.01-30 microM) in cascade bioassay and in isolated aortic ring preparations were unaffected by pretreatment with any of these agents both in terms of their EC50 and maximal responses. Endothelium-independent relaxations to sodium nitroprusside (0.001-10 microM) were similarly unaffected. 5. We conclude that the endothelial F-actin microfilament and microtubule networks are involved in the mechanotransduction pathway for flow-evoked EDRF release in rabbit abdominal aorta. However, these cytoskeletal elements appear to play no role in acetylcholine-induced EDRF release in this tissue.     

Absence of effect of calcium antagonists on endothelium-dependent relaxation in rabbit aorta.

The effect of chronic feeding of New Zealand White rabbits with nicardipine (60 mg kg-1 daily for 5 weeks) on the endothelium-dependent relaxation (EDR) to acetylcholine (ACh) was examined in vitro. The effect of acute exposure to nicardipine and diltiazem (10 mumol l-1) in the tissue bath was also examined. A bioassay system for endothelium-dependent relaxation factor (EDRF) in which a rabbit aortic ring with endothelium removed was used as recipient and a segment of rabbit aorta with endothelium as donor (producing EDRF in response to ACh) was developed. This system enabled the effect of nicardipine on the synthesis/release and on the relaxation to EDRF to be studied separately. The maximum relaxations to ACh in control and nicardipine-fed animals were 43.6 +/- 5.5 and 53.8 +/- 6.7% (mean +/- s.e. mean) of the contractile response to noradrenaline (NA, 1 mumol l-1) (n = 6, P greater than 0.05). Similarly the EDR to ACh was not significantly altered by acute exposure (30 min) to nicardipine or diltiazem. The maximum relaxations without and with nicardipine were 32.4 +/- 4.2% and 28.0 +/- 3.1% of the contraction to NA (1 mumol l-1) (n = 11, P greater than 0.05). The corresponding data for diltiazem were 42.1 +/- 5.7 and 36.4 +/- 7.3% respectively (n = 11, P greater than 0.05). Both calcium antagonists inhibited the contraction induced by potassium (100 mmol l-1). Nicardipine and diltiazem in concentrations of 100 mumol l-1 reduced the potassium-induced contraction to 33.0 +/- 9.0% and 53.8 +/- 6.7% of control respectively (n = 6, P less than 0.05). In the bioassay experiments the infusion of nicardipine on (a) the recipient tissue only and (b) the donor and the recipient tissue had no significant effect on the relaxant response observed in the recipient tissue when superfused with Krebs-bicarbonate buffer containing ACh via the donor tissue (n = 6, P greater than 0.05). These results indicate that nicardipine and diltiazem had no significant effect on synthesis/release and the relaxant response to EDRF in the rabbit aorta. Thus the translocation of Ca2+ accompanying the EDR to ACh in the rabbit aorta is likely to utilize Ca2+ channels not blocked by these calcium antagonists.     

Impairment of endothelium-dependent relaxation: an early marker for atherosclerosis in the rabbit.

1. Cholesterol feeding of rabbits impairs the endothelium-dependent relaxation (EDR) evoked by acetylcholine (ACh) in the aorta. The experiments described in this paper were undertaken to examine the influence of age upon this phenomenon. 2. Rabbits aged 8 weeks and 46 weeks were fed a diet containing 2% cholesterol and other lipids for 4 weeks. Age-matched control animals were fed a standard rabbit diet. The concentrations of cholesterol and triglycerides in plasma were measured and the extent of atherosclerosis was estimated by staining the aortae with Sudan Red. Light and electron microscopy were undertaken also. 3. Rings of aorta were prepared for recording isometric tension. They were contracted with noradrenaline (NA) and EDR elicited by adding ACh. 4. The young rabbits showed weight gain, hypercholesterolaemia, prominent Sudan Red staining, together with scanning and transmission electron microscopic (SEM and TEM) features of cholesterol-induced atherosclerosis. The older animals showed significant weight loss and hypercholesterolaemia. The aortae of these animals showed no significant sudanophilia or light microscopic features of atherosclerosis. The SEM appearances were similar to the young animals fed cholesterol. 5. EDR to ACh was significantly impaired in both groups of cholesterol-fed rabbits. The maximal relaxations to ACh in young control and cholesterol-fed rabbits were 46.4 +/- 2.9% and 24.0 +/- 4.3% (mean +/- s.e. mean, n = 8, P less than 0.05) of the contractile response to NA (1 mumol 1(-1]. The corresponding results in the age control and cholesterol-fed rabbits were 31.8 +/- 3.9% and 9.1 +/- 1.5% (n = 9, P less than 0.05). 6. The young rabbits were far more susceptible to cholesterol-induced atherosclerosis than older animals and these changes were accompanied by loss of EDR. In the older animals and these changes were accompanied by loss of EDR. In the older animals the loss of the latter property was not accompanied by a significant degree of atherosclerosis although hypercholesterolaemia was present.     

EFFECTS OF ARACHIDONATE DEFICIENCY ON ENDOTHELIUM- DEPENDENT VASCULAR REACTIONS

1. The release of endothelium-derived relaxing factor (EDRF), which appears to be impaired in vessels chronically exposed to hypertension, may involve mobilization of arachidonate from phospholipids. In this study the effects of arachidonate deficiency on endothelium-dependent responses were examined in rat isolated aorta. 2. Weanling rats were fed an essential fatty acid-deficient (EFAD) diet for 8 weeks which reduced plasma and aortic phospholipid arachidonate content from 17 to 1.8% and from 21 to 8%, respectively. After this time the rats were killed and the reactivity of aortic rings was studied in organ baths. 3. In aortic rings from control rats the concentration-response curves for the contractile action of phenylephrine were shifted to the left 3.5-fold by removal of the endothelium, and the maximum was not altered. 4. In contrast, in EFAD rings with endothelium, the maximal vasoconstriction to phenylephrine was less than in control rings, and removal of the endothelium increased the maximum (from 1.9 +/- 0.2 to 3.2 +/- 0.1 g, P less than 0.05) and reduced the EC50 7-fold. 5. In EFAD rings precontracted with phenylephrine (0.3 mumol/l) the relaxations produced by the endothelium-dependent dilator acetylcholine were not significantly different from those produced in control rings. The dilator actions of sodium nitroprusside were also similar in EFAD and control rings. 6. Thus, endothelium-dependent dilatation in the aorta is not impaired by partial depletion of phospholipid arachidonate. However, contractile responses to alpha-adrenoceptor agonists are depressed by spontaneously released EDRF in rat aorta, so that the results suggest that depletion of phospholipid arachidonate either augments spontaneous release of EDRF, or impairs EDRF inactivating mechanisms.     

Endothelium-derived relaxing factor and the effects of acetylcholine and histamine on resistance blood vessels.

1. The role of endothelium-derived relaxing factor (EDRF) in the action of vasodilator (acetylcholine, histamine, nitroprusside) and vasoconstrictor (noradrenaline, vasopressin) drugs on vascular resistance in the isolated perfused kidney and mesentery of the rat was studied. 2. Acetylcholine (EC50 = 0.18 +/- 0.05 nmol and 3.1 +/- 0.06 nmol, n = 8) and histamine (EC50 = 31.2 +/- 4.9 nmol and 46.2 +/- 3.9 nmol, n = 8) produced dose-related vasodilatation in noradrenaline-preconstricted (i.e. 'high tone') rat renal and mesenteric blood vessels. The response to both vasodilators (but not nitroprusside) was abolished by infusion of CHAPS (4.7 mg ml-1, 30 s). By use of an immunocytochemical staining procedure CHAPS was demonstrated to remove vascular endothelial cells lining intrarenal blood vessels. 3. Gossypol (3 microM), metyrapone (10 microM) and nordihydroguaiaretic acid, (NDGA, 30 microM), presumed inhibitors of EDRF biosynthesis, reduced or abolished the response to acetylcholine and histamine in perfused kidney and mesentery of the rat without affecting vasodilatation due to nitroprusside. Mepacrine (10 microM) similarly abolished the response to acetylcholine and histamine but in addition, reduced the response to nitroprusside in both preparations. 4. Methylene blue (100 microM), a presumed antagonist of the effect of EDRF, abolished vasodilatation due to acetylcholine and histamine and reduced the response to nitroprusside in perfused rat kidney and mesentery. Superoxide dismutase, SOD (15 u ml-1), was without effect.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of hypercholesterolaemia and atherosclerosis on alpha-adrenoceptor-mediated vasoconstriction in conscious rabbits and rabbit aorta.

Rabbits were fed a diet containing 1% cholesterol for 4 or 8 weeks and the constrictor responses to alpha-adrenoceptor agonists, as well as endothelium-dependent and endothelium-independent dilatation, were examined both in vivo and in vitro. The high cholesterol diet caused a significant elevation of plasma cholesterol concentration but no macroscopic evidence of atherosclerosis after 4 weeks whereas after 8 weeks there was a significant development of atherosclerotic lesions in the thoracic and abdominal aorta. In conscious rabbits pressor responses to the non-selective alpha-adrenoceptor agonist noradrenaline and the selective alpha 1-adrenoceptor agonist phenylephrine were enhanced after 4 weeks but returned to control levels after 8 weeks on the diet. The pressor responses to the alpha 2-adrenoceptor agonist B-HT 920 were reduced by the development of atherosclerosis. In the isolated thoracic aorta from these rabbits contractile responses to noradrenaline were impaired by hypercholesterolaemia whereas responses to phenylephrine were unaffected. Endothelium-dependent relaxation was impaired by hypercholesterolaemia both in vivo and in vitro after 4 and 8 weeks on the diet whereas endothelium-independent relaxation was not affected. These results indicate that the effect of hypercholesterolaemia on alpha-adrenoceptor-mediated constriction is dependent on: (1) the absence or presence of atherosclerotic lesions, (2) the size of the artery and (3) the subtype of alpha-adrenoceptor involved in the response. There does not appear to be any relationship between the loss of endothelium-dependent relaxation in hypercholesterolaemia and the observed changes in adrenergic vasoconstriction.     

Decrease in serum LDL cholesterol with microcrystalline chitosan.

Peroral microcrystalline chitosan (MCCh; 3 capsules, each 400 mg b.i.d.) or placebo was given for 8 weeks in a double-blind manner to 51 healthy obese women just before routine hospital and home meals. Weight records, serum lipids (total, LDL and HDL cholesterol, triglycerides) and safety laboratory parameters were monitored before the trial and at 4, 6 and 8 weeks of treatment. In a subgroup of subjects with a body mass index > or = 30 who had not changed their eating habits, serum LDL cholesterol decreased 0.57 +/- 0.72 mmol/l (n = ll) at 4 weeks in the MCCh group and 0.10 +/- 0.60 mmol/l (n = 14) in the placebo group (p < 0.05). At 8 weeks, LDL cholesterol reduction was 0.48 +/- 0.91 mmol/l in the MCCh group and 0.26 +/- 0.57 mmol/l in the placebo group (p > 0.1). In all subjects, the reduction in LDL cholesterol at 4 weeks was 0.48 +/- 0.72 mmol/l (n = 24) in MCCh subjects and 0.18 +/- 0.58 mmol/l (n = 27) in placebo subjects (p = 0.057), and 0.52 +/- 0.69 mmol/l and 0.31 +/- 0.63 mmol/l, respectively, at 8 weeks (p > 0.1). MCCh did not significantly alter serum total and HDL cholesterol (p > 0.1), but slightly increased serum triglycerides compared to placebo (p = 0.015-0.06). No reductions in weight were observed in any treatment group. Chitosan was well tolerated and no serious adverse events or changes in safety laboratory parameters were noted including serum fat-soluble vitamins A and E, and serum Fe++ and transferrin.     

Decreased aortic glutathione levels may contribute to impaired nitric oxide-induced relaxation in hypercholesterolaemia

The aim of this study was to determine if the decrease in aortic total glutathione (GSH) levels in hypercholesterolaemia is related to the impairment of relaxation to acetylcholine (ACh) and exogenous nitric oxide (NO). Isometric tension and vascular GSH levels were measured in thoracic aortic rings from rabbits fed for 12 weeks with 0.5% cholesterol diet. Hypercholesterolaemia decreased aortic GSH levels and impaired relaxation to ACh and NO. To determine if GSH depletion impaired the response to NO, normal rabbit thoracic aorta was incubated with 1,3-bis [2-chloroethyl]-1-nitrosourea (BCNU; 0.2 mmol L(-1)), a GSH reductase inhibitor, or diazine-dicarboxylic acid bis [N, N dimethylamide] (diamide; 1 mmol L(-1)), a thiol oxidizing agent. BCNU or diamide decreased aortic GSH levels and impaired ACh and NO-induced relaxation. The effects of diamide on GSH levels and relaxation were partially prevented by co-incubation with GSH ester (GSE; 2 mmol L(-1)). Increasing GSH with GSE significantly enhanced NO-induced relaxation in aorta from both hypercholesterolaemic and normal rabbits, however relaxation of hypercholesterolaemic rabbit aorta was not restored to normal. These data suggest that other factors, perhaps related to the long-term decrease in GSH levels, are responsible for reduced NO bioactivity in hypercholesterolaemia.     

Release and vascular activity of endothelium-derived relaxing factor in atherosclerotic rabbit aorta.

A diet containing 0.3% cholesterol was given to male New Zealand rabbits for 16 weeks; this produced atherosclerotic lesions (fatty streaks) on 80% of the intimal surface of the thoracic aorta and on 45% of the intimal surface of the abdominal aorta. The endothelium-dependent relaxations induced by acetylcholine, substance P and ionophore A23187 were inhibited in the atherosclerotic aortas. Besides the endothelium-independent relaxations induced by nitroglycerine, the relaxations induced by atrial natriuretic peptide (ANF) were also significantly reduced in the more atherosclerotic thoracic aorta. In bioassay experiments it was found that acetylcholine and substance P caused a smaller release of endothelium-derived relaxing factor (EDRF) from atherosclerotic thoracic aortas than from control thoracic aortas: the EDRF released by the vasodilators evoked less relaxation in atherosclerotic detector abdominal aortas than in control detector abdominal aortas. Nitric oxide evoked significantly less transient relaxation in the atherosclerotic thoracic and abdominal aortas than in the respective control tissues. The data indicate that as experimental atherosclerosis in the rabbit progresses, both vascular activity and EDRF release become affected; this leads to a complete loss of endothelium-dependent relaxation in the more atherosclerotic blood vessels.     

1-Methylnicotinamide (MNA) prevents endothelial dysfunction in hypertriglyceridemic and diabetic rats

For many years, 1-methylnicotinamide (MNA), a primary metabolite of nicotinamide, has been considered inactive. Recently however, it has been discovered that MNA possesses anti-thrombotic and anti-inflammatory activity. In the present study we investigated whether chronic administration of MNAto hypertriglyceridemic or diabetic rats would reverse endothelial dysfunction characterized by the impairment of nitric oxide (NO)-dependent vasodilatation. Hypertriglyceridemia in rats was induced by fructose-rich (60%) diet, while diabetes was induced by streptozotocin injection (70 mg/kg). After eight weeks, in hypertriglyceridemic or diabetic rats treated or non-treated with MNA(100 mg/kg), we analyzed the magnitude of endothelium-dependent or endothelium-independent vasodilatation in aorta induced by acetylcholine or S-nitroso-N-acetyl-penicilamine (SNAP), respectively, as well as plasma concentration of: cholesterol, triglycerides, glucose, HbA(1c), fructosamine, peptide C, endogenous MNAand its metabolites (M2PY, M4PY). In diabetic rats plasma concentration of glucose, HbA(1c) and fructosamine was elevated (402.08 +/- 19.01 vs. 82.06 +/- 5.41 mg/dl, p < 0.001; 9.55 +/- 0.56 vs. 4.93 +/- 0.24%, p = 0.052 and 2.53 +/- 0.10 vs. 1.14 +/- 0.06 mmol DTF/mg protein, p < 0.001 in diabetic and control rats, respectively). In hypertriglyceridemic rats plasma concentration of triglycerides was elevated (4.25 +/- 0.27 vs. 1.55 +/- 0.12 mmol/l, p < 0.001 in hypertriglyceridemic and control rats, respectively). In both models the NO-dependent vasodilatation in aorta induced by acetylcholine was significantly impaired as compared to control rats, while the response to SNAP was largely preserved. In hypertriglyceridemic rats, 4 weeks of treatment with MNA(100 mg/kg, po) resulted in a three to six-fold increase in endogenous levels of MNA and its metabolites (M2PY and M4PY), the fall in triglycerides concentration in plasma (from 4.25 +/- 0.27 to 2.22 +/- 0.14 mmol/l, p < 0.001), and the preservation of the NO-dependent vasodilatation. In diabetic rats chronic treatment with MNAalso prevented the impairment of NO-dependent vasodilatation, while it displayed only a mild effect on hyperglycemia and did not lower triglycerides concentration. In summary, MNAtreatment decreased plasma triglycerides concentration in hypertriglyceridemic, but not in diabetic rats, while it prevented the development of endothelial dysfunction in aorta in both of these models. Accordingly, the ability of MNAto reverse endothelial dysfunction seems to be independent of its hypolipemic activity.     

Differential role of extra- and intracellular calcium in the release of EDRF and prostacyclin from cultured endothelial cells.

1. The effects of extracellular Ca2+ on the release of endothelium-derived relaxing factor (EDRF) and prostacyclin (PGI2), and on the intracellular free calcium concentration [( Ca2+]i), were studied in cultured bovine aortic endothelial cells. 2. Receptor-mediated stimulation of endothelial cells with bradykinin (10 nM) elicited a transient release of EDRF (assayed by its stimulant effect on purified soluble guanylate cyclase) and of PGI2 (measured by radioimmunoassay for 6-keto prostaglandin F1 alpha). 3. Bradykinin (10 nM) also increased [Ca2+]i (measured with the fluorescent probe indo-1) from 125 +/- 11 nM to 631 +/- 59 nM, with the same time course as for autacoid release. 4. In Ca2+-free medium, [Ca2+]i was still increased by bradykinin but declined faster (within 1 min) to resting levels than in the presence of extracellular Ca2+. 5. PGI2 release was almost completely abolished in Ca2+-free medium. The intracellular calcium antagonist TMB-8 evoked a similar inhibition of PGI2 release. 6. In contrast, bradykinin-induced EDRF release was not significantly affected by TMB-8 but was completely abolished in Ca2+-free medium. 7. When endothelial cells were stimulated with the receptor-independent drug thimerosal (an inhibitor of the enzyme acyl-CoA-lysolecithin-acyl-transferase; 5 microM), a long-lasting release of EDRF (greater than 90 min) and PGI2 (greater than 20 min) was observed. 8. In contrast to bradykinin stimulation, thimerosal-induced autacoid release was associated with only a slight increase of [Ca2+]i to 201 +/- 13 nM after 40 min.(ABSTRACT TRUNCATED AT 250 WORDS)     

Electrophysiological and other aspects of the relaxant action of isoprenaline in guinea-pig isolated trachealis.

In guinea-pig isolated trachealis isoprenaline (0.001-0.1 mumol l-1) caused concentration-dependent relaxation. Propranolol (1 mumol l-1) antagonized the effects of isoprenaline by more than 100 fold but did not modify the relaxant action of sodium nitrite. The tracheal relaxant actions of isoprenaline and ATP were unaffected by apamin (0.1 mumol l-1) but apamin profoundly antagonized the effects of noradrenaline and ATP on guinea-pig isolated taenia caeci. Tetraethylammonium (TEA; 8 mmol l-1) and procaine (5 mmol l-1) each evoked tracheal spasm but neither agent antagonized the isoprenaline-evoked relaxation of the trachealis. Trachealis exposed to K+-rich (120 mmol l-1) Krebs solution developed near-maximal tension. Both isoprenaline and sodium nitrite relaxed the K+-depolarized tissue though concentration-effect curves for both relaxants were moved to the right compared to those obtained in non-depolarized tissues. The maximal effect of sodium nitrite was markedly reduced. Intracellular electrophysiological recording showed that isoprenaline (0.01-1 mumol l-1) caused hyperpolarization and reduced or abolished slow wave discharge in trachealis muscle. These effects were accompanied by relaxation. Propranolol (1 mumol l-1) virtually abolished both the electrical and mechanical responses to isoprenaline (0.1 mumol l-1). Apamin (0.1 mumol l-1) did not alter the spontaneous electrical activity of trachealis cells or their electrical and mechanical responses to isoprenaline (0.1 mumol l-1). TEA (8 mmol l-1) caused depolarization and often increased slow wave amplitude and induced spike discharge. Isoprenaline (0.01 mumol l-1) failed to hyperpolarize TEA-treated trachealis cells. Higher concentrations of isoprenaline suppressed TEA-induced spasm, caused hyperpolarization and thereby increased slow wave or spike amplitude. Slow wave or spike frequency decreased as the hyperpolarization progressed but abolition of slow waves or spikes sometimes required more than 4 min exposure to isoprenaline. Procaine (5 mmol l-1) increased the amplitude of slow waves and induced spike discharge. Procaine markedly reduced the hyperpolarization induced by isoprenaline (0.1 and 1 mumol l-1) but had little effect on isoprenaline-induced relaxation. It is concluded that isoprenaline activates beta-adrenoceptors in guinea-pig trachealis and thereby evokes relaxation and hyperpolarization of the smooth muscle. The hyperpolarization does not involve the opening of apamin-sensitive K+-channels and it probably plays a supportive rather than a crucial role in the process by which isoprenaline-induced relaxation is achieved.     

Hyperphosphataemia and hypocalcaemia induced by hypertonic phosphate enema--an experimental study and review of the literature.

1. The study objective was to determine the hyperphosphataemic and hypocalcaemic effect of hypertonic phosphate enema. The study was conducted in a department of Internal Medicine at a University Medical Center. 2. Fourteen patients were studied. Patients' mean age (+/- s.d.) was 78.5 +/- 9 years. The creatinine clearance was 48.2 +/- 17.4 ml min-1 (mean +/- s.d.). 3. 500 ml (approx. 7 ml kg-1) of Fleet enema (FE - Na2HPO4.7H2O 224 mmol l-1 and NaH2PO4.H2O 1160 mmol l-1) were administered to each patient. Blood was drawn before FE administration and 1/2, 1, 3, 5, 12 and 24 h thereafter. Serum was analysed for levels of inorganic phosphorus and for calcium. 4. The serum inorganic phosphorus level rose from 1.01 +/- 0.3 mmol l-1 to 1.4 +/- 0.5 mmol l-1 (P = 0.001) 1 h after FE was administered. Serum calcium decreased from 2.32 +/- 0.12 mmol l-1 to 2.12 +/- 0.1 mmol l-1 (P less than 0.001) 12 h after FE was administered. 5. We conclude that FE carries a potential risk for acutely ill elderly patients. To avoid untoward effects due to hyperphosphataemia and hypocalcaemia, the phosphate load must be adjusted to the patient's renal function, i.e. enema volume is to be lowered when phosphate concentration is high, so that if renal function is compromised the amount of phosphate absorbed does not exceed renal excretion capacity.     

Endothelium-dependent increase in vascular sensitivity to phenylephrine in long-term streptozotocin diabetic rat aorta.

1. The effect of short- and long-term streptozotocin (STZ)-induced diabetes (12 and 52 weeks) on the vascular response to phenylephrine was examined in the isolated thoracic aorta with and without intact endothelium from diabetic, age matched control rats and diabetic rats treated with insulin. 2. Twelve weeks after induction of diabetes, aortae with intact endothelium demonstrated no changes either in sensitivity (defined as pD2) or contractility (defined as the maximal developed tension per aortic tissue wet weight) to phenylephrine. 3. In contrast, 52 weeks after induction of diabetes, aortae with intact endothelium demonstrated an increased sensitivity to phenylephrine while contractility to phenylephrine was not changed. Insulin treatment partially corrected the increased sensitivity to phenylephrine observed in diabetic rat aorta. 4. Removal of endothelium abolished the difference in phenylephrine sensitivity between diabetic and control aortae at 52 weeks. 5. Pretreatment of intact aortae with methylene blue, an inhibitor of endothelium-derived relaxing factor (EDRF), abolished the difference in phenylephrine sensitivity between control and diabetic rat aortae at 52 weeks, while pretreatment with indomethacin, an inhibitor of cyclo-oxygenase, had no effect. These results suggest that decreases in production or release of EDRF might be responsible for the increased vascular sensitivity to phenylephrine observed in long-term STZ diabetic rats. 6. Acetylcholine-induced relaxation, which is EDRF-dependent, was less in diabetic rat aortae with intact endothelium at 52 weeks, but not at 12 weeks. These results further support the theory that decreases in capacity of the endothelium to synthesize or release EDRF may occur in long-term STZ diabetic rats.     

Endothelium-derived hyperpolarizing factor but not NO reduces smooth muscle Ca2+ during acetylcholine-induced dilation of microvessels.

1. We hypothesized that nitric oxide (NO) and the endothelium-dependent hyperpolarizing factor (EDHF) may dilate microvessels by different cellular mechanisms, namely Ca2+-desensitization versus decrease in intracellular free calcium. 2. Effects of acetylcholine (ACh) and the NO donors sodium nitroprusside (SNP, 0.1 - 10 micromol l(-1)) and S-Nitroso-N-acetyl-D, L-penicillamine (SNAP, 0.01 - 10 micromol l-1) on intracellular calcium ([Ca2+]i, fura 2) and vascular diameter (videomicroscopy) were studied in isolated resistance arteries from hamster gracilis muscle (194+/-12 microm) pretreated with indomethacin and norepinephrine. Membrane potential changes were determined using 1, 3-dibutylbarbituric acid trimethineoxonol (DiBAC4(3)). 3. ACh (0.1 and 1 micromol l-1)-induced dilations were associated with a [Ca2+]i decrease (by 13+/-3 and 32+/-4%) and hyperpolarization of vascular smooth muscle (VSM, by 12+/-1% at 1 micromol l-1 ACh). Nomega-nitro-L-arginine (L-NA, 30 micromol l(-1)) partially inhibited the dilation but did not affect VSM [Ca2+]i decreases or hyperpolarization. In contrast, the KCa channel inhibitors tetrabutylammonium (TBA, 1 mmol l(-1)) and charybdotoxin (ChTX, 1 micromol l(-1)) abolished the ACh-induced [Ca2+]i decrease and the hyperpolarization in VSM while a significant dilation remained (25 and 40%). This remaining dilation was abolished by L-NA. ChTX did not affect [Ca2+]i increase and hyperpolarization in endothelial cells. SNP- or SNAP-induced dilations were not associated with decreases in VSM [Ca2+]i or hyperpolarization although minor transient decreases in VSM [Ca2+]i were observed at high concentrations. 4. These data suggest that ACh-induced dilations in microvessels are predominantly mediated by a factor different from NO and PGI2, presumably EDHF. EDHF exerts dilation by activation of KCa channels and a subsequent decrease in VSM [Ca2+]i, NO dilates the microvessels in a calcium-independent manner.     

A comparison of acipimox and nicotinic acid in type 2b hyperlipidaemia.

The side effect profiles and lipid lowering efficacy of nicotinic acid (1 g three times daily) and its analogue acipimox (250 mg three times daily) in type 2b hyperlipidaemia were compared in a double-blind placebo controlled study. In the nicotinic acid group (n = 7) at 12 weeks there were significant reductions (P less than 0.05) with respect to placebo (n = 9) in total cholesterol (median and range) 6.6 mmol l-1 (4.8-8.4) vs 8.8 mmol l-1 (7.5-9.5), triglyceride 1.4 mmol l-1 (0.5-4.6) vs 2.8 mmol l-1 (1.5-9.5) and apoprotein B 88.6 mg dl-1 (62.1-114) vs 121.9 mg dl-1 (88.0-170.7). In contrast there was no significant alteration in lipids in the acipimox group (n = 12). Nicotinic acid was associated with a high incidence of side effects, principally cutaneous flushing, while acipimox was well tolerated by all patients.     

Reduction of plasma cholesterol by lovastatin normalizes erythrocyte membrane fluidity in patients with severe hypercholesterolaemia.

The effect of lovastatin on erythrocyte membrane composition and fluidity was investigated in eight patients with severe hypercholesterolaemia (mean LDL-cholesterol of 7.2 mmol l-1). Lovastatin was administered at a dosage of 40-80 mg for 20 weeks and was discontinued for 5 weeks thereafter. Parallel to a 47% fall in plasma LDL cholesterol, there was a significant reduction (P < 0.01) in erythrocyte membrane cholesterol:phospholipid molar ratio, while erythrocyte membrane fluidity assessed by diphenylhexatriene (DPH) fluorescence polarization increased significantly (P < 0.01). Discontinuation of lovastatin resulted in the reversal of erythrocyte membrane composition and fluidity to pre-treatment values.     

A comparison of basal and agonist-stimulated release of endothelium-derived relaxing factor from different arteries

1. The release of endothelium-derived relaxing factor (EDRF) from rabbit aorta and pig coronary artery vessels in response to acetylcholine (ACh), substance P (SP) and the calcium ionophore A23187 has been studied by means of a bioassay cascade system. 2. A technique is described which allows the quantification of EDRF release rates from vessels of different sizes, perfused at different flow rates and with different donor-recipient transient times. 3. Rabbit aorta and pig coronary arteries, perfused at flow rates which equalize endothelial shear stress, released EDRF at a similar basal rate. 4. In response to ACh, rabbit aortic endothelium released EDRF at a significantly greater maximum rate than pig coronary artery endothelium. 5. In response to SP, both endothelium types released EDRF; SP was a significantly more potent agonist in pig coronary artery than in rabbit aorta, but maximum SP-induced EDRF release from rabbit aorta was twice that of pig coronary artery. 6. These data indicate that different endothelium types can release EDRF at widely different rates, according to the agonist used, and that the previously obtained lack of relaxant response to ACh in pig coronary artery was due to a lack of EDRF release rather than concomitant smooth muscle constriction.     

A comparison of the effects of simvastatin and pravastatin monotherapy on muscle histology and permeability in hypercholesterolaemic patients.

1. In this double-blind, placebo controlled, prospective study, it was assessed whether simvastatin or pravastatin monotherapy have adverse effects on muscle histology and muscle membrane permeability in hypercholesterolaemic patients. 2. Twenty-four patients, seven females and 17 males, with primary hypercholesterolaemia (LDL cholesterol levels > or = 4.14 mmol l-1) were selected from the outpatient lipid clinic of a 650 bed academic medical centre. 3. After a 6-week lipid lowering diet and placebo period, patients were randomized into two groups of 12 subjects with similar characteristics, to receive either simvastatin or pravastatin in dosages of 10-40 mg day-1 for three periods of 6 weeks. After each 3-week period the dose was adjusted to LDL cholesterol to aim for equipotent dosage. 4. All subjects performed a 45 min, lean body mass standardized bicycle ergometer test, before and after 18 weeks of treatment. As parameter for muscle damage, the exercise-induced rise of the muscle proteins, creatine kinase (CK) and myoglobin (Mb), relative to pre-exercise levels, were determined 1 and 8 h after the test. Forty-eight hours after each test a biopsy was taken from the quadriceps muscle and histology was judged by three independent observers. 5. Eighteen weeks of monotherapy with simvastatin and pravastatin did not affect the exercise induced release of CK and Mb, neither were any differences observed in muscle histology before and after treatment with either of the drugs. 6. Although simvastatin doses were lower than pravastatin, reductions in total- and LDL-cholesterol were greater in the simvastatin treated patients than in the pravastatin treated group.(ABSTRACT TRUNCATED AT 250 WORDS)