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The peptide hormone relaxin produces dose-dependent stimulation of adenylyl cyclase activity in rat tissues (striatum, cardiac and skeletal muscle) and the muscle tissues of invertebrates, i.e., the bivalve mollusk Anodonta cygnea and the earthworm Lumbricus terrestris, adenylyl cyclase stimulation being more marked in the rat striatum and cardiac muscle. Our studies of the type of relaxin receptor involved in mediating these actions of relaxin involved the first synthesis of peptides 619-629, 619-629-Lys(Palm), and 615-629, which are derivatives of the primary structure of the C-terminal part of the third cytoplasmic loop of the type 1 relaxin receptor (LGR7). Peptides 619-629-Lys(Palm) and 615-629 showed competitive inhibition of adenylyl cyclase stimulation by relaxin in rat striatum and cardiac muscle but had no effect on the action of relaxin in rat skeletal muscle or invertebrate muscle, which is evidence for the tissue and species specificity of their actions. On the one hand, this indicates involvement of the LGR7 receptor in mediating the adenylyl cyclase-stimulating action of relaxin in rat striatum and cardiac muscle and, on the other, demonstrates the existence of other adenylyl cyclase signal mechanisms for the actions of relaxin in rat skeletal muscle and invertebrate muscle, not involving LGR7 receptors. The adenylyl cyclase-stimulating effect of relaxin in the striatum and cardiac muscles was found to be decreased in the presence of C-terminal peptide 385-394 of the alpha(s) subunit of the mammalian G protein and to be blocked by treatment of membranes with cholera toxin. These data provide evidence that in the striatum and cardiac muscle, relaxin stimulates adenylyl cyclase via the LGR7 receptor, this being functionally linked with G(s) protein. It is also demonstrated that linkage of relaxin-activated LGR7 receptor with the G(s) protein is mediated by interaction of the C-terminal half of the third cytoplasmic loop of the receptor with the C-terminal segment of the alpha(s) subunit of the G protein.

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In recent years, one of the rapidly developing directions in molecular endocrinology and nanobio technology is the peptide strategy, which has become widely used for studying the molecular mechanisms of transduction of hormonal signals into the cell and for designing highly selective and highly effective reg ulators of hormonal signaling systems [1,2]. It is based on the search and development of peptides cor responding in structure to the functionally important parts of signaling proteins-receptors, heterotrimeric G proteins, and enzymes that generate second mes sengers. The most promising direction in the peptide strategy is the synthesis and study of peptides derived from serpentine type receptors, because at the level of these receptors not only the specific recognition of an external signal but also the choice of the pathway of its transduction into the cell takes place and, therefore, the intracellular targets of the hormone are deter mined. We and other authors demonstrated that pep tides corresponding to the cytoplasmic loops (CLs) of serpentine type receptors selectively interact with G proteins, trigger signaling cascades in the absence of hormone, affect the transduction of the signal gener ated by them through a homologous receptor, thus functioning as regulators of intracellular signaling [3][4][5][6][7][8][9].One of the urgent problems of modern endocrinol ogy is the search for an effective regulator of the thy roid gland and the entire hypothalamic pituitary thy roid axis, which act at the stage of activation of the thyroid stimulating hormone (TSH) receptor by the hormone. Disturbances that occur at this signal trans duction stage lead to a wide spectrum of thyroid gland diseases, including autoimmune thyroiditis and thy roid cancer. The purpose of the study was to develop selective regulators of the TSH sensitive signaling pathways on the basis of the peptides derived from the C terminal region 612-627 of the third intracellular loop (C ICL 3) of the TSH receptor. We also studied the activity of the peptides in vitro by their effects on the basal and hormone stimulated level of GTP bind ing of heterotrimeric G s and G q proteins, which are components of these cascades, and in vivo by the effect of intranasal administration of peptides on the level of thyroid hormones in the blood plasma of experimental animals. It should be noted that mutations in the C ICL 3 of the TSH receptor disturb its interaction with G s proteins and lead to loss of the ability of the mutant receptor to stimulate adenylate cyclase activity and cAMP dependent signaling pathways [10].Using solid phase peptide synthesis, we synthe sized the peptide Gln Tyr Asn Pro Arg Asp Lys Asp Thr Lys Ile Ala Lys Arg Nle Ala 612-627 Lys Ala amide (I), in which Met 626 is replaced with norleu cine having similar physicochemical properties. We also synthesized a palmitoylated analogue of this peptide (II), in which the side ε amino group of the lysine residue following Ala 627 is modified with the palmitic acid residue. The peptides were syn...

We studied the effect of intraperitoneal and intratesticular administration of NKDTKIAKKNle-A(562-572) peptide and its palmotoylated analog NKDTKIAKK-Nle-A(562-572)-K(Palm)A to male rats on adenylate cyclase activity in the testicular membranes in vitro and on plasma testosterone levels. Peptide NKDTKIAKK-Nle-A(562-572)-K(Palm)A stimulated basal adenylate cyclase activity and reduced activity of the enzyme in testicular membranes stimulated by chorionic gonadotropin. After intratesticular administration in a dose of 200 μg/kg, it significantly increased testosterone so that 1, 3 and 5 h after administration its level was increased by 74, 44 and 35%, respectively. Administered intraperitoneally in a lower dose (50 μg/kg), the peptide had little effect on testosterone level. Unmodified peptide was inactive.