Renal handling of plasma high density lipoprotein

Renal tubular reabsorption and hydrolysis of plasma high density lipoprotein (HDL3) were studied. Rabbit proximal straight nephron segments were microperfused in vitro with iodinated HDL3. Progressive luminal uptake and cellular accumulation of radiolabeled material were observed during an initial phase, followed by a reduction in sequestration and the appearance of 125I-label in the bathing medium. To detect proteolysis, collected perfusates and bathing media were analyzed for trichloracetic acid soluble radioactivity. 125I-HDL3 in the luminal fluid was intact, but metabolites appeared in the bathing medium. Electron microscopic radioautography demonstrated endocytic uptake of 125I-HDL3 at the luminal membrane of the proximal tubule and movement of grains into lysosome-like dense bodies. Incubation of radiolabeled HDL3 in the presence of renal homogenates resulted in proteolytic activity with an acidic pH optimum. Analytical cell fractionation studies indicated that hydrolysis of the protein component is associated with lysosomes derived from proximal kidney tubules. Collectively, the data show that plasma HDL3 can be reabsorbed in the proximal nephron by a mechanism involving endocytosis at the luminal membrane, followed by proteolysis at lysosomes.

Subcellular sites of insulin hydrolysis in renal proximal tubules

The subcellular sites of insulin degradation as measured by trichloroacetic acid precipitation were defined for rabbit renal proximal tubule cells. Fractionation in linear sucrose gradients of the postnuclear supernates prepared from isolated proximal tubule segments revealed three pools of insulin hydrolytic activity. Insulin hydrolytic activity assayed at pH 3.5 distributed in the gradients in a manner nearly identical to the activity of the lysosomal enzymes, N-acetyl-beta-glucosaminidase and alpha-mannosidase. At pH 7.4 the insulin-degrading activity distributed in a bimodal fashion with the major component following the cytosolic enzyme, phosphoglucomutase, and the minor component nearly identically overlapping with the activity of the inner mitochondrial enzyme, cytochrome oxidase. Upon microperfusion of 125I-insulin through proximal straight nephron segments, metabolites of the hormone were not observed in the collected perfusates for six of eight experiments. Average values for percent intact insulin in the original and collected perfusates showed no significant difference. These data suggest that three potential sites for insulin hydrolysis are present in proximal tubule cells, including lysosomes, the cytosol, and mitochondria. The results do not support the concept of degradation occurring at the brush border or contraluminal membranes.

Chiropractic college libraries in the United States and Canada, 1981-1982

Libraries in thirteen chiropractic colleges in the United States and Canada were surveyed in 1981/82. Data include operating expenditures, library resources, staffing levels and salaries, and size of physical plant. The survey identified wide differences among the population in all variables measured.

Prospective assessment of recurrence risk in sudden infant death syndrome siblings

Knowledge of the likelihood of a repetition of sudden infant death syndrome within a sibship, particularly in the next sibling, is important to parents. Methodologic considerations with respect to the studies of recurrence risk already published indicate that the rates reported are overestimates. This suspicion is confirmed by our study based on 826,162 infants surviving the first week of life on file in the Medical Birth Registry of Norway. A total of 1062 (1.3 per 1,000) infants died of SIDS; five deaths occurred as the second case in a family. The recurrence risk for the nextborn sibling was 5.6 per 1000, and for all subsequent siblings 4.8 per 1000, which would seem encouragingly low from a counseling point of view.

Sudden infant death syndrome and hypertriiodothyroninemia: comparison of neonatal and postmortem measurements

Serum triiodothyronine concentrations in victims of sudden infant death syndrome, when compared with those of both living and dead controls, were found to be elevated to a degree comparable to those found in a previous study. Thyroxine, thyroid-stimulating hormone, and thyroglobulin values were not elevated. Neonatal triiodothyronine and thyroxine values, determined on specimens collected within a few days of birth for most of the sudden infant death syndrome victims, did not differ significantly from those of comparable peers in their birth cohort. These results indicate that hypertriiodothyroninemia may serve as a useful postmortem diagnostic marker for the syndrome but not as a premortem predictor. Parenthetically, thyroid hormones appear to remain stable in either a frozen or dried state for up to two years.

Physical activity and primary cardiac arrest

To explore the relationship between vigorous physical activity and primary cardiac arrest (PCA), we identified, through emergency service incident reports, 163 cases of PCA aged 25 to 75 years. Control subjects matched for age, sex, residence, and the absence of prior clinical heart disease or major comorbidity were identified from the community. Spouses of subjects were interviewed to quantify leisure-time activity (LTA) during the prior year. Energy expended in high-intensity LTA, requiring 60% of maximum oxygen intake, was determined. The risk of PCA was 55% to 65% lower in persons in the two upper quartiles of high-intensity LTA than in persons without high-intensity LTA (95% confidence interval of relative risk, 0.22 to 0.85). Because this association was demonstrated in a clinically healthy population without prior morbidity, our data support the hypothesis that high-intensity LTA protects against PCA.

Renal tubular processing of small peptide hormones

Reabsorption and/or degradation of proteins or peptides are functions of the proximal tubule. Large polypeptides or proteins are reabsorbed by luminal endocytosis and hydrolyzed by lysosomal enzymes. Our recent studies indicate that small linear peptides are hydrolyzed at the luminal membrane, with reabsorption of metabolites. The renal transport and hydrolysis of radiolabeled Al, All, BKN, oxytocin, glucagon, insulin, and LHRH were studied. Techniques for in vivo microinfusion of surface tubules in rats, arterial infusion in filtering and nonfiltering rat kidneys in vivo, and in vitro microperfusion of isolated rabbit nephron segments were used. Reabsorption of radiolabeled material was measured and the intact peptide or its metabolites were identified and quantified in urine, renal venous blood, bathing medium, and/or collection fluid. In addition, peptides were incubated in the presence of isolated renal membrane preparations to identify a probably cellular site of hydrolysis. The findings indicate that in proximal, but not distal tubules, radiolabeled Al, All, BKN, glucagon, and LHRH are hydrolyzed by brush border enzymes at the luminal membrane, followed by reabsorption of metabolites. In addition, it was found that, similar to the small intestine, the proximal tubule reabsorbed small peptide fragments, which were further degraded intracellurarly, In vivo inhibition studies with excess peptides revealed that hydrolysis is a more specific process than studies with excess peptides revealed that hydrolysis is a more specific process than reabsorption of metabolites. Large or small, complex peptides like insulin, oxytocin, or vasopressin that contain disulfide bridges are not hydrolyzed at the luminal brush border of the proximal tubule. In vivo sequestration and slow degradation of insulin by rat tubules suggest that this peptide is reabsorbed by endocytosis and degraded in lysosomes. Thus, as the molecular complexity or weight of a peptide increases, the mechanism for renal tubular degradation, instead of depending on luminal membrane hydrolysis, may primarily involve endocytosis and lysosomal digestion. This recently described mechanism for hydrolysis and transport of small linear peptides in the proximal nephron is characterized by having a high capacity and is analogous to membrane hydrolysis described for intestinal microvilli. The process may be biologically important to (1) conserve amino acids, (2) inactivate toxic peptides, and (3) help regulate circulating levels of peptide hormones.

Epidemiologic comparisons of incidence of toxic shock syndrome

Despite many imperfections in the nationwide reporting of toxic shock syndrome, the available data provide some useful information. The crude toxic shock morbidity rate has been estimated as approximately 0.50 per 100 000 United States population per year. This morbidity rate exceeds those for paralytic poliomyelitis, tetanus, tularemia, diphtheria, and typhoid fever, and is about one half of the rate for meningococcal infections and pertussis. The estimate of 8.9 cases of toxic shock syndrome per 100 000 menstruating women is similar to the crude rates for primary and secondary syphilis and mumps. From these comparisons, the incidence of toxic shock syndrome does not appear as low as some might suppose.

Sudden infant death syndrome and maternal age: etiologic implications

During a 12-year period (1969 through 1980), 431 episodes of sudden infant death syndrome (SIDS) occurred in King County, Washington. Longitudinal analysis of these data confirms the inverse association of SIDS occurrence with maternal age, which has been reported repeatedly from previous cross-sectional analyses. Risk of SIDS increases with increasing birth order, but the inverse maternal age gradient remains constant within each birth-order category. Available evidence suggests that maternal age may be a more important clue to SIDS causation than previously supposed. Assessment of established SIDS risk factors in relation to maternal age deserves further attention. The role of nutrition of pregnancy in relation to maternal age and SIDS risk may also be a productive avenue for future investigation.

The reliability, validity, and utility of three data modes in assessing marital relationships

Data from individual interviews, four questionnaires, and two analogue situations for 12 married couples were examined by six clinical judges and evaluated with regard to various aspects of interpersonal functioning. Orders of presentation were counterbalanced in a Latin square design. Ratings were made after each kind of data had been reviewed, after a case conference, and following discussion leading to consensus. Reliabilities were computed for the sets of variables and for each data mode. The convergent and discriminant validities of judgments based on the three data modes were examined by means of a multitrait-multimethod matrix. The utilities of the data modes and of increasing amounts of information were gauged by correlating partial estimates with average judgments of all judges based on all data following case conference. Among the findings were reasonably high levels of reliability for some aspects of interpersonal functioning but very low agreement regarding recommended treatment, quite high convergent validity across the three data modes, and modest but significantly superiority of the interview over the other procedures for assessing marital relationships.

Differences between renal tubular processing of glucagon and insulin

Renal processing of glucagon and insulin was compared. Iodinated glucagon (mol wt 3,674, linear molecule) or insulin (mol wt 6,000, two chains with disulfide bonds) was microinfused into surface nephrons of the rat kidney, and the radiolabel recovered in the urine was quantified and characterized. Proximal but not distal reabsorption of both peptides was observed, and uptake varied similarly as a function of tubular length. After proximal microinfusion, [125I]glucagon was largely degraded to [125I]tyrosine in the urine, but remained intact after distal infusion. [125I]Insulin was recovered as intact peptide following both proximal and distal microinfusion. Prolonged tubular sequestration of 125I label was observed following proximal microinfusion of [125I]insulin, with efflux requiring longer than 1 h for completion. No measurable cellular sequestration of [125I]glucagon was observed. Incubation of both peptides with rabbit renal microvilli membranes resulted in enzymatic hydrolysis of [125I]glucagon but relatively little or no degradation of [125I]insulin. It is concluded that glucagon and insulin are reabsorbed in the proximal tubule by predominantly different mechanisms.

Handling of luteinizing hormone-releasing hormone by renal proximal tubular segments in vitro

[pyroglutamyl-3,4-3H]Luteinizing hormone-releasing hormone (LHRH) was microperfused through isolated segments of rabbit proximal straight tubules and incubated with isolated brush border microvilli from rabbit renal tubules. About 4.8% of perfused 3H label was reabsorbed into the bathing medium per millimeter of tubule length per minute, and 1% or less of perfused label was sequestered per millimeter of nephron segment. The 3H label content of the bathing medium varied linearly with perfusion time (30 min), suggesting a constant rate of reabsorption. Analysis by high performance liquid chromatography showed that the collection fluid and brush border incubation medium contained significant amounts of labeled pGlu-His, pGlu-His-Trp, and pGlu-His-Trp-Ser, as well as LHRH, while the bathing medium contained pGlu, pGlu-His, pGlu-His-Trp-Ser, a very small amount of pGlu-His-Trp, and no LHRH. These data suggest that the partial hydrolysis of [3H]LHRH to these peptide metabolites takes place in proximal tubules through contact digestion by brush border enzymes. The metabolites and/or hormone are probably reabsorbed and broken down further within the cell to produce pGlu, which becomes an additional metabolite found in the bathing medium.

The sudden infant death syndrome--reassessment of growth retardation in relation to maternal smoking and the hypoxia hypothesis

Data from an earlier study on postnatal growth and the sudden infant death syndrome (SIDS) by Peterson et al. (Am J Epidemiol 1974;99:389-94) were reanalyzed in light of new evidence on the effects of maternal smoking on prenatal and postnatal growth and on the relative risk of SIDS. The data set available for reanalysis consisted of weight and length (crown to heel) measurements at birth and autopsy for 155 babies diagnosed with SIDS in King County, Washington, in 1968-1971. The comparison group consisted of 270 contemporary living peers with weight and length data available. This reanalysis reveals that the retarded growth pattern of SIDS victims is remarkably similar to those of babies born to mothers who smoke during pregnancy. Known and suspected effects of maternal smoking on the fetus and neonate can account for increased susceptibility of death from a variety of causes, including SIDS. The association, if confirmed by further studies, could help clarify the pathogenesis of SIDS in victims with postmortem evidence of antemortem hypoxia with or without a history of periodic apnea.

Erythrocyte transketolase activity and sudden infant death

Postmortem heart blood aspirates from 24 consecutive sudden infant deaths and 23 consecutive infant deaths from other causes yielded evidence of erythrocyte transketolase activity (ETKA) in every instance. ETKA measurements from cadaver specimens have not been previously reported. ETKA values did not correlate with the interval from death to sampling or with age at death. Activity coefficients from postmortem material corresponded closely to those from previous studies on living subjects which suggests that the method of Bayoumi and Rosalki yields valid measurements at least for 77 h postmortem. Statistical comparisons of the sudden infant deaths with non-sudden infant deaths revealed no significant differences. This investigation failed to disclose evidence in favor of the hypothesis, advanced by Read, that unsuspected thiamin deficiency may explain some cases of the sudden infant death syndrome.

Epidemiologic comparisons of the sudden infant death syndrome with other major components of infant mortality

All 1998 resident infant deaths in the 1969--1977 King County, Washington birth cohort of 139,132 resident live births comprise the data base for epidemiologic comparisons of the sudden infant death syndrome (SIDS) with eight other major infant mortality components: hyaline membrane disease; respiratory distress syndrome; asphyxia of the newborn; immaturity; birth injury; congenital malformation; infection; and "all other." These components were compared with respect to age at death; sex; race; prior fetal loss; prior live-born, now dead; birth plurality; birth weight; maternal age; birth order; marital status; prenatal care; and season of death in an attempt to determine the uniqueness of these purported SIDS risk factors. Only the age at death distribution unequivocally distinguished SIDS from the other components. The combination of low maternal age and multiparity was demonstrated to be putatively synergistic for risk of SIDS, hyaline membrane disease, and respiratory disease syndrome. Only deaths from infection exhibited seasonal variation similar to SIDS. These observations probably reflect secondary associations with as yet unidentified primary risk factors relatable to maternal experience.

Renal tubular transport and catabolism of proteins and peptides

The kidney plays an important role in the metabolism of proteins and peptides. Current evidence indicates that only the proximal tubule possesses the mechanism for degradation or transport of these substances and reabsorption of metabolic products. Proteins and large polypeptides filtered at the glomerulus are absorbed from proximal tubular fluid by luminal endocytosis into apical vacuoles. These fuse with primary lysosomes, where hydrolysis occurs followed by diffusion of metabolites out of the cells and into the blood. Recent evidence indicates that small linear peptides are handled by a different mechanism. It is likely that small peptides are degraded at the luminal surface of the brush border of proximal tubules, which contains many hydrolytic enzymes, by the process of membrane or contact digestion with reabsorption of the breakdown products. The probable biological significance of proximal tubular mechanisms for handling of proteins and peptides are conservation of amino acids, inactivation of toxic substances, and participation in the regulation of the circulating level of protein and peptide hormones.

The sudden infant death syndrome and infant botulism

Fecal and serum specimens taken from 30 cases of sudden infant death and from eight cases of nonsudden infant death that were diagnosed at a single facility in King County, Wash., were examined for the presence of Clostridium botulinum organisms and toxin. Organisms, but not toxin, were recovered from a fecal specimen in one case of sudden infant death, results that parallel those from studies previously reported by investigators in California. Studies made in our laboratory of a nonfatal case of infant botulism revealed that an estimated 366,000 mouse minimal lethal doses of toxin were excreted in feces collected by purging the infant. Organisms and toxin were excreted for at least 15 days after the infant was hospitalized. Observations made in our laboratory of atypical responses in mice to both fecal and serum extracts, coupled with recently described experiments in which mice were used as an animal model for infant botulism in humans, provide a biologically plausible foundation for the hypothesis that C. botulinum may be implicated etiologically in some sudden infant deaths. Additional microbiologic, physiologic, and toxicologic data are needed to adequately test this hypothesis.

Myocardial tissue concentrations of magnesium and potassium in men dying suddenly from ischemic heart disease

Optimum tissue levels of magnesium and potassium ions are essential to the structure and function of the myocardium. We hypothesized that an inapparent deficiency of one or both of these elements might contribute to sudden cardiac death in a susceptible person, and in this study investigated levels of these elements in the myocardium of men experiencing sudden death to determine if there was such an association. Subjects dying suddenly with ischemic heart disease had significantly lower levels of myocardial tissue magnesium and potassium than the controls (men dying of acute trauma). The four lowest potassium values were obtained for the only men in the group with a history of angina (P less than 0.0005). Three of the men with angina also had the lowest tissue magnesium levels (P less than 0.005). The intriguing finding gives support to the hypothesis.