Phe-Met-Arg-Phe amide trifluoroacetate is an activator of K+ current, with ED50 of 23 nM in the peptidergic caudodorsal neurons.
In the molluscan central nervous system, Phe-Met-Arg-Phe amide (FMRFa) acts on K+ channels in sensory, motor-, and neuroendocrine neurones. Phe-Met-Arg-Phe amide activates a novel K+ current that is characterized by a combined voltage- and receptor-dependent gating mechanism, with both factors being necessary for opening of the channels[1]. Phe-Met-Arg-Phe amide (1 μM) significantly inhibits glucose stimulated (300 mg/dL) insulin release (p<0.005) and somatostatin release (p<0.01) from the isolated perfused pancreas. Phe-Met-Arg-Phe amide (FMRF-NH2) (1 and 10 μM) is without effect on glucagon secretion, either in low glucose (50 mg/dL), high glucose (300 mg/dL), or during arginine stimulation (5 mM)[2].
Phe-Met-Arg-Phe amide (FMRFamide) stimulates growth hormone secretion in conscious OVX rats. The presence of Phe-Met-Arg-Phe amide-like immunoreactivity in neuronal elements in the hypothalamus suggested a role for this in the hypothalamic control of the anterior pituitary function. The injection of 200 ng (313.8 picomoles) of FMRFamide (in 2 uL) produces a significantly increased plasma GH 15 min after injection. The GH-increasing effect of 400-800 ng (627-1255 picomoles) of FMRFamide is already developed after 5 min and lasted up to 30 min[3].
[1]. Kits KS, et al. Phe-Met-Arg-Phe-amide activates a novel voltage-dependent K+ current through a lipoxygenasepathway in molluscan neurones. J Gen Physiol. 1997 Nov;110(5):611-28. [2]. Sorenson RL, et al. Phe-met-arg-phe-amide (FMRF-NH2) inhibits insulin and somatostatin secretion and anti-FMRF-NH2 sera detects pancreatic polypeptide cells in the rat islet. Peptides. 1984 Jul-Aug;5(4):777-82. [3]. Ottlecz A, et al. Phe-Met-Arg-Phe-amide (FMRFamide) stimulated growth hormone secretion in conscious OVX rats. Neuropeptides. 1987 Feb-Mar;9(2):161-7.