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Query: UMLS:C0242706 (hyperoxia)
 5,219 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Angiotensin-converting enzyme (ACE) activity in the guinea pig fetal-placental unit was assessed at the different oxygen tensions found in utero, during labor, and at birth. To determine fetal-placental ACE activity, we separately perfused in situ term guinea pig fetuses and their placentas via the umbilical vessels under controlled conditions of flow, temperature, and pH. ACE activity was defined as the percent of angiotensin I (AO) or bradykinin (BK) in Krebs-Henseleit solution cleared by a single passage through the placenta or fetus. Peptide concentrations were measured by radioimmunoassay (RIA). Using BK as substrate, we found that placental and fetal ACE activities were reflected by 45% (SD = 10) and 24% (SD = 7) clearances, respectively, at a perfusate PO2 of 29 mm Hg. Maternal hypoxia (PaO2 = 28 mm Hg) decreased placental ACE activity to 16% (SD = 8) and maternal hyperoxia (PaO2 = 191 mm Hg) increased placental ACE activity to 56% (SD = 9). Using a perfusate PO2 of 95 mm Hg, fetal and placental ACE activity increased in less than 5 minutes to 75% (SD = 10) and 77% (SD = 9), respectively. Similar results were obtained using AI as substrate. We conclude that: fetal-placental ACE activity exhibits a chronically reduced level of activity appropriate to the low oxygen tension found in the fetal-placental unit; the placenta is the primary site of ACE activity in the fetus; maternal oxygenation modulates fetal-placental ACE activity; and fetal ACE activity acutely increases with increased fetal oxygenation and thus may play an important physiological role in the regulation of circulating levels of BK and AII and the circulatory adjustments at birth.
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PMID:Angiotensin-converting enzyme activity and its modulation by oxygen tension in the guinea pig fetal-placental unit. 389 3

L-Arginine can be metabolized by nitric oxide (NO) synthase (NOS) to produce NO or by arginase to produce urea and L-ornithine. In the liver, arginase (the AI isoform) is a key enzyme in the urea cycle. In extrahepatic organs including the lung, the function of arginase (the AII isoform) is less clear. Because we found that lung AII was upregulated during 100% O2 exposure in preliminary experiments, we sought to characterize expression of the arginase isoforms and inducible NOS and to assess the functions of arginase in hyperoxic lung injury. Male Sprague-Dawley rats were exposed to 100% O2 for 60 h. Protein expression of AI and AII and their cellular distribution were determined. The activities of arginase and NOS were also measured. Expression of arginase was correlated with that of ornithine decarboxylase, a biochemical marker for tissue repair, in a separate group of rats allowed to recover in room air for 48 h. We found by Western blot analyses that both AI and AII proteins were upregulated after 60 h of hyperoxic exposure (403 and 88% increases by densitometry, respectively) and, like ornithine decarboxylase, remained elevated during the recovery phase. Arginase activity increased by 37%. Immunostaining showed that increases in AI and AII were mainly in the peribronchial and perivascular connective tissues. NOS activity was unchanged and inducible NOS was not induced, but the level of nitrogen oxides in the lung decreased by 67%. Our study showed in vivo induction of arginase isoforms during hyperoxia. The strong expression of arginase in the connective tissues suggests that the function of pulmonary arginase may be linked to connective tissue elements, e.g., fibroblasts, during lung injury and recovery.
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PMID:Induction of arginase isoforms in the lung during hyperoxia. 968 40