Effect of phorbol myristate acetate-induced lung injury on airway blood flow

The effects of phorbol myristate acetate (PMA) induced lung injury on the pulmonary and systemic blood flow contributions to the trachea and main bronchi (upper airways) were assessed in anesthetized dogs by injecting 15 μm radiolabeled microspheres into the right and left heart, respectively. Upper airway blood flow was studied in lungs given the following treatments: (1) PMA; (2) PMA in lungs pretreated with the thromboxane synthetase inhibitor OKY-046, and (3) PMA in lungs pretreated with the antioxidant catalase. After microsphere injections, the tracheal cartilage, tracheal muscle-mucosa, and main bronchi were excised. The results of this study indicate that under normal conditions, tracheal mucosa [33–52 ml·min⁻·(100 g)⁻¹] and tracheal cartilage [18–27 ml·min⁻¹·(100 g)⁻¹] blood flow is primarily systemic while both the systemic [12–18 ml·min⁻¹·(100 g)⁻¹] and pulmonary [6–12 ml·min⁻¹·(100 g)⁻¹] circulations contribute substantial amounts of blood flow to the main bronchi. PMA significantly decreased the systemic blood flow contribution to the tracheal cartilage and muscle-mucosa, and both the systemic and pulmonary blood flow contributions to the main bronchi to less than 50% of control values, an effect that was inhibited by catalase, but not by OKY-046. These results suggest that the effect of PMA-induced lung injury on the pulmonary and systemic blood flow contributions to the upper airways is at least partially mediated by oxygen radical production, probably hydrogen peroxide (H₂O₂), but not by the production of the arachidonic acid metabolite thromboxane.     

Quantification of gluconeogenesis in cirrhosis: Response to glucagon

Background & Aims: Accelerated starvation and early recruitment of alternate fuels in cirrhosis have been attributed to reduced availability of hepatic glycogen. The aim of this study was to measure gluconeogenesis (as a marker of protein oxidation) in relation to total glucose production and glucagon-stimulated glycogenolysis. Methods: Glucose and urea production, gluconeogenesis, and glycogenolysis were calculated using stable isotope methods before and during glucagon infusion (3 ng · kg⁻¹ · min⁻¹) in 5 cirrhotic patients and 5 matched controls before and after glycogen repletion. Results: In the basal state, cirrhotic patients had a normal rate of glucose production, but the contribution of gluconeogenesis was increased (74.3% ± 4.1% vs. 55.6% ± 12.1%; P < 0.005). Glycogen repletion normalized the rate of gluconeogenesis. The glycemic response to glucagon (3 ng · kg⁻¹ · min⁻¹) was blunted in cirrhotic patients because of a lower rate of glycogenolysis (0.63 ± 0.23 vs. 1.22 ± 0.23 mg · kg⁻¹ · min⁻¹; P < 0.01) and was not affected by glycogen repletion. Despite increased gluconeogenesis, the simultaneously measured rate of urea synthesis was lower in cirrhotic patients (3.11 ± 1.02 vs. 5.0 ± 1.0 mg/kg; P < 0.05). Conclusions: These data show that in cirrhosis, glucose production is sustained by an increased rate of gluconeogenesis. The hepatic resistance to glucagon action is not caused by reduced glycogen stores.GASTROENTEROLOGY 1998;115:1530-1540     

Persistent increased lung response to methacholine after normobaric hyperoxia in rabbits

This study was performed to determine the occurrence and time course of airway hyperreactivity following exposure to normobaric hyperoxia. Twenty-six rabbits were studied. Twelve served as control (group 1), and 14 were exposed to normobaric hyperoxia (Fi_O2 ≥ 95%) for 48 h: 9 rabbits (group 2) were studied after 1 day of recovery in room air and 5 (group 3) after 7 days. The rabbits were anesthetized, curarized and artificially ventilated. Respiratory resistance (Rrs) and elastance (Ers) and their respective changes induced by cumulative doses of aerosolized methacholine were assessed by the multiple linear regression analysis of airway pressure, tidal flow and volume. Weight-specific Rrs and Ers were significantly higher in group 2 (respectively, 87.7 ± 6.5 cmH₂O·L⁻¹·sec·kg and 1100.2 ± 87.1 cmH₂O·L⁻¹·kg, mean ± SEM) than in group 1 (respectively, 65.2 ± 3.2 cmH₂O·L⁻¹·sec·kg and 904.4 ± 49.7 cmH₂O·L⁻¹·kg (P < 0.05)), but were not different from group 3 (79.4 ± 7.9 cmH₂O·L⁻¹·sec·kg and 952.3 ± 125.0 cmH₂O·L⁻¹·kg, respectively). The dose of methacholine required to increase Rrs by 50% (PD_Rrs50) was significantly lower in both treated groups: 0.37 ± 0.11 mg in group 2 and 0.51 ± 0.19 mg in group 3 vs 2.07 ± 0.51 mg in group 1 (P < 0.05)). PD_Ers50 was significantly lower in group 2 (0.45 ± 0.15 mg) and 3 (0.75 ± 0.43 mg) compared with controls (1.11 ± 0.26 mg (P < 0.05)). These results show that hyperoxia induces an increase in Rrs and Ers, and airway hyperreactivity in the rabbit. The latter is prolonged beyond the immediate post-exposure period.     

Right-sided pulmonary aplasia: Longitudinal lung function studies in two cases and comparison to results from term healthy neonates

Agenesis of the right lung was diagnosed prenatally in two neonates born at 36 and 37 weeks, respectively. Computed tomographic scans and magnetic resonance imaging indicated that both cases had a Type 2 pulmonary agenesis, which was confirmed later by bronchoscopy. Both patients were clinically stable during the neonatal period. Serial pulmonary function tests revealed a decrease in specific respiratory system compliance (sCrs) in both neonates and a marked discrepancy between functional residual capacity measured by the nitrogen washout technique (FRCN ₂) and by plethysmography (FRC_pleth) on follow-up. Early decrease of respiratory system compliance (Crs) and increase of respiratory system resistance (Rrs) in one infant preceded the onset of tracheal stenosis, which remained asymptomatic until the age of 8 weeks, when the infant developed acute respiratory failure requiring intubation and mechanical ventilation with high airway pressures. Aortopexy, implantation of a tissue expander into the right hemithorax, and laser ablation of fibrotic tissue at the site of tracheal stenosis were performed to achieve successful extubation. The second infant remained asymptomatic. Values for lung mechanics and volumes for both infants with pulmonary aplasia were as follows: Crs, 3.43 and 10.60 mL · kPa⁻¹ · kg⁻¹; sCrs, 0.23 and 1.28 kpa⁻¹; Rrs, 11.1 and 7.4 kpa · s · L⁻¹; FRCN ₂, 14.9 and 10.2 mL · kg⁻¹; FRC_pleth, 28.2 and 25.8 mL · kg⁻; FRCN ₂: FRC_pleth ratio, 0.56 and 0.54 for patients 1 and 2, respectively. These values differed considerably from results of a control group of nine term healthy neonates (Crs, 10.0 ± 1.8 mL · kPa⁻¹ · kg⁻¹; sCrs, 0.43 ± 0.08 kpa⁻¹; Rrs, 5.10 ± 0.55 kpa · s · L⁻¹; FRCN ₂, 24.0 ± 2.5 mL · kg⁻¹; FRC_pleth, 31.1 ± 6.0 mL · kg⁻¹; FRCN ₂:FRC_pleth ratio, 0.78 ± 0.10). In conclusion, serial assessment of lung mechanics and pulmonary gas volumes detects airway obstruction early in neonates with unilateral lung agenesis. Bronchoscopy is recommended. Along with conventional surgical procedures, an expandable implant may improve management or prevent respiratory failure in selected cases. Pediatr Pulmonol. 1998; 26:138–144. © 1998 Wiley-Liss, Inc.     

Age-related ozone effects on glucose utilization in rat lungs

We examined the relationship between animal age and pulmonary biochemical effects of O₃ exposure using young to adult rats ranging in age from 24 to 90 days. Glucose uptake and production of pyruvate and lactate, determined in lung tissue slices, were used as indices of O₃-produced metabolic alterations. In control rats, the lung weights increased with animal age until they stabilized between 60 and 90 days of age. The rate of glucose metabolism, expressed per lung, increased with animal age paralleling the increase in lung weights. After exposure to 0.8 ppm (1568 ug/m³) O₃ for 3 days, the lung weights and all three parameters of glucose metabolism increased in exposed rats relative to their age-matched controls. These increases were relatively small for younger rats but much larger for adult rats. Regression of percent differences in these parameters between control and exposed rat lungs against animal age indicates that the response to O₃ was age-related.     

Estimating exercise Dlo2 and diffusion limitation in patients with interstitial fibrosis

Inert gas elimination studies in interstitial fibrosis ascribe all of the resting and most (58–83%) of the exercise (A-a)P_O2 difference to ventilation-perfusion in equality. The previous paper (Hughes, J.M.B., D.N.A. Lockwood, H.A. Jones and R.J. Clark, Respir. Physiol., 1990) suggests from estimates of global Dl_O2/Q̇β ratios a larger role diffusion limitation on exercise. Gas exchange data from that paper was analyzed at rest and on exercise for five patients with interstitial fibrosis. Hypoxemia at rest was attributed toV̇a/Q̇ inequality which was quantified using a log-normal lung model. Dl_O2 was calculated by Bohr integration. The base 10 LogSDQ̇ at rest averaged 0.5 ± 0.1 (SEM) the assumption that V̇a/Q̇ inequality remained unchanged on exercise, Dl_O2 (exercise) was estimated to be 14.3 ± 1.9 ml·min⁻¹·Torr⁻¹. At that level of Dl_O2, diffusion limitation accounted for 36% ± 8(SEM)% of the total (A-a)P_O2 difference using the log-normal Q̇a/Q̇ model. But estimates of Dl_O2/Q̇β assuming a homogeneous lung, ascribed 96% of the (A-a)P_O2 gradient on exercise to diffusion limitation. The discrepancy was shown to be related to the shape of the oxygen equilibrium curve and high alveolar P_O2 values. On the other hand, analysis in terms of oxygen contents showed that 68 ± 5% of the (A-a) content difference was accounted for by diffusion limitation. This differs substantially from estimates based on partial pressure alone.     

Effects of perfusate viscosity on the perfused rat kidney

Elevation of blood hematocrit has been shown to result in little effect upon renal blood flow despite the resulting elevation in whole blood viscosity (L. Share, Amer. J. Physiol.171, 159–163, 1952). Perfused rat kidneys were used to study the effects of doubling the perfusate viscosity from 0.858 to 1.768 cP. A portion of the bovine serum albumin (BSA) that was present in the low viscosity perfusate (5 g% BSA) was replaced by a high molecular weight dextran (4 g% BSA + 1.4 g% dextran) so as to double the perfusate viscosity but keep the colloid osmotic pressure constant. [¹⁴C]Inulin was used to measure glomerular filtration rate (GFR) and absolute filtrate reabsorption (T_H2O). Perusion with the high viscosity perfusate reduced the arterial flow by 50% and doubled the total renal flow resistance from 4.5 ± 0.4 (SD) to 9.1 ± 0.8 mm Hg·gKw (gram kidney weight)·min·g^?1. Thus, the kidney was not capable of autoregulating the perfusate flow in response to a viscosity alteration. Both GFR and T_H2O were reduced with increased viscosity (GFR, 1.18 ± 0.16 (SD) to 0.96 ± 0.200 g/min/gKw (P < 0.05) and T_H2O, 0.75 ± 0.07 to 0.59 ± 0.09 g/min/gKw, P < 0.005); however, these reductions were accompanied by a fall in ATP content of the kidneys from 1.43 ± 0.15 (SD) to 1.15 ± 0.11 μmoles ATP/gKw. This indicates that a reduction in metabolic rate due to lower O₂ delivery (lower flow) may have been responsible for these latter results.     

Cardiac output but not high pulmonary artery pressure varies with FIO2 in exercising horses

Horses have high mean pulmonary artery pressure (Ppa) both at rest and during exercise (≈30 and ≥ 80 mmHg, respectively). The mechanisms are unknown. To see if hypoxic pulmonary vasoconstriction (HPV) plays a role, we compared pulmonary artery pressure-flow (Ppa-Q) curves when inspired O₂ fraction (Fi_O2) was 0.16, 0.21, and 0.30, in 5 noraml Thoroughbred horses standing quitely and while galloping at 10 and 14 m/sec on a level treadmill. We calculated O₂ consumption (V̇_O2) from measurements of respired gas composition and flow, and calculated Q̇ from V̇_O2 and measurements of oxygen content in arterial and mixed venous blood (Ca_O2 and Cv̄_O2).V̇_O2 was 3.8, 74 and 128 ml·mim⁻¹·kg⁻¹, at rest and at 10 and 14 m/sec, and did not vary with Fi_O2 at any speed. At 14 m/sec only, when Fi_O2 was lowered to 0.16, Ca_O2 fell (to 14.7 from 20 ml/dl on air), Q̇ increased (to 0.86 from 0.66 L·min⁻¹·kg⁻¹ on air), and stroke volume increased (to 4.1 from 3.2 ml·kg⁻¹ on air). Slopes and intercepts of Ppa-Q̇ curves did not vary with Fi_O2. We concled that HPV does not contribute to the high Ppa of exercising horses breathing air near sea level.     

Chronic treatment with a superoxide dismutase mimetic prevents vascular remodeling and progression of hypertension in salt-loaded stroke-prone spontaneously hypertensive rats

Oxidative stress has been implicated in the pathogenesis of hypertension. The aim of the present study was to determine whether increased generation of vascular superoxide anion (·O₂⁻) contributes to blood pressure elevation by influencing vascular function and structure in severely hypertensive rats. Sixteen-week-old stroke-prone spontaneously hypertensive rats (SHRSP) (n = 12) were randomly divided into two groups to receive the superoxide dismutase mimetic, tempol (4-hydroxy-2,2,6,6-tetramethyl piperidinoxyl) (1 mmol/L in drinking water) or tap water. Both groups were fed a high-salt diet (4% NaCl). Systolic blood pressure (SBP) was measured weekly for 6 weeks by the tail-cuff method. Rats were killed, and vascular structure (media:lumen ratio) and endothelial function (acetylcholine [Ach]–induced vasodilation) were assessed in small mesenteric arteries mounted as pressurized preparations. Vascular ·O₂⁻ concentration was measured by lucigenin (5 μmol/L) chemiluminescence. Plasma total antioxidant status was assessed spectrophotometrically. The SBP increased significantly (P < .01) in the control group, whereas progression of hypertension was prevented in the tempol-treated group. Tempol reduced (P < .01) the media:lumen ratio (7.2% ± 0.01%) compared with that in controls (12.0% ± 0.01%). Maximal Ach-induced dilation was altered in control rats (40% ± 9%) but was not influenced by tempol (57% ± 1 7%). Vascular ·O₂⁻ concentration was lower (P < .01) and plasma total antioxidant concentration was higher (P < .05) in the treated group compared with the control. In conclusion, tempol prevents progression of hypertension. These processes are associated with attenuated vascular remodeling, decreased vascular ·O₂⁻ concentration, and increased antioxidant status. Our data suggest that oxidative stress plays an important role in vascular damage associated with severe hypertension in salt-loaded SHRSP.     

Lifespan,oxygen consumption and hydroxyl radical scavenging capacity of two strains of Drosophila melanogaster

Two strains of Drosophila melanogaster were compared for lifespan, metabolic rate, and ability to scavenge in vitro generated hydroxyl radicals. The mean lifespan and oxygen consumption data were: Samarkand, 68.7 ± 21.4 days and 44.4 ± 2.6μl O₂·mg⁻¹·24hrs⁻¹; Swedish C, 43.7 ± 11.5 days and 54.4 ± 4.6μl O₂·mg⁻¹·24hrs⁻¹. In an experiment in which hydroxyl radicals were formed in vitro and their reaction products with 2-deoxy-D-ribose measured, we found that tissue homogenates of Samarkand flies exhibited a 39% inhibition of radical production compared to 10% by the Swedish C strain. These data are in agreement with the free radical theory of aging and suggest that both the respiration rate (O₂ consumption) and the efficiency of Drosophila tissues to scavenge hydroxyl radicals are important determinants of lifespan in this insect.     

Pulmonary transit time and diffusion limitation during heavy exercise in athletes

To investigate relationships between pulmonary transit times (PTT) and pulmonary diffusion limitation during exercise, 10 high aerobic capacity athletes (V̇_O2max = 5.15 ± 0.52 l · min⁻¹) who had multiple inert gas elimination analysis evidence suggestive of diffusion disequilibrium were studied at rest and maximal exercise. Diffusing capacity for oxygen (Dl_O2) was calculated from the inert gas data. First pass radionuclide angiography was performed using ^99mTechnecium labeled erythrocytes and whole lung PTT and pulmonary blood volume (PBV) were calculated. PTT decreased from 9.32 ± 1.41 sec at rest, to 2.91 ± 0.30 sec during exercise and was correlated with diffusion limitation suggested by the inert gases (r = -0.58, P < 0.05). PBV increased during exercise to over 25% of whole blood volume and correlated with Dl_O2 (r = 0.82, P < 0.01). These data suggest that diffusion limitation is related to shortened PTT in athletes and that maximal recruitment of PBV may defend against diffusion limitation.     

Ion transport and metabolic effects of amiloride in canine tracheal mucosa

We studied the interaction between Cl transport and the Na entry step at the luminal side of the canine tracheal epithelium by testing the effects of amiloride, an inhibitor of apical membrane Na conductance. The tracheal mucosa was mounted as a flat sheet in Ussing chamber and bathed with Krebs-Henseleit solution. In six experiments²²Na and³⁶Cl transepithelial fluxes were determined. Under basal conditions net Na absorption was 0.45±0.10 μEq/cm²·h ( ±SE) and declined to 0.07±0.08 after 0.1 mM amiloride was added to the mucosal bath. No changes were found in Cl fluxes. Addition of amiloride (0.1 mM) to the luminal bath usually caused a 10–20% decline in short circuit current (SCC). However, these alterations in SCC were often transient when the bathing media contained Cl. In contrast, in the absence of Cl the inhibition of SCC by 0.01 mM mucosal amiloride was predictable, large, and stable (ΔSCC=−21±6 μA/cm²,N=5). Addition of higher concentration of amiloride (2–4 mM) to the submucosal side (N=6) caused significant decline in net Cl secretion from 1.67±0.37 to 0.06±0.25 μEq/cm² · h (P<0.02). These changes were probably caused by inhibition of tissue metabolism since 2 mM amiloride caused a 73% fall in tissue oxygen consumption. Ouabain (0.1 mM), which inhibits Na-K-ATPase and therefore both Na and Cl transport, reduced tissue O₂ consumption by 34%. The Na entry step at the luminal membrane is amiloride sensitive, but does not appear to be crucial for the maintenance of the Cl secretory process. Luminal membrane conductance appears to be primarily a Cl-conductance. About one third of tissue O₂ demands are utilized for transport of Na and Cl. This work was supported by the Medical Research Service of the Veterans Administration and by Eleanor B. Pillsbury Foundation, University of Illinois     

Brain function rescue effect of lactate following hypoglycaemia is not an adaptation process in both normal and Type I diabetic subjects

Aims/hypothesis. We have previously shown that lactate protects brain function during insulin-induced hypoglycaemia. An adaptation process could, however, not be excluded because the blood lactate increase preceded hypoglycaemia.¶Methods. We studied seven healthy volunteers and seven patients with Type I (insulin-dependent) diabetes mellitus with a hyperinsulinaemic (1.5 mU · kg^–1· min^–1) stepwise hypoglycaemic clamp (4.8 to 3.6, 3.0 and 2.8 mmo/l) with and without Na-lactate infusion (30 μmol · kg^–1· min^–1) given after initiation of hypoglycaemic symptoms.¶Results. The glucose threshold for epinephrine response was similar (control subjects 3.2 ± 0.1 vs 3.2 ± 0.1, diabetic patients = 3.5 ± 0.1 vs 3.5 ± 0.1 mmol/l) in both studies. The magnitude of the response was, however, blunted by lactate infusion (AUC; control subjects 65 ± 28 vs 314 ± 55 nmol/l/180 min, zenith = 2.6 ± 0.5 vs 4.8 ± 0.7 nmol/l, p < 0.05; diabetic patients = 102 ± 14 vs 205 ± 40 nmol/l/180 min, zenith = 1.4 ± 0.4 vs 3.2 ± 0.3 nmol/l, p < 0.01). The glucose threshold for symptoms was also similar (C = autonomic 3.0 ± 0.1 vs 3.0 ± 0.1, neuroglycopenic = 2.8 ± 0.1 vs 2.9 ± 0.1 mmol/l, D = autonomic 3.2 ± 0.1 vs 3.2 ± 0.1, neuroglycopenic 3.1 ± 0.1 vs 3.2 ± 0.1 mmol/l) but peak responses were significantly attenuated by lactate (score at 160 min C = 2.6 ± 1 vs 8.8 ± 1, and 0.4 ± 0.4 vs 4.8 ± 1, respectively; p = 0.02–0.01, D = 1.3 ± 0.5 vs 6.3 ± 1.7, and 2.3 ± 0.6 vs 5.7 ± 1.1 p = 0.07–0.02). Cognitive function deteriorated in both studies at similar glucose thresholds (C = 3.1 ± 0.1 vs 3.0 ± 0.1, D = 3.2 ± 0.1 vs 3.3 ± 0.2 mmol/l). Although in normal subjects a much smaller impairment was observed with lactate infusion (Δ four-choice reaction time at 160 min = 22 ± 12 vs 77 ± 31 ms; p = 0.02), in Type I diabetic patients lactate infusion was associated with an improvement in cognitive dysfunction (0.2 ± 0.4 vs –38 ± 0.2 Δ ms, p = 0.0001).¶Conclusion/interpretation. A blood lactate increase after the development of hypoglycaemic symptoms reduces counterregulatory and symptomatic responses to insulin-induced hypoglycaemia and favours brain function rescue both in normal and diabetic subjects. These findings confirm that lactate is an alternative substrate to glucose for cerebral metabolism under hypoglycaemic conditions. [Diabetologia (2000) 43: 733–741]     

Non-invasive tracing of liver intermediary metabolism in normal subjects and in moderately hyperglycaemic NIDDM subjects. Evidence against increased gluconeogenesis and hepatic fatty acid oxidation in NIDDM

Summary To test whether gluconeogenesis is increased in non-insulin-dependent diabetic (NIDDM) patients we infused (post-absorptive state) healthy subjects and NIDDM patients with [6,6-²H₂]glucose (150 min) and [3-¹³C]lactate (6 h). Liver glutamine was sampled with phenylacetate and its labelling pattern determined (mass spectrometry) after purification of the glutamine moiety of urinary phenylacetylglutamine. After correction for ¹³CO₂ re-incorporation (control test with NaH¹³CO₃ infusion) this pattern was used to calculate the dilution factor (F) in the hepatic oxaloacetate pool and fluxes through liver Krebs cycle. NIDDM patients had increased lactate turnover rates (16.18 ± 0.92 vs 12.14 ± 0.60 μmol · kg⁻¹· min⁻¹, p < 0.01) and a moderate rise in glucose production (EGP) (15.39 ± 0.87 vs 12.52 ± 0.28 μmol · kg⁻¹· min⁻¹, p = 0.047). Uncorrected contributions of gluconeogenesis to EGP were 31 ± 3 % (control subjects) and 17 ± 2 % (NIDDM patients). F was comparable (1.34 ± 0.02 and 1.39 ± 0.09, respectively) and the corrected percent and absolute contributions of gluconeogenesis were not increased in NIDDM (25 ± 3 % and 3.8 ± 0.5 μmol · kg⁻¹· min⁻¹) compared to control subjects (41 ± 3 % and 5.1 ± 0.4 μmol · kg⁻¹· min⁻¹). The calculated pyruvate carboxylase over pyruvate dehydrogenase activity ratio was comparable (12.1 ± 2.6 vs 11.2 ± 1.4). Lastly hepatic fatty oxidation, as estimated by the model, was not increased in NIDDM (1.8 ± 0.4 vs 1.6 ± 0.1 μmol · kg⁻¹· min⁻¹). In conclusion, in the patients studied we found no evidence of increased hepatic fatty oxidation, or, despite the increased lactate turnover rate, an increased gluconeogenesis. [Diabetologia (1998) 41: 212–220] Received: 4 July 1997 and in revised form: 16 September 1997     

Gas conductance and metabolism of shorebird eggs: variation within and between species

Fresh egg mass (M₀; g), water vapor conductance of the egg shell (G_H2O; mg·[Torr·d]⁻¹), and neonate mass (M_n; g) were measured in the ruff (Philomachus pugnax), common redshank (Tringa totanus), northern lapwing (Vanellus vanellus), black-tailed godwit (Limosa limosa), and Eurasian curlew (Numenius arquata). In addition, the development of embryonic O₂ consumption (Ṁ_O2; ml·d⁻¹) and CO₂ production (Ṁ_CO2; ml·d⁻¹) were measured in these species, except the ruff. In northern lapwing and black-tailed godwit eggs the coefficients of variation for G_H2O were 3.8 and 2.3 times higher, respectively, than those for M₀. In these two species only about 10% of the variation for G_H2O was attributable to M₀, and about 77% to differences between clutches, suggesting a strong maternal component. In the northern lapwing, embryonic Ṁ_O2 plateaued prior to internal pipping, but not in the common redshank and black-tailed godwit. The latter result is in contrast to embryonic patterns previously described for other precocial species. In shorebirds the occurrence of an embryonic Ṁ_O2 plateau is not related to the neonatal level of cold-induced thermogenesis.     

Metformin and Exercise: no Additive Effect on Blood Lactate Levels in Healthy Volunteers

Metformin administration has been associated with substantial rises in blood lactate concentrations in individual Type 2 diabetic patients. Exercise also leads to increases in blood lactate levels. The objective of this study was to determine whether metformin administration augments the rise in plasma lactate concentrations during intermittent exercise in healthy subjects, when compared to placebo. Twelve healthy males (age 28 ± 5 years, body mass index 22.7 ± 1.3 kg m⁻²) took either 1.7 g metformin or placebo daily for 4 consecutive days before being subjected to strenuous intermittent exercise. On the morning of the fourth day exercise was performed on an upright bicycle ergometer at a work load of 200 W for 2 min alternating with 2 min rest for an overall duration of 60 min. Maximal plasma lactate levels during exercise (metformin: 4.1 ± 2.6 mmol l⁻¹, placebo: 4.5 ± 2.6 mmol l⁻¹), areas under the plasma lactate curve (207 ± 121 vs 222 ± 133 mmol l⁻¹ h⁻¹), blood pyruvate levels at the end of exercise (0.06 ± 0.04 vs 0.07 ± 0.04 mmol l⁻¹), lactate/pyruvate ratio (65 ± 41 vs 60 ± 36), serum insulin (25.4 ± 8.9 vs 32.3 ± 13.0 pmol l⁻¹), and plasma glucose (4.4 ± 0.3 vs 4.5 ± 0.3 mmol l⁻¹) did not differ significantly between metformin and placebo administration. Administration of metformin did not lead to an augmented rise in endogenous plasma lactate concentrations during intermittent exercise in healthy fasting subjects under the experimental design chosen. © 1997 by John Wiley & Sons, Ltd.     

Isolation and metabolism of granular pneumocytes from rat lungs

A population of rat lung cells enriched in granular pneumonocytes (type II cells) was prepared by modification of the method of Kikkawa (Lab. Invest.30, 76, 1974). Lungs were minced, mechanically agitated and incubated with a fluorochemical emulsion and 1% trypsin. The isolated cells were centrifuged in a discontinuous Ficoll gradient. Granular pneumonocytes were identified by the presence of cytoplasmic inclusions on Papanicolaou and acid phosphatase staining and a strongly positive alkaline phosphatase reaction. The yield at the interface between 1.058 and 1.100 density Ficoll was (4.0 ± 1.5) × 10⁶ (mean ± SD) cells per g of lung tissue consisting of 72.7 ± 9.0% granular pneumonocytes and 20.3 ± 8.4% alveolar macrophages. O₂ uptake by the cells at room temperature was 46.9 ± 5.8 nmol/h per 10⁶ cells (mean ± SE; n=5). Respiration was inhibited by oligomycin and subsequently stimulated by an uncoupler of oxidative phosphorylation. During incubation with [U-¹⁴C] glucose, the cells produced¹⁴CO₂, lactate and pyruvate at rates of 17.0 ± 2.9, 17.1 ± 1.6 and 8.7 ± 0.8 nmol/h/10⁶ cells, respectively. These results show that a cell population enriched in granular pneumonocytes can be isolated by lung trypsinization. The cells in this preparation show respiration that is coupled to oxidative phosphorylation and intact glycolytic pathways.     

Studies on the regulation of myocardial blood flow in man II. Effects of acute arterial hypoxia

To determine whether adjustment of myocardial blood flow (MBF), myocardial oxygen consumption (MVO₂) and myocardial substrate uptake (MSU) to acute arterial hypoxia is influenced by training effects on the heart, 7 trained and 7 untrained healthy individuals were investigated. MBF (argon method), MVO₂ and MSU of glucose, lactate and free fatty acids were measured at rest during normoxia and two different stages of acute arterial hypoxia: a) 12.82 vol% O₂; b) 8.74 vol% O₂. Measurements were carried out during hemodynamic and respiratory steady state conditions. Myocardial flow and metabolism of athletes were significantly (p<0.01) lower compared to untrained subjects. In the trained cohort, MBF increased from 65 ± 19 to 73 ± 16 (a) and 98 ± 23 (b) ml/min·100 g. MVO₂ remained at normoxic control level of 8.00 ± 2.27 ml/min·100g. In the untrained group, MBF increased from 77 ± 15 to 84 ± 20 (a) and 108 ± 18 (b) ml/min · 100g. Again, there was no significant deviation in MVO₂ from the normoxic level of 10.11 ± 1.90 ml/min·100g. Decrease in arterial oxygen content was overcompensated by an increase in coronary conductance resulting in a significantly improved efficiency of myocardial perfusion during severe hypoxia. MSU of glucose, lactate and free fatty acids as well as calculated ATP production did not change significantly during hypoxia. It is concluded that training effects on the heart do not influence regulation of MBF, MVO₂ and MSU during moderate or severe acute arterial hypoxia. Reaction of coronary smooth muscle tone to a decrease in oxygen partial pressure is independent from training effects. However, both acute arterial hypoxia and physical training exert synergetic effects on the heart by reducing myocardial oxygen consumption per heart beat. Thus, it is assumed that adaptive properties of myocardial blood flow and metaboüsm to severe hypoxia are more pronounced in trained than in untrained individuals.     

Lipid-dependent control of hepatic glycogen stores in healthy humans

Aims/hypothesis. Non-esterified fatty acids and glycerol could stimulate gluconeogenesis and also contribute to regulating hepatic glycogen stores. We examined their effect on liver glycogen breakdown in humans.¶Methods. After an overnight fast healthy subjects participated in three protocols with lipid/heparin (plasma non-esterified fatty acids: 2.2 ± 0.1 mol/l; plasma glycerol: 0.5 ± 0.03 mol/l; n = 7), glycerol (0.4 ± 0.1 mol/l; 1.5 ± 0.2 mol/l; n = 5) and saline infusion (control; 0.5 ± 0.1 mol/l; 0.2 ± 0.02 mol/l; n = 7). Net rates of glycogen breakdown were calculated from the decrease of liver glycogen within 9 h using ¹³C nuclear magnetic resonance spectroscopy. Endogenous glucose production was measured with infusion of D-[6,6-²H₂]glucose.¶Results. Endogenous glucose production decreased by about 25 % during lipid and saline infusion (p < 0.005) but not during glycerol infusion (p < 0.001 vs lipid, saline). An increase of plasma non-esterified fatty acids or glycerol reduced the net glycogen breakdown by about 84 % to 0.6 ± 0.3 μmol · kg^–1· min^–1 (p < 0.001 vs saline: 3.7 ± 0.5 μmol · kg^–1· min^–1) and by about 46 % to 2.0 ± 0.4 μmol · kg^–1· min^–1 (p < 0.01 vs saline and lipid), respectively. Rates of gluconeogenesis increased to 11.5 ± 0.8 μmol · kg^–1· min^–1 (p < 0.01) and 12.8 ± 1.0 μmol · kg^–1· min^–1 (p < 0.01 vs saline: 8.2 ± 0.7 μmol · l^–1· min^–1), respectively.¶Conclusion/interpretation: An increase of non-esterified fatty acid leads to a pronounced inhibition of net hepatic glycogen breakdown and increases gluconeogenesis whereas glucose production does not differ from the control condition. We suggest that this effect is not due to increased availability of glycerol alone but rather to lipid-dependent control of hepatic glycogen stores. [Diabetologia (2001) 44: 48–54]     

Potentiation of Pulmonary Arteriolar Vasoconstriction to Endothelin-1 by Inhibition of Nitric Oxide Synthesis in the Intact Lung

Objective : To observe pulmonary arteriolar effects of endothelin-1 (ET-1) in the intact lung and determine if constriction to ET-1 is potentiated by inhibition of nitric oxide (NO) synthesis. Methods : In anesthetized male Sprague-Dawley rats with open chest, the lungs were ventilated with air through the lower trachea and in vivo responses of pulmonary arterioles were examined by video microscopy. Observations were made when the lungs were statically inflated with oxygen to a pressure of approximately 10 cm H₂O for brief periods. A lens with a dipping cone was held at the pleural surface. ET-1 (10^?7–10^?5 M; approximately 0.1 ml) was applied topically to the fluid layer under the dipping cone. Results : ET-1 (10^?6 M) constricted parent arterioles 60 ± 5 µm in diameter by 52 ± 12% (range: 20–100%) and branches 45 ± 3 µm in diameter by 36 ± 4% (19–48%). Constriction persisted and there was a dramatic long-lasting decrease in flow. Alveolar walls quickly became pale, indicating reduced capillary perfusion. A lower concentration of ET-1 (10^?7 M) constricted (p < 0.05) parent arterioles 61 ± 4 µm in diameter by 7 ± 3% initially, and by 13 ± 8% after 14 ± 2 minutes, while smaller branches did not respond. In separate experiments, infusion of the NO synthase inhibitor L-NAME (1 mg/kg per minute), modestly (10 ± 3%) decreased (p < 0.05) baseline parent arteriolar diameter from 72 ± 7 µm to 64 ± 5 µm. Branch diameter changed insignificantly from 42 ± 7 µm to 38 ± 7 µm. After l -NAME, ET-1 (10^?7 M) constricted (p < 0.05) parent arterioles by 17 ± 4% initially and 40 ± 14% after 14 ± 2 minutes. Concurrently, branches constricted (p < 0.05) by 14 ± 4% and 26 ± 15%. Conclusions : Arterioles less than 80 µm in diameter were very responsive to ET-1, which could be a factor in altering pulmonary microvascular resistance. Inhibition of NO synthesis appears to potentiate constriction to ET-1.