After acute lung injury, repair of the alveolar epithelium occurs on a substrate undergoing cyclic mechanical deformation. While previous studies showed that mechanical stretch increased alveolar epithelial cell necrosis and apoptosis, the impact of cell death during repair was not determined. We examined epithelial repair during cyclic stretch (CS) in a scratch-wound model of primary rat alveolar type II (ATII) cells and found that CS altered the balance between proliferation and cell death. We measured cell migration, size, and density; intercellular gap formation; cell number, proliferation, and apoptosis; cytoskeletal organization; and focal adhesions in response to scratch wounding followed by CS for up to 24 h. Under static conditions, wounds were closed by 24 h, but repair was inhibited by CS. Wounding stimulated cell motility and proliferation, actin and vinculin redistribution, and focal adhesion formation at the wound edge, while CS impeded cell spreading, initiated apoptosis, stimulated cytoskeletal reorganization, and attenuated focal adhesion formation. CS also caused significant intercellular gap formation compared with static cells. Our results suggest that CS alters several mechanisms of epithelial repair and that an imbalance occurs between cell death and proliferation that must be overcome to restore the epithelial barrier.

Granules of the submaxillary gland of the white mouse contain both kallikrein and renin. The granules were separated and concentrated in sequential centrifugation procedures. They were more stable at room temperature and in hypertonic sucrose solutions than in the cold or in isotonic solution. The amylase, acid phosphatase, renin, kallikrein, and benzoyl-L-arginine ethyl ester esterase contents of the granules were determined. Kallikrein and renin showed a similar distribution pattern after fractionation. Granular renin released the equivalent of 9. Electron micrographs of the isolated granules showed various forms; some were spherical and symmetrical, and others were amorphous. ADDITIONAL KEY WORDSsubmaxillary gland bradykinin angiotensin subcellular fractions electron microscopy differential centrifugation insoluble enzyme polymers kallidin• Granules originating from the rat submaxillary gland contain large amounts of kallikrein ( 1 ) . The appearance of these particles in electron micrographs is similar to that of pancreatic zymogen granules (2). Although the presence of renin in granules has been gaining acceptance, a definite relationship between granules and renin activity has not yet been established (3,4 ) . In addition to kallikrein, renin was found in the submaxillary glands of the white mouse (5-8). Renin activity is concentrated in the striated ducts which have granulated cells. These findings led us to study the subcellular distribution of renin and its relationship to kallikrein in the submaxillary gland of the white mouse. In the present communication we deal withFrom the Departments of Pharmacology and Pathology, University of Oklahoma, School of Medicine, Oklahoma City, Oklahoma 73104.This work was supported in part by U. S. Public Health Service Grant HE 08764 from the National Institutes of Health.When this work was done Dr. Miwa was a fellow of the Oklahoma Heart Association. His permanent address is Department of Medicine, Tohoku University, Sendai, Japan.Accepted for publication August 5, 1968.the isolation of an active, granular layer that contains both kallikrein and renin.Methods White male Swiss Webster mice (A. Sutter Co.) were killed by a sudden blow on the head without using anesthesia. The mice were over 90 days old and weighed about 50 g. Fresh, minced submaxillary glands were homogenized in batches of six pairs in a Dounce hand homogenizer. In the first series of experiments, the tissues were placed in a medium of 0.25M sucrose solution buffered with 0.005M Tris, pH 7.4, in an ice bath. A 10% (w/v) homogenate was prepared and filtered through four layers of gauze. The filtered homogenate was then fractionated using isotonic sucrose solutions and a refrigerated centrifuge as previously described (1).In the second series of experiments, all procedures were done at room temperature in a 0.88M sucrose solution buffered with 0.005M Tris, pH 7.4. The unbroken cells and tissues were removed by centrifugation at 120 g for 5 minutes using a Sorvall RC-2 centrifuge. The step was rep...

Studies were conducted in anesthetized dogs to determine whether the mesenteric vasodilator response to histamine is mediated by H1 receptors alone or whether H2 receptors are also involved in the response. Evidence favoring a role for both receptors included: 1) the vasodilator response to histamine was inhibited by either the H1-receptor antagonist, tripelennamine, or the H2-receptor antagonist, metiamide; 2) both the H1 agonist, 2-methylhistamine, and the H2 agonist, 4-methylhistamine, induced dilator responses in the mesenteric circulation; and 3) two temporal patterns of vasodilation could be distinguished, namely a transient spike and subsequent fade of blood flow (seen with either the H1 agonist or with histamine after H2-receptor blockade) and a sustained and stable increase in flow (seen with either the H2 agonist or with histamine after H1 blockade). Metiamide appeared to be a potent inhibitor of the mesenteric vasodilator response to histamine at least equal to tripelennamine.

All epithelial cells require retinoic acid for growth, maintenance, and differentiation. Although the epithelial cells that line the gastrointestinal tract are exposed to extreme retinoid concentration fluctuations in luminal fluid, whether proliferation and differentiation in these cells are significantly affected is not known. We have investigated this question using Caco-2 cells as a model because, although they are derived from a colon adenocarcinoma, they differentiate spontaneously in a manner similar to enterocytes in the small intestine. We found that retinoic acid caused maximum inhibition of cell growth and ornithine decarboxylase activity during the proliferative period. Retinoic acid increased brush border enzyme activities only in differentiating cells but stimulated transglutaminase activity in cells at all stages. In untreated proliferating cells, we found an early peak of transglutaminase activity that has not been reported before. Retinoic acid in intestinal cells acts through its nuclear receptor, RAR beta. The nuclear distribution of this receptor has not been demonstrated. In this study, we show that RAR beta responds to increasing concentrations of retinoic acid with a shift to the nuclear membrane in undifferentiated cells and progressive aggregation, diffusion, and loss in differentiated cells. We conclude that retinoic acid can inhibit proliferation and stimulate differentiation in Caco-2 cells depending on concentration and cell stage, and that these effects are accompanied by changes in distribution, as well as by the loss of RAR beta.

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