Roles of transmembrane prolines and proline-induced kinks of the lutropin/choriogonadotropin receptor

The lutropin/choriogonadotropin receptor is a seven-helix transmembrane (TM) receptor. A unique feature of TM helices is the content of Pro, which generally is absent in alpha helices of globular proteins. Because Pro disrupts helices and introduces a approximately 26 degrees kink, it has been speculated that Pro plays a crucial role in the structure of TM helices, exoloops, and cytoloops of TM receptors. To examine the roles of the five TM Pros of the lutropin/choriogonadotropin receptor, these residues were individually substituted. Mutant receptors were examined for surface expression, hormone binding, and cAMP induction. Surface expression was monitored after introducing the flag epitope into the receptors. Flag epitopes slightly affected cAMP induction but not hormone binding or surface expression of receptors as monitored by immunofluorescence microscopy and 125I-anti-flag antibody. The results indicate that Pro479 in TM 4 and Pro598 in TM 7 play important yet contrasting roles. Pro479 is crucial for hormone binding at the cell surface but not after solubilization of the receptor. This is more likely due to the Pro side chain than the Pro-induced kink. Pro598 is important for surface expression. The kinks of Pro463 of TM 4, Pro562 of TM 6, or Pro591 of TM 7 are not important because the substitution of Phe for these residues did not significantly impact surface expression, hormone binding, and cAMP induction.

The effect of pass/fail grading and weekly quizzes on first-year students' performances and satisfaction

BACKGROUND

In 1992-93 the University of Michigan Medical School revised its first-year curriculum. An evaluation system using honors, high-pass, pass, and fail grading and only two examinations (a midterm and a final) was replaced with a system using pass/fail grading and weekly quizzes in addition to the two examinations. The objective was to increase students' satisfaction while maintaining a high level of achievement.

METHOD

Students' performance scores and survey data from the final year of the former system (1991-92, 222 students) and the first year of the new system (1992-93, 195 students) were used to investigate whether overall performance decreased and whether the students liked the new approach to grading. Statistical methods used were one-sample t-tests, Student's t-test, and Fisher's Z-test.

RESULTS

Under the new system, the average scores for courses remained well above passing, and no evidence was found that the students achieved at lower levels than had their predecessors with the former, more traditional grading system. Also, higher cumulative pre-final scores (i.e., scores on the weekly quizzes as well as the midterm) did not predict lower, "just passing" achievement on final examinations. The students' responses to the surveys included comments that pass/fail grading eased anxiety and reduced competition while encouraging the students' co-operation.

CONCLUSION

Despite concerns that implementing pass/fail grading for all first-year courses would result in lower overall performance and decreased motivation among students, during the first year of implementation these fears proved to be unfounded as the students continued to perform well and reported greater satisfaction with the new system.

A re-evaluation of the urinary parameters of acid production and excretion in patients with chronic renal acidosis

We have studied acid-base balance in 32 patients attending the renal clinic of Mount Sinai Hospital. The parameters of acid-base balance measured included acid production measured as urinary sulfate and organic anions, net acid excretion measured as urinary ammonia plus titratable acid minus bicarbonate, and net GI absorption of alkali measured by a new method utilizing urinary electrolytes. Net GI absorption of alkali by urinary electrolytes measures alkali addition to the body from the GI tract as well as from any other sources, including bone. All patients had a creatinine clearance less than 80 ml/min and they were divided into two groups: those with normal serum bicarbonate (Group 1; N = 12) and those with subnormal serum bicarbonate (Group 2; N = 20). Hydrogen ion balance was -0.6 +/- 9 mEq/day in the first group, while those in the second group had a hydrogen ion balance of +16 +/- 5 mEq/day. A group of 8 normal controls had a hydrogen ion balance of -0.3 +/- 5 mEq/day. When the sum of all cations was compared with the sum of all anions in the urine, a cation gap of exactly the same magnitude as the positive hydrogen ion balance was found in patients with low serum bicarbonate. In conclusion, our data show that patients with decreased GFR and low serum bicarbonate appear to have a significantly positive hydrogen ion balance. However, we believe that the positive hydrogen ion balance is only apparent, but not real for the following reasons.(ABSTRACT TRUNCATED AT 250 WORDS)

Glycosylation, dimerization, and heparin affinity of lipoprotein lipase in 3T3-L1 adipocytes

The relationship between glycosylation, dimerization, and heparin affinity of lipoprotein lipase (LPL) was studied in 3T3-L1 adipocytes. Three forms of LPL subunits were found in normal cells; totally endo H-resistant (57 kDa), partially sensitive (54 kDa), and totally sensitive (51 kDa) forms. LPL in normal cells was active, dimeric, and showed high affinity for heparin. LPL in cells treated with tunicamycin, preventing the transfer of N-linked oligosaccharide chain, was unglycosylated (51 kDa) and inactive. LPL proteins were found as an aggregate, and had low affinity for heparin. After treatment with castanospermine, an inhibitor of ER glucosidase I, 80% of LPL activity was inhibited. Most of LPL proteins were totally endo H-sensitive, present as an aggregate, and had low affinity for heparin. LPL in cells treated with deoxymannojirimycin, an inhibitor of Golgi mannosidase I, was active, dimeric, and had high affinity for heparin as in normal cells. But LPL subunits were all endo H-sensitive. These results suggest that core glycosylation and subsequent removal of glucose residue is required, but processing after Golgi mannosidase I is not necessary for dimerization and acquisition of high heparin affinity of LPL.

Acid-base balance in chronic peritoneal dialysis patients

Endogenous acid production has never been measured directly in dialysis patients and an empiric formula is used to estimate acid production from their protein catabolic rate. We have studied acid-base balance in 19 stable CAPD patients attending the peritoneal dialysis clinic of Mount Sinai Hospital. They obtained a 24 hour collection of peritoneal dialysis fluid and urine while consuming their usual diet and performing their usual activities. Total alkali gain was calculated from net GI alkali absorption plus urinary net acid excretion plus alkali gain from dialysate, while total acid production was measured directly from the urinary and dialysate excretions of sulfate and organic anions. Net GI alkali absorption was estimated from the difference between cations (Na + K+Ca + Mg) and anions (Cl + 1.8P) in the 24 hour dialysate and urine collections minus the daily total amount of lactate infused. All of our patients had a normal or high serum bicarbonate concentration, which was stable with time. Total alkali gain was virtually identical to total acid production (54.2 vs. 52.4 mEq/day) which suggests that these patients were in neutral acid-base balance. Net GI alkali absorption (22.7 mEq/day) was one of the same range as that of chronic renal failure patients not on dialysis and represented almost one half of the total daily alkali gain. The daily acid production of 52.4 mEq/day was numerically equal to 84% of the protein catabolic rate expressed as g/day, which is similar to the predicted value of 77% of PCR reported in the literature.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of a highly focused case on the effect of small-group facilitators' content expertise on students' learning and satisfaction

BACKGROUND

There has been considerable debate over the need for content expertise to lead a successful small-group discussion for medical students. Some authors feel process expertise related to the conduct of a small group is of more value than content expertise related to the case. At least one study has presented data that suggest content expertise can lead to teacher domination of the learning environment. In an earlier study, the present authors found that students learned more and were more satisfied with small-group instruction when the instruction was facilitated by a faculty member who was an expert in the content of the case. That study also identified no tendency for content experts to dominate the sessions (e.g., through lecturing or otherwise controlling the learning environment). The purpose of the present study was to explore the efficacy of a carefully designed and highly focused case problem to remove the influence of group facilitators' content expertise on students' learning outcomes.

METHOD

The 211 students in the University of Michigan Medical School class of 1994 were randomly assigned to 28 groups in a microbiology and immunology course in the fall of 1991; each small group was led by a faculty facilitator. Complete data were available from 27 groups: 13 groups led by experts and 14 groups led by non-experts. Data collection included observers' codings of interactions between the students and the facilitators (interactional analysis), test scores, and students' ratings of the experience.

RESULTS

Unlike in the previous study, group leaders who were content experts devoted significantly more time to teacher-directed activities than did non-content-expert leaders. However, overall, 62% of the time was devoted to student-initiated activity. The results of the multiple-choice tests that were related specifically to the goals of the case indicated there was no significant difference between the students' performances in the groups led by experts and those led by non-experts. With respect to students' satisfaction, all students gave consistently high ratings to the experience and there was no difference between groups led by expert and non-expert facilitators.

CONCLUSION

The data from this study suggest that a facilitator's content expertise alone does not determine the amount of teacher-directed behavior in a group, the amount of students' learning, or students' satisfaction. The focus built into the case and the amount of facilitator's training directly related to the content of the case are also significant variables related to students' learning, teacher's behavior, and students' satisfaction.

Adapting a diabetes patient education program for use as a university course

A study was conducted to determine if a patient education program, "Life With Diabetes," could be converted to an undergraduate course. The course consisted of seven 2-hour sessions with presentations by a physician, dietitian, psychologist, and clinical nurse specialists. Topics included definition, treatment, nutrition, monitoring, children, older adults, and patient empowerment. A total of 52 students (45 without diabetes, 7 with diabetes) have completed this one-credit course. A patient diabetes knowledge test and a 50-item Diabetes Attitude Survey were administered before and after the course. For the students without diabetes, mean knowledge posttest scores improved significantly, and significant changes were seen on the attitude subscales, with posttest scores moving closer to those of a national panel of diabetes experts. Students with diabetes scored closer to the national panel on the pretest and improved significantly only on the patient autonomy subscale. This course measurably improved knowledge and attitudes among undergraduates, suggesting that a patient education program can be adapted successfully to provide additional training opportunities for diabetes education programs.

Renal stone risk factors in patients with type IV renal tubular acidosis

Renal stone formation is uncommon in patients with type IV renal tubular acidosis (RTA). This study was undertaken to explore the urinary biochemical and physicochemical factors in patients with type IV RTA in order to elucidate the mechanisms that protect them from renal stone formation. Twelve subjects with type IV RTA and 12 matched subjects with a similar degree of kidney impairment but without RTA were studied. Both groups of patients had low urinary excretion of calcium, phosphorus, uric acid, and citrate, probably reflective of kidney impairment. Patients with type IV RTA had a significantly lower urinary pH and urinary excretion of calcium than their matched controls. Hypocitraturia was present in both groups without any significant difference between them. This study suggests that the major protection from renal stone formation in type IV RTA results from impaired renal function and ensuing reduction in renal excretion of stone-forming substances, such as calcium and uric acid.

Alkali absorption and citrate excretion in calcium nephrolithiasis

The role of net gastrointestinal (GI) alkali absorption in the development of hypocitraturia was investigated. The net GI absorption of alkali was estimated from the difference between simple urinary cations (Ca, Mg, Na, and K) and anions (Cl and P). In 131 normal subjects, the 24 h urinary citrate was positively correlated with the net GI absorption of alkali (r = 0.49, p < 0.001). In 11 patients with distal renal tubular acidosis (RTA), urinary citrate excretion was subnormal relative to net GI alkali absorption, with data from most patients residing outside the 95% confidence ellipse described for normal subjects. However, the normal relationship between urinary citrate and net absorbed alkali was maintained in 11 patients with chronic diarrheal syndrome (CDS) and in 124 stone-forming patients devoid of RTA or CDS, half of whom had "idiopathic" hypocitraturia. The 18 stone-forming patients without RTA or CDS received potassium citrate (30-60 mEq/day). Both urinary citrate and net GI alkali absorption increased, yielding a significantly positive correlation (r = 0.62, p < 0.0001), with the slope indistinguishable from that of normal subjects. Thus, urinary citrate was normally dependent on the net GI absorption of alkali. This dependence was less marked in RTA, confirming the renal origin of hypocitraturia. However, the normal dependence was maintained in CDS and in idiopathic hypocitraturia, suggesting that reduced citrate excretion was largely dietary in origin as a result of low net alkali absorption (from a probable relative deficiency of vegetables and fruits or a relative excess of animal proteins).

The relationship between diabetes-related attitudes and patients' self-reported adherence

This study involved 1202 patients who were placed into low adherence or high adherence groups based on their answers to questionnaires. The attitudes of each group were compared for a variety of adherence behaviors. Patients who reported high levels of adherence tended to have attitudes more in accord with diabetes experts. Members of the high adherence group strongly supported the need for special training for health care professionals who treat diabetes, favored team care, accepted the importance of patient compliance, acknowledged the seriousness of non-insulin-dependent diabetes mellitus (NIDDM), and recognized the relationship between glucose control and complications. Differences in attitudes between high- and low adherence groups were more prevalent for difficult adherence areas, eg, diet and exercise, than for easy adherence areas, eg, carrying sweets or diabetic identification. An understanding of patients' attitudes can help diabetes educators and patients develop realistic and relevant self-care plans.

Medical student use of history and physical information in diagnostic reasoning

Clinical data gathering is central to clinical competence. Although research has demonstrated the value to experienced clinicians of information obtained from the history, little is known of how medical students use this information. In the present study, two case simulations (in rheumatoid arthritis and systemic lupus erythematosis) were developed to assess medical student information gathering and utilization. The results indicate that most of the students were already considering the correct diagnosis as a possibility after the presenting complaint and patient description. However, the medical history exerted the strongest influence on transforming the correct diagnosis from just another diagnostic possibility into the favored diagnostic candidate. Students who failed to list the correct diagnosis in the differential diagnosis after obtaining the history were significantly less likely to reach the correct diagnosis at the end of the case. These results confirm the critical importance of the history in medical problem solving.

A comparison of the diabetes-related attitudes of health care professionals and patients

The following study compares the diabetes-related attitudes of sampled health care professionals and patients with diabetes. Attitudes were measured with a revised version of the Diabetes Attitude Scale (DAS) which includes seven factors representing attitudes towards: (1) the need for special training in order to provide diabetes care; (2) patient compliance; (3) the seriousness of noninsulin-dependent diabetes (NIDDM); (4) the relationship between blood glucose levels and the complications of diabetes; (5) the impact of diabetes on the patient's life; (6) patient autonomy; and (7) team care. The highest levels of agreement among patients and professionals concerned the seriousness of NIDDM and the relationship between blood glucose control and the development of the complications of diabetes. The most striking finding of the study was that patients tended to express a significantly more judgmental, moralistic attitude toward patient behavior than did health care professionals.

Renal hypouricemia and absorptive hypercalciuria: a real syndrome

We describe a case of renal hypouricemia due to increased tubular secretion of urate associated with absorptive hypercalciuria. This association has been described in the past, but this is the first time that high plasma levels of 1,25-dihydroxyvitamin D have been reported. A possible cause-and-effect relation between altered uric acid transport and altered vitamin D metabolism in the proximal tubule is suggested.

Effects of expert and non-expert facilitators on the small-group process and on student performance

At the University of Michigan Medical School in 1990, the authors investigated the effects of faculty facilitators' levels of content expertise on the educational process and learning outcomes of small-group teaching sessions. The study was conducted in a microbiology course for second-year students in which four small-group sessions were used to replace 38 hours of lecture and laboratory time. The interactions between 11 expert and ten non-expert faculty facilitators and 156 students were observed and coded. The students' levels of knowledge and satisfaction were measured. The results indicate that, although significant differences in faculty-student interactions were not observed, the students in the 11 groups led by the content experts had higher levels of satisfaction and higher examination scores.

Perceived effectiveness, cost, and availability of patient education methods and materials

To determine the efficacy of and need for patient education methods and media, a needs assessment was sent to 816 members of the American Association of Diabetes Educators. Respondents (n = 325, 40%) included 62% RNs, 36% RDs, 1% other; 62% CDEs. Their mean number of years experience in diabetes education was 8.5, and 99% routinely provided patient education. Respondents indicated that videotapes and slide tapes were the most educationally effective media and books and audiotapes were the least effective. Booklets and videotapes were the most cost-effective and computer-assisted instruction the least effective. While respondents perceived one-to-one counseling, skills training, and diabetes content sessions to be the three most educationally effective methods, support groups and large and small discussion groups were seen as the three most cost-effective educational methods. Among nine potential barriers to quality patient education listed, educators rated lack of third-party reimbursement as a major barrier most frequently and national availability of quality education materials as a barrier least frequently.

Disorders of sodium metabolism: hypernatremia and hyponatremia

OBJECTIVE

Discussion of abnormal plasma sodium concentrations with an emphasis on the pathogenesis, diagnosis, and treatment.

DATA SOURCES

Relevant literature in the English language and the authors' clinical experience.

STUDY SELECTION

No special study has been carried out for the present discussion.

DATA EXTRACTION

The information from the literature and the data from the authors' clinical experience have been used to illustrate important points in the discussion.

DATA SYNTHESIS

A most important aspect in the approach to hypernatremia is determination of the mechanism responsible for impaired water intake. Various mechanisms of abnormal water loss can be determined from measurement of urine osmolality. Hypernatremia is treated by water replacement and measures to reduce abnormal water loss. In most instances, hyponatremia is caused by inappropriate concentration of urine because of either appropriate or inappropriate antidiuretic hormone secretion. The determination of appropriateness of antidiuretic hormone secretion requires the assessment of effective arterial volume. Treatment depends on the pathogenetic mechanism.

CONCLUSIONS

Abnormal plasma sodium concentration results from abnormal water intake or water output. Treatment is guided by determining the pathogenetic mechanism.

Effect of meal on the physiological and physicochemical actions of potassium citrate

The effect of meals on the physiological and physicochemical actions of potassium citrate was examined in 8 patients with nephrolithiasis maintained on a constant metabolic dietary regimen. Potassium citrate (20 mEq. 3 times per day), whether given with food or on an empty stomach, significantly increased urinary pH, citrate and potassium, and decreased urinary calcium and ammonium. Moreover, potassium citrate decreased urinary saturation of calcium oxalate and uric acid, although it slightly increased that of brushite. However, there was no significant difference in these measures when the drug was given with meals from the time when it was given on an empty stomach. Thus, the effect of potassium citrate on urinary risk factors is unaffected by food.

Determinants of magnitude of pseudohyperkalemia in thrombocytosis

The release of potassium from platelets is a well-known cause of pseudohyperkalemia in thrombocytosis. In predicting the magnitude of pseudohyperkalemia associated with thrombocytosis, previous investigations considered only the amount of potassium released from platelets during blood clotting, although the increment in serum potassium during blood clotting depends on the quantity of potassium released from platelets as well as the volume of distribution of the released potassium, which is inversely proportionate to the hematocrit. The present study proposes a new mathematical formula to predict the magnitude of increase in serum potassium during blood clotting, and accuracy of this formula has been tested in a patient with thrombocytosis.

Hyperkalemia in diabetes mellitus

Potassium filtered at the glomerulus is almost completely reabsorbed before the distal tubule; it must therefore be secreted into the collecting duct. The rate of potassium secretion is determined by a number of factors, notably aldosterone, distal sodium delivery, and serum potassium. Normal serum potassium is maintained by the interplay of passive leak of potassium from the cells and its active return to the cells. Transmembrane potassium distribution is influenced largely by acid-base equilibrium and hormones including insulin and catecholamines. In the diabetic with ketoacidosis hyperkalemia, in the face of potassium depletion, is attributable to reduced renal function, acidosis, release of potassium from cells due to glycogenolysis, and lack of insulin. Chronic hyperkalemia in diabetics is most often attributable to hyporeninemic hypoaldosteronism but other conditions including urinary tract obstruction may also contribute. A variety of clinical situations (e.g., volume depletion) and drugs (e.g., nonsteroidal antiinflammatory agents, and heparin) may acutely provoke hyperkalemia in susceptible individuals.

The association between community physician's attendance at a medical center's CME courses and their patient referrals to the medical center

This study attempts to quantify an overall association between CME course attendance and referrals. Attendance at formal CME courses given by the University of Michigan Medical School and referrals to the University Hospitals were examined over a two-year period. Attendance and referrals were linked to physicians in Michigan identified through the Michigan Department of Licensing and Regulation and through the American Medical Association. For physicians who are office-based and likely to be in active practice (age less than 70), those who attended at least one of the University's CME courses referred more patients than those who did not attend one (means of 1.9 referrals per physician and 1.3 referrals per physician, p less than .001). The causal direction of the relationship is not clear, but probably operates in both directions. It is reasonable for medical center marketers to consider CME as an indirect method for marketing clinical services. It is also reasonable for CME directors to identify referring physicians as high-priority groups for marketing CME. Both marketing efforts may be significantly enhanced by linking data bases for referrals and for CME attendance. CME directors must also ensure that marketing efforts do not compromise the objectivity and integrity of the content of the institution's CME program.

Prevention of myelinolysis in rats by dexamethasone or colchicine

The purpose of the present investigation was to determine whether dexamethasone, an agent known to preserve the blood-brain barrier, and colchicine, an agent that impairs mobilization of macrophages, can prevent demyelinating lesions associated with rapid correction of hyponatremia in the experimental animal. Hyponatremia was induced in rats with Pitressin and water. After 4 days hyponatremic rats received hypertonic saline alone or hypertonic saline plus dexamethasone or colchicine. All of the 9 rats that received only 5% NaCl developed demyelinating disease, while 3 of 6 rats treated with dexamethasone and 5 of 15 rats treated with colchicine showed no CNS abnormality. The results of our investigation might help understand the pathogenetic mechanism of central pontine myelinolysis in humans, a disease attributed to rapid correction of hyponatremia.

The first kidney stone

The proper approach to diagnosis and management in patients with a first episode of a calcium-containing kidney stone is controversial, and we have reviewed the literature in a search for objective information. Six large retrospective studies show the "natural cumulative recurrence rate of renal stones" to be 14% at 1 year, 35% at 5 years, and 52% at 10 years. Randomized studies of the use of either thiazides or allopurinol suggest a modest beneficial effect of about 35% over placebo. Considering that the risk of this specific therapy is about 5%, the morbidity associated with renal stones is limited, and relatively less invasive procedures can often replace nephrolithotomy, we conclude that use of specific drug therapy, namely thiazides or allopurinol, is not warranted in patients with a first kidney stone and, therefore, that extensive metabolic evaluation is unnecessary.

Danger of central pontine myelinolysis in hypotonic dehydration and recommendation for treatment

Isotonic saline is the fluid most commonly used for treatment of asymptomatic hypotonic dehydration, but as shown in the case presented in this article, rapid increase in serum sodium may follow administration of isotonic saline, leading to the development of central pontine myelinolysis (CPM). Because the necessity of rapid correction is less, whereas the risk of CPM is greater with chronic asymptomatic hyponatremia than with acute hyponatremia, use of a half normal saline might be more appropriate than normal saline for treating certain patients with hypotonic dehydration with asymptomatic hyponatremia. The calculations indicate that half normal saline will expand the extracellular volume quite effectively, but the rate of increase in serum sodium will be considerably slower than that with normal saline.

Comparison of surrogate and subject reports of dietary practices, smoking habits and weight among married couples in the Tecumseh Diet Methodology Study

Agreement between surrogate and subject reports of current food frequencies and other eating habits, smoking behavior and weight was assessed in 1982-1983 for 180 husbands and wives, aged 45 through 64 years. Agreement was measured by per cent exact agreement and weighted kappa for frequencies of 30 itemized foods or food groups, and for surrogate- and subject-based quintiles of frequencies of eight broad food groups and of vitamin A and C consumption indexes. Surrogate and subject mean frequencies were generally similar, but at the individual level of analysis, agreement varied widely. Agreement was greatest, among the food items and groups, for alcoholic beverages, and among the other items, for smoking status. Extreme misclassification by quintile was very small, but only 40% of persons self-classified in either extreme quintile were similarly classified by their spouses. This level of misclassification may result in the dilution of real relationships between diet and health.

Correspondence between perceptions of change in diet and 15-year change in diet reports in the Tecumseh Diet Methodology Study

As part of an effort to assess the most reliable method of obtaining information about long-term dietary intake, a study was conducted of the correspondence between perception of change in diet and measured change in reported diet from 1967 to 1982. Respondents were 1,201 men and women participants in the Tecumseh Food Frequency Study of 1967-1969 who were 45-64 years of age in 1982-1983, the time of the Diet Methodology Study. Perceptions of change were obtained by asking respondents directly if they thought they currently ate each of 12 food groups more often, less often, or as often as they did during the year of their earlier interview. Measured change was obtained by subtracting each respondent's baseline frequency for each of the 12 food groups from his or her current frequency. For 10 of the 12 food groups, correspondence was found between perception of change and measured change; fats and oils added at the table and meat were the exceptions. Significant linear relationships were found between perceptions and measured change for all food groups except fats and oils. However, greatly varying coefficients were associated with terms such as more often or as often as before, thereby limiting the potential utility of combining perceptions of change with current frequencies to obtain a reliable measure of baseline frequencies.

Reproducibility of reports of frequency of food use in the Tecumseh Diet Methodology Study

Frequency reports in 1967-1969 for 83 foods were compared to frequency reports for the same foods asked retrospectively in 1982-1983 about use in 1967-1969 for 1,184 respondents aged 45-64 in the Tecumseh Community Health Study cohort. Food frequency reports of the current (1982-1983) diet were also compared to baseline reports to indicate diet stability and to retrospective reports to indicate the influence of current diet on retrospective reporting. Comparisons were also made for 13 food groups and vitamin A and C indices. Short-term reproducibility of seven foods, measured by two reports 1-3 weeks apart in 1967-1969, was compared to long-term reproducibility for the same foods. Short-term reproducibility was consistently greater than long-term. Reproducibility was associated positively with stability of use. For the two nutrient indices and nine of the ten food groups examined, mean intake estimated from the retrospective report differed significantly from mean intake from the baseline report. Agreement between retrospective and current reports exceeded agreement between retrospective and baseline reports, indicating that retrospective reports were greatly influenced by current behavior; yet, the retrospective reports were better indicators of baseline consumption than were the current reports. While misclassification from use of the retrospective report to measure baseline consumption was large, risk differences may still be detected with usual sample sizes.

The effects of occupation and smoking on respiratory disease mortality

The effects of occupation and smoking on respiratory symptoms and ventilatory lung function were examined in 1957 among random samples of men 25 to 34 and 55 to 64 yr of age from 4 occupational categories (miners, foundry workers, mixed dust and chemical workers, and non-dust-exposed workers) living in an industrial English town. Mortality has been established 20 yr after the initial survey. This report focuses on the effects of smoking, lung function, and respiratory symptoms among the older men. All-cause mortality was very similar in the nondusty, foundry, and mixed dust groups, but slightly lower in the miners and ex-miners. In contrast, smokers had 2 times the death rates of nonsmokers. There was consistency in the smoking effect within each occupational group. Poor lung function and to some extent bronchitic symptoms in 1957 were predictive of mortality by 1977, regardless of smoking habits. However, the effect of symptoms in the absence of concomitant poor lung function, though consistent, was small.

Metabolic utilization and renal handling of D-lactate in men

This study was carried out to investigate the renal handling of d- and l-lactate and the extent of their metabolism in men. Ten healthy male subjects were given an intravenous (IV) infusion of a racemic mixture of d- and l-lactate. At an infusion rate of 1.0 to 1.3 meq/kg body weight of each isomer, d-lactate achieved a concentration in plasma of 1.7 to 3.0 meq/L, and l-lactate 2.8 to 4.2 meq/L. At these levels, fractional excretion of d-lactate ranged from 40% to 65%, while fractional excretion of l-lactate was always less than 5%. At a higher infusion rate, 1.8 to 2.0 meq/kg/h, plasma concentrations of d- and l-lactate reached 4.5 to 6.0 meq/L, and 4.0 to 6.7 meq/L, respectively. Fractional excretion of d-lactate then ranged from 61% to 100%, while that of l-lactate ranged from 9% to 30%. At plasma concentrations of d-lactate less than 3.0 meq/L, reabsorption of l-lactate was nearly complete, but when plasma d-lactate exceeded 3.0 meq/L, reabsorption of l-lactate was considerably impaired. Similarly, for a given concentration of plasma d-lactate, its reabsorption was more efficient when the plasma l-lactate concentration and fractional excretion of l-lactate were low than when they were high. At an infusion rate of d-lactate of 1.0 to 1.3 meq/L, about 90% of the infused lactate was metabolized, and at a higher infusion rate, still more than 75% of the infused lactate was metabolized.(ABSTRACT TRUNCATED AT 250 WORDS)

A mechanism of hypoxemia during hemodialysis. Consumption of CO2 in metabolism of acetate

The present study is an investigation of the role of acetate metabolism in dialysis-induced hypoxemia and of the relative roles of acetate metabolism, bicarbonate loss, and CO2 gas (g) loss in causation of hypoxemia. The loss of CO2 (g) measured in 23 patients during acetate dialysis was found to be negligible (0.21 +/- 0.01 mmol/min). The HCO-3 loss was substantial (3.4 +/- 0.5 mmol/min), but its predicted effect on dialysis hypoxemia was modest. The infusion of acetate at 4 mmol/min into 6 normal volunteers decreased the respiratory exchange ratio (R) from 0.83 +/- 0.06 to 0.71 +/- 0.06 with constant O2 consumption (VO2) and reduced net CO2 production (VCO2). In another experiment, the infusion of sodium acetate into 9 normal volunteers resulted in a similar reduction in R (from 0.82 +/- 0.04 to 0.71 +/- 0.04) and arterial pO2 (from 92.3 +/- 1.1 to 78.3 +/- 1.7 mm Hg). The results indicate that acetate metabolism can lead to reduction in R and hypoxemia and suggest that the same mechanism is responsible for hypoxemia during hemodialysis using acetate dialysate.

Bartter's syndrome due to a defect in salt reabsorption in the distal convoluted tubule

Bartter's syndrome is generally attributed to a primary defect in salt reabsorption either in the ascending limb of Henle's loop or in the proximal tubule. 2 siblings presented here have all the clinical and biochemical features of Bartter's syndrome but seem to have defective salt reabsorption in the distal convoluted tubule. A surreptitious use of diuretics was ruled out. Free water clearance was reduced in both patients and also was low after the addition of furosemide when compared with controls. Urine osmolalities following overnight dehydration were 883 and 1,000 mosm/l. The reduced maximal free water clearance argues against a proximal defect, and the normal urine concentration against a Henle's loop defect. Low free water clearance after furosemide suggests a defect in the distal convoluted tubule.

Mortality of Reserve Mining Company employees in relation to taconite dust exposure

Analysis of mortality among men who were employed by Reserve Mining Company from 1952 to 1976 has been carried out. Follow-up was conducted with standard methods, including searches by the Social Security Administration. Occupational exposures to dust were based on personal samples taken over the past five years by the industrial hygiene department of the company. Smoking habits were obtained by mailed questionnaires or telephone interviews. A modified life table method was used to compare death rates of the employees with those expected for white males in the state of Minnesota. Comparisons were also made with US rates for white males. The results showed that the death rates for all causes were significantly below expectation. Deaths from malignant diseases were marginally below those expected for the state. Exposures to total dust, to silica dust, or to fiber were low. There was no relationship between mortality and estimated lifetime dust exposures, nor was there any suggestion that deaths from malignant neoplasms were increased after 15 to 20 years latency. In contrast, there was a strong relationship between smoking habits and mortality from all causes, from cardiovascular diseases, and from cancer. This study does not suggest any increase in cancer mortality from taconite exposure.

Osmometry of CO2 in gas samples

Measurement of solute concentrations in biologic fluids by an osmometric technique has been described previously. Here, we describe an osmometric technique for measuring CO2 in gas samples. A solution of NaOH is injected into a graduated syringe containing the gas sample and CO2 is trapped in the reaction: 2NaOH + CO2 leads to Na2CO3 + H2O. The decrease in osmolality of the NaOH solution allows estimation of pCO2 in the original gas sample.

Osmometry of CO2 in gas samples

Measurement of solute concentrations in biologic fluids by an osmometric technique has been described previously. Here, we describe an osmometric technique for measuring CO2 in gas samples. A solution of NaOH is injected into a graduated syringe containing the gas sample and CO2 is trapped in the reaction: 2NaOH + CO2 leads to Na2CO3 + H2O. The decrease in osmolality of the NaOH solution allows estimation of pCO2 in the original gas sample.

Pseudohypoaldosteronism following kidney transplantation

A 56-year-old woman received a kidney transplant and presented subsequently with evidence of volume contraction, hyponatremia and hyperkalemia. Urinary sodium excretion was inappropriately high for the degree of volume contraction and urinary potassium excretion inappropriately low for the degree of hyperkalemia. Marked elevation of plasma renin activity and plasma aldosterone suggested that the renal tubules were unresponsive to mineralocorticoids. The defect was shown to be transient. The mechanisms leading to the defect are discussed.

The mechanism of hyperchloremic acidosis during the recovery phase of diabetic ketoacidosis

To determine the mechanism of hyperchloremic acidosis during recovery from diabetic ketoacidosis (DKA), serial measurements were made in eight patients of serum and urinary electrolytes and organic acids, and of urinary net acid. On admission, the average decrease in serum total CO2 was 17.5 mmol/L, corresponding to the excess anion gap, 18.5 meq/L, and the serum organic acids, 17.1 meq/L. With the treatment, the anion gap and organic acids decreased by 16.1 and 14.7 meq/L, respectively, but the serum CO2 increased only by 8.4 mmol/L; serum electrolyte balance was maintained by increase in chloride concentration. Fluid retention was insufficient to explain the disparity between the increase in CO2 and the decrease in organic acids. Renal loss of bicarbonate precursors during treatment was modest and was exceeded by renal bicarbonate production. The disparity between the increase in serum CO2 and the decrease in organic acids during treatment of DKA may be explained to a large extent by a difference in volume of distribution between bicarbonate and organic anions. The renal loss of ketone anions before admission, however, is ultimately responsible for the persistence of substantial metabolic acidosis.

Heparin-induced hyperkalemia: report of a case

A 77-year-old diabetic man with a creatinine clearance of 23--27 ml/min developed hyperkalemia while receiving heparin for peripheral arterial insufficiency. Discontinuation of this agent led to resolution of hyperkalemia as the plasma aldosterone concentration multiplied by sixfold. Renal insufficiency may have predisposed this patient to the development of hyperkalemia when heparin therapy suppressed aldosterone synthesis.