[Analgesic activity of dipeptide Tyr-Pro].

The effect of dipeptide Tyr-Pro, present in representatives of most families of opioid peptides, and two its analogs, Tyr-Pro-NH2 and Tyr-Pro-OMe, on analgesic activity was studied in different tests (tail-flick test, tail pinch (Haffner's) test, formalin test, and acetic acid writing test) describing different organization levels of pain sensitivity. Intraperitoneal administration of the dipeptide decreased the pain threshold in all above-mentioned tests. Coadministration of the dipeptide and naloxone or naloxone methiodide insignificantly decreased the dipeptide analgesic effect in the tail-flick and acetic acid writing tests. Its analogs Tyr-Pro-NH2 and Tyr-Pro-OMe demonstrated a similar analgesic activity in the tail-flick test and a higher activity in the acetic acid writing test. Administration of individual amino acids (Tyr or Pro) or their mixture had no effect on the pain threshold.

[Comparative analysis of analgesic activities of dermorphin, [DPro6]-dermorphin, and their C-terminal tripeptides].

Analgesic activities of dermorphin (DM), [DPro6]-DM, and their C-terminal tripeptides were comparatively studied. Analgesic activity was evaluated in tail flick, hot plate, tail pinch, formalin, and acetic acid writhing tests describing different levels of organization of pain sensitivity. Intraperitoneal administration of the peptides decreased the pain threshold in all these tests. The C-terminal tripeptides DM(5-7) and [DPro6]-DM(5-7) demonstrated analgesics activity comparable or sometimes higher than that of the full-length molecules. The effect of DM, [DPro6]-DM, and C-terminals fragments DM(5-7) and [DPro6]-DM(5-7) decreased after co-administration with naloxone, which points to the opioid nature of analgesic activity of the peptides.

[The relationship between the structure of dermorphines and their thermoregulatory activity].

The effect of structural modifications in the molecule of dermorphin on the functional state of thermoregulation of rats under cold, neutral, and hot environment has been studied. Thermoregulatory and vasomotor activities of 43 peptides (fragments and analogs) were tested in comparison with dermorphin. The role of amino acid residues in the second, third, fourth, and sixth positions was studied. Different fragments of dermorphin molecule proved to underlie different types of thermoregulatory activity (the hypothermic effect was observed in the N-terminal tripeptide, while the N-terminal hexapeptide had the vasodilator activity), and targeted modification of dermorphin molecule makes it possible to separate the hypothermic, vasodilatory, and vasoconstrictive activities. It was proposed that dermorphin is the ligand not only for micro-opioid receptors.

[Comparative study of the physical dependence on proline analog of dermorphin and morphine].

On the model of acute physical dependence, naloxone treatment of animals dependent on D-Pro6 peptide ([D-Pro6]DM) (a demorphin analog) led to tremor, shaking, convulsions, and rare jumps typical of morphine-dependent animals. The variety and intensity of reactions depended on the naloxone dose and the interval between naloxone and peptide injections. In the state of reject syndrome upon peptide and morphine subchronic treatments according to identical schedules, the symptoms in [D-Pro6]DM dependent animals were much less pronounced than in morphine-dependent ones.

[Analgesic activity of dermorphin and its proline analogs].

Dermorphin (Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2; DM) and its analogs obtained via stereochemical transformation of L-Pro6 to D-Pro6 peptide in DM ([Dpro6]DM) and via dehydration of L-Pro6 peptide ([dHPro6]DM) were characterized with respect to the analgesic activity in rats tested under conditions corresponding to various levels of pain sensitivity organization. The drugs were introduced by intraperitoneal injections in various doses (0.1, 1.0, and 10 mg/kg). In the case of acetic-acid induced convulsions (writhing), DM and [Dpro6]DM produced analgesic action in the minimum dose, while the analogous effect of [dHPro6]DM was observed only in greater doses. In the tail-clamp (Haffner) test, DM and [Dpro6]DM also inhibited nociception while the latter compound was ineffective. In the grid-shock test, [Dpro6]DM showed a higher activity than [dHPro6]DM, whereas DM did not produce analgesic action. Thus, all the studied peptides exhibit pronounced analgesic activity, and the replacement of L-Pro6 in DM by its stereomer D-Pro is more effective than the substitution of dHPro6.

[Study of thermoregulatory activity of a fragment of natural dermorphin precursor Arg-dermorphin and its analogs].

We studied the effect of a fragment of natural dermorphin (DM) precursor Arg-DM and its analogs (Pro-DM, 4Amino-Pro-DM, Mike et-DM, Kre-DM, Arg-[DArg2]-DM, and Arg-[DAla4]-DM after intraperitoneal administration on the functional status of the thermoregulation system in rats. The obtained data demonstrated that the hypothermic and vasomotor effects of Arg-DM were temperature-dependent and had the same pattern as DM (Emel'yanova et al., 1996). In the thermoneutral and room environment, the peptide induced a two-phase vascular response. The first phase was vasodilation; it was twice as strong as for DM and was not removed by naloxone pretreatment. The second phase was vasoconstriction; it was blocked by naloxone. Replacement of Arg with 4Amino-Pro, Met, and Kre as well as DAla2 to DArg2 or Gly4 to DAla4 replacements in the Arg-DM molecule affected the thermoregulatory activity of the peptide. For instance, only the vasodilation response was observed for Arg-[DAla2]-DM and Arg-[DAla4]-DM while only the vasoconstriction response was observed for 4Amino-Pro-DM.

[Thermoregulatory activity of dermorphin fragments]. / Termoreguliatornaia aktivnost' dermofinov.

We studied the effect of C-terminal truncation of the dermorphin (DM) molecule and analogs of its N-terminal tetrapeptide, [DOrn2]-DM(1-4), [DArg2]-DM(1-4), [DAla4]-DM(1-4), [DArg2, DAla4]-DM(1-4), Arg-DM(1-4), Arg-[DArg2]-DM(1-4), Arg-[DAla4]-DM(1-4), and Arg-[DArg2, DAla4]-DM(1-4), on the functional status of the thermoregulation system in rats at different ambient temperatures. For the first time, we demonstrate that the N-terminal tetrapeptide is the minimal fragment with the hypothermic effect. Only the N-terminal octapeptide exerted the vasomotor effect. Amino acid substitutions in the tetrapeptide affected its hypothermic effect. [DArg2]-DM(1-4) and [DArg2, DAla4]-DM(1-4) had the greatest effect. Addition of Arg to the N-terminus of DM(1-4) analogs changed their thermoregulatory activity. The greatest thermoregulatory effect was observed for Arg-[DArg2]-DM(1-4) and Arg-[DArg2, DAla4]-DM(1-4).

[Effect of structural changes of Pro6 in dermorphin molecule on its antinociceptive activity]. / Vliianie strukturnykh izmenenii Pro6 v molekule dermorfina na anal'geticheskuiu aktivnost'.

We studied effect of dermorphin (H-Tyr-DAla-Phe-Gly-Tyr-Pro-Ser-NH2) and its analogs with modified amino acid residue proline in position 6, H-Tyr-DAla-Phe-Gly-Tyr-[DPro]-Ser-NH2, H-Tyr-DAla-Phe-Gly-Tyr-[dehydro-Pro]-Ser-NH2, and H-Tyr-DAla-Phe-Gly-Tyr-[D-dehydro-Pro]-Ser-NH2, on nociception in the tail-flick and hot plate tests after intraperitoneal injection. Replacement of LPro with the stereoisomer DPro as well as Pro dehydration (LdHPro) was shown to increase antinociceptive activity. Replacement of LdHPro with DdHPro cancelled the activity in the tail-flick test. All three dermorphin analogs retained antinociceptive activity in the hot plate test; however, the effect of dermorphin was more pronounced.

[Effect of dermorphin analogs on thermoregulation of rats under various thermal conditions]. / Vliianie analogov dermorfina na termoreguliatsiiu krys v razlichnykh temperaturnykh rezhimakh.

We studied the influence of dermorphin (dermorphin) analogs with stereochemical modification of the amino acid residue proline in position 6 (Pro6), Tyr-D-Ala-Phe-Gly-Tyr-Hyp-Ser-NH2, Tyr-D-Ala-Phe-Gly-Tyr-[D-Pro]-Ser-NH2, Tyr-D-Ala-Phe-Gly-Tyr-[dehydro-Pro]-Ser-NH2, and Tyr-D-Ala-Phe-Gly-Tyr-[D-dehydro-Pro]-Ser-NH2, after their intraperitoneal injection at 0.5 mg/kg dose in the cold (4-7 degrees C), thermoneutral (27-28 degrees C), and hot (31-33 degrees C) environment. Stereochemical modifications of amino acid residue Pro6 proved to induce specific changes in the thermoregulatory effect of the peptide. Substitution of DPro6 for Pro6 has the most dramatic consequences: it considerably attenuates the thermoregulatory effect of dermorphin in the cold environment, cancels it in the hot environment, and inverts the dermorphin-specific thermoregulatory response in thermoneutral conditions. The data obtained indicate the important role of Pro6 residue in realization of this physiological activity of dermorphins.

[Dermorphins--a natural opioids with unique primary structure that determines their biological specificity]. / Dermorfiny--prirodnye opioidy s unikal'noi pervichnoi strukturoi, opredeliaiushchei spetsifiku ikh biologicheskoi aktivnosti.

Based on the authors' and published data, the spectrum of biological activities of dermorphins was theoretically analyzed for the first time from the viewpoint of specific structural features of their molecule that determine selective affinity to mu-opiate receptors. It was shown that specific distribution of dermorphins and corresponding opiate receptors in tissues and organs, especially in the CNS structures, determines the role of dermorphins in the regulation of functions of the most important physiological systems.

[Biologically active peptides isolated from the brain of hibernating ground squirrels]. / Biologicheski aktivnye peptidy, bydelennye iz mozga zimospiashchikh suslikov.

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.