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Biomedical subjects

M Weinstock

Publications and source records attributed to M Weinstock.

At least 127 records · Page 7Linked to original sources
PubMed1974

Synthesis, migration, and release of precursor collagen by odontoblasts as visualized by radioautography after (3H)proline administration.

The elaboration of dentin collagen precursors by the odontoblasts in the incisor teeth of 30-40-g rats was investigated by electron microscopy, histochemistry, and radioautography after intravenous injection of tritium-labeled proline. At 2 min after injection, when the labeling of blood proline was high, radioactivity was restricted to the rough endoplasmic reticulum, indicating that it is the site of synthesis of the polypeptide precursors of collagen, the pro-alpha chains. At 10 min, when the labeling of blood proline had already declined, radioactivity was observed in spherical portions of Golgi saccules containing entangled threads, and, at 20 min, radioactivity appeared in cylindrical portions containing aggregates of parallel threads. The parallel threads measured 280-350 nm in length and stained with the low pH-phosphotungstic acid technique for carbohydrate and with the silver methenamine technique for aldehydes (as did extracellular collagen fibrils). The passage of label from spherical to cylindrical Golgi portions is associated with the reorganization of entangled into parallel threads, which is interpreted as the packing of procollagen molecules. Between 20 and 30 min, prosecretory and secretory granules respectively became labeled. These results indicate that the cylindrical portions of Golgi saccules transform into prosecretory and subsequently into secretory granules. Within these granules, the parallel threads, believed to be procollagen molecules, are transported to the odontoblast process. At 90 min and 4 h after injection, label was present in predentin, indicating that the labeled content of secretory granules had been released into predentin. This occurred by exocytosis as evidenced by the presence of secretory granules in fusion with the plasmalemma of the odontoblast process. It is proposed that pro-alpha chains give rise to procollagen molecules which assemble into parallel aggregates in the Golgi apparatus. Procollagen molecules are then transported within secretory granules to the odontoblast process and released by exocytosis. In predentin procollagen molecules would give rise to tropocollagen molecules, which would then polymerize into collagen fibrils.

Animals↗
PubMed1974

Beta-adrenoceptor blocking agents and responses to adrenaline and 5-hydroxytryptamine in rat isolated stomach and uterus.

1 Four beta-adrenoceptor blocking agents, (+/-)- and (+)-propranolol, practolol and oxprenolol, were found to antagonize, apparently competitively, the responses of both the rat isolated stomach and uterus to 5-hydroxytryptamine (5-HT).2 The pA(2) values for each of these agents as antagonists of the contractile action of 5-HT on the rat stomach were found to be: (+/-)-propranolol, 6.08; (+)-propranolol, 4.94; practolol, 3.43; and oxprenolol, 5.99. These values were very similar to the corresponding figures for antagonism of 5-HT-induced contractions of the uterus.3 pA(2) values for antagonism of adrenaline-induced relaxations by the four blocking agents on the rat stomach and uterus did not differ from the values for 5-HT blockade.4 To antagonize contractile responses to acetylcholine of the rat stomach it was necessary to give 100 times more (+/-)-propranolol than was needed to antagonize responses to 5-HT.

Adrenergic beta-Antagonists↗
PubMed1974

The role of supersensitivity to acetyl- choline in the production of tolerance to morphine in stimulated guinea-pig ileum.

1 Morphine caused a dose-dependent reduction in both the height of contraction and acetylcholine release from coaxially stimulated strips of guinea-pig ileum.2 Exposure of the tissue to morphine for 90 min produced acute tolerance to the effect of subsequent doses of morphine on contraction height.3 There was no change in the ability of morphine to suppress acetylcholine release.4 The responses of morphine-tolerant ileum to exogenous acetylcholine were enhanced 3 to 10-fold.5 If the ileum did not show tolerance to morphine it did not become more sensitive to acetylcholine.6 The results presented suggest that tolerance to morphine could result from a form of disuse supersensitivity.

Acetylcholine↗
PubMed1974

Supersensitivity to isoprenaline induced in rats by prolonged isolation.

1 The effect of isoprenaline on diastolic blood pressure and heart rate was determined in anaesthetized male rats which had been housed individually for 6-8 weeks after weaning, and compared with its effect in group-housed litter-mate controls.2 Isoprenaline caused a significantly greater fall in diastolic pressure in isolated rats and a greater increase in heart rate.3 Low doses of noradrenaline (5-10 ng) caused vasodepressor responses in isolated, but not in group-housed rats.4 The pressor response to noradrenaline, which was smaller in isolated rats, was increased to the level of group-housed controls by (+/-)-propranolol.5 Prolonged isolation of rats may bring about an increase in sensitivity of beta-adrenoceptors to isoprenaline and noradrenaline.

Animals↗
PubMed1972

Factors influencing the adrenergic neurone blocking action of propranolol.

1. The reversal by propranolol of its own adrenergic neurone blocking effect in the cat can be prevented by cutting the splanchnic nerves or by ligating the adrenal veins.2. In the absence of secretion from the adrenal medulla the nerve blocking action of propranolol is more complete, but can still be reversed by repeated injections or a constant infusion of adrenaline.3. Prior treatment with adrenaline or noradrenaline also prevents the development of the blocking action of propranolol in the cat and in the isolated guinea-pig vas deferens.4. It is suggested that in the cat, propranolol stimulates the release of catecholamines from the adrenal medulla which antagonize its nerve blocking effect.

Animals↗