Of four naturally occurring frenatin peptides tested, frenatin 2D (DLLGTLGNLPLPFI.NH₂) from Discoglossus sardus was the most potent and effective in producing concentration-dependent stimulation of insulin release from BRIN-BD11 rat clonal β-cells without displaying cytotoxicity. The peptide also stimulated insulin release from 1.1B4 human-derived clonal β-cells and isolated mouse islets and improved glucose tolerance concomitant with increased circulating insulin concentrations in mice following intraperitoneal administration. The insulinotropic activity of frenatin 2D was not associated with membrane depolarization or an increase in intracellular [Ca²⁺] but incubation of the peptide (1 μM) with BRIN-BD11 cells produced a modest, but significant (P < 0.05), increase in cAMP production. Stimulation of insulin release was abolished in protein kinase A-downregulated cells but maintained in protein kinase C-downregulated cells. Circular dichroism studies showed that, in the presence of dodecylphosphocholine micelles, frenatin 2D exhibited a helical content of 35% and a turn content of 28%. Substitution of the Thr⁵, Asn⁸, Pro¹⁰, and Ile¹⁴ residues in frenatin-2D by Trp and interchange of Pro¹² and Phe¹³ led to loss of insulinotropic activity but the [D1W] and [G7W] analogues were as potent and effective as the native peptide. Frenatin 2D (1 μM) also stimulated proliferation of BRIN-BD11 cells and provided significant protection of the cells against cytokine-induced apoptosis. It is concluded that the insulinotropic activity of frenatin 2D is mediated predominantly, if not exclusively, by the K_ATP channel-independent pathway.

在测试的四种天然存在的 frenatin 肽中，来自Discoglossus sardus 的frenatin 2D (DLLGTLGNLPLPFI.NH ₂ )在产生浓度依赖性刺激 BRIN-BD11 大鼠克隆 β 细胞的胰岛素释放方面最有效，而且不显示细胞毒性。该肽还刺激了 1.1B4 人源性克隆 β 细胞和分离的小鼠胰岛的胰岛素释放，并改善了葡萄糖耐量，同时增加了小鼠腹膜内给药后循环胰岛素浓度。frenatin 2D 的促胰岛素活性与膜去极化或细胞内 [Ca ²⁺] 但肽 (1 μM) 与 BRIN-BD11 细胞的孵育产生了适度但显着（P < 0.05）的 cAMP 产量增加。胰岛素释放的刺激在蛋白激酶 A 下调的细胞中被消除，但在蛋白激酶 C 下调的细胞中得以维持。圆二色性研究表明，在十二烷基磷酸胆碱胶束的存在下，frenatin 2D 的螺旋含量为 35%，转角含量为 28%。Frenatin-2D中的 Thr ⁵、Asn ⁸、Pro ¹⁰和 Ile ¹⁴残基被 Trp 取代以及 Pro ¹²和 Phe ^{13 的}互换导致促胰岛素活性丧失，但 [D1W] 和 [G7W] 类似物与天然肽一样有效。Frenatin 2D (1 μM) 还刺激了 BRIN-BD11 细胞的增殖，并为细胞提供了显着的细胞因子诱导的细胞凋亡保护。得出的结论是，frenatin 2D 的促胰岛素活性主要（如果不是唯一的话）由 K _ATP通道非依赖性途径介导。