Abstract. Oxytalan connective tissue fibers are a separate and distinct fiber type. Although current histochemical methods cannot distinguish pre‐elastic from oxytalan fibers, the two fiber types are readily distinguished by electron microscopy. Oxytalan fibers are found in periodontal membranes of all teeth of man, monkeys, rats, guinea pigs and mice. Increased numbers and size of oxytalan fibers are observed in periodontal membranes of teeth subjected to increased stress, such as those used for bridge abutments. Edwards (1968) observed increased size and number of oxytalan fibers in periodontal membranes of dog incisors subjected to orthodontic forces. Some oxytalan fibers serve to support the blood and lymphatic vessels leading to the teeth. Oxytalan fibers appear to have a protein component and a stainable component digestible with β‐glucuronidase after peracetic acid digestion. Oxytalan fibers develop in repair tissues of the periodontal membrane. Although oxytalan fibers probably develop in relation to tumors developed from dental tissues, electron microscopy must be employed to distinguish oxytalan from developing elastic tissues inasmuch as histochemical methods are inadequate.

In previous studies it has not been possible to determine net intrarenal formation of angiotensin II (ANG II) from arteriovenous ANG II concentrations because of the high intrarenal ANG II degradation rates (DR). This study was designed to determine ANG II-DR and to estimate net intrarenal ANG II formation during normal and enhanced renin secretion rate (RSR). In anesthetized dogs, plasma renin activity and ANG II were measured in arterial and renal venous blood by radioimmunoassay during four periods: control, renal arterial constriction (RAC), angiotensin converting enzyme (ACE) inhibition (MK 422), and MK 422 plus systemic arterial ANG II infusion. ANG II-DR was determined in each dog from the arterial-renal venous ANG II concentration difference during the period of ANG II infusion in the presence of ACE inhibition; this value was used to estimate net ANG II formation by predicting the amount of arterially delivered ANG II that escaped degradation. The average percent ANG II-DR calculated during ANG II infusion (range of 0.05 to 0.20 microgram/min) was 89 +/- 2%. In response to RAC, RSR increased from 11 +/- 3 to 24 +/- 5 ng ANG I X h-1 X min-1 X g-1. Arterial ANG II (67 +/- 11 pg/ml) and renal venous ANG II (29 +/- 6 pg/ml) increased to 133 +/- 18 and 61 +/- 10 pg/ml, respectively. Net intrarenal ANG II formation increased from 44 +/- 11 to 83 +/- 13 pg X min-1 X g-1 after renal arterial constriction. There was a significant relationship between the change in RSR and the change in ANG II formation rate.(ABSTRACT TRUNCATED AT 250 WORDS)

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The effects of exposing rats to hypoxia (10% O2) at normal atmospheric pressure for periods of 14 or 28 days on angiotensin-converting enzyme (ACE) activity and stores of angiotensin I (ANG I) and angiotensin II (ANG II) in lung, kidney, brain, and testis were examined. ACE activity was measured by spectrophotometric assay, and active sites of ACE were estimated by measuring the binding of 125I-351A [N-(1-carbonyl-3-phenyl-propyl)-L-lysyl-L-proline], a highly specific active site-directed inhibitor of ACE, to tissue homogenates and perfused lungs. Hypoxia exposure produced progressive reductions in ACE activity in lung homogenates and in ACE inhibitor binding to perfused lungs. ANG II levels in lungs from hypoxia-adapted animals were significantly less than air controls, suggesting that the reduction in intrapulmonary ACE activity was associated with reduced local generation of ANG II. ACE activity was increased in kidney and unchanged in brain and testis of hypoxia-adapted rats compared with air controls. Thus the effects of chronic hypoxia on catalytically active ACE and ACE active sites in the intact animal were organ specific. Adaptation to chronic hypoxia did not significantly alter plasma renin activity or ANG I or ANG II levels or serum ACE content. The hypoxia-induced alterations in lung and kidney ACE were reversible after return to a normoxic environment.