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J J Cummings

Publications and source records attributed to J J Cummings.

10 recordsLinked to original sources
PubMed1992

Acetylcholine increases pulmonary blood flow in intact fetuses via endothelium-dependent vasodilation.

In vitro, acetylcholine causes vasodilation by releasing endothelium-derived relaxing factor (EDRF) from endothelial cells. EDRF may be nitric oxide, derived from the amino acid L-arginine (L-Arg), by a process that is inhibited by NG-monomethyl-L-arginine (L-NMMA) and restored by L-Arg. We studied the effect of L-NMMA and L-Arg on the increase in pulmonary blood flow caused by acetylcholine in unanesthetized intrauterine near-term fetal lambs. Three protocols were employed. In each protocol, acetylcholine (0.48 +/- 0.15 micrograms/kg) was injected at 15-min intervals for 120 min. In the control protocol, nothing else was given. In the second protocol, L-NMMA (14 +/- 5 mg/kg) was given at 35 min. In the third protocol, L-NMMA was given at 35 min followed by L-Arg (138 +/- 73 mg/kg) at 80 min. In the control protocol, acetylcholine increased pulmonary blood flow 179 +/- 17% while it decreased pulmonary arterial pressure 15 +/- 1% and did not affect left atrial pressure. The response to each injection lasted less than 1 min and did not change throughout the experiment. L-NMMA completely blocked, whereas L-Arg completely restored, the effect of acetylcholine on pulmonary blood flow. We conclude that acetylcholine increases pulmonary blood flow in the fetal lamb via the release of EDRF derived from L-Arg. We speculate that endothelium-dependent vasodilation may play a role in the increase in pulmonary blood flow at birth.

Acetylcholine↗
PubMed1992

Increased pulmonary vascular filtration pressure does not alter lung liquid secretion in fetal sheep.

The purpose of this study was to determine whether an increase in pulmonary vascular filtration pressure affects net production of liquid within the lumen of the fetal lung. We studied 14 chronically catheterized fetal lambs [130 +/- 3 (SD) days gestation] before, during, and after a 4-h rapid (500 ml/h) intravenous infusion of isotonic saline. In seven fetuses we measured pulmonary arterial and left atrial pressures, lung lymph flow, and protein osmotic pressures in plasma and lymph. In eight lambs with a chronically implanted tracheal loop cannula, we measured the change in luminal lung liquid volume over time by progressive dilution of tracheally instilled 125I-albumin, which stays within the lung lumen. Saline infusion increased pulmonary vascular pressures by 2-3 mmHg and decreased the plasma-lymph difference in protein osmotic pressure by 1 mmHg. Lung lymph flow increased from 1.9 +/- 0.6 to 3.9 +/- 1.2 (SD) ml/h; net production of luminal lung liquid did not change (12 +/- 5 to 12 +/- 6 ml/h). Thus an increase in net fluid filtration pressure in the pulmonary circulation, which was sufficient to double lung lymph flow, had no significant effect on luminal lung liquid secretion in fetal sheep.

Animals↗
PubMed1992

A controlled clinical comparison of four different surfactant preparations in surfactant-deficient preterm lambs.

Four pulmonary surfactant preparations (natural sheep surfactant, Exosurf, Infasurf, and Survanta) were compared with no treatment in 29 newborn lambs at 126 +/- 1 days gestation. Fetuses were delivered by Cesarean section under general anesthesia and treated with either the manufacturer's recommended dose of a commercial surfactant, 100 mg phospholipid/kg of natural sheep surfactant, or no surfactant (control group). Lambs were mechanically ventilated with 100% oxygen until moribund from respiratory failure or until killed at 24 h after delivery. Lambs surviving to 12 h received surfactant retreatment (of the same type) if hypoxemic. All lambs were surfactant deficient at birth, having less than 0.1 mg/ml of phospholipid measured in the lung liquid. All control lambs developed early respiratory failure and died within 8 h after delivery. Survival was significantly prolonged by natural surfactant (p less than 0.02), Infasurf (p less than 0.0001), and Survanta (p less than 0.02). Natural surfactant, Infasurf, and Survanta significantly improved arterial oxygenation and ventilatory compliance compared with no treatment. These effects lasted as long as 24 h in lambs given Infasurf, but no more than 6 h in lambs given natural surfactant or Survanta. After death, static pressure-volume lung mechanics were significantly better for lambs given natural sheep surfactant, Infasurf, or Survanta. Lambs given Exosurf were no different than control lambs in any variable measured. Thus, in 126-day gestation surfactant-deficient newborn lambs, natural sheep surfactant, Infasurf, and Survanta, but not Exosurf, Improve oxygenation, lung mechanics, and survival.

Animals↗
PubMed1992

Ion transport regulation of lung liquid secretion in foetal lambs.

To test the hypothesis that liquid formation in the foetal lung reflects the balance between Cl- secretion and Na+ absorption by the respiratory tract epithelium, we studied the independent and combined effects of selective ion transport inhibitors on basal production of lung liquid in foetal lambs. We prepared 19 foetal lambs (gestation 125 +/- 4, term = 147 days) with chronic indwelling catheters for subsequent measurement of luminal liquid production over time (JV). Using an impermeant tracer technique, we measured JV before and after tracheal instillation of 2 different inhibitors of ion transport: bumetanide, a Na(+)-K(+)-2Cl- co-transport inhibitor, and amiloride, a Na+ transport inhibitor. In 7 foetuses we sequentially added bumetanide (10(-4) M) and 2 different concentrations of amiloride (10(-6) M, 10(-4) M) to the liquid within the lung lumen. After we gave bumetanide, JV decreased from 12 +/- 4 ml/h to 0 +/- 5 ml/h and subsequently increased during the 2 periods of amiloride exposure (10(-6) M: 6 +/- 5 ml/h; 10(-4) M: 7 +/- 7 ml/h). In 5 control studies we gave bumetanide, followed by only amiloride vehicle. JV for all time periods in the control studies was similar to the experimental group, demonstrating no effect of amiloride. In 5 foetuses we administered the 2 concentrations of amiloride before bumetanide. There was no change in JV with either concentration of amiloride (baseline: 13 +/- 2 ml/h; 10(-6) M amiloride: 15 +/- 5 ml/h; 10(-4) M amiloride: 13 +/- 6 ml/h).(ABSTRACT TRUNCATED AT 250 WORDS)

Amiloride↗
PubMed1991

Intrapulmonary terbutaline and aminophylline decrease lung liquid in fetal lambs.

To see if phosphodiesterase inhibition might enhance the effect of beta-adrenergic stimulation on fetal lung liquid secretion, we studied the independent and combined effects of intrapulmonary terbutaline and aminophylline on net production of lung luminal liquid over time (Jv) in fetal lambs with chronically placed tracheal loop catheters. We calculated Jv during baseline and experimental periods (90-120 min each) by measuring serial concentrations of 125I-albumin, an impermeant tracer that was well mixed in the luminal liquid. In 21 experiments, tracheal instillation of terbutaline (10(-5) M) decreased Jv from 11 +/- 1 (mean +/- SEM) to -3 +/- 2 mL/h. In six other studies, aminophylline (10(-3) M) alone had no significant effect on Jv. In 12 experiments, we gave the two drugs sequentially: terbutaline decreased Jv from 11 +/- 2 to -3 +/- 2 mL/h and aminophylline further decreased Jv to -8 +/- 2 mL/h. Amiloride (10(-4) M), an inhibitor of epithelial Na+ transport, reversed the combined effect of terbutaline and aminophylline, increasing Jv to 8 +/- 1 mL/h. Thus, phosphodiesterase inhibition enhances the beta-adrenergic effect of terbutaline on Na(+)-dependent absorption of liquid from the lung lumen of fetal lambs.

Amiloride↗
PubMed1990

Effects of chronic alcohol consumption on the steady-state kinetics properties of cytochrome oxidase in rat liver.

The effect of chronic alcohol consumption on steady-state kinetic characteristics of cytochrome oxidase in rat liver was studied using submitochondrial particles prepared from ethanol-fed and control rats. Preparations from both control and alcoholic rats had equivalent apparent Km values for cytochrome c of 13 microM in the presence of phenazine methosulfate or 19 microM with N,N,N',N'-tetramethylphenylene diamine as oxidation-reduction mediators at physiological ionic strength. Both preparations showed comparable stimulation (approx. 3-fold) of oxidase activity following detergent solubilization of the membrane and similar temperature dependence for oxidase activity. Under all conditions, preparations from alcohol-fed rats displayed 30 to 50% lower rats of cytochrome oxidase activity per unit membrane protein than those from control rats. The diminution in specific activity per mg protein was accompanied by a similar decline in heme aa3 content, as has been noted in previous studies. When expressed on a turnover number basis, the molecular activity of cytochrome oxidase (natoms O/min per nmol heme a) was equivalent in both alcoholic and control preparations. The results indicate that the intrinsic kinetic characteristics of cytochrome oxidase are not changed by alcohol consumption. The data suggest that the characteristic decline in heme aa3 content and cytochrome oxidase specific activity seen in ethanol-fed rats does not arise from alterations in the accessibility of the oxidase towards cytochrome c, or from changes in bulk phase lipid composition or physical properties. The results support the conclusion that ethanol consumption decreases the membrane content of functionally active oxidase molecules, but does not change the catalytic properties of these oxidase molecules.

Alcoholism↗
PubMed1990

Lung overexpansion increases pulmonary microvascular protein permeability in young lambs.

To study the effects of inflation pressure and tidal volume (VT) on protein permeability in the neonatal pulmonary microcirculation, we measured lung vascular pressures, blood flow, lymph flow (QL), and concentrations of protein in lymph (L) and plasma (P) of 22 chronically catheterized lambs that received mechanical ventilation at various peak inflation pressures (PIP) and VT. Nine lambs were ventilated initially with a PIP of 19 +/- 1 cmH2O and a VT of 10 +/- 1 ml/kg for 2-4 h (base line), after which we overexpanded their lungs with a PIP of 58 +/- 3 cmH2O and a VT of 48 +/- 4 ml/kg for 4-8 h. QL increased from 2.1 +/- 0.4 to 13.9 +/- 5.0 ml/h. L/P did not change, but the ratio of albumin to globulin in lymph relative to the same ratio in plasma decreased, indicating altered protein sieving in the pulmonary microcirculation. Seven other lambs were mechanically ventilated for 2-4 h at a PIP of 34 +/- 1 cmH2O and a VT of 23 +/- 2 ml/kg (base line), after which their chest and abdomen were bound so that PIP increased to 54 +/- 1 cmH2O for 4-6 h without a change in VT. QL decreased on average from 2.8 +/- 0.6 to 1.9 +/- 0.3 ml/h (P = 0.08), and L/P was unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

A controlled trial of dexamethasone in preterm infants at high risk for bronchopulmonary dysplasia.

We evaluated the use of dexamethasone in preterm infants to decrease morbidity associated with bronchopulmonary dysplasia in a randomized, double-blind, placebo-controlled trial. Thirty-six preterm infants (birth weight, less than or equal to 1250 g and gestational age, less than or equal to 30 weeks) who were dependent on oxygen and mechanical ventilation at two weeks of age received a 42-day course of dexamethasone (n = 13), an 18-day course of dexamethasone (n = 12), or saline placebo (n = 11). The starting dose of dexamethasone was 0.5 mg per kilogram of body weight per day, and it was progressively lowered during the period of administration. Infants in the 42-day dexamethasone group, but not those in the 18-day group, were weaned from mechanical ventilation significantly faster than control infants (medians 29, 73, and 84 days, respectively; P less than 0.05), and from supplemental oxygen (medians 65, 190, and 136 days, respectively; P less than 0.05). No clinical complications of steroid administration were noted. Follow-up of all 23 survivors at 6 and 15 months of age showed good outcome (normal neurologic examinations and Bayley Developmental Indexes greater than or equal to 84) in 7 of the 9 infants in the 42-day dexamethasone group, but in only 2 of the 9 infants in the 18-day dexamethasone group and 2 of the 5 in the placebo group (P less than 0.05). We conclude that dexamethasone therapy for 42 days improves pulmonary and neurodevelopmental outcome in very-low-birth-weight infants at high risk for bronchopulmonary dysplasia.

Bronchopulmonary Dysplasia↗
PubMed1989

Lung fluid balance in lambs before and after premature birth.

The purpose of this study was to see if lung vascular protein permeability is greater in preterm lambs with respiratory distress than it is in lambs without lung disease. We measured pulmonary vascular pressures, lung lymph flow, and concentrations of protein in lymph and plasma of 10 chronically catheterized preterm lambs (gestation 133 +/- 1 d) for 2-4 h before and for 4-8 h after delivery by cesarean section. All lambs were treated with mechanical ventilation after birth and received a constant intravenous infusion of glucose-saline solution at an hourly rate of 10 ml/kg. Respiratory failure developed in six lambs, in which there was a sustained threefold postnatal increase in lung lymph flow and lymph protein flow, with an even greater increase in pleural liquid drainage. Concentrations of protein in lymph and pleural liquid were almost identical, averaging approximately 75% of the plasma protein concentration. In the four preterm lambs without lung disease, lymph flow and lymph protein flow were either near or below fetal values by 6-8 h after birth, and there was little or no pleural liquid drainage. Extravascular lung water averaged 7.3 +/- .8 g/g dry lung in lambs with respiratory failure compared to 4.8 +/- .5 g/g dry lung in lambs without lung disease. Thus, pulmonary edema with abnormal leakage of protein-rich liquid from the lung microcirculation into the interstitium is an important pathological feature of the respiratory disease that often occurs after premature birth.

Animals↗