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Abstract
Islets of rat fetuses born to mothers fed a low protein diet (LP) have a depressed insulin secretion in vitro in response to secretagogues. These fetuses have lower plasma levels of taurine than controls. The aim of this study was to analyze the effect of taurine on fetal islets insulin secretion. After 5 days of culture in serum containing standard RPMI medium, islets were cultured for 2 days in serum-free DME/F12 medium with 8·2 or 16·7 mm glucose alone or with taurine at 0·3 or 3 mm. They were then incubated for 120 min in Krebs Ringer solution with glucose alone (5·6 or 16·7 mm) or glucose (5·6 mm) added to leucine or arginine (both at 10 mm). In both concentrations of glucose, taurine increased the fractional insulin release by islets stimulated with secretagogues tested during the incubation. The effect did not seem to be mediated by changes in cAMP content. In a second set of experiments, islets cultured in RPMI medium for 7 days were incubated in the presence of Krebs Ringer solution with leucine (10 mm) or with sulfur amino acids (taurine at 10 mm, methionine or cysteine at 5 mm) for 120 min. Taurine and methionine stimulated insulin release at the same magnitude as leucine, whereas cysteine had no effect. In conclusion, taurine enhances insulin secretion by fetal islets, at least in vitro. Low taurine levels in fetuses from LP mothers might be implicated in their depressed insulin secretion.
Journal of Endocrinology (1996) 151, 501–506
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An isocaloric low-protein (LP) diet (8% instead of 20% in controls) given to dams during gestation reduces the fractional insulin release of stimulated fetal islets. The LP diet lowers the plasma concentration of taurine in both pregnant rats and their fetuses. This study reports the effect of taurine on the in vitro release of insulin from control and LP fetal islets. Direct stimulation with taurine, methionine or leucine increased the release of insulin from control islets. Nevertheless, no effect on LP islets was observed with either taurine or methionine. The release of insulin from LP islets was reduced with leucine. The in vitro addition of taurine (0. 3 or 3 mM) to the culture medium increased the release of insulin from the control islets in response to arginine or leucine, but it did not restore the reduced responsiveness of LP islets to these amino acids. When 2.5% taurine was added to the drinking water of control or LP dams (groups C+T and LP+T) throughout gestation, the concentration of taurine increased in the serum of dams and fetuses of both groups. The release of insulin from the LP+T fetuses was restored to control levels when stimulated with taurine, methionine, leucine or arginine. In conclusion, taurine stimulated control fetal islets in vitro, but failed to do so in LP islets. However, the addition of taurine to the diet of LP dams restored to normal the release of insulin from LP fetal islets, indicating the importance of taurine during development for a normal fetal beta cell function.
