More than 20 peptides have been isolated and sequenced from the brain of hibernating ground squirrel Citellus undulatus. Some of the isolated peptides were chemically synthesized and investigated for the spectrum of biological activity. One of the isolated peptides, neokyotorphin (Thr-Ser-Lys-Tyr-Arg), earlier known as a weak analgetic, is found to have a cardiotropic and thermoregulatory activity. Neokyotorphin activates in vitro voltage-dependent calcium and blocks ATP-dependent potassium currents in the frog atrial fibres. Intraperitoneal injection of this peptide in hibernating ground squirrels speeds up the arousal of animals increasing sharply the heart rate and oxygen consumption. Intraperitoneal and intranasal administrations of neokyotorphin in rats raises body temperature in thermoneutral conditions (26-28 degrees C) exerting no effects at low (4-6 degrees C) and high (31-32 degrees C) environmental temperatures. Another isolated peptide, Asp-Tyr, blocks the inward voltage-dependent calcium current in the frog atrial fibres and slightly increases the outward potassium current. Sulfated analogue of this dipeptide (aspartyl-O-sulfate-tyrosine) more effectively blocks the inward voltage-dependent calcium current in the frog atrial fibres and have no effects on the outward potassium current.
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