A kinetic study of lung DNA-synthesis during simulated chronic high altitude hypoxia.

Abstract

A kinetic study of lung DNA-synthesis during simulated chronic high-altitude hypoxia. Rats were exposed to chronic hypobaric hypoxia at a simulated altitude of 4250 m for 3, 6, 9, 12, 20, and 35 al., 1963;Burton et al., 1967;Barer et al., 1970; Abrahams et al., 1971;McMurtry et al., 1973). The pulmonary hypertension is the result of a fixed increase in pulmonary vascular resistance due to structural changes in the pulmonary blood vessels that occur in the course of long-term hypoxia.Although the histological changes are well documented by Arias-Stella and Saldafia (1962) and by Heath (1959), it is not clear whether they are hypertrophic or hyperplastic, and we are also ignorant of the time course of these changes. In order to investigate the mechanism involved and to monitor the onset and the kinetics of the expected cellular proliferation the present cytokinetic study of pulmonary response to chronic hypoxia was designed. MethodsThirty female Wistar rats weighing 220-250 g were used for the experiments. They were randomly divided into groups of three: six groups were kept in a decompression chamber for 3, 6, 9, 12, 20, and 35 days respectively and were exposed to a simulated altitude of 4250 m. Three groups were taken as controls at the beginning of the 'Supported by the Deutsche Forschungsgemeinschaft grant No. Si 207/2 study and on day 3, 12, and 35 respectively. The animals were exposed to hypoxia for 22 hours daily and they were allowed access to food and water. After anaesthesia with 2 mg/kg pentobarbital sodium (Nembutal') a medium thoracotomy was performed, and the middle lobe of the right lung was excised and cut into slices. Two hundred milligram portions of each lung were immediately incubated in 3 ml Krebs-Ringer medium containing 20 ,tCi of 3H-thymidine (H3-thymidine, 24 6 Ci/mmol, Amersham-Buchler, Braunschweig) at 35°C for 60 minutes. The incubation was stopped by the addition of 5 ml icecold 3N TCA. The slices were homogenised in 10 ml 5% TCA (w/w) and centrifuged at 3000 g for 5 minutes. The DNA of the sediment was hydrolysed in 5 ml 5% TCA at 95°C for 30 minutes. The insoluble material was removed by centrifugation. One hundred microlitre samples of the supernatant were measured in duplicate for both radioactivity and DNA (Burton, 1968). The DNA synthesis rate was expressed as specific radioactivity (cpm/,tg DNA). Liver slices in portions of approximately 300 mg were run as controls. ResultsRats that were exposed to chronic hypobaric hypoxia (440 Torr) for a variable period of time (3-35 days) increased their lung DNA synthesis considerably. Figure 1 shows a rapid and continu-578 on 7 May 2018 by guest. Protected by copyright.

Resident cell lineages are preserved in pulmonary vascular remodeling

“…The earliest studies addressing the cellular composition and changes were based on ultrastructural analysis and in vivo labeling of proliferating cells from chronic hypoxia and monocrotaline‐exposed rats, and postulated that new smooth muscle cells differentiate from precursor smooth muscle cells – the pericyte and intermediate cell . As cell type‐specific and inducible Cre recombinase‐expressing rats are not available, validation of these observations is limited to murine models.…”

Increased gene expression for VEGF and the VEGF receptors KDR/Flk and Flt in lungs exposed to acute or to chronic hypoxia. Modulation of gene expression by nitric oxide.

“…However, evidence for vascular cell proliferation (as in Fig. 1) has been presented by many investigators (1,30,31).…”

“…This remodeling process involves hypertrophy of the precapillary vascular smooth muscle cells, proliferation of endothelial cells and pericytes, and enhanced vascular permeability (1)(2)(3). Since hypoxia per se does not cause hyperplasia of cultured pulmonary vascular smooth muscle cells, it is reasonable to assume that, in vivo, hypoxia and vascular cell growth factors act synergis-tically on growth and differentiation of pulmonary vascular cells (4).…”

PAF receptor blockade inhibits lung vascular changes in the rat monocrotaline model

“…The insoluble material was removed by centrifugation. Samples of the supernatant (100/xl) were measured for both radioactivity and DNA [25]. The DNA synthesis rate was expressed as specific radioactivity (dpm//zg DNA).…”