Liver fat storage pathways: methodologies and dietary effects

PURPOSE OF REVIEW

Nonalcoholic fatty liver is the result of an imbalance between lipid storage [from meal, de novo lipogenesis (DNL) and fatty acid (FA) uptake] and disposal (oxidation and VLDL output). Knowledge on the contribution of each of these pathways to liver fat content in humans is essential to develop tailored strategies to prevent and treat nonalcoholic fatty liver. Here, we review the techniques available to study the different storage pathways and review dietary modulation of these pathways.

RECENT FINDINGS

The type of carbohydrate and fat could be of importance in modulating DNL, as complex carbohydrates and omega-3 FAs have been shown to reduce DNL. No effects were found on the other pathways, however studies investigating this are scarce.

SUMMARY

Techniques used to assess storage pathways are predominantly stable isotope techniques, which require specific expertise and are costly. Validated biomarkers are often lacking. These methodological limitations also translate into a limited number of studies investigating to what extent storage pathways can be modulated by diet. Further research is needed to elucidate in more detail the impact that fat and carbohydrate type can have on liver fat storage pathways and content.

Patterns of proliferation related to vasculature in human head-and-neck carcinomas before and after transplantation in nude mice

PURPOSE

The predictive potential of tumor cell kinetic parameters may be improved when they are studied in relation to other microenvironmental parameters. The purpose of this investigation was to quantitatively categorize human tumor samples according to proliferation patterns. Second, it was examined whether these characteristics are retained after xenotransplantation.

METHODS AND MATERIALS

Fifty tumor samples from head-and-neck cancer patients were immunohistochemically stained for Ki-67 and vessels. Also, parts of the samples were transplanted into nude mice. Tumors were categorized according to previously described patterns of proliferation. Vascular and proliferation patterns were analyzed using an image processing system.

RESULTS

The 50 tumors were categorized into four patterns of proliferation by visual assessment: marginal (6), intermediate (10), random (21), and mixed (12). One tumor could not be classified. These patterns were quantified by calculating the Ki-67 labeling index in distinct zones at increasing distance from vessels yielding good discrimination and significant differences between patterns. The probability of growth after xenotransplantation was significantly higher for tumors with a labeling index and vascular density above the median value compared to tumors with both parameters below the median (82% vs. 35%). Fifty percent of the tumors retained their proliferation patterns after xenotransplantation.

CONCLUSION

The categorization by proliferation pattern previously described by others was reproduced quantitatively and spatially related to the vascular network using a computerized image processing system. The combination of quantitative and architectural information of multiple microenvironmental parameters adds a new dimension to the study of treatment resistance mechanisms. Tumor models representative of the various patterns can be used to further investigate the relevance of these architectural patterns.

Reproducibility of ultrasound blood flow measurement of the superior mesenteric artery before and after exercise

This study examines the reproducibility of gastro-intestinal blood flow measurements in the superior mesenteric artery (SMA) both before and immediately after exercise with Doppler ultrasound measurements. Twelve well-trained males (mean +/- SD: age 25.9 +/- 3.8 yr; VO2max 4.8 +/- 0.91 x min(-1)) were measured twice (trial 1 and 2) with a 1 week interval before and immediately after 1 hr cycling at 70% VO2max. Duplex scanning was performed with the athletes in supine position immediately after transition from a chair (before exercise) or bicycle (after exercise). The variability of three measurements before exercise was studied within both trials (short-term reproducibility) and the mean pre-exercise values were compared between the trials (long-term reproducibility). In addition, post-exercise measurements were compared in the same way. Reproducibility was tested using the coefficient of variation and Cronbach's alpha. Mean pre-exercise blood flow was 424 +/- 66 ml/min (n = 12) in trial 1 and 375 +/- 38 ml/min (n = 11) in trial 2. Immediately after exercise blood flow had decreased by 49% to 214 +/- 36 ml/min (p <0.01) in trial 1 and by 38% to 234 +/- 36 ml/min (p < 0.01) in trial 2. Blood flow before and after exercise was not significantly different between trials (paired t-test) and therefore reproducible at the group level. Before exercise a good to fair reproducibility was observed both at the short-term (Cronbach's alpha: 0.88 in trial 1, 0.73 in trial 2, n = 11), and at the long-term (alpha = 0.80, n= 11). In contrast, long-term reproducibility immediately after exercise was poor (alpha = -0.99, n = 8 and alpha = 0.36, n = 7 after the first and second cycling period, respectively). In conclusion, duplex scanning of SMA after a sitting-supine transition in well-trained subjects is not a reproducible method at the individual level for intestinal blood flow measurements immediately after exercise.

Potential benefits and hazards of physical activity and exercise on the gastrointestinal tract

This review describes the current state of knowledge on the hazards of exercise and the potential benefits of physical activity on the gastrointestinal tract. In particular, acute strenuous exercise may provoke gastrointestinal symptoms such as heartburn or diarrhoea. A substantial part (20-50%) of endurance athletes are hampered by these symptoms which may deter them from participation in training and competitive events. Nevertheless, these acute symptoms are transient and do not hamper the athlete's health in the long term. The only exception is repeated gastrointestinal bleeding during training and competition, which in the long term may occasionally lead to iron deficiency and anaemia. In contrast, repetitive exercise periods at a relatively low intensity may have protective effects on the gastrointestinal tract. There is strong evidence that physical activity reduces the risk of colon cancer by up to 50%. Less convincing evidence exists for cholelithiasis and constipation. Physical activity may reduce the risk of diverticulosis, gastrointestinal haemorrhage, and inflammatory bowel disease although this cannot be substantiated firmly. Up to now, underlying mechanisms are poorly understood although decreased gastrointestinal blood flow, neuro-immuno-endocrine alterations, increased gastrointestinal motility, and mechanical bouncing during exercise are postulated. Future research on exercise associated digestive processes should give more insight into the relationship between physical activity and the function of the gastrointestinal tract.

Noninvasive assessment of the functional neovasculature in 9L-glioma growing in rat brain by dynamic 1H magnetic resonance imaging of gadolinium uptake

Pathophysiologic parameters of the functional neovasculature and the blood-brain barrier of 9L-glioma in rat brain were measured noninvasively by dynamic 1H magnetic resonance imaging studies of gadolinium (Gd)-DTPA uptake. Changes of apparent [Gd-DTPA] uptake in time (CT[t]) were analyzed in a slice through the center of 10 9L-gliomas using fast T1 measurements. The distribution of the contrast agent was spatially correlated with the distribution of perfused microvessels as determined by immunohistochemical analysis. This method permits a distinction between perfused and nonperfused microvessels with a disrupted blood-brain barrier. In transverse slices of the whole tumor, a spatial correlation was observed between CT maps and the two-dimensional distribution of perfused microvessels. In the next step, Gd-DTPA uptake rates were spatially related to the perfused microvessel density (Np) or vascular surface area (Sp). In tumor voxels with perfused microvessels, a linear correlation was found between Gd-DTPA uptake rate constants (k values) and Np or Sp. No correlation was observed between k values and the total microvessel density. These are the first data that show a relation between Gd-DTPA uptake rates and parameters of the functional neovasculature in 9L-glioma growing in rat brain. Now that Gd-DTPA uptake studies can be related to parameters of the functional neovasculature, they may be used more efficiently as a prognostic tool before or during therapy.

The effect of a sports drink on gastroesophageal reflux during a run-bike-run test

The effects of different modes of prolonged exercise and different drinks on gastroesophageal reflux and reflux-related symptoms were examined. In a cross-over design seven male triathletes performed two tests at one week intervals (50 min periods of alternately running, cycling and running at 70-75% VO2max), with supplementation of either a conventional sports drink (7% carbohydrates) or tap water. Gastroesophageal reflux (percentage time and number of periods esophageal pH < 4) was measured with an ambulant pH system before, during and after exercise. Percentage reflux time (+/- SEM) during running, cycling, running and recovery was 24.0 +/- 4.6, 8.2 +/- 4.8, 17.6 +/- 8.4 and 11.8 +/- 4.0 with carbohydrates and 7.4 +/- 2.9, 0 +/- 0, 2.4 +/- 1.4 and 0.2 +/- 0.2 with water, respectively. Reflux lasted longer during exercise as compared to the rest situation (5.6 + 1.4%), especially with carbohydrates, and lasted longer with carbohydrates than with water (P < 0.05; Wilcoxon signed rank test). In general, reflux lasted longer during running than during cycling (P < 0.05). Data on the number of reflux periods are concordant to these results. Chest pain was reported by one subject during running with carbohydrates. Heartburn during running was reported by two subjects with water and by one with carbohydrates. In conclusion, physical exercise increases gastroesophageal reflux, dependent on the mode of exercise and beverage used.

Gastrointestinal mucosal integrity after prolonged exercise with fluid supplementation

PURPOSE

Studies on the effect of exercise on gastrointestinal (GI) mucosal integrity have been limited to occult-blood tests, which were often nonspecific for human blood. The aim of our study was to investigate more aspects of this integrity.

METHODS

We examined the effect of prolonged exercise and carbohydrate (CHO) supplementation on mucosal integrity in 22 male triathletes by measuring fecal lysozyme, alpha1-antitrypsin, and occult-blood loss, which was examined by two tests specific for human blood (Colon-Albumin and Monohaem test). Exercise consisted of two 150-min tests (alternately running, cycling, and running at 70-75% VO2max), either with a 7.0% CHO drink or water (W). Furthermore, GI symptoms during exercise were registered by questionnaire.

RESULTS

Three subjects showed human albumin only in the first stool after exercise: twice with W and once with CHO. However, human hemoglobin (Hb) could not be detected in these samples. Four other subjects showed an elevated lysozyme concentration after exercise with CHO but not with W. Elevated alpha1-antitrypsin values were found in three of seven specimens in which either positive albumin tests and/or an elevated lysozyme concentration were demonstrated. Twenty-one subjects (95%) reported one or more GI symptoms during exercise. Incidence rates of different GI symptoms varied from 5 to 68%. Most symptoms were more frequent and lasted longer during running than during cycling but did not differ significantly between supplements and were not related to any mucosal integrity parameter.

CONCLUSIONS

GI blood loss during exercise is of no clinical importance, at least in our study design with a group of well-trained male subjects who consumed a relatively high amount of fluid (up to 2.3 L). Nevertheless, an increased alpha1-antitrypsin and lysozyme concentration may indicate a transient local mucosal damage with an inflammatory response.

The effect of omeprazole on gastro-oesophageal reflux and symptoms during strenuous exercise

BACKGROUND

Strenuous exercise exacerbates gastro-oesophageal reflux and symptoms and this may be diminished by antisecretory medication with omeprazole.

METHODS

Fourteen well-trained athletes (13 men, one woman), who indicated suffering from either heartburn, regurgitation or chest pain during competition running, performed two experimental trials at 2-week intervals using a randomized, double-blind, placebo-controlled crossover design. During the 6 days preceding the trial and on the trial day itself either 20 mg of omeprazole or a placebo was administered. Two hours after a low-fat breakfast and 1 h after the last study dose, the trial started with five successive 50-min periods: rest, three running periods on a treadmill, and recovery. Reflux (percentage time and number of periods oesophageal pH <4) was measured with an ambulant pH system during these periods.

RESULTS

Compared to rest, reflux lasted significantly longer and occurred more frequently during the first running period, irrespective of the intervention, whereas during the second running period this effect was only observed with the placebo. Reflux occurred for longer and more frequently with the placebo than with omeprazole, but this was significant during the first two running periods only. Seven subjects reported heartburn, regurgitation and/or chest pain during exercise, irrespective of the intervention. Only a minority of the symptom periods was actually associated with acid reflux and in all cases this concerned periods with heartburn.

CONCLUSIONS

Running-induced acid reflux, but not symptoms, were decreased by omeprazole, probably because most symptoms were not related to acid reflux.

Gastrointestinal symptoms in long-distance runners, cyclists, and triathletes: prevalence, medication, and etiology

OBJECTIVE

The aim of this study was to determine the prevalence of exercise-related gastrointestinal (GI) symptoms and the use of medication for these symptoms among long-distance runners, cyclists, and triathletes, and to determine the relationship of different variables to GI symptoms.

METHODS

A mail questionnaire covering the preceding 12 months was sent to 606 well-trained endurance type athletes: 199 runners (114 men and 85 women), 197 cyclists (98 men and 99 women), and 210 triathletes (110 men and 100 women) and sent back by 93%, 88%, and 71% of these groups, respectively. Symptoms were evaluated with respect to the upper (nausea, vomiting, belching, heartburn, chest pain) or lower part of the GI tract (bloating, GI cramps, side ache, urge to defecate, defecation, diarrhea). For statistical analysis, Mann-Whitney U test, Fisher exact test, or Student t test were used.

RESULTS

Runners experienced more lower (prevalence 71%) than upper (36%) GI symptoms during exercise. Cyclists experienced both upper (67%) and lower (64%) symptoms. Triathletes experienced during cycling both upper (52%) and lower (45%) symptoms, and during running more lower (79%) than upper (54%) symptoms. Bloating, diarrhea, and flatulence occurred more at rest than during exercise among all subjects. In general, exercise-related GI symptoms were significantly related to the occurrence of GI symptoms during nonexercise periods, age, gender, diet, and years of training. The prevalence of medication for exercise-related GI symptoms was 5%, 6%, and 3% for runners, cyclists, and triathletes, respectively.

CONCLUSIONS

Long-distance running is mainly associated with lower GI symptoms, whereas cycling is associated with both upper and lower symptoms. Triathletes confirm this pattern during cycling and running. The prevalence of medication for exercise-related GI symptoms is lower in the Netherlands in comparison with other countries, in which a prevalence of 10-18% was reported. More research on the possible predisposition of athletes for GI symptoms during exercise is needed.

Characterization and validation of noninvasive oxygen tension measurements in human glioma xenografts by 19F-MR relaxometry

PURPOSE

The aim of this study was to characterize and to validate noninvasive 19F-magnetic resonance relaxometry for the measurement of oxygen tensions in human glioma xenografts in nude mice. The following three questions were addressed: 1. When perfluorocarbon compounds (PFCs) are administrated intravenously, which tumor regions are assessed by 19F-MR relaxometry? 2. Are oxygen tension as detected by 19F-MR relaxometry (pO2/relaxo) comparable to Eppendorf O2-electrode measurements (pO2/electrode)? 3. Can 19F-MR relaxometry be used to detect oxygen tension changes in tumor tissue during carbogen breathing?

METHODS AND MATERIALS

Slice-selective 19F-MR relaxometry was carried out with perfluoro-15-crown-5-ether as oxygen sensor. The PFC was injected i.v. 3 days before the 19F-MR experiments. Two datasets were acquired before and two after the start of carbogen breathing. The distribution of PFCs and necrotic areas were analyzed in 19F-Spin Echo (SE) density MR images and T2-weighted 1H-SE MR images, respectively. One day after the MR investigations, oxygen tensions were measured by oxygen electrodes in the same slice along two perpendicular tracks. These measurements were followed by (immuno)histochemical analysis of the 2D distribution of perfused microvessels, hypoxic cells, necrotic areas, and macrophages.

RESULTS

The PFCs mainly became sequestered in perfused regions at the tumor periphery; thus, 19F-MR relaxometry probed mean oxygen tensions in these regions throughout the selected MR slice. In perfused regions of the tumor, mean PO2/relaxo values were comparable to mean PO2/electrode values, and varied from 0.03 to 9 mmHg. Median pO2/electrode values of both tracks were lower than mean pO2/relaxo values, because low pO2 electrode values that originate from hypoxic and necrotic areas were also included in calculations of median pO2/electrode values. After 8-min carbogen breathing, the average PO2/relaxo increase was 3.3 +/- 0.8 (SEM) mmHg and 2.1 +/- 0.6 (SEM) after 14 min breathing.

CONCLUSIONS

We have demonstrated that PFCs mainly became sequestered in perfused regions of the tumor. Here, mean PO2/relaxo values were comparable to mean PO2electrode values. In these areas, carbogen breathing was found to increase the PO2/relaxo values significantly.

Gastrointestinal symptoms during long-distance walking

PURPOSE

Gastrointestinal (GI) symptoms are common during prolonged intense exercise. To examine whether GI symptoms are also common during prolonged exercise of lower intensity, we obtained data on incidence, duration, and severity of GI symptoms during four consecutive days walking with a total distance of 203 km for men and 164 km for women.

METHODS

The research population consisted of 79 men and 76 women, aged 30-49 yr, who responded to a questionnaire and a diary concerning anthropometric data, activity pattern, dietary intake, and GI symptoms.

RESULTS

The results show that 24% of the subjects experienced one or more symptoms. Nausea, headache, and flatulence were the most frequent symptoms. Nine subjects dropped out during the race, two of whom indicated that they stopped as a result of one or more GI symptoms. Logistic regression analysis revealed that the occurrence of GI symptoms was a significant exercise-limiting factor. Univariate analysis showed that incidence and duration of GI symptoms were significantly related to the subjects' experience (number of prior participations to the event), body weight loss during walking, and several components of the diet before and during the event. A significant relationship between GI symptoms and age, gender, training status, and walking speed could not be found.

CONCLUSIONS

We conclude that GI symptoms during long-distance walking can impair exercise performance, although these symptoms occur less frequently and are less severe in comparison with prolonged intense exercise.

Hemorheological response to prolonged exercise--no effects of different kinds of feedings

Thirty-one male triathletes performed three experimental trials at one week intervals, with either a semi-solid or liquid carbohydrate feeding, or a liquid placebo. Exercise consisted of three hours of alternately cycling, running, cycling, and running at 75% VO2 max. Venous blood samples were taken before and immediately after the exercise. Viscometry was performed with a Contraves LS-30 viscometer and erythrocyte deformability was measured with the LORCA, a laser diffractometric system. Exercise caused a significant increase in whole blood and plasma viscosity, hematocrit, and osmolality, and a very small, but significant decrease in erythrocyte deformability, irrespective of the feedings consumed. Changes were not related to exercise performance, as defined by the maximal test time, probably due to a large fluid intake. The intake of different amounts of carbohydrate had no influence on the hemorheological parameters, probably since water content was equal among feedings. Erythrocyte deformability changes were small in comparison with the other hemorheological changes and a correlation between erythrocyte deformability and other parameters was absent. This may be due to erythrocyte properties to counterbalance volume shifts to ensure an optimal oxygen delivery in the microcirculation.

Exercise performance as a function of semi-solid and liquid carbohydrate feedings during prolonged exercise

Aim of this study was to examine the effects of a semi-solid and a liquid carbohydrate feeding on exercise performance. Thirty-two male triathletes performed three exercise trials (3 hours maximal at 75% VO2max) with either a semi-solid feeding (S), an iso-caloric liquid feeding (F) or a liquid placebo (P). Exercise consisted of cycling (bout 1 and 3) and running (bout 2 and 4). Survival analysis revealed that the median maximum test time (MTT) with F, S and P was 180, 126 and 120 min, respectively. Median MTT was longer with F than with S (sign-test; p < 0.05) or P (p < 0.001), with no difference between S and P. Mean power output during supra-maximal tests after bout 2 (W1) and at the end of exercise (Wend) were 371, 365, 362 and 334, 332, 321 W with F, S and P, respectively. Differences between F and P were significant (p < 0.01). Regression analysis identified five variables that were associated with 93% of the variance in MTT. The variance in W1 was explained for 83% by three variables. Wend was explained (90%) by three variables. A significant dietary contribution to MTT and Wend was found, but not to W1. This suggests that the influence of the feedings on performance is different among performance tests.

Hydrogen breath test as a simple noninvasive method for evaluation of carbohydrate malabsorption during exercise

The aim of this study was to examine hydrogen (H2) production with the hydrogen breath test (HBT) after ingesting primarily digestible carbohydrate (CHO) during 3 h of 75% maximal oxygen consumption exercise. This was done to indicate CHO overflow in the colon which may occur when gastric emptying, intestinal transit and CHO absorption are not matched and CHO accumulates in the colon where it is subject to bacterial degradation. Further, this study was designed to assess breath H2 production as a function of the type of CHO ingested and the type of exercise. A group of 32 male triathletes performed three exercise trials at 1-week intervals with either a semisolid (S) intake, an equal energy fluid intake (F) or a fluid placebo (P). Each trial consisted of cycling (sessions 1 and 3) and running (sessions 2 and 4). The mixed-expired H2 concentrations in the resting and "recovery" periods (5 min after each session) did not change significantly in time and did not differ among intakes. There were also no significant differences in H2 concentrations between resting and "recovery" conditions. During exercise, H2 concentrations decreased three to six-fold in comparison to resting and recovery levels and differed among intakes (ANOVA; P < 0.05). The H2 concentrations were almost continuously lower with P than with F and S. The H2 concentrations were significantly higher during running than during cycling. During exercise, we found that CHO overflow could be compared among intakes and between exercise types by using the HBT, provided the influence of other factors on H2 excretion--ventilation and intestinal blood flow--was similar for each condition.

Gastrointestinal problems as a function of carbohydrate supplements and mode of exercise

The aim of the study was to examine prevalence and duration/seriousness of gastrointestinal (GI) problems as a function of carbohydrate-rich (CHO) supplements and mode of exercise. The relationship between GI problems and a variety of physiological and personal factors (age, exercise experience) was also examined. Thirty-two male tri-athletes performed three experimental trials at 1-wk intervals, each trial on a different supplement: a conventional, semisolid supplement (S; 1.2 g CHO, 0.1 g protein, and 0.02 g fat.kg BW-1 x h-1); an almost isocaloric fluid supplement (F; 1.3 g CHO.kg BW-1 x h-1, no fat, no protein); and a fluid placebo (P). The 3 h of exercise started at 75% VO2max and consisted of alternately cycling (bouts 1 and 3) and running (bouts 2 and 4). GI symptoms were monitored by a questionnaire. Analysis of variance revealed that nausea lasted longer with P as compared with S (P < 0.05). Bloating lasted longer during bout 3 with P as compared with F and S (P < 0.05). Accounting for confounding factors, most GI symptoms occurred more frequently and lasted longer during running than during cycling. Multiple regression analysis revealed significant relationships between nausea and urge to defecate, between an urge to defecate, GI cramps and flatulence, and between belching and side ache. From all other factors energy depletion, CHO malabsorption, exercise intensity, exercise experience, and age were significantly related to GI symptoms during the exercise.

Gastrointestinal problems as a function of carbohydrate supplements and mode of exercise

The aim of the study was to examine prevalence and duration/seriousness of gastrointestinal (GI) problems as a function of carbohydrate-rich (CHO) supplements and mode of exercise. The relationship between GI problems and a variety of physiological and personal factors (age, exercise experience) was also examined. Thirty-two male tri-athletes performed three experimental trials at 1-wk intervals, each trial on a different supplement: a conventional, semisolid supplement (S; 1.2 g CHO, 0.1 g protein, and 0.02 g fat.kg BW-1 x h-1); an almost isocaloric fluid supplement (F; 1.3 g CHO.kg BW-1 x h-1, no fat, no protein); and a fluid placebo (P). The 3 h of exercise started at 75% VO2max and consisted of alternately cycling (bouts 1 and 3) and running (bouts 2 and 4). GI symptoms were monitored by a questionnaire. Analysis of variance revealed that nausea lasted longer with P as compared with S (P < 0.05). Bloating lasted longer during bout 3 with P as compared with F and S (P < 0.05). Accounting for confounding factors, most GI symptoms occurred more frequently and lasted longer during running than during cycling. Multiple regression analysis revealed significant relationships between nausea and urge to defecate, between an urge to defecate, GI cramps and flatulence, and between belching and side ache. From all other factors energy depletion, CHO malabsorption, exercise intensity, exercise experience, and age were significantly related to GI symptoms during the exercise.

Production of chickens with marginal vitamin A deficiency

Marginally vitamin A-deficient 1-d-old chickens capable of remaining healthy for at least 6 weeks were produced using a two-generation model. In this model, hens fed on diets with a limited vitamin A content were used to obtain 1-d-old chickens which were marginally deficient in vitamin A. Only hens with a narrow range of plasma retinol values (0.60-0.85 mumol/l) were satisfactory for this purpose. Above this range the 1-d-old chickens were not marginally vitamin A deficient. Below this range egg production and hatchability were affected to some extent depending on the degree of vitamin A deficiency. Even when egg production and hatchability remained at a high level in such birds, the 1-d-old chickens produced were not sufficiently strong to survive the first weeks of life. The advantages of the two-generation model for producing marginally vitamin A-deficient chickens are the increased uniformity and predictability of the chickens with respect to body-weight, general health and vitamin A status. However, it does take about 3 months to produce such chickens.

Reproducibility of urinary 3-methylhistidine excretion in human subjects consuming freely selected diets

Eight males and six females consumed their normal diet for 9 weeks, except for weeks 3 and 9 when they followed a self-selected diet free of 3-methylhistidine (3MH) for five subsequent weekdays (days 1 to 5). Timed 24-hours urine collections were obtained on days 3, 4, and 5 of these 3MH-free dietary periods and on one day during weeks 1 and 7. At the group level, no differences in 3MH excretion (P greater than .05) between days 3, 4, and 5 in weeks 3 and 9 and between these weeks were observed. Reproducibility at the individual level was indicated by the within-subject coefficient of variation (CVw). CVw within weeks 3 and 9 was 2.5% and 5.1% for men and 4.8 and 8.0% for women. CVw between these weeks was highest when more than one measurement per week was performed. Relating 3MH to creatinine decreased the CVw between weeks. If muscle protein breakdown is to be measured at the individual level, a reasonably large biologic variation is to be taken into account and repeated measurements should be done to decrease the CVw.

[Experimental studies on the regeneration capability and prognosis of hydronephrosis]

There are conflicting opinions regarding the ability of kidneys to return to normal functioning following removal of an obstruction. Opinions also differ on the precision of radioactive iodine for the measurement of functional ability in obstructed kidneys. We tried to assess the value of nuclear medical methods in comparison to the classical physiological clearance methods. Furthermore, we tried to answer the following questions: how long can an obstruction be present before total recovery becomes impossible and when is it no longer worthwhile to perform conservative surgery?