The impact of ANG II and IV on INS-1 cells and on blood glucose and plasma insulin

The impact of angiotensin (ANG) for peripheral, global effects is well known. Local ANG systems including that of the insulin-releasing β cell are not well investigated. In insulin-secreting cell line (INS-1), AT₁ and AT₄ receptors for ANG II and IV were demonstrated by Western blots. Only small amounts of ANG II-binding sites of low affinity were observed. ANG II and SARILE displaced binding of ¹²⁵I-ANG II. ANG II and IV as well as their non-degradable analogs SARILE and Nle-ANG IV increased the glucose-induced insulin release in a bell-shaped way; the maximum effect was at ～1?nM. The increase was antagonized by 1 µM losartan or 10 µM divalinal (AT₁ and AT₄ receptor antagonists, respectively). The insulin release was accompanied by a ⁴⁵Ca²⁺ uptake in the case of ANG II and ANG IV. Divalinal abolished the effect of ANG IV and Nle-ANG IV on this parameter. ANG IV reduced the increase in blood glucose during a glucose tolerance test with corresponding, albeit smaller effects on plasma insulin. Using confocal laser scanning microscopy, transfected insulin-regulated aminopeptidase (IRAP) with AT₄ receptors was shown to be accumulated close to the nucleus and the cytosolic membrane, whereas GLUT4 was not detectable. IRAP was inhibited by ANG IV. In conclusion, AT₁ and AT₄ receptors may be involved in diabetic homeostasis. Effects are mediated by insulin release, which is accompanied by an influx of extracellular Ca²⁺. The impact of ANG IV/IRAP agonists may be worth being used as antidiabetics.