David L. Beckman

Circulating catecholamines in cats before and after lethal head injury.

Summary Several particulate compounds such as Celite, glass powder, tin oxide, diamond powder, and three different cellulose products, Microcrystalline Cellulose, Solka Flok, and Cellophane Spangles, stimulated population growth in C. briggsae. Since inert diamond particles form a poor adsorbent, and since large particles did not enter the gut of the nematode, our results suggest that stimulation is not the result of nutrient adsorption or phagocytosis, but rather due to the physical presence of particles.

EFFECTS OF PEROXYNITRITE ON PULMONARY EDEMA AND THE OXIDATIVE STATE

Excess nitric oxide (NO) generation in the presence of superoxide anion (O2-) leads to the formation of peroxynitrite which may result in lung injury. Oxidant-mediated lung injury has a critical role in pulmonary diseases. We therefore determined whether peroxynitrite causes lung fluid accumulation, lipid peroxidation, and formation of nitrotyrosine using an isolated perfused rat lung model. The lung weight gain during bolus peroxynitrite infusion increased in a dose-dependent manner over a range of 3 to 30 mumole. Concomitantly, bronchoalveolar lavage Ficoll also increased, indicative of increased endothelial permeability. Peroxynitrite increased the production of thiobarbituric acid reactive substances, an index of lipid peroxidation. Furthermore, nitrotyrosine levels in lung tissue rose with increased concentration of peroxynitrite, as determined by Western blot using antinitrotyrosine antibodies. These results suggest that peroxynitrite, formed from NO and O2-, leads to increased pulmonary fluid accumulation, possibly through lipid peroxidation and/or nitration of cell membrane proteins.Excess nitric oxide (NO) generation in the presence of superoxide anion (O2-) leads to the formation of peroxynitrite which may result in lung injury. Oxidant-mediated lung injury has a critical role in pulmonary diseases. We therefore determined whether peroxynitrite causes lung fluid accumulation, lipid peroxidation, and formation of nitrotyrosine using an isolated perfused rat lung model. The lung weight gain during bolus peroxynitrite infusion increased in a dose-dependent manner over a range of 3 to 30 mumole. Concomitantly, bronchoalveolar lavage Ficoll also increased, indicative of increased endothelial permeability. Peroxynitrite increased the production of thiobarbituric acid reactive substances, an index of lipid peroxidation. Furthermore, nitrotyrosine levels in lung tissue rose with increased concentration of peroxynitrite, as determined by Western blot using antinitrotyrosine antibodies. These results suggest that peroxynitrite, formed from NO and O2-, leads to increased pulmonary fluid accumulation, possibly through lipid peroxidation and/or nitration of cell membrane proteins.

Pulmonary Damage and Head Injury

Summary Experiments were carried out to investigate the effect of severe head injury on the lungs of 42 unanesthetized rats. Cerebral trauma was induced by means of a captive bolt mechanism producing sufficient force to cause immediate unconsciousness or death, apparently of respiratory origin, usually within a few minutes. Rats which showed any signs of regaining consciousness after trauma (36%) were immediately given a lethal dose of sodium pentobarbital. Gross pulmonary damage including edema and congestion and increased lung wt./body ratios were found in 92% of those rats dying from the impact and in 40% of the rats killed by the lethal dose of anesthetic given after impact. Pathology reports indicated the occurrence of moderate to severe brain and lung damage in traumatized rats. Control experiments in which animals succumbed during exposure to low oxygen have demonstrated that this pulmonary pathology cannot be attributed simply to low oxygen. Results indicate that hypoxia alone in rats does not induce the severe form of pulmonary damage resulting from cerebral trauma. It is tentatively concluded that these pulmonary changes are due in large part to nervous mechanisms of central origin. The data lend substantial support to the evidence previously reported that similar pathology which attends severe epileptiform convulsions induced by the toxic action of oxygen at high pressure and by chemical convulsants such as Metrazol and picrotoxin is in large part of CNS origin, and that this effect is mediated through the sympathetics and alterations in the cardiopulmonary hemodynamics and possibly also through changes in the pulmonary parenchyma itself.

Influence of blood glucose on convulsive seizures from hyperbaric oxygen.

Previous evidence suggests a causal relationship between blood glucose levels and the development of generalized epileptiform seizures. In the present study rats were pretreated with glucose, alloxan, or insulin prior to exposure to 6 atmospheres absolute (ATA) oxygen in a hyperbaric chamber. The results showed that the administration of glucose prior to oxygen exposure increased the time-to-seizure by 90% and alloxan by 110%, whereas in contrast insulin decreased the time-to-seizure by 55%. Blood glucose levels were consistently elevated in rats following oxygen exposure. A trend towards reduced lung damage by glucose and alloxan pretreatment was suggested by the data, although no changes were significant. Our results showed that prior administration of glucose or alloxan offered partial protection from oxygen toxicity in rats, whereas insulin generally augmented the reaction.

Protection from Oxygen-Induced Seizures by Clonazepam and Propylene Glycol

Abstract General anesthetics, ganglionic blocking agents, anticonvulsants, and antioxidants have been shown to afford protection from seizures caused by exposure to hyperbaric oxygen. In the present study cats were exposed to 5 ATA oxygen in pairs in a hyperbaric chamber until both the control and pretreated cat convulsed or for a maximum 120 min exposure. Small amounts of four common antiepileptic agents and propylene glycol in amounts far less than previously reported (0.1 to 0.2 ml/kg) were initially tested for potential anticonvulsant activity. Two agents, clonazepam and propylene glycol, offered significant protection in delaying the onset of seizures whereas carbamazepine, valproic acid, and trimethadione appeared to hasten the onset of seizure activity. The time to seizures was increased nearly five times by clonazepam and over three times by very small amounts of propylene glycol.

EFFECT OF NITRIC OXIDE ON LUNG SURFACTANT SECRETION

Lung surfactant is secreted from epithelial type II cells into alveolar airspace in response to airborne and circulating stimuli. Nitric oxide (NO) can be generated by constitutive and inducible nitric oxide synthases (cNOS and iNOS) in pulmonary endothelial and epithelial cells. The authors therefore examined the effects of NO on lung surfactant secretion using an isolated perfused rat lung model and primary culture of type II cells. Infusion of L - N G -nitroarginine methyl ester (L -NAME) (100 μ M), an inhibitor of cNOS and iNOS, via pulmonary circulation for 90 minutes resulted in a decrease of lung surfactant secretion (1.55% ± 0.15% in control versus 0.79% ± 0.16% in L -NAME-treated lungs, P <. 05). However, aminoguanide, an inhibitor of iNOS, had no effect, indicating that the decline of lung surfactant secretion is due to the specific blockage of cNOS rather than iNOS activity in perfused lungs. A reduction of cGMP level by 1H-[1,2,4] oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) (25 μ M), a specific inhibitor of guanylyl cyclase, inhibited surfactant secretion by 64%. Furthermore, KT5823 (1 μ M), an inhibitor of protein kinase G, depressed surfactant secretion by 40%. These results suggest that physiological concentrations of NO are required for lung surfactant secretion and NO-mediated secretion is at least partly via a rise of cGMP level and activation of protein kinase G. In primary culture of alveolar type II cells, spermine NONOate (SPER/NO), a NO donor, increased basal phosphatidylcholine (PC) secretion in a dose-dependent manner. Maximal stimulation was observed at 1 μ M. However, in the ATP-stimulated type II cells, SPER/NO displayed a biphasic effect on PC secretion. At low concentrations (0.1 to 1 μ M), SPER/NO increased ATP-stimulated PC secretion, whereas at a high concentration (100 μ M), SPER/NO inhibited the secretion. The results suggest that NO may play an important role in lung surfactant secretion.

Neurogenic pulmonary edema in a pulmonary normotensive model

Abstract In the present study our aim was to determine whether or not neurogenic pulmonary edema would develop from a brief pulse of intracranial pressure (ICP) in the absence of any obvious pulmonary hypertension. There were three groups of cats: sham-operated controls, ICP only, and ICP plus variable occlusion of the pulmonary artery. Partial occlusion of the pulmonary artery was carried out by placing a ligature around the pulmonary trunk and mechanically constricting the artery to maintain pulmonary arterial pressure (PAP) and left atrial pressure (LAP) at pre-ICP levels. In sham-operated animals the extravascular lung water/blood free dry weight ratio (EVLW/BFDW) was 3.26 ± 0.07 and broncho-alveolar lavage (BAL) protein, 6.49 ± 0.62 mg/g lung. ICP-only caused a rise in PAP, left atrial pressure, and EVLW/BFDW to 3.67 ± 0.08 (P < 0.05). ICP with partial occlusion of the pulmonary artery prevented any rise in PAP or LAP while EVLW/BFDW rose to 3.67 ± 0.10 (P < 0.05) and BAL protein was 8.37 ± 1.27 mg/g lung. Our results show that EVLW/BFDW can increase with neurogenic pulmonary edema in cats in the absence of an obvious increase in pulmonary arterial or left atrial pressure.

Pulmonary surface tension and head injury.

Previous studies have shown that exposure of monkeys to lethal experimental head injury by means of a captive-bolt mechanism results in a decreased lung compliance and a high minimum surface tension. Such changes which occurred in the absence of any increase in lung weight/body weight ratios were ameliorated by the prior administration of various sympathetic blocking agents. Exposure of monkeys and cats to stimulation of the pulmonary sympathetics via the stellate ganglion also resulted in similar compliance and surface tension changes without any increase in lung weight. The present experiments were carried out in order to determine the effect of lethal mechanical head injury in the cat on the surface tension of the alveolar lining layer and reasons for any possible changes. Previous reports have shown that the addition of very small amounts of cholesterol to lung wash fluid raised the minimum surface tension to abnormal levels. The results from the present study show that a sudden lethal blow to the occiput in cats results in an abnormally high minimum surface tension (over 20 dynes/cm) in the lung wash fluid and a nearly 200% increase in cholesterol content. There was little or no change in lung wet weight/dry weight ratios or gross lung appearance following this head injury. Thus the results from the present study strongly suggests that the previously reported decreased lung compliance and high minimum surface tension following a blow to the head may be due in part at least to the presence of increased intra-alveolar cholesterol.

Aspiration pneumonitis and pulmonary phospholipids.

Peptic aspiration pneumonitis (Mendelsons syndrome) results when gastric acid is aspirated into the lung, as may occur during anesthesia. In the present study, 0.1 N HCl was insufflated via the endotracheal tube into pentobarbital-anesthetized dogs in an amount sufficient to cause severe pulmonary damage. At death, the thorax was opened, the lungs grossly examined, and either weighed and desiccated for determination of wet/dry lung weight ratios, rinsed with saline for removal of alveolar surface phospholipids, or homogenized for whole lung phospholipid determination. Gross appearance and wet/dry lung weight ratios indicated severe pulmonary edema. The surface tension values of the lung wash were elevated over control values. Lysophophatidyl-choline (LPC) showed a striking increase over control values. Because LPC is a potent hemolytic agent which builds up in the lung following this pulmonary insult, and because increased hemorrhaging gradually develops following experimental acid insufflation, it is concluded that LPC is most probably causally related to the hemorrhagic pneumonia of Mendelsons syndrome.

Stellate ganglion stimulation with alpha and beta adrenergic blockade: effect on lung lipids and compliance in cats

Stellate ganglion stimulation (SGS) can alter lung lipids and reduce static lung compliance, although the mechanisms remain unclear. Phentolamine and propranolol were administered to anesthetized cats prior to stimulation in order to investigate SGS effects on lung lipids and compliance mediated via alpha and beta adrenergic pathways. Analysis of lung lavage revealed that SGS alone decreased cholesterol and the cholesterol/DSPC ratio which might be expected to decrease lung compliance. Alpha and beta blockade alone resulted in no changes from control in cholesterol or DSPC. Alpha blockade plus SGS yielded increased rather than decreased cholesterol and DSPC, while beta blockade prevented any change. A reduction in both static and dynamic lung compliance caused by SGS also was blocked by both alpha and beta blockade. Thus both the alpha and beta blockade prevented the SGS-induced decreases in cholesterol, cholesterol/DSPC ratio, and lung compliance. Furthermore, alpha blockade plus SGS resulted in increased TPL as well as cholesterol and DSPC. The data are consistent with the view that DSPC and cholesterol are released into the subphase by beta adrenergic mechanisms, and that their relative amounts may influence surface properties.