Changes In Protein Secretion Research Articles

Simultaneous mechanisms on exocrine pancreatic secretion initiated by alcohol in the conscious dog.

Modifications of pancreatic secretion induced by the infusion of alcohol were investigated in seven Thomas fistula dogs. Acute intravenous injections of low doses of alcohol induced a significant increase of all parameters of pancreatic secretion. On the contrary the acute intravenous injection of high doses of alcohol induced a significant decrease of pancreatic secretion. A prolonged-alcohol intravenous infusion producing a stable blood alcohol level provoked at first a decrease of pancreatic secretion, significant only for protein output, followed by a significant increase of all parameters of pancreatic secretion. A spontaneous return to prealcohol values of pancreatic secretion was observed in all cases even if the blood alcohol level remained high and stable and despite four hours of experimentation. Upon the background of a stable blood alcohol level, pentolinium did not suppress alcohol-induced stimulation of water and bicarbonate outputs but did abolish the postalcohol changes in protein secretion. Furthermore, atropine abolished all postalcohol changes in pancreatic secretion. Consequently, there are two responses (inhibition and stimulation) to alcohol which coexist in normal dogs. They are related to the blood alcohol levels and are transitory. These responses involve the vagus nerves. Alcohol appears to stimulate the exocrine pancreas through receptors at different levels of the nervous system.

Secretion of proteins and glycoproteins by the rat epididymis: regional differences, androgen-dependence, and effects of protease inhibitors, procaine, and tunicamycin.

Protein synthesis and secretion by the epididymis was studied in vitro by incubating tissue pieces with radioactive amino acids or one of a variety of radioactive sugars. When amino acids were used asprecursors, about 15% of the incorporated radioactivity was released into the medium; the release was 36-65% in the case of sugar precursors. In different regions of the epididymis, pronounced variations were apparent in the profile of secreted proteins formed from amino acids or from galactose, mannose, or fucose. Total protein synthesis as measured by l� 5) methionine incorporation was decreased by ‘\�30% following castration of animals, and the proportion of incorporated radioactivity which was secreted was reduced from 15% to 10%. Only a few qualitative changes were evident in the types of protein secreted. Compared with general protein synthesis, the incorporation of sugars into glycoproteins was affected by castration to a much greater extent, with mannose incorporation being reduced by up to 90% in the cauda. Protease inhibitors (TLCK, TPCK, PMSF, benzamidine, phenanthroline) reduced total protein synthesis from �“ SI methionine but did not alter the profile of secreted proteins. Procaine also reduced total protein synthesis, and in the caput, but not the cauda, it caused a marked change in the pattern of secreted proteins. This differential effect of procaine did not appear to be due to an effect on “signal peptidasc.” Tunicaxnycin had little effect on protein synthesis and secretion by the epididymis when [“SI methionine was used as the precursor, although it did cause pronounced changes in protein secretion by testicular tissue. Greater effects of tunicamycin were evident when radioactive sugars were used as precursors, particularly in the case of [3 HI mannose. The incorporation of this precursor was reduced to 69% and 49% of normal in the caput and cauda, respectively. However, tunicamycin did not alter the profile of secreted radioactive proteins resulting from any of the incubations with radioactive sugars.

Effect of atropine and vagotomy on response of transplanted pancreas.

It is well established that atropine and vagotomy inhibit pancreatic enzyme secretion in response to intestinal stimulants such as fat or amino acids. These effects are usually attributed to interference with hypothetical vagal cholinergic mechanisms that facilitate release of cholecystokinin. To determine whether atropine or vagotomy interferes with release of humoral stimulants of pancreatic enzyme secretion, we studied their effect on protein secretion from an autotransplanted portion of pancreas in response to intestinal stimulants in dogs. The transplanted pancreas was as sensitive as the intact pancreas to stimulation by exogenous caerulein, a cholecystokinin-like peptide, and this response was not altered by atropine or vagotomy. Therefore, if vagotomy or atropine interferes with release of humoral pancreatic stimulants, they would be expected to reduce the response of the transplanted pancreas just as they do of the intact pancreas. Truncal vagotomy caused no significant change in protein secretion from the transplant in response to intestinal perfusion with sodium oleate or tryptophan. Atropine was tested only against sodium oleate and caused no change in response. We conclude that release of humoral pancreatic excitants of protein secretion in response to intestinal stimulants is not significantly changed by atropine or vagotomy.

Changes in protein secretion by rat submandibular salivary glands after enlargement caused by repeated amputation of the lower incisor teeth

The lower incisors of male rats were repeatedly amputated at 3- or 4-day intervals for about 1 month. Four days after the last amputation, submandibular saliva was collected from the anaesthetized rats by intra-oral cannulation, using methoxamine (6 mg/kg), an α-adrenomimetic drug, as an acute secretory stimulus. The rats showed enlarged submandibular and sublingual glands and the protein concentration was significantly less in submandibular saliva than in controls. The types of protein secreted by the rat submandibular gland in response to methoxamine normally differ from those secreted in response to isoprenaline. In the enlarged glands, methoxamine stimulation caused the secretion of proteins similar, by polyacrylamide gel electrophoresis, to those normally secreted in response to isoprenaline, suggesting that repeated lower incisor amputation had caused the glands to lose their normal responsiveness to α-adrenergic agonists. An abnormal protein was also secreted, identical electrophoretically and immunologically with one secreted by the enlarged submandibular glands of rats exposed to chronic isoprenaline administration.