Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.24.3 (collagenase)
 18,340 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Pancreatic islets of Wistar rats were prepared by digestion with collagenase and then washed and isolated at three different temperatures (4, 22 and 37 degrees C). The efficiency of washing with regard to proteolytic and collagenolytic activities in the wash buffer was not affected by the temperatures used. The islet thiol:protein-disulphide oxidoreductase activity (EC 1.8.4.2) was apparently unchanged, whereas washing temperatures lower than 37 degrees C resulted in a diminished insulin content. The insulin secretion of islets, isolated at 4 degrees C, is reduced in response to glucose without changing the sigmoidal shape of dose-response curve.
 ...
PMID:Investigations on isolated islets of Langerhans in vitro. Influence of temperature changes during preparation on some parameters of insulin metabolism. 17 3

Exposure of hamster pancreatic islets to hyaluronidase during isolation by means of collagenase inhibits the insulinotropic action of several chemically different sulfonylureas, leucine, and glucagon without affecting glucose-stimulated insulin secretion. This inhibition is reversible for tolbutamide and leucine but irreversible for glucagon. Hyaluronidase inhibits reversibly the insulinotropic action of tolbutamide without affecting that of glucose also in mouse and rat isolated pancreatic islets . These findings suggest the existence of functionally related pancreatic beta cell receptors for tolbutamide and leucine different from those for glucose and glucagon and illustrate the potential usefulness of hyaluronidase as an enzymatic probe applicable toward investigating the cellular mechanism of action of key insulinotropic agents.
 ...
PMID:Hyaluronidase-induced inhibition of the insulinotropic action of sulfonylureas, leucine, and glucagon in rodent isolated pancreatic islets. 17 48

In this report we describe some modifications of the collagenase digestion technique for the preparation of pancreatic islets, that we have found helpful in preparing isolated islets of Langerhans from rabbits and hamsters. These modifications include disrupting the pancreatic acinar tissue by directly infiltrating it with Hanks' solution, periodically monitoring the progress of the collagenase digestion of the pancreatic tissue with the dissecting microscope, and purifying the islets by serial passage of the digested tissue through three Petri dishes containing Hanks' solution. This technique results in the successful isolation of the fragile and irregular rabbit islets as well as the isolation of the sturdier and more uniformly shaped hamster islets. The isolated respond to a glucose stimulus with an increase in radioimmunoassayable insulin secretion. We also describe a filtration technique for the preparation of isolated islets for histological examination. Isolated islets are retained on Millipore filters. The filters are then fixed, stained and mounted. Finally, we present realistic photographs of rabbit and hamster islets, as they appear under the dissecting microscope, during various stages of purification and isolation.
 ...
PMID:Preparation of islets of Langerhans from rabbits and hamsters by the collagenase digestion technique. 17 31

Adenyl cyclase activity of rat pancreatic islet membrane was increased by secretin, pancreozymin, and isoproterenol, while ACTH, glucagon, growth hormone, and insulin had no effect. Both secretin and isoproterenol activations were enhanced by prostaglandin E1 (PGE1) and GTP. Isoproterenol activation was additive with PGE1, as was that of secretin with PGE1, but only in the presence of GTP. Secretin activation in the presence of PGE1 and GTP was equivalent to NaF stimulation. Kinetic analysis indicated that secretin and GTP increased the maximum velocity of the adenyl cyclase and tended to decrease the apparent affinity of the enzyme for ATP. Glucagon activation of islet membrane adenyl cyclase was dependent upon prior treatment of the membrane preparation with EGTA and the use of inhibitors of proteolytic enzymes during the collagenase digestion phase of islet preparation. These results suggest that hormonal regulation of insulin secretion may be affected by PGE1 and guanine nucleotide modulation of the adenyl cyclase activation process.
 ...
PMID:Hormonal regulation of pancreatic islet adenyl cyclase. 17 51

During the digestion of pancreatic pieces with collagenase for prepartion of isolated islets the enzymes in incubation medium (collangenolytic and/or proteolytic) can alter the secretion behavior of A- and B-cells. Insulin release after such an enzymatic attack is characterized by an enhanced basal secretion and a diminished and delayed glucose response. Overdigestion results in a decreased glucagon secretion in response to arginine, a diminished insulin content, and a decreased thiol-protein-disulfide-oxidoreductase activity of the islets. Increased albumin concentrations did not prevent the collagenase effect.
 ...
PMID:Investigations on isolated islets of Langerhans in vitro. XIII. Experiments concerning the preparation conditions with collagenase. 17 1

The procedure of Berry and Friend for isolation of intact hepatocytes has been adapted to mouse livers. The ultrastructure of these cells was satisfactorily preserved. Isolated mouse hepatocytes secreted proteins and triacylglycerols. These secretory processes were inhibited by colchicine, indicating a likely involvement of the microtubular system for their normal occurrence. Ultracentrifugation of medium incubated with hepatocytes, followed by electrophoresis and electron microscopic examination of the floating fraction (density less than 1.006) allowed to conclude that secreted triacylglycerols were very low density lipoproteins. Glycogenolysis and lipogenesis were stimulated or inhibited, respectively, by low concentrations of glucagon (10(-10) M). Other metabolic parameters were influenced by the hormone but were less sensitive to its action. Inhibition of lipogenesis by glucagon was associated with a decrease in acetyl CoA carboxylase activity. This decrease does not appear to be related to intracellular fatty acyl-CoA accumulation secondary to hepatic lipase activation by the hormone. Insulin was effective alone or counteracted glucagon effects on lipogenesis or glycogenolysis only when exposure of cells to collagenase was held minimal. This suggests that, during isolation of hepatocytes, insulin receptors may, for unknown reasons, be more fragile than those of glucagon.
 ...
PMID:Secretory processes, carbohydrate and lipid metabolism in isolated mouse hepatocytes. Aspects of regulation by glucagon and insulin. 17 77

The effects of various sugars on the simultaneous release of insulin and accumulation of cyclic AMP were studied in collagenase isolated rat pancreatic islets. D-Glucose stimulated the formation of cyclic AMP at 3 and 60 min of incubation, whether measured by a label incorporation technique, or by the protein kinase binding assay of Gilman. Only D-glucose and D-mannose were able to stimulate insulin release and cyclic [3H]AMP accumulation in the absence of other substrate. D-fructose had a stimulatory effect in the presence of 3.3 mM D-glucose only at a high concentration (33.8 mM), and enhanced the effects of 8.3 mM glucose when added at the concentration of 8.3 mM. D-Galactose was effective only together with 8.3 mM D-glucose. The order of potency of these hexoses, both regarding insulin secretion and cyclic [3H]AMP accumulation, was glucose-mannose-fructose-galactose. L-Glucose and 3-O-methylglucose had no effects at 60 min when incubated together with 8.3 mM D-glucose, whereas at 3 min, 3-O-methylglucose induced a small stimulation of the cyclic [3H]AMP response. D-mannoheptulose and D-glucosamine inhibited the insulin and cyclic [3H]AMP responses to 27.7 mM glucose. Mannoheptulose suppressed completely the glucose effect on cyclic nucleotide accumulation within 90 s. Although under all incubation conditions, the threshold stimulatory or inhibitory concentration of a given agent was identical for insulin release and cyclic [3H]AMP accumulation, these two variables showed quantitative differences in incubations of 60 min, the magnitude of the changes in insulin secretion being larger than that for the cyclic nucleotide. It is suggested that modulation of islet cyclic AMP level is an important step in the transmission of the effect of various sugars on insulin release; however, glucose and possibly other sugars may also enhance insulin release by additional mechanisms not involving the adenylate cyclase-cyclic AMP system of the beta-cell.
 ...
PMID:Effect of hexoses and mannoheptulose on cyclic AMP accumulation and insulin secretion in rat pancreatic islets. 18 Oct 79

Standardization of a technic for isolating large numbers of pancreatic islets is described. This procedure employed collagenase digestion of rat pancreatic tissue in a cylindrical wire screen in order to separate isolated islets from undigested pancreas. From this basic protocol the following conditions were established: (1) the duration of the initial digestion period was found to be optimal at six minutes; (2) three subsequent digestions of one minute each effected maximum islet yield; (3) the optimal initial collagenase concentration was found to be 1,000 U. (Worthington)/ml.; and (4) proper reductions of collagenase concentrations during the three subsequent digestions were found to be 50 per cent of each preceding incubation period. This method, combined with Ficoll gradient separation, yielded a mean of 800 islets per two rat pancreases. The isolated islets appeared morphologically intact, contained 0.36 +/- 0.05 mug. protein/islet, and demonstrated a normal biphasic release of insulin in response to stimulative levels of D-glucose. The present method provides a means for obtaining a large mass of viable islet cell tissue in a short time.
 ...
PMID:Standardization fo a digestion-filtration method for isolation of pancreatic islets. 18 6

Amphibian epithelia specialized in trans-cellular sodium transport lose their capacity to react to insulin by a stimulation of this process upon treatment with collagenase; baseline activity and responsiveness to other hormones (vasopressin, aldosterone) bringing about such a stimulation are preserved. This renders it likely that proteases contaminating most collagenase preparations exert a detrimental effect on the receptors held responsible for interaction between insulin and its target cells in the tissues examined.
 ...
PMID:Disappearance of insulin response after enzymatic treatment of sodium-transporting amphibian epithelia. 18 80

Twelve pancreases from human infants one year old or less were analyzed for tissue insulin and amylase content before and after dispersal of pancreatic fragments by mincing and collagenase digestion. Tissue insulin and amylase content provide an index of pancreatic islet mass and exocrine digestive enzyme content, respectively. The results were compared with similar anaylses performed on juvenile and adult human pancreases before and after islet isolation and on intact and dispersed neonatal rat and adult rat pancreas. Infant human pancreas has an average tissue insulin concentration of 1,128 mug./gm. of tissue and a total insulin content of 1,718 mug/pancreas, as against values of 140 mug./gm. of tissue and 7,209 mug./pancreas for adult human pancreas. Average tissue amylase concentration is 0.24 mg./gm. of tissue in infant human pancreas and 3.0 mg./gm. of tissue in adult human pancreas. The insulin/amylase ratio in infant pancreas is 4,800, as against 46 in the adult pancreas. Neonatal rat pancreas, which can be dissociated and transplanted without separation of islet and exocrine components, has a similarly high tissue insulin and low tissue amylase content when compared with adult rat pancreases. Infant human pancreas has a total islet mass 24 per cent that of an adult human pancreas, and neonatal rat pancreas has a total islet mass 11 per cent of that of an adult rat pancreas. One neonatal rat pancreas prepared by minimal collagenase digestion can cure diabetes when transplanted via the portal vein to a rat. Following dispersal of infant human pancreas by collagenase digestion, the islet content and the insulin/amylase ratio of the recovered tissue equals or exceeds that which usually can be isolated from adult cadaver pancreases. Infant human pancreas is a rich source of islet tissue that is relatively uncontaminated by exocrine digestive enzymes. After dispersal, infant human pancreas may be ideal for transplantation to selected diabetic patients.
 ...
PMID:Infant human pancreas. A potential source of islet tissue for transplantation. 18 47


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>