5-Hydroxytryptamine uptake by lungs of hamsters with pulmonary emphysema

Lung MK 351A uptake after hypoxia adaptation and subsequent hyperoxia exposure

This study investigated the effects of hypoxia adaptation (10% O2 for 4 days) on rat lung angiotensin-converting enzyme (ACE) content before and after hyperoxia exposure (greater than 95% O2 for 2 days). The rationale for this investigation was that hyperoxia exposure decreases lung ACE, while hypoxia adaptation produces tolerance (improved survival) to oxygen toxicity in rats. Rats were exposed to air, hypoxia, hyperoxia alone, or hypoxia followed immediately by hyperoxia. The lungs were then excised and perfused in vitro at 12 ml/min with buffer. Lung ACE content was quantitated by measuring the single-pass binding of an iodinated ACE inhibitor, 125I-MK 351A, a derivative of lisinopril. We showed previously that 125I-MK 351A binding correlates quantitatively with ACE activity in lung homogenates and isolated, perfused lungs. Lung internal surface area was estimated by measuring the mean alveolar diameter of 5 micron hematoxylin and eosin sections from lungs fixed in inflation (25 cmH2O transpulmonary pressure). Hypoxia adaptation per se had no effect on 125I-MK 351A binding or estimated alveolar surface area, while hyperoxia exposure caused a significant decrease in both 125I-MK 351A binding and alveolar surface area. These hyperoxia-induced decreases were prevented partially by hypoxia adaptation, indicating a protective effect on both ACE content and surface area. 125I-MK 351A binding in isolated perfused lungs changed in parallel with histologically estimated surface area. These results indicate that hypoxia preadaptation minimizes the oxygen-induced decrease in lung microvascular ACE content.

Studies on the mechanism of decreased angiotensin I conversion in rat lungs injured with alpha-naphthylthiourea

Lung endothelial cell injury may be an important early event in the pathogenesis of increased permeability pulmonary edema. Since angiotensin converting enzyme (ACE) is located on the luminal surface of the endothelial cell membrane, we sought to determine whether the conversion of angiotensin I (AI) to angiotensin II is decreased after acute lung injury to rats, induced by alpha-naphthylthiourea (ANTU), and we investigated the mechanism of the decrease. We found that lungs isolated from rats treated 4 h earlier with ANTU at a dose of 15 mg/kg body weight (BW) had decreased AI conversion when perfused with Krebs-Henseleit at a constant flow rate of 30 ml/min/kg BW. When perfusate flow rate was increased from 30 to 50 ml/min/kg BW, lungs isolated from rats treated with 10 mg/kg BW ANTU also had decreased AI conversion when compared to controls treated with a vehicle, Tween 80. Investigating the mechanism of decreased AI conversion, there were no differences among experimental groups in pulmonary arterial pressures or effluent perfusate pH or pO2. There was no correlation between lung wet/dry weight ratios and the extent of AI conversion among control rat lungs. Lung homogenate and serum ACE activity did not differ among control rats and rats pretreated with the two doses of ANTU. Ultrastructural studies revealed an increased percentage of capillaries with blebbing of endothelial cells in lungs injured with ANTU, as compared to controls, but no evidence of increased endothelial cell denudation in injured lungs. We conclude that angiotensin I conversion is decreased after ANTU lung injury and that the extent of decrease is related to the dose of ANTU and to perfusate flow rate. Although we cannot exclude decreased vascular surface area perfused as a cause of decreased conversion, we speculate that subtle changes in the luminal endothelial cell membrane may have caused decreased AI conversion after ANTU lung injury.

Early metabolic changes in response to lung injury: extrapolation from animals to humans

The pulmonary capillary endothelium provides a nonthrombogenic, semipermeable barrier between pulmonary blood and tissues. In recent years, particular attention has been focused on the ability of these cells to metabolize a variety of circulating biologically active substances either by interiorizing the substance through specific membrane transport processes or by directly altering the substance by way of enzymatic activity at the plasma membrane. Serotonin, norepinephrine, and several prostaglandins are examples of biologically active substances that are removed from the circulation by the pulmonary endothelium by way of specific transmembrane transport processes. Concomitant with the increased interest in metabolic functions of the pulmonary endothelium, there has been a growing awareness of the central role of endothelial cell abnormalities in the pathogenesis of various lung injuries and disease states. During the past several years, considerable evidence has accumulated in support of the hypothesis that alterations in the metabolic functions of the lung provide a method of detecting lung injury in vivo, and tests of the metabolic functions of the lung have progressed from in vitro systems to animal models to humans. This paper reviews some of the evidence responsible for this progression and discusses some of the limitations inherent in the extrapolation of lung metabolism studies from animal models to humans. In this discussion, particular emphasis is placed on the pulmonary uptake and metabolism of serotonin, norepinephrine, and prostaglandins E and F by mammalian lungs.

The diseased lung and drugs

Among the numerous ways by which drug-lung relationships can be discussed we chose to examine three questions: Is the lung capable of directly modulating drug pharmacokinetics? Knowing that the pulmonary circulation can exert very selective and efficient clearance and catabolism of biogenic molecules such as serotonin (5-HT), norepinephrine (N.E.), prostaglandins PGE2 and PGF2 alpha, and bradykinin, as well as activation of angiotensin (A)I to AII, a similar behavior has been sought for drugs. Uptake of circulating drugs occurs clearance of biogenic amines, the significance of which remains to be fully evaluated, and iatrogenic phospholipidosis localization of which in the lung might result from the elevated drug concentration in the tissue. Lung cells contain enzymes, among them mixed function oxidases (MFO), which enables them to metabolize xenobiotics even in the intact organ. Although blood supply to the lung is higher than that to the liver, the comparatively low MFO content of the former organ predicts only a marginal pulmonary metabolic contribution in vivo. On the otherhand, enzymatic activity upon drugs can generate instable reactive metabolites which, even in minute amounts are toxic and can damage cells; furthermore, it is hypothesized that the relatively high bronchiolar Clara cell MFO content explains the striking susceptibility of the long to xenobiotics. Do lung diseases indirectly influence drug pharmacokinetics? Hindrance to blood flow is common in respiratory failure (R.F.), from both reduced area and hypoxic vasoconstriction, resulting in altered flow distribution to the liver and kidney.