Involvement of the carboxy-terminal residue in the active site of the histidine-containing protein, HPr, of the phosphoenolpyruvate:sugar phosphotransferase system of Escherichia coli

Histidine-containing protein, HPr, of the Escherichia coli phosphoenolpyruvate:sugar phosphotransferase system has an active site that involves His-15, which is phosphorylated to form a N delta 1-P-histidine, Arg-17, and the carboxy-terminal residue Glu-85. Mutant HPrs with alterations to the three C-terminal residues, Glu-85, Leu-84, and Glu-83, were produced by site-directed mutagenesis. The properties of these mutants were assessed by kinetic analysis of enzyme I, enzyme IImannose, enzyme IIN-acetylglucosamine, and enzyme IImannitol, and the phosphohydrolysis properties of the HPr mutants. The results show that it is the C-terminal alpha-carboxyl of Glu-85 that is involved in the active site, and this involvement may be restricted to the phosphoryl donor action of HPr. The contribution of this alpha-carboxyl group is modest as the deletion of Glu-85 resulted in the reduction of the enzyme II activity (kcat/Km) to about 33%. Removal of both Glu-85 and Leu-84 yields an HPr that is an impaired substrate of both the enzyme I and enzyme II reactions. Glu-83 appears to have no role in the active site.

Expression of biologically active heterodimeric bovine follicle-stimulating hormone in milk of transgenic mice

Follicle-stimulating hormone (FSH; follitropin) is a pituitary glycoprotein composed of two post-translationally modified subunits, which must properly assemble to be biologically active. FSH has been difficult to purify and to obtain in quantities sufficient for detailed biochemical studies. We have targeted FSH expression to the mammary gland of transgenic mice by using cDNAs encoding the bovine alpha and FSH beta subunits and a modified rat beta-casein gene-based expression system. Lines of bigenic mice expressing both subunits have been generated either by coinjection of the subunit transgenes or by mating mice that acquired and expressed transgenes encoding an individual subunit. Up to 60 international units (15 micrograms) of biologically active FSH per ml was detected in the milk of the bigenic mice. These lines provide a model system for studying the post-transcriptional mechanisms that effect the expression and secretion of this heterodimeric hormone.

Lipid responses of hypercholesterolemic men to oat-bran and wheat-bran intake

The hypocholesterolemic effects of oat bran (OB) have been recently challenged. To carefully document the hypocholesterolemic effects of OB, 20 hypercholesterolemic men admitted to a metabolic ward were randomly allocated to either OB or wheat bran (WB) for 21 d after a 7-d control-diet period. Control and treatment diets were designed to be identical in energy content and nutrients, differing only in the amount of soluble fiber. After 21 d, OB significantly decreased total cholesterol by 12.8% (P less than 0.001), low-density-lipoprotein cholesterol by 12.1% (P less than 0.004), and apolipoprotein B-100 by 13.7% (P less than 0.001) whereas WB had no significant effect. High-density-lipoprotein cholesterol and apolipoprotein A-I did not change significantly in either group. Serum triglycerides decreased by 10% in both groups but the decrease was only significant (P less than 0.04) in WB subjects. OB but not WB significantly reduced total cholesterol and other atherogenic lipoprotein fractions independent of other dietary changes.

Hypocholesterolemic effects of different bulk-forming hydrophilic fibers as adjuncts to dietary therapy in mild to moderate hypercholesterolemia

Hypercholesterolemia is a significant risk factor for coronary heart disease, and the hypocholesterolemic effects of psyllium are well established. This placebo-controlled, parallel study compared psyllium with methylcellulose, calcium polycarbophil, and placebo as dietary adjuncts in treating mild to moderate hypercholesterolemia. Of 163 men and women recruited with serum cholesterol levels above 5.17 mmol/L (200 mg/dL), 105 completed 8 weeks of an American Heart Association step I diet and then augmented the diet with one of the fiber supplements for 8 additional weeks. Incremental differences from placebo for low-density lipoprotein cholesterol were -8.8% for psyllium, -3.2% for methylcellulose (not significant), and +8.7% for calcium polycarbophil; and for total cholesterol the differences were -4.3% for psyllium (not significant), -1.4% for methylcellulose (not significant), and +5.9% for calcium polycarbophil. Compliance was 94% to 96%, and only mild gastrointestinal side effects were observed. In managing mild to moderate hypercholesterolemia, methylcellulose and calcium polycarbophil provide little or no additional benefit, while psyllium significantly enhances the American Heart Association diet effects.

Upper airway cooling and l-menthol reduce ventilation in the guinea pig

Cooling of the upper airway, which stimulates specific cold receptors and inhibits laryngeal mechanoreceptors, reduces respiratory activity in unanesthetized humans and anesthetized animals. This study shows that laryngeal cooling affects the pattern of breathing in the guinea pig and assesses the potential role of cold receptors in this response by using a specific stimulant of cold receptors (l-menthol). The response to airflows (30 ml/s, 10-s duration) through the isolated upper airway was studied in 23 anesthetized (urethan, 1 g/kg ip) guinea pigs breathing through a tracheostomy. Respiratory airflow, tidal volume, laryngeal temperature, and esophageal pressure were recorded before the challenges (control), during cold airflows (25 degrees C, 55% relative humidity), and during warm airflows (37 degrees C, saturated) with or without the addition of l-menthol. Whereas warm air trials had no effect, cold air trials, which lowered laryngeal but not nasal temperature, reduced ventilation (VE) to 85% of control, mainly by prolonging expiratory time (TE, 145% of control), an effect abolished by laryngeal anesthesia. Addition of l-menthol to the warm airflow caused a greater reduction in VE (41% of control) by prolonging TE (1,028% of control). Nasal anesthesia markedly reduced the apneogenic effect of l-menthol but did not affect the response to cold air trials. In conclusion, both cooling of the larynx and l-menthol in the laryngeal lumen reduce ventilation. Exposure of the nasal cavity to l-menthol markedly enhances this ventilatory inhibition; considering the stimulatory effect of l-menthol on cold receptors, these results suggest a predominant role of nasal cold receptors in this response.

Effect of l-menthol on laryngeal receptors

We have studied the effect of l-menthol on laryngeal receptors. Experiments have been conducted in 11 anesthetized dogs that breathed through a tracheostomy. We have recorded the activity of 23 laryngeal cold receptors and 19 mechanoreceptors. Constant flows of air, 15-50 ml/s (low) and 100-150 ml/s (high), passing for 10 s through the isolated upper airway in the expiratory direction, lowered laryngeal temperature and activated the cold receptors. This cold-induced discharge promptly ceased upon withdrawal of the airflow. Addition of l-menthol to the airflow evoked, for a similar decrease in temperature, a greater peak activation of the cold receptors than airflow alone (low flows 164%, high flows 111%); statistical significance was reached only for the lower flow. This activity outlasted the cessation of airflow by 30-120 s, even at a time when laryngeal temperature had returned to control (low flow 237%, high flow 307% of similar trials with airflow alone). Four laryngeal cold receptors were also tested with l-menthol added to a warm, humidified airflow that did not change laryngeal temperature; all of them were stimulated with a long-lasting discharge. Nine cold receptors were also tested with d-neomenthol and d-isomenthol; both isomers stimulated the receptors. None of the 19 mechano-receptors tested was affected by l-menthol. We conclude that l-menthol constitutes a specific stimulant of laryngeal cold receptors and could provide a useful tool for the study of their reflex effects.

Response of laryngeal receptors to water solutions of different osmolality and ionic composition

Water-responsive laryngeal receptors with fibres in the superior laryngeal nerve were studied to characterize the specific physicochemical properties of aqueous solutions that activate these endings. The responses to water (37 degrees C) of 141 receptors were studied in 39 anaesthetized dogs breathing through a tracheostomy with the larynx functionally isolated. Of the 89 receptors stimulated by water, 53 were also challenged with isosmotic (275-315 mOsm) solutions of dextrose and sodium gluconate at 37 degrees C. Receptors that only responded to water (n = 31) with a long delay, long duration discharge were generally respiratory modulated. On the other hand, laryngeal receptors that responded to all test solutions (n = 22) with a short delay, short duration discharge were generally not respiratory modulated. We conclude that the former type of receptor responds to lower osmolality, whereas the latter responds to the lack of chloride ions in the test solutions. These two types of receptor may be responsible for the cough and bronchoconstriction induced by inhaled aerosols of different osmolalities and ionic compositions.

Cooling mediates the ventilatory depression associated with airflow through the larynx

Although constant airflow through the upper airway has been shown to induce ventilatory depression in anesthetized newborn animals, the role of laryngeal temperature in this response has not been studied. Experiments were performed in fourteen 1-5 day-old anesthetized puppies breathing through a tracheostomy. Tidal volume and laryngeal temperature were recorded while a constant stream of air (15-25 ml/sec) at room temperature was passed in the expiratory direction for 20 sec through the isolated upper airway. Warm (35-37 degrees C), humidified air at the same flow served as control. When laryngeal temperature was decreased by 7.5 +/- 0.9 degrees C, a marked change in breathing pattern was observed (VT = 54 +/- 5, TI = 187 +/- 33, TE = 636 +/- 179, VT/TI = 45 +/- 10% of control; n = 9). Warm air at the same flow induced no significant changes. Superior laryngeal nerve section abolished the effects of cooling on breathing pattern. In 5 puppies we compared the effect of 'fast' and 'slow' laryngeal cooling. Fast trials altered breathing pattern earlier than slow trials. We conclude that the depressant effect of airflow through the upper airway is entirely due to a decrease in laryngeal temperature and is mediated by superior laryngeal nerve afferents.

Carbon dioxide-responsive laryngeal receptors in the dog

The purpose of this study was to relate the carbon dioxide (CO2) response of laryngeal receptors to their behavior during the breathing cycle (i.e. their response to transmural pressure changes, laryngeal movement or decreases in temperature) or during exposure to irritant stimuli (water or cigarette smoke). In 9 anesthetized mongrel dogs breathing spontaneously through a tracheostomy, unit activity from the superior laryngeal nerve was recorded while warmed and humidified gas mixtures (air or 10% CO2 in O2) were passed, for 1 min, through the functionally isolated upper airway in the expiratory direction. None of the 10 cold receptors studied were affected by CO2. Eleven of 20 laryngeal non-modulated mechano-receptors were stimulated (from 0.3 to 1.6 imp/sec) by exposure to CO2. These CO2-responsive receptors were also stimulated by known irritant stimuli (cigarette smoke, water), although not all receptors which responded to these irritants were stimulated by CO2. Twelve of 33 respiratory-modulated receptors were affected by CO2; 4 were stimulated and 8 inhibited. Receptors inhibited by CO2 were also inhibited by negative pressure while receptors stimulated by CO2 were also stimulated by negative pressure. These results show that CO2-responsive laryngeal receptors are not specialized endings. Although it is not clear to what extent each separate group of laryngeal receptors is involved, each may contribute to the reflex bradypnea which has been observed during exposure of the upper airway to elevated levels of CO2. However, the importance of CO2-responsive laryngeal receptors in physiological conditions remains unclear.

Propionate inhibits hepatocyte lipid synthesis

Oat bran lowers serum cholesterol in animals and humans. Propionate, a short-chain fatty acid produced by colonic bacterial fermentation of soluble fiber, is a potential mediator of this action. We tested the effect of propionate on hepatocyte lipid synthesis in rats using [1-14C]acetate, 3H2O, and [2-14C]mevalonate as precursors. Propionate produced a statistically significant inhibition of cholesterol biosynthesis from [1-14C]acetate at a concentration of 1.0 mM and from 3H2O and [2-14C]mevalonate at concentrations of 2.5 mM. Propionate also produced a significant inhibition of fatty acid biosynthesis at concentrations of 2.5 mM using [1-14C]acetate as a precursor. The demonstration of propionate-mediated inhibition of cholesterol and fatty acid biosynthesis at these concentrations suggests that propionate may inhibit cholesterol and fatty acid biosynthesis in vivo and may mediate in part the hypolipidemic effects of soluble dietary fiber. Further studies are needed to clarify this action of propionate and to establish the exact mechanisms by which the inhibition occurs.

Oat-bran cereal lowers serum total and LDL cholesterol in hypercholesterolemic men

Oat bran lowers serum lipid concentrations in healthy and hyperlipidemic subjects. To determine the effects of a ready-to-eat oat-bran cereal on lipid concentrations, we fed control (corn flakes) and oat-bran cereal diets for 2 wk to 12 men with undesirably high serum total-cholesterol concentrations. Subjects were randomly assigned to one of the two diets upon admission to the metabolic ward. After completing the first diet, subjects completed 2 wk on the alternate diet. Intakes of carbohydrate, protein, fat, and cholesterol were virtually identical on the two diets. The oat-bran cereal provided 25 g oat bran/d. The oat-bran cereal diet compared with the corn flakes diet lowered serum total-cholesterol and serum LDL-cholesterol concentrations significantly by 5.4% (p less than 0.05) and 8.5% (p less than 0.025), respectively. Final body weights on each of the diets were similar. Ready-to-eat oat-bran cereal provides a practical means to incorporate soluble fiber into the diet to lower serum cholesterol.

High-carbohydrate, high-fiber diets increase peripheral insulin sensitivity in healthy young and old adults

To examine extra-alimentary effects of high-carbohydrate, high-fiber (HCF) diets, insulin-mediated glucose disposal employing the euglycemic clamp and hepatic glucose output (HGO) employing [6,6-2H2]glucose were measured in 12 healthy young and old individuals before and after 21-28 d of an HCF diet. Diet lowered fasting concentrations of glucose from 5.3 +/- 0.2 to 5.1 +/- 0.1 mmol/L (p less than 0.01) and insulin from 66.0 +/- 7.9 to 49.5 +/- 5.7 pmol/L (p less than 0.01). Fasting serum cholesterol decreased from 5.17 +/- 0.18 to 3.80 +/- 0.20 mmol/L (p less than 0.01) in young individuals and from 6.15 +/- 0.52 to 4.99 +/- 0.49 mmol/L (p less than 0.01) in elderly individuals. Fasting serum triglyceride concentrations, basal HGO, and insulin suppression of HGO were unchanged by the diet. Glucose disposal rates increased from 18.87 +/- 1.66 before 23.87 +/- 2.78 mumol.kg-1.min-1 after the diet (p less than 0.02). Therefore, HCF diets may improve carbohydrate economy by enhanced peripheral sensitivity to insulin.

High-fiber diet for diabetes. Safe and effective treatment

Persons with diabetes are at increased risk for cardiovascular disease. Maintaining normal lipid levels is, therefore, a key goal in diabetes management. A high-carbohydrate, high-fiber diet provides effective, positive, and safe treatment for diabetes and lowers the associated risk for coronary artery disease.

Serum lipid response of hypercholesterolemic men to single and divided doses of canned beans

Dried beans lower serum lipid concentrations in healthy and hyperlipidemic subjects. To determine the effects of canned beans on serum lipid concentrations, 24 hyperlipidemic men ate one of three bean diets for 21 d in a metabolic ward. Diets A and B included 227 g canned beans (120 g beans with 107 g tomato sauce) daily, in a single dose for diet A and in a divided dose for diet B. Diet C included 182 g canned beans (162 g beans with 20 g tomato sauce) daily in a divided dose. All bean diets combined lowered serum cholesterol and triglyceride concentrations 10.4% (p less than 0.001) and 10.8% (p less than 0.025), respectively. Diet B was as effective as diet C, and the groups on those diets had greater cholesterol reductions than did the group on diet A. Serum cholesterol reduction was positively correlated (p less than 0.01) with intake of total dietary fiber and soluble fiber. The ratios of low- to high-density-lipoprotein cholesterol remained constant for all groups. Body weight decreased 1.0-1.5 kg for all groups despite constant energy intakes. Canned beans may make an important contribution to hyperlipidemia management.

Acute changes in osmolality and renin and respiratory control of arterial PCO2 and [H+]

To investigate whether osmoreceptor mechanisms or the renin-angiotensin system might be involved in respiratory regulation of H+ homeostasis, plasma osmolality was acutely lowered by approximately 10 mOsm in 7 awake mongrel dogs by a gastric water load (20 ml.kg-1 distilled, deionized water). Plasma renin activity (PRA) was measured as an indicator of angiotensin II levels. During these studies PaCO2 and [H+]a reflected the spontaneous level of ventilation (VE); higher levels of VE were correlated with lower PaCO2 and [H+]a, indicating a nonchemical drive to breathe. Stimulation of ventilation to lower PaCO2 following the water load was positively correlated with increase in PRA and decrease in plasma osmolality, but not with change in osmolality alone. An increased VE, a decreased ventilatory response curve (VRC) threshold for PaCO2, and a lower PaCO2 occurred with increase in PRA. Conversely, a lower or acutely decreased PRA, due to administration of arginine vasopressin, was correlated with a lower VE, an increase in the VRC threshold for PaCO2, and a higher PaCO2. Ventilatory control of PaCO2 during acute lowering of osmolality may be related to a central inter-action between osmolality and the renin-angiotensin system.

Water-responsive laryngeal receptors in the dog are not specialized endings

The primary purpose of this study was to ascertain whether laryngeal receptors activated by water are specialized endings or whether they also respond to other stimuli, such as pressure, temperature and laryngeal motion as they occur during the breathing cycle. In 35 anesthetized mongrel dogs, breathing spontaneously through a lower cervical tracheostomy, water and other test solutions at approximately 37 degrees C were injected into the functionally isolated larynx with a small catheter. Of the 130 receptors studied, none of the cold receptors (N = 13) responded to water, whereas approximately 60% of all laryngeal mechanoreceptors (72 of 117) responded with either a short delay, short duration or a long delay, long duration response. In general the former pattern of response was exhibited by nonrespiratory-modulated receptors, whereas the latter was typical of respiratory-modulated receptors. The specific nature of the stimulus (hypotonicity or lack of chloride ion) of the water response was further studied in 53 receptors with isoosmotic solutions of dextrose and sodium gluconate. The long delay, long duration response was dependent on a decreased osmolality, while the short delay, short duration response was dependent on the lack of chloride ion of the test solutions. All water-responsive receptors tested (N = 17) were blocked within 50 sec by topically applied 2% lidocaine and thus presumed to be superficial. However, 10 receptors which did not respond to water were also blocked within 50 sec, suggesting that not all superficial receptors are stimulated by water. Based on these observations, we propose that changes in osmolality or ionic composition of the laryngeal surface liquid could play an important role in modifying reflexes involved in the maintenance of upper airway patency.

Cow dung, rock salt, and medical innovation in the Hindu Kush of Pakistan: the cultural transformation of neonatal tetanus and iodine deficiency

In mountain villages of Chitral District in northwestern Pakistan, dried cow dung is used as Westerners would use talcum powder when babies are swaddled and rock salt is consumed in tea and other foods. Both substances are esteemed as conveying beneficial 'heat' and 'strength'. Unfortunately, however, cow dung sometimes contains a bacterium that causes neonatal tetanus, and the resulting toxin may enter through the baby's unhealed umbilical cord and cause death. Further, rock salt contains no iodine, and Chitral's soil is so iodine-deficient that goiter is very common. Thus local health workers advocate use of talcum powder rather than cow dung, immunization against tetanus, and replacement of rock salt by powdered iodized salt. The present report documents widespread community acceptance of these innovations despite the fact that the biomedical model of tetanus and goiter was not well understood and indigenous concepts of the causes of the diseases remained virtually undisturbed. Most of the villagers were Ismaili Muslim followers of the Aga Khan; their receptivity to such health messages was influenced by the high value that their religion places on advancement through 'education' and was correlated with their proximity to Ismaili health workers whom they trusted. A major implication of this research for primary health care programs is that when one is attempting to change existing health practices, explication of biomedical models should not be the only focus of concern. Attentiveness to the context in which behavior changes are introduced and interpreted is at least equally important. Further, the fact that new knowledge was added to the old without replacing it illustrates the complexity of human cognition and points to limitations in the KAP (knowledge-attitude-practice) model of health belief and behavior. This report adds to a small but important body of literature documenting the dynamic nature of medical pluralism in the developing world.

Recent advances in carbohydrate nutrition and metabolism in diabetes mellitus

The last decade has brought a tremendous turnaround in nutritional recommendations for diabetes management, moving from low-carbohydrate, high-fat diets to high-carbohydrate, high-fiber, low-fat diets. Clinical studies which furthered understanding of carbohydrate metabolism greatly contributed to the change. This paper reviews recent advances in selected aspects of carbohydrate nutrition and metabolism in diabetes mellitus.

V.A. Cooperative Study of antiplatelet agents in diabetic patients after amputation for gangrene: unobserved, sudden, and unexpected deaths

We report on unobserved, sudden, and unexpected deaths that occurred in a randomized multicenter trial. The long-term effects of aspirin plus dipyridamole on major vascular outcome variables were studied in 231 non insulin-dependent diabetic men with either a recent amputation for gangrene or active gangrene. Depending upon the definition of sudden death used, there were 14, 22, or 17 deaths in the drug group versus 6, 6, or 3 deaths in the placebo group (p = 0.04, 0.001, or 0.001, respectively). Total deaths from atherosclerotic vascular disease or deaths from all causes did not differ in the two treatment groups. Since this finding of a secondary end point is found only after multiple analyses of the data, it must be interpreted with caution. However, it is suggested that further studies on effects of antiplatelet agents on sudden deaths should be performed.

Adherence to high-carbohydrate, high-fiber diets

Successful diabetes management demands a high degree of adherence. Adherence to medical prescriptions, particularly special diets, is notoriously poor. A study of 40 individuals with IDDM and NIDDM who were followed an average of 23 months found good or excellent dietary adherence in 70% of subjects; only 5% demonstrated poor adherence. Adherence was assessed objectively based on carbohydrate, fat, and fiber intakes reported in 24-hour food recalls, 7-day food frequency surveys, and home food records. High dietary fiber intake may independently enhance adherence, perhaps by increasing satiety or because of the simplicity of the concept. Good communication between the health professional and patient is also fundamental to all stages of dietary adherence. Use of adherence-enhancing techniques throughout adoption of new diet behaviors promotes long-term adherence to high-carbohydrate, high-fiber diets.

Metabolic effects of fructose supplementation in diabetic individuals

With new diabetes diet guidelines recommending high carbohydrate intake, questions arise regarding acceptable intake of simple sugars. Whereas several short-term studies report flattened glycemic and insulin response to fructose consumption, some also report increased serum triglyceride levels. Few studies examine the effects of long-term fructose consumption. We evaluated the long-term safety of fructose consumption in 14 middle-aged men with diabetes. Subjects followed an ambulatory high-fiber high-carbohydrate control diet at home for 8 wk, entered the hospital for 5 days on this diet, and spent the next 7 days on a similar diet supplemented with 50-60 g fructose. They continued the fructose diet at home for 23 wk, then resumed a postcontrol diet for an additional 16 wk. In the hospital, glycemic control improved significantly on the fructose-supplemented diet compared with the hospital control diet. In the ambulatory setting, no significant differences in plasma glucose, glycohemoglobin, serum cholesterol, triglycerides, lactate, or urate occurred between precontrol, fructose, or postcontrol periods. Fasting serum lactate was higher by 0.5 meq/L during the ambulatory fructose period than during the precontrol period. Body weight also increased during the ambulatory fructose period due to higher calorie intake. Adherence to fructose consumption was excellent and improved adherence to carbohydrate and fat recommendations. If total calorie intake is controlled to promote desirable body weight, crystalline fructose used with a high-carbohydrate high-fiber low-fat diet appears to be safe and acceptable for diabetic individuals.