Acute hyperglycaemia does not alter coronary vascular function in isolated, perfused rat hearts.

AIM: The purpose of this study was to evaluate the hypothesis that acute hyperglycaemia in hearts of rats without diabetes alters coronary vascular responses to nitric oxide (NO), adenosine (ADO) and phenylephrine (PHE). METHODS: Coronary function was studied in isolated, Langendorff-perfused, non-beating rat hearts that were perfused with an oxygenated Krebs-Henseleit solution containing 40 mM KCl to arrest the hearts. Changes in coronary vascular resistance were assessed by measuring changes in coronary perfusion pressure under constant flow conditions. Coronary responses to ADO, sodium nitroprusside (SNP), PHE and L-NAME (inhibitor of NO synthase) were studied either under normoglycaemic conditions (100 mg/dl d-glucose) or after 60 min of hyperglycaemic perfusion (500 mg/dl d-glucose). d-mannitol was used as a hyperosmotic control. RESULTS: Hyperglycaemia did not alter vasodilator responses to ADO or SNP in the presence or absence of L-NAME. Furthermore, hyperglycaemia, compared with normoglycaemia, did not alter vasoconstrictor responses induced by L-NAME or PHE. CONCLUSIONS: Sixty minutes of exposure to 500 mg/dl of d-glucose in an isolated, non-beating, buffer-perfused rat heart did not significantly affect coronary vascular smooth muscle vasodilator responses to NO and ADO or alter alpha(1)-adrenoceptor-mediated vasoconstrictor responses to PHE. Furthermore, an unchanged vasoconstrictor response to L-NAME suggests that acute hyperglycaemia did not alter NO bioavailability.

Insight into the catalytic mechanism of DNA polymerase beta: structures of intermediate complexes.

The catalytic reaction mediated by DNA polymerases is known to require two Mg(II) ions, one associated with dNTP binding and the other involved in metal ion catalysis of the chemical step. Here we report a functional intermediate structure of a DNA polymerase with only one metal ion bound, the DNA polymerase beta-DNA template-primer-chromium(III).2'-deoxythymidine 5'-beta,gamma-methylenetriphosphate [Cr(III).dTMPPCP] complex, at 2.6 A resolution. The complex is distinct from the structures of other polymerase-DNA-ddNTP complexes in that the 3'-terminus of the primer has a free hydroxyl group. Hence, this structure represents a fully functional intermediate state. Support for this contention is provided by the observation of turnover in biochemical assays of crystallized protein as well as from the determination that soaking Pol beta crystals with Mn(II) ions leads to formation of the product complex, Pol beta-DNA-Cr(III).PCP, whose structure is also reported. An important feature of both structures is that the fingers subdomain is closed, similar to structures of other ternary complexes in which both metal ion sites are occupied. These results suggest that closing of the fingers subdomain is induced specifically by binding of the metal-dNTP complex prior to binding of the catalytic Mg(2+) ion. This has led us to reevaluate our previous evidence regarding the existence of a rate-limiting conformational change in Pol beta's reaction pathway. The results of stopped-flow studies suggest that there is no detectable rate-limiting conformational change step.

Mothers and others: who invests in children's health?

We estimate the impact of family structure on investments made in children's health, using data from the 1988 National Health Interview Survey Child Health Supplement. Controlling for household size, income and characteristics, we find that children living with step-mothers are significantly less likely to have routine doctor and dentist visits, or to have a place for usual medical care, or for sick care. Who invests in children's health? It appears these investments are made, largely, by a child's mother, and that step-mothers are not substitutes for birth-mothers in this domain.

The effects of economic and population growth on national saving and inequality.

This is a progress report on ongoing research into the effects of economic and population growth on national saving rates and inequality. The theoretical basis for the investigation is the life cycle model of saving and inequality. We report evidence that is conditional on the validity of the model, as well as evidence that casts doubt on it. Using time series of cross-sectional household surveys from Taiwan, Thailand, Britain, and the United States, we show that it is possible to force a life cycle interpretation on the data on consumption, income, and saving, but that the evidence is not consistent with large rate-of-growth effects, whereby economic and population growth enhances rates of national saving. The well-established cross-country link between economic growth and saving cannot be attributed to life cycle saving, nor will changes in economic or population growth exert large effects on saving within individual countries. There is evidence in favor of the life cycle model's prediction that within-cohort inequality of consumption and of total income--though not necessarily inequality of earnings--should increase with the age of the cohort. Decreases in the population growth rate redistribute population toward older, more unequal, cohorts, and can increase national inequality. We provide calculations on the magnitude of these effects.

Surfactant therapy prior to the interhospital transport of preterm infants.

The risk-to-benefit ratio of surfactant treatment of outborn preterm infants prior, as opposed to after, transportation to a perinatal center is not known. The objective of this study was to document current practice and to examine clinical outcomes in North America. In phase I (December, 1991 to January, 1992) questionnaires were distributed to 114 perinatal centers in the United States and Canada. The centers returned 98 surveys. Over half (50.5%) of the centers report giving surfactant rescue prior to infant transport, but only a minority (9.5%) of the centers report doing so for prophylaxis. In phase II (January, 1992 to December, 1992), clinical outcomes of surfactant-eligible babies requiring interhospital transport at a university hospital were evaluated to determine which infants ultimately received surfactant and when. The infants were compared between groups and did not differ significantly in gestational age, birthweight, sex type, number of multiple births, five-minute Apgar scores, or whether antenatal steroids were used. In phase II, the 66 consecutive, ventilator-dependent, outborn infants with average, and median, gestational age of 28 weeks were compared. The infants receiving surfactant prior to transport, when compared to the infants that got it after transport (9 hours later), did not do any better. There was 6% more survival without bronchopulmonary dysplasia in the group receiving surfactant after transport (65.2% versus 59.3%, p = 0.665). The infants receiving surfactant after transport were off the ventilator sooner (95% C.I. 6.0-28.7 versus 11.8-25.9 days) and discharged from the perinatal center earlier (95% C.I. 37.8-70.8 versus 47.9-69.0 days). Furthermore, arterial blood gases before and after transport reveals that there were no short-term advantages in administering surfactant prior to transport when compared to waiting for reevaluation at the perinatal center. These findings suggest that surfactant can be used safely prior to the interhospital transport of preterm infants, but this treatment does not seem to confer benefit over waiting for reevaluation, and possible surfactant treatment, at the tertiary perinatal center.

Activation of the 5-HT1C receptor expressed in Xenopus oocytes by the benzazepines SCH 23390 and SKF 38393.

1. A cloned 5-HT1C receptor expressed in Xenopus laevis oocytes was used to characterize the action of four dopamine D1-selective benzazepines at the 5-HT1C receptor. Additionally, the apparent binding of the D1-selective benzazepines to 5-HT1C receptors was measured in the choroid plexus of the pig. 2. In voltage-clamped oocytes expressing the cloned 5-HT1C receptor, 5-hydroxytryptamine (5-HT) elicited a characteristic inward current response with an EC50 of 13 nM. SCH 23390 acted as a stereoselective agonist (or partial agonist) with an EC50 of about 550 nM. SKF 38393 (1 microM-1 mM), SKF 77434 (100 microM), and SKF 82958 (100 microM) also acted as agonists (or partial agonists) at the cloned 5-HT1C receptor. SKF 38393 was not stereoselective at the 5-HT1C receptor. 3. The response to SCH 23390 activated slowly and, although the response contained many oscillations characteristic of the activation of the phosphatidylinositol signal transduction system, SCH 23390 rarely elicited the rapid spike-like response seen routinely in response to 5-HT. However, the responses to SKF 38393, SKF 77434, and SKF 82958 were identical in appearance to the response to 5-HT, except that the responses to the benzazepines were smaller. These comparisons were made by applying both a benzazepine and 5-HT to each individual oocyte expressing the cloned 5-HT1C receptor. 4. Consistent with the responses measured in oocytes, SCH 23390 bound stereoselectively to 5-HT1C receptors in the choroid plexus of the pig (Ki = 6.3 nM), and SKF 38393 bound non-stereoselectively with lower affinity (Ki = 2.0-2.2 microM).5. It is concluded that while these benzazepines demonstrate selectivity for the dopamine D1 receptor, they also can act as agonists or partial agonists at the 5-HT1c receptor in situ and as expressed in Xenopus oocytes. The oocyte expression system is useful for studies of the functional pharmacology of these 5-HTic receptors. Information about the pharmacological actions and variations in stereoselectivity among dopamine and 5-HT receptors should be of interest in modelling the interactions of ligands with these G-protein coupled receptors, and in the testing of such models through receptor mutagenesis.

Voltage dependence of Na/K pump current in Xenopus oocytes.

Stage V and VI (Dumont, J.N., 1972, J. Morphol. 136:153-180) oocytes of Xenopus laevis were treated with collagenase to remove follicular cells and were placed in K-free solution for 2 to 4 days to elevate internal [Na]. Na/K pump activity was studied by restoring the eggs to normal 3 mM K Barth's solution and measuring membrane current-voltage (I-V) relationships before and after the addition of 10 microM dihydroouabain (DHO) using a two-microelectrode voltage clamp. Two pulse protocols were used to measure membrane I-V relationships, both allowing membrane currents to be determined twice at each of a series of membrane potentials: (i) a down-up-down sequence of 5 mV, 1-sec stair steps and (ii) a similar sequence of 1-sec voltage pulses but with consecutive pulses separated by 4-sec recovery periods at the holding potential (-40 mV). The resulting membrane I-V relationships determined both before and during exposure to DHO showed significant hysteresis between the first and second current measurements at each voltage. DHO difference curves also usually showed hysteresis indicating that DHO caused a change in a component of current that varied with time. Since, by definition, the steady-state Na/K pump I-V relationship must be free of hysteresis, the presence of hysteresis in DHO difference I-V curves can be used as a criterion for excluding such data from consideration as a valie measure of the Na/K pump I-V relationship. DHO difference I-V relationships that did not show hysteresis were sigmoid functions of membrane potential when measured in normal (90 mM) external Na solution. The Na/K pump current magnitude saturated near 0 mV at a value of 1.0-1.5 microA cm-2, without evidence of negative slope conductance for potentials up to +55 mV. The Na/K pump current magnitude in Na-free external solution was approximately voltage independent. Since these forward-going Na/K pump I-V relationships do not show a region of negative slope over the voltage range -110 to +55 mV, it is not necessary to postulate the existence of more than one voltage-dependent step in the reaction cycle of the forward-going Na/K pump.

Effect of parenteral medications on tcPO2/PaO2 ratios.

We studied the effect of parenteral infusions on transcutaneous arterial oxygen tension ratios in 31 newborn rabbits. Tolazoline and prostaglandin E1 produced a significant fall in skin PO2 values (P less than 0.01). Antibiotics, bicarbonate, diazepam, and dopamine infusions produced no change in PO2 ratios.

Osmolality of carbohydrate solutions and gastric emptying in the newborn.

Gastric emptying in normal newborns was studied with use of a double marker technique. The volume of 200 to 400 mOsm carbohydrate solutions emptied from the stomach in 30 minutes was determined. To evaluate isocaloric solutions of different osmolalities, the osmolality of a 400-mOsm glucose solution was decreased to 300 and 200 mOsm/L by replacing a portion of the glucose with glucose oligosaccharides (GOSs). Because GOSs could be rapidly hydrolyzed in the duodenum, the effect of osmolality alone was studied by adding xylose to a 200-mOsm glucose solution to increase the osmolality to 300 and 400 mOsm/L. The volumes of the various solutions emptied in 30 minutes were not significantly different. These findings suggest that decreasing formula osmolality from 400 to 200 mOsm offers no intrinsic advantage with regard to gastric emptying.

Red blood cell volume in preterm neonates.

In the high-risk neonate, the direct determination of the red cell volume by radionuclide dilution technique appears to be the singularly definitive method of defining treatment efficacy, and is thus a useful evaluation and management tool for the pediatrician. For effective patient management, the red blood cell(RBC) volume of 69 preterm and term neonates was determined. The method utilized, Tc-99m-labeled RBCs, provided a fast and accurate answer with a large reduction in the absorbed radiation dose. In the population studied within a high-risk newborn ICU, the mean RBC volumes between the preterm and term neonates were without significant difference. Grouping and analysis of the RBC volume data with respect to birth weight, gestational ages, and 1- and 5-minute Apgar scores revealed on statistical difference. The mean value found in our population, 32.2 +/- 9.2 ml/kg, however, does differ from those previously reported in which the determinations were made using an indirect estimation from the plasma compartment.

Evaluation and testing of in vitro labeled technetium Tc-99m red blood cells in two animal models for neonatal RBC volume determinations.

The present study was designed to evaluate the red blood cell (RBC) radiolabeling technique utilizing the short half-lived radionuclide technetium-99m and to compare the results with the well-recognized standard chromium-51 method. The procedure was evaluated in a canine and a newborn lamb model utilizing dual radionuclide labeling and counting techniques. With the express purpose of providing a significant radiation dose reduction, the procedure presented was adapted for utilization in a neonatal patient population. Statistical analysis of the data revealed that there was no significant difference in the radiolabeling efficiency for the two methods (Cr-51, 86.6%; Tc-99m, 92.4%). Assessment of the in vitro stability for technetium-99m RBCs showed that less than a 4% loss of radiolabel from the RBC was seen in a 4-hr time span in the canine model (15 min, 90.5%; 2 hr, 88.9%; 4 hr, 86.6%) when compared to the 15 min equilibrium sample. Evaluation of newborn lamb RBC volumes showed that the technetium-99m RBC volume did not significantly differ from the chromium-51 labeling technique (Cr-51, 24.0 ml/kg; Tc-99m, 23.2 ml/kg). Summarization of the whole-body radiation dose showed that greater than a 30-fold reduction in absorbed dose was achieved in the newborn (Cr-51, 30.0 mrad; Tc-99m, 0.9 mrad). The modified procedure presented for the radiolabeling of the RBC with the short half-lived radionuclide technetium-99m provides a technique comparable to the utilized standard chromium-51 RBC method, yet with a large reduction in absorbed radiation dose. This procedure is presented as a superior technique for the determination of pediatric RBC volumes.

Low dose pulse methotrexate therapy in rheumatoid arthritis.

Thirty-two patients with definite or classical rheumatoid arthritis were treated with low dose pulse methotrexate (MTX). A therapeutic response was shown in 2/3 of the patients by statistically significant joint changes and improved global response. Greater than one-half of those who improved demonstrated a drop in sedimentation rate. Eight patients discontinued treatment because of inefficacy and 2 because of gastrointestinal distress. One patient died of neoplasm. Five liver biopsies performed in patients with abnormal liver enzymes demonstrated no MTX related changes. We conclude that MTX may be an effective alternative to other more toxic immunosuppressive regimens and should undergo future evaluation.

Collection and use of autologous fetal blood.

A prospective study was completed to evaluate the feasibility of autologous fetal blood collection. Following puncture on the umbilical vein, fetal blood was drawn into sterile heparinized plastic syringes and aliquots were subjected to coagulation and culture studies. None of the blood samples exhibited significant growth of bacterial pathogens and all patients had normal coagulation studies at 24 hours of age. These data demonstrate that fetal blood can be safely collected and given to infants subjected to shock or iatrogenic blood loss.

Uric acid excretion: quantitative assessment from spot, midmorning serum and urine samples.

Uric acid excretion can be measured in milligrams of urinary uric acid per decilitre of glomerular filtrate by obtaining the product of urinary uric acid and serum creatinine concentrations and dividing by the urine creatinine (all concentrations in mg/dL). In 29 normal adult men, the excretion rate in spot, midmorning samples was 0.4 +/- 0.1 (SD) mg of uric acid per decilitre of glomerular filtrate. Eight of 36 untreated gouty men excreted acid at a rate more than three standard deviations above normal. Excretion of uric acid is conveniently and physiologically assessed by this simple method.

Manometric diagnosis of lower esophageal sphincter incompetence in infants: use of a small, single-lumen perfused catheter.

Lower esophageal sphincter (LES) pressure is frequently measured to diagnose LES incompetence in adults. The multilumen perfused catheters with large diameters that are used for ths purpose are not suitable for small infants. We measured LES pressure in ten normal newborns with a small, single-lumen perfused catheter and compared our values with those obtained with the standard adult apparatus. Higher pressures were recorded with the single-lumen catheter. Chloral hydrate sedation had no effect on LES pressure. Two-day-old infants had LES pressures comparable to those of adults and older children. The technique was applied to the diagnosis of LES incompetence in 23 infants. Infants with LES incompetence (chalasia) were correctly separated from infants with chronic vomiting secondary to all other causes. Single-lumen manometric studies provide a simple, reliable, and safe method of assessing LES incompetence in small infants.

Effect of uterine artery insulin infusions on umbilical glucose uptake in sheep.

Although glucose is an important fuel for fetal oxidative metabolism, regulation of its availability to the mammalian fetus is poorly understood. This study was performed to determine the effect of infusions of insulin into the uterine arterial circulation on umbilical uptake of glucose in chronically instrumented, unstressed sheep. Twenty-eight determinations of umbilical glucose uptake and diffusion clearance of glucose by the placenta were made in four ewes. Immediately following a control study during which saline was infused into the uterine artery, porcine regular insulin diluted in saline was infused at 0.05 to 8.1 mU/min . kg uterine weight for 20--30 min and the determinations were repeated. Subsequent studies were performed at the conclusion of additional infusions of insulin to a maximum of 21.6 mU/min . kg. There was a significant increase in umbilical glucose uptake during initial insulin infusions (4.47 +/- 0.6 mg/min . kg fetus) compared to the control studies (3.08 +/- 0.6 mg/min . kg) associated with an increase in diffusion clearance (13.8 +/- 1.9 ml/min . kg fetus vs. 8.99 +/- 1.8 ml/min . kg). When the total cumulative dose of exogenous insulin, It, was 162 mU/kg uterine weight or less, the umbilical uptake of glucose, Q, may be expressed as a function of maternal arterial blood glucose concentration in milligrams per dl, [A], and of It.