The effects of PGE1, PGE2 and PGD2 on somatostatin, insulin and glucagon secretions were investigated at various glucose concentrations using the isolated perfused rat pancreas. At glucose concentrations varying from 0 to 16.7 mM, PGE1 and PGE2 enhanced somatostatin release in a glucose dose-dependent manner. PGE1 did not significantly stimulate insulin secretion at glucose concentrations of 4.4 mM or less, but did at glucose concentrations of 8.8 mM or more, PGE2 augmented insulin release at 4.4 and 16.7 mM glucose, but not in the absence of glucose. Glucagon release was induced by PGE1 and PGE2 in a biphasic pattern with the maximal response in the absence of glucose. Like PGE1 and PGE2, PGD2 stimulated insulin and glucagon release in a glucose-related fashion. PGD2, however, was not capable of stimulating somatostatin release at various glucose concentrations even in the presence of 16.7 mM glucose. In conclusion, PGE1, PGE2, and PGD2 increase insulin and glucagon secretion in a glucose-dependent manner. PGE1 and PGE2 also stimulate somatostatin release, but PGD2 has no effect on somatostatin secretion at the doses studied.
In studying the mechanism of urine-formation inthe kidney , it is important to decide whetheror not the renal tubules play a role in the elimination of urinary substances apart from their action of reabsorp tion. One of us (TAMURA)1) has already confirmed that there aremany dyes which are eliminated from both theglomerulus and the tubules . Concerning the urinary constituents , STARLING and VERNEY's experiments2) with heart-lung-kidney preparation demonstrated very clearly that someurinary substances such as urea and sulphate must be eliminated, in part, from the tubules. Butin their perfusion with defibrinated blood containing cyanide , it is necessary to consider how far the glomerular capsule was able to maintain its physiological permeability, since the glomerular filtration was recently found to be dependent not merely on a simple physical force but also on an unknown (physiological) factor , and consequently to be easily altered by poisoning (HILLet al .,3) TAMURA et al.4) and HOEBER et al.5)).In our experiments, therefore , in order to determine more thoroughly the seat of elimination of theurinary constituents , the T AMURA method6) was applied , in which the toad's kidney is perfused with saline solution through one of the renal arteries , all the others b eing ligatured, and the kidney is supplied with natural blood from the renal portal vein and its branches , thus through theglomeruli the saline solution circulates , separated from the natural blood-flow surrounding the tubules. In all the experiments , to know whether or not the inorganic substances were eliminated bythe tubules , 0.65%
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