LDL cholesterol targets rarely achieved in familial hypercholesterolemia patients: A sex and gender-specific analysis

BACKGROUND AND AIMS

Despite lipid lowering therapy (LLT), reaching LDL-C targets in patients with familial hypercholesterolemia (FH) remains challenging. Our aim was to determine attainment of LDL-C target levels and reasons for not reaching these in female and male FH patients.

METHODS

We performed a cross-sectional study of heterozygous FH patients in five hospitals in the Netherlands and Norway. Clinical characteristics and information about LLT, lipid levels and reasons for not being on LDL-C treatment target were retrospectively collected from electronic medical records.

RESULTS

We studied 3178 FH patients (53.9% women), median age 48.0 (IQR 34.0-59.9) years. Median LDL-C before treatment and on-treatment was higher in women compared to men (6.2 (IQR 5.1-7.3) and 6.0 (IQR 4.9-7.2) mmol/l (p=0.005) and 3.0 (IQR 2.4-3.8) and 2.8 (IQR 2.3-3.5) mmol/L (p<0.001)), respectively. A minority of women (26.9%) and men (28.9%) reached LDL-C target. In patients with CVD, 17.2% of women and 25.8% of men reached LDL-C target. Women received less often high-intensity statins and ezetimibe. Most common reported reasons for not achieving the LDL-C target were insufficient effect of maximum LLT (women 17.3%, men 24.3%) and side effects (women 15.2%, men 8.6%).

CONCLUSIONS

In routine practice, only a minority of women and men with FH achieved their LDL-C treatment target. Extra efforts have to be made to provide FH patients with reliable information on the safety of statins and their long-term effects on CVD risk reduction. If statin treatment is insufficient, alternative lipid lowering therapies such as ezetimibe or PCSK9-inhibitors should be considered.

Profiling of immune-related gene expression in children with familial hypercholesterolaemia

BACKGROUND

Innate and adaptive immune responses are pivotal in atherosclerosis, but their association with early-stage atherosclerosis in humans is incompletely understood. In this regard, untreated children with familial hypercholesterolaemia may serve as a human model to investigate the effect of elevated low-density lipoprotein (LDL)-cholesterol.

OBJECTIVES

We aimed to study the immunological and inflammatory pathways involved in early atherosclerosis by examining mRNA molecules in peripheral blood mononuclear cells (PBMCs) from children with FH.

METHODS

We analysed the level of 587 immune-related mRNA molecules using state-of-the-art Nanostring technology in PBMCs from children with (n = 30) and without (n = 21) FH, and from FH children before and after statin therapy (n = 10).

RESULTS

176 genes (30%) were differentially expressed between the FH and healthy children at P < 0.05. Compared to healthy children, the dysregulated pathways in FH children included the following: T cells (18/19); B cells (5/6); tumour necrosis factor super family (TNFSF) (6/8); cell growth, proliferation and differentiation (5/7); interleukins (5/9); toll-like receptors (2/5); apoptosis (3/7) and antigen presentation (1/7), where the ratio denotes higher expressed genes to total number of genes. Statin therapy reversed expression of thirteen of these mRNAs in FH children.

CONCLUSION

FH children display higher PBMC expression of immune-related genes mapped to several pathways, including T and B cells, and TNFSF than healthy children. Our results suggest that LDL-C plays an important role in modulating expression of different immune-related genes, and novel data on the involvement of these pathways in the early atherosclerosis may represent future therapeutic targets for prevention of atherosclerotic progression.

Intake of a Protein-Enriched Milk and Effects on Muscle Mass and Strength. A 12-Week Randomized Placebo Controlled Trial among Community-Dwelling Older Adults

OBJECTIVES

To investigate the effect of 20 g protein with breakfast and evening meal on muscle mass, muscle strength and functional performance in older adults.

DESIGN

A double-blinded randomized controlled study.

SETTING

Oslo and Akershus University College of Applied Sciences, Norway.

PARTICIPANTS

Healthy community-dwelling men and women (≥ 70 years) with reduced physical strength and/or performance.

INTERVENTION

Subjects were randomly assigned to receive either protein-enriched milk (2 x 0.4 L/d; protein group) or an isocaloric carbohydrate drink (2 x 0.4 L/d; control group) with breakfast and evening meal for 12 weeks.

MEASUREMENTS

The primary endpoints were muscle mass measured by dual X-ray absorptiometry, and tests of muscle strength (one repetition maximum test of chest press and leg press) and functional performance (handgrip strength, stair calimb and repeated chair rise).

RESULTS

In total, 438 subjects were screened, 50 subjects were randomized and 36 completed the study. Chest press improved significantly in the protein (1.3 kg (0.1-2.5), p=0.03) and the control group (1.5 kg (0.0-3.0), p=0.048), but with no difference between the groups (p=0.85). No significant change in leg press (p=0.93) or muscle mass (p=0.54) were observed between the protein and the control group. Nor did we observe any significant differences in the functional performance tests (p>0.05 for all tests) between the groups.

CONCLUSION

Increased protein intake (2 x 20 g/d) did not significantly improve muscle mass, muscle strength or functional performance in healthy older weight stable adults. Whether intake of > 20 g protein to each meal is necessary for preservation of muscle mass and strength in older adults should be further investigated in a larger study. This underscores the need for well-designed studies that can differentiate between the effect of protein intake and increased energy. This trial was registered at Clinicaltrials.gov (ID no. NCT02218333).

Lifelong benefits on myocardial infarction mortality: 40-year follow-up of the randomized Oslo diet and antismoking study

BACKGROUND

The effects of saturated fat on atherosclerotic vascular disease are currently debated.

OBJECTIVES

In the Oslo cardiovascular study initiated in 1972/1973, a 5-year randomized intervention was conducted in healthy middle-aged men at high risk of coronary heart disease to compare the effects on coronary heart disease incidence of diet and antismoking advice versus control (no intervention). A significant reduction (47%) in first myocardial infarction incidence was observed. We have followed mortality up to 40 years to establish whether a lifelong benefit on mortality risk of myocardial infarction could be observed.

METHODS

In the present study, a total of 16 203 men (63% of those invited), aged 40-49 years, participated in a screening examination. Overall, 1232 men with total serum cholesterol levels of 6.9-8.9 mmol L(-1) (80% smokers) were included in the study. The dietary intervention consisted of mainly decreasing the intake of saturated fats and increasing fish and vegetable products, as well as weight reduction in overweight subjects. Smokers were advised to stop smoking. Cox regression analysis was used for statistical analyses.

RESULTS

The intervention group showed a sustained reduced risk of death at first myocardial infarction (hazard ratio 0.71, 95% confidence interval 0.51-1.00; P = 0.049), compared to control subjects up to 40 years. During follow-up, the beneficial effect developed gradually but proportionally up to about 15 years after randomization. Later, the curves were parallel. All-cause mortality decreased in the period 8-20 years after randomization, but not thereafter.

CONCLUSIONS

Receiving advice about a healthy lifestyle led to a long-term reduced risk of coronary mortality during the following 40 years. Our results suggest that systematically providing effective counselling for a healthy lifestyle for 5 years can lead to lifelong benefits.

Oxidized LDL level is related to gene expression of tumour necrosis factor super family members in children and young adults with familial hypercholesterolaemia

OBJECTIVE

Familial hypercholesterolaemia (FH) is associated with increased risk of premature atherosclerosis. Inflammation is a key event in atherogenesis, and we have previously reported an inflammatory imbalance between tumour necrosis factor (TNF)α and interleukin-10 in children with FH. Based on the potential role of TNF-related molecules in inflammation, we investigated the regulation of other members of the TNF superfamily (TNFSF)/TNF receptor superfamily (TNFRSF) in children and young adults with FH and matched healthy controls.

METHODS

Expression of TNFSF/TNFRSF genes in peripheral blood mononuclear cells (PBMCs) was quantified in children and young adults with FH prior to (n = 42) and after statin treatment (n = 10) and in controls (n = 25) by quantitative real-time polymerase chain reaction.

RESULTS

First we found that, compared with controls, the mRNA levels of OX40L, BAFFR and TRAILR1 were significantly higher, whereas TRAIL and TRAILR3 were significantly lower in children and young adults with FH. Secondly, levels of oxidized low-density lipoprotein (oxLDL) were significantly raised in the FH group, and correlated with the expression of OX40L, BAFFR and TRAILR1. Thirdly, oxLDL increased mRNA levels of BAFFR, TRAILR1 and TRAILR4 in PBMCs ex vivo from individuals with FH. Fourthly, OX40, acting through OX40L, enhanced the oxLDL-induced expression of matrix metalloproteinase-9 in THP-1 monocytes in vitro. Finally, after statin treatment in children with FH (n = 10), mRNA levels of OX40L and TRAILR1 decreased, whereas levels BAFF, TRAIL and TRAILR3 increased.

CONCLUSION

Our findings suggest the involvement of some TNFSF/TNFRSF members and oxLDL in the early stages of atherogenesis; this may potentially contribute to the accelerated rate of atherosclerosis observed in individuals with FH.

Metabolism of very long chain polyunsaturated fatty acids in isolated rat germ cells

Which cell type is responsible for the high levels of very long chain polyunsaturated fatty acids in testis and whether this fatty acid pattern is a result of a local synthesis are not presently known. In this study, fatty acid conversion from 20:4n-6 to 22:5n-6 and from 20:5n-3 to 22:6n-3 was investigated in isolated rat germ cells incubated with [1-14C]-labeled fatty acids. The germ cells elongated the fatty acids from 20- to 22-carbon atoms and from 22- to 24-carbon atoms but had a low delta6 desaturation activity. Thus, little [14C]22:5n-6 and [14C]22:6n-3 were synthesized. When Sertoli cells were incubated with [1-14C]20:5n-3 for 24 h, an active fatty acid elongation and desaturation were observed. In vivo germ cells normally have a higher content of 22:5n-6 or 22:6n-3 than Sertoli cells. An eventual transport of essential fatty acids from Sertoli cells to germ cells was thus studied. Different co-culture systems were used in which germ cells were on one side of a filter and Sertoli cells on the opposite side. When isolated pachytene spermatocytes or round spermatids were added to the opposite side of a semipermeable filter, approximately 1 nmol [14C]22:6n-3 crossed the filter. Little of this was esterified in the germ cells. Similarly, in using [1-14C]20:4n-6 in identical experiments, very little [14C]22:5n-6 was esterified in germ cells on the opposite side of the filter. Although the very active synthesis of 22:5n-6 and 22:6n-3 observed in Sertoli cells suggests a transport of these compounds to germ cells, this was not experimentally determined.

Studies on the metabolism of essential fatty acids in isolated human testicular cells

The essential fatty acid 22:6(n-3) is a minor component of the Western diet, but a major fatty acid in human testis and semen. In mature spermatozoa, the physical and fusogenic properties of the plasma membrane are probably influenced by its particular fatty acid composition. In this study, the synthesis of 22:6(n-3) and 22:5(n-6) was investigated in isolated human testicular cells. [1-(14)C]20:4(n-6), [1-(14)C]20:5(n-3), [1-(14)C]22:4(n-6) and [1-(14)C]22:5(n-3) were incubated in a 'crude' cell suspension (consisting of a mixture of the cells in the seminiferous tubule), and in fractionated pachytene spermatocytes and round spermatids. The esterification of fatty acids in lipid and phospholipid classes and the fatty acid chain elongation and desaturation were measured. The crude cell suspension metabolized the fatty acids more actively than did the fractionated germ cell suspension, indicating that types of cell other than the germ cells are important for fatty acid elongation and desaturation and thus the production of 22:6(n-3). This finding is in agreement with previous results in rats that indicated that the Sertoli cells are the most important type of cell for the metabolism of essential fatty acids in the testis. Some [1-(14)C]20:5(n-3) was elongated to [(14)C]22:5(n-3) in the fractionated germ cells, but very little was elongated further to [(14)C]24:5(n-3),possibly restricting the formation of [(14)C]22:6(n-3). In the fractionated germ cells, the fatty acid substrates were recovered primarily in the phospholipid fraction, indicating an incorporation in the membranes, whereas in the crude cells, more substrates were esterified in the triacylglycerol fraction. In the phospholipids, more radioactivity was recovered in phosphatidylcholine than in phosphatidylethanolamine and more radioactivity was recovered in phosphatidylethanolamine than in phosphatidylinositol or phosphatidylserine.

Differences in the conversion of the polyunsaturated fatty acids [1-(14)C]22:4(n-6) and [1-(14)C]22:5(n-3) to [(14)C]22:5(n-6) and [(14)C]22:6(n-3) in isolated rat hepatocytes

The reasons why most cellular lipids preferentially accumulate 22:6(n-3) rather than 22:5(n-6) are poorly understood. In the present work the metabolisms of the precursor fatty acids, [1-(14)C]20:4(n-6), [1-(14)C]22:4(n-6) versus [1-(14)C]20:5(n-3), [1-(14)C]22:5(n-3) in isolated rat hepatocytes were compared. The addition of lactate and L-decanoylcarnitine increased the formation of [(14)C]24 fatty acid intermediates and the final products, [(14)C]22:5(n-6) and [(14)C]22:6(n-3). In the absence of lactate and L-decanoylcarnitine, no [(14)C]24 fatty acids and [(14)C]22:5(n-6) were detected when [1-(14)C]22:4(n-6) was the substrate, whereas small amounts of the added [1-(14)C]22:5(n-3) was converted to [(14)C]22:6(n-3). Lactate reduced the oxidation of [1-(14)C]22:4(n-6) and [1-(14)C]22:5(n-3) while L-decanoylcarnitine did not. No significant differences between the total oxidation or esterification of the two substrates were observed. By fasting and fructose refeeding the amounts of [(14)C]24:4(n-6) and [(14)C]24:5(n-3) were increased by 2.5- and 4-fold, respectively. However, the levels of [(14)C]22:5(n-6) and [(14)C]22:6(n-3) were similar in hepatocytes from fasted and refed versus fed rats. With hepatocytes from rats fed a fat free diet the levels of [(14)C]24 fatty acid intermediates were low while the further conversion of the n-6 and n-3 substrates was high and more equal, approx. 33% of [1-(14)C]22:4(n-6) was converted to [(14)C]22:5(n-6) and 43% of [1-(14)C]22:5(n-3) was converted to [(14)C]22:6(n-3). The moderate differences found in the conversion of [1-(14)C]22:4(n-6) versus [1-(14)C]22:5(n-3) to [(14)C]22:5(n-6) and [(14)C]22:6(n-3), respectively, and the equal rates of oxidation of the two substrates could thus not explain the abundance of 22:6(n-3) versus the near absence of 22:5(n-6) in cellular membranes.

Metabolism of some radiolabeled essential fatty acids in isolated rat hepatocytes is affected by dietary ethanol

The metabolism of the essential fatty acids [1-14C]20:4n-6, [1-14C]20:5n-3 and [1-14C]22:6n-3 was studied in rat hepatocytes fed ethanol in two different diets. Using a diet with a low lipid content ethanol (1) reduced the elongation of eicosapentaenoic acid, (2) reduced the esterification of docosahexaenoic acid (DHA) in phospholipids (PL), (3) increased the oxidation of DHA, (4) increased the ratio of esterification of DHA in phosphatidylethanolamine (PE) compared to phosphatidylcholine (PC) (PE/PC ratio), (5) altered the formation of PL molecular species, and (6) induced a decrease in the endogenous content of the hepatocytes of arachidonic acid and linoleic acid and an increase in oleic acid, 20:3n-9 and DHA. Using a high lipid diet, only the above-mentioned effect (4) was induced by ethanol, not the effects (1)-(3) and (5)-(6).

The pathway from arachidonic to docosapentaenoic acid (20:4n-6 to 22:5n-6) and from eicosapentaenoic to docosahexaenoic acid (20:5n-3 to 22:6n-3) studied in testicular cells from immature rats

The concentration-dependent metabolism of 1-(14)C-labelled precursors of 22:5n-6 and 22:6n-3 was compared in rat testis cells. The amounts of [(14)C]22- and 24-carbon metabolites were measured by HPLC. The conversion of [1-(14)C]20:5n-3 to [3-(14)C]22:6n-3 was more efficient than that of [1-(14)C]20:4n-6 to [3-(14)C]22:5n-6. At low substrate concentration (4 microM) it was 3.4 times more efficient, reduced to 2.3 times at high substrate concentration (40 microM). The conversion of [1-(14)C]22:5n-3 to [1-(14)C]22:6n-3 was 1.7 times more efficient than that of [1-(14)C]22:4n-6 to [1-(14)C]22:5n-6 using a low, but almost equally efficient using a high substrate concentration. When unlabelled 20:5n-3 was added to a cell suspension incubated with [1-(14)C]20:4n-6 or unlabelled 22:5n-3 to a cell suspension incubated with [1-(14)C]22:4n-6, the unlabelled n-3 fatty acids strongly inhibited the conversion of [1-(14)C]20:4n-6 or [1-(14)C]22:4n-6 to [(14)C]22:5n-6. In the reciprocal experiment, unlabelled 20:4n-6 and 22:4n-6 only weakly inhibited the conversion of [1-(14)C]20:5n-3 and [1-(14)C]22:5n-3 to [(14)C]22:6n-3. The results indicate that if both n-6 and n-3 fatty acids are present, the n-3 fatty acids are preferred over the n-6 fatty acids in the elongation from 20- to 22- and from 22- to 24-carbon atom fatty acids. In vivo the demand for 22-carbon fatty acids for spermatogenesis in the rat may exceed the supply of n-3 precursors and thus facilitate the formation of 22:5n-6 from the more abundant n-6 precursors.

Monounsaturated trans fatty acids, elaidic acid and trans-vaccenic acid, metabolism and incorporation in phospholipid molecular species in hepatocytes

The incorporation of [14C]elaidic acid (trans18:1(n-9)) in phosphatidylcholine and phosphatidylethanolamine molecular species in isolated rat liver cells has been studied, and the results compared with the incorporation, previously published (B. Woldseth et al. Biochim Biophys Acta 1993; 1167: 296-302), of [14C]palmitic acid (16:0) and [14C]stearic acid (18:0) and with that of [14C]oleic acid (cis18:1(n-9)). The pattern of incorporation in phospholipid molecular species is similar to that of [14C]stearic acid and different from that of [14C]palmitic acid. In phosphatidylcholine [14C]trans18:1-18:2 and [14C]trans18:1-20:4 were the most abundant species, and in phosphatidylethanolamine [14C]trans18:1-20:4 was the predominant species. With increasing concentration of [14C]elaidic acid increasing amounts of [14C]trans18:1-[14C]trans18:1 were found. The total incorporation in phospholipids was less than that of [14C]stearic acid, but more than that of [14C]palmitic acid. The distribution in percent of [14C]elaidic acid in phospholipid classes was 8.8% in phosphatidylinositol, 1.8% in phosphatidylserine, 59.1% in phosphatidylcholine and 30.3% in phosphatidylethanolamine with 0.1 mmol l-1 substrate concentration. More [14C]elaidic acid than [14C]palmitic acid or [14C]stearic acid was oxidized. The incorporation in phospholipids of [14C]elaidic acid was very different from that of [14C]oleic acid. The main species with [14C]oleic acid were 16:0-[14C]cis18:1 in phosphatidylcholine, and [14C]cis18:1-20:4 in phosphatidylethanolamine. In some experiments [14C]18:2(n-6) was incubated together with unlabelled elaidic or unlabelled trans-vaccenic acid (trans18:1(n-7)). In these experiments, more trans18:1-18:2 was formed from elaidic acid than from trans-vaccenic acid, especially in phosphatidylethanolamine.

A comparative study of the metabolism of n-9, n-6 and n-3 fatty acids in testicular cells from immature rat

Dietary 18 and 20-carbon fatty acids of the n-6 and the n-3 families are metabolized to 22:5,n-6 and 22:6,n-3 by a sequence of specific desaturases and chain elongation via 24-carbon intermediates. This pathway is regulated so that more 22:6,n-3 than 22:5,n-6 is found in the tissues. Rat testis is an exception since 22:5,n-6 is present in large proportions in this organ. Therefore rat testis appears to be interesting for studies of the detailed synthesis of 22:5,n-6 compared with that of 22:6,n-3. By using fresh preparations of rat testicular cells from 19-day-old rats enriched in Sertoli cells, we compared the metabolism of 1-14C-labelled n-3, n-6 and n-9 fatty acids. The testicular cells actively synthesized 22:6,n-3 and 22:5, n-6, but not 22:4,n-9 from the 18 and 20-carbon precursors. Of 200 mol 14C-labelled C18 and C20 fatty acids added initially, approximately 20-40 mol were found as 24-carbon intermediates after 24 h of incubation. This indicates that the balanced capacity of elongation, desaturation and chain shortening favours the accumulation of 24-carbon intermediates in these cells. One exception was [1-14C]20:3,n-9 which was efficiently elongated to 22:3,n-9 but not to C24 fatty acids. Our data suggests that the poor elongation of n-9 fatty acids from C22- to C24 may be an important hindrance in the synthesis of 22:4,n-9. The efficient synthesis of 22:5,n-6 may also partly explain why this is the major 22-carbon fatty acid in rat testis.

Results of intensive long-term treatment of familial hypercholesterolemia

Fifty-seven patients with familial hypercholesterolemia (FH) with mean age of 48 years (range 30 to 69), participated in a follow-up examination 5.5 years after the completion of a 1-year trial with lovastatin, cholestyramine, probucol, or omega-3 fatty acids. The goals were to record quality of life, compliance to treatment, adverse effects, and clinical outcome. The quality of life was similar to that in a Norwegian reference population. The factors causing most distress to patients were keeping a diet low in saturated fats, taking medication, and fear of death. The medication was mostly prescribed in maximum dosages. At follow-up, the reduction in total cholesterol was 36% (p < 0.05), low-density lipoprotein (LDL) cholesterol 38% (p < 0.05), triglycerides 20% (p < 0.05) compared with being on diet therapy only. High-density lipoprotein (HDL) cholesterol increased 8% (p < 0.05). Intake of saturated and monounsaturated fat increased 1.5% and 1.7% (p < 0.05), respectively; polyunsaturated fat was unchanged. Three patients experienced myocardial infarction, of whom 2 died and 1 developed angina pectoris. Before the start of lovastatin treatment, 27 coronary events occurred per 1,000 patient-years in this group compared with 12 events per 1,000 patient-years thereafter. Of 28 patients reporting adverse events, 4 discontinued lovastatin and 3 discontinued cholestyramine. Several practical and psychological difficulties were associated with FH. Long-term intensive lipid-lowering therapy was possible in FH outpatients without loss of effect and with good compliance to therapy. Intensive therapy, today is, however, not sufficient for many FH patients to reach a therapeutic goal of LDL cholesterol < 4.0 mmol/L. More potent lipid-lowering agents are needed.

The metabolism of 22:5(-6) and of docosahexaenoic acid [22:6(-3)] compared in rat hepatocytes

Elevated levels of 22:5(-6), which is the elongated and desaturated product of arachidonic acid, is induced by selective n-3 fatty acid deficiency, especially in brain cortex. Less elongation and desaturation of 20:4(-6) than of 20:5(-3) has been found in intact rat liver cells in previous studies and is probably the main reason why so little 22:5(-6) is found under adequate nutritional conditions. The present study compares the metabolism of 22:5(-6) with the metabolism of 22:6(-3), the main n-3 fatty acid in mammals. Freshly isolated rat liver cells were incubated with [1-14C]22:5(-6) and [1-14C]22:6(-3). Oxidation and esterification in triacylglycerols, diacylglycerols and phospholipids were studied. The phospholipid classes were separated and the different molecular species identified. Rats with essential fatty acid deficiency were compared with control rats. 22:5(-6) was found to be a good substrate for membrane phospholipid biosynthesis and was conserved well in the phospholipid fraction of the rat liver cells for more than 3 h of incubation. More 22:5(-6) was esterified in the total phospholipid fraction and less was incorporated in triacylglycerols than observed with 22:6(-3) in hepatocytes from control animals. This was not the case in animals with essential fatty acid deficiency. 22:5(-6) was esterified to a greater extent in phosphatidylcholine than 22:6(-3) in control cells but not in essential fatty acid deficiency cells. More 22:5(-6) was coupled with 18.0 in the sn-1 position of the phospholipid molecular species than 22:6(-3) was in control cells.

Studies on the metabolism of [1-14C]5.8.11-eicosatrienoic (Mead) acid in rat hepatocytes

The oxidation, esterification and formation of chain elongated and desaturated products of [1-14C]5,8,11-eicosatrienoic (Mead) acid was studied. Liver cells from essentially fatty acid deficient (EFAD) and control rats were used. The metabolism of [1-14C]20:4, n-6 and [1-14C]20:5, n-3 were studied under the same experimental conditions. More 20:3, n-9 than 20:4, n-6 and 20:5, n-3 was oxidised both in EFAD and control cells. 20:3, n-9 was elongated to [14C]22:3, n-9 in both cell types and significant amounts of [14C]22:4, n-9 were formed in EFAD cells. Less 20:3, n-9 was esterified in phospholipids and more in triacylglycerol than observed with 20:4, n-6 and 20:5, n-3 in both cell types. 20:3, n-9 was mainly esterified in phosphatidylcholine and little was esterified in phosphatidylethanolamine compared to 20:4, n-6 and 20:5, n-3. In comparison, 20:3, n-9 was rather efficiently esterified in phosphatidylinositol as 18:0-20:3. [14C]22:4, n-9 formed from 20:3, n-9 in EFAD hepatocytes was esterified in triacylglycerol, not in phospholipids, unlike [14C]22:5, n-6 and [14C]22:6, n-3 which were mainly esterified in phospholipids.

Effects of adrenaline on excitation-induced stimulation of the sodium-potassium pump in rat skeletal muscle

Experiments were performed on isolated rat soleus and extensor digitorum longus (EDL) muscles of 4-week-old rats. In the soleus, direct electrical stimulation for 10 min induced a frequency-dependent increase in the ouabain-suppressible 86Rb+ uptake, which was maximal (+110%) at a frequency of 2 Hz. In the EDL this frequency only induced a 31% increase. A supramaximal concentration of adrenaline (10 mumol l-1) stimulated ouabain-suppressible 86Rb+ uptake by 80% and 27% in soleus and EDL, respectively. The combined effect of stimulation at 2 Hz and adrenaline was not significantly larger than each of the interventions alone in either of the muscles. The fractional loss of 22Na+ from soleus muscle was increased by around 50% by the exposure to adrenaline, electrical stimulation at 2 Hz or a combination of both. The effect of electrical stimulation on 22Na+ efflux was not prevented by addition of propranolol (1 or 10 mumol l-1). The results indicate that the stimulation of active Na+-K+ transport induced by adrenaline or electrical stimulation is much more pronounced in soleus (slow-twitch) muscle than in EDL (fast-twitch) muscle. Since it has been suggested that an accumulation of K+ ions in the extracellular space may play a role in the development of fatigue (Bigland-Ritchie 1984), our findings might be related to the fact that slow-twitch muscles have a much higher resistance to fatigue than fast-twitch muscles (Burke et al. 1971).