Functional state of adenylate cyclase signaling system in testis and ovary of fasted rats

Sensitivity of the adenylate cyclase signaling system (ACSS) to polypeptide hormones and biogenic amines is studied in testis and ovary of rats after the 2- and 4-day fasting as compared with control animals. In tissues of the fasted rats there is shown a decrease in the basal activity of adenylate cyclase (AC) and of the basal level of the GTP binding of heterotrimeric G protein. An increase of duration of fasting from 2 to 4 days led to intensification of these changes. In the fasted rats, the stimulating effects of chorionic gonadotropin, PACAP-38. and isoproterenol on the AC activity realized via G protein of the stimulatory type are enhanced, whereas the inhibitory effects of somatostatin on the AC activity realized via G protein of the inhibitory type are reduced. In testis of the fasted rats the stimulating effect of serotonin acting on AC via both types of G proteins are increased, while the inhibitory effects of the hormone decrease. Thus, under conditions of fasting, in rat testis and ovary the ACSS sensitivity to regulatory effects of hormones is changing: its stimulatory effects are increased, while its inhibitory effects, on the contrary, are decreased. We suggest these changes is one of the key mechanisms of adaptation of organism to deficiency of nutritional resources to be aimed at intensifying the tissues catabolic processes, preferably, lypolysis.     

Effect of insulin on characteristics of contractile responses of fast and slow skeletal muscles of rats with acute streptozotocin-induced diabetes

Comparison of amplitude-time characteristics of fast extensor digitorum longus muscles (m. EDL) isolated from control rats and rats with model of acute streptozotocin-induced diabetes mellitus (DM) 12 and 30 days after treatment with streptozotozin did not reveal significant changes of strength of single normalized contractile responses as compared with control. In slow (m. Soleus) muscles of rats with the 30-day long SD, essential changes of the amplitude-time characteristics of such contractile responses were observed: a decrease of their amplitude and an increase of duration. In the diabetic rats treated with insulin there develops resistance of skeletal muscles of both types to action of exogenous insulin. Both in control and in diabetic animals the exhausting stimulation of m. EDL with trains from 5 impulses did not reveal significant differences at early (up to 3 min) terms of development of fatigue. Under similar conditions, fatigue of m. Soleus in rats of the both diabetic groups developed significantly faster as compared with control (already in 30 s after the beginning of stimulation). Insulin at a concentration of 0.5–1 nM produced a dose-dependent decrease of amplitude of single contractile responses in fast and slow muscles of rats with the acute SD model (the negative inotropic action). Earlier, we demonstrated in healthy rats the similar action of insulin, but at the higher concentrations [1]. Insulin at a concentration of 10 nM did not produce an essential effect on dynamics of depression of responses in the course of development of fatigue at tetanical stimulation of m. EDL and m. Soleus both in control and in diabetic rats, but affected essentially the dynamics of change of duration of the half-decay (T_hd) of their tetanical responses. The presence of insulin in the washing solution led to stabilization of the period of muscle relaxation in the course of development of fatigue in all studied animal groups.     

Functional role of membrane-bound adenylyl cyclases and coupled to them receptors and G-proteins in regulation of fertility of spermatozoa

The cAMP-dependent signaling cascades play the key role in regulation of fertility of spermatozoa. Synthesis of cAMP in spermatozoa is realized both by soluble, and by transmembrane (membrane-bound) forms of adenylyl cyclases (AC). For the recent years numerous data appeared about the presence in spermatozoa at different stages of their maturation of a wide spectrum isoforms of membrane-bound AC and their regulation by hormones and hormone-like substances via the coupled to B-proteins receptors (GPCR). Agonists of GPCR in spermatozoa can be adenosine, biogenic amines, peptide hormones, odorants. Study of structural-functional organization and regulatory properties of AC of the signal system in spermatozoa is of great practical significance for reproductive technologies, as via the membrane-bound AC forms and signal cascades there are controlled such processes as motility and chemotaxis of spermatozoa, their capability for capacitation acrosomal reaction. In the review there are summarized and analyzed data on functioning and role of AC of signal system in spermatozoa of human and vertebrate animals and are discussed achievements and unsolved problems in this field.     

Regulation of adenylyl cyclase activity in rat testes by acylated derivatives of peptide 562–572 of a luteinizing hormone receptor

One area of the search for hormonal signaling systems regulators is development of peptides that correspond to the cytoplasmic regions of G protein-coupled receptors (GPCR). Modification of such peptides with hydrophobic radicals increases their efficiency and selectivity. However, at present it has not been studied how the activity of the peptide depends on the localization of hydrophobic radicals, their number, and chemical nature. The aim of this work consisted in synthesis of peptide 562–572 derivatives modified by fatty-acid radicals and corresponding to the C-terminal region of the luteinizing hormone receptor (LHR) and in the study of regulatory effects of the acylated LHR peptides on the basal and hormone-stimulated activity of adenylyl cyclase (AC) in rat tissues. To elucidate the effects of localization of hydrophobic radicals and of their number, modifications of peptide 562–572 were carried out only at the N-or at the C-terminus or at both ends. To study the effect of hydrophobicity, residues of palmitic (Pal) and decanoic (Dec) acids were chosen. Using a solid-phase strategy synthesis was performed of the unmodified peptide NKDTKIAKK-Nle-A^562-572-KA (1) and five of its acylated analogues, N[K(Dec)]DTKIAKK-Nle-A^562-572-KA (2), NKDTKIAKK-Nle-A^562-572-[K(Dec)]A (3), N[K(Dec)]DTKIAKK-Nle-A^562-572-[K(Dec)]A (4), N[K(Pal)]DTKIAKK-Nle-A^562-572-KA (5), and NKDTKIAKK-Nle-A^562-572-[K(Pal)]A (6). Peptide 6 modified with palmitate at the C-terminus to a large extent increased the basal AC activity and reduced the AC stimulating effect of human chorionic gonadotropin (hCG) in testes of rats; peptides 3 and 4 modified with decanoate at the C-terminus were less effective, but exceeded in activity the unmodified peptide 1; and peptides 2 and 5 acylated at the N-terminus were little active. The action of peptides was characterized by tissue and the receptor specificity. Thus, modification of the LHR peptide 562–572 with fatty-acid radicals at the C-terminus enhances its regulatory effect on the functional activity of the adenylyl cyclase system in rat testes, which indicates a promising modification of GPCR peptides with hydrophobic radicals. These data confirm the hypothesis that the hydrophobic radical is to be localized in the locus of GPCR peptide, where a transmembrane domain is located in the receptor.     

Peptidergic signaling brain systems in diabetes mellitus

One of the key causes of development of diabetes mellitus (DM) and its complications is change in the functional activity of hormonal signaling systems regulated by hormones of different natures, as is shown by literature data and by the results of our study on animal models of DM and on human DM of types 1 and 2. The brain peptidergic systems regulated by melanocortin receptor agonists, neuropeptide Y, glucagon-like peptide-1, kisspeptines, and somatostatin, play an important role in etiology and pathogenesis of DM. However, the data on interrelations between the functional state of these systems and the development of DM and its complications are scarce and contradictory. The changes in the peptidergic systems are usually the result of metabolic and functional disregulations caused by DM but in some cases may themselves become the cause of DM, as is shown in the case of the melanocortin signaling system. This review is focused on functioning of the brain peptidergic systems in DM and on the possible role of changes of their activity in development of the disease. The hypothesis of central genesis of type 2 DM, which based on data on the generation of insulin resistance and disturbances of carbohydrate and lipid metabolism in response to changes of functional activity of the brain signaling systems regulated by neuropeptides, is discussed.     

Effect of intranasal insulin and serotonin on functional activity of the adenylyl cyclase system in myocardium, ovary, and uterus of rats with prolonged neonatal model of diabetes mellitus

The disturbances in hormonal signaling systems, adenylyl cyclase system (ACS) in particular, occur at the early stages of diabetes mellitus (DM) being one of the key causes of its complications. Since the correlation between the severity of DM and severity of disturbances in ACS is established, studying ACS activity can be used for monitoring DM and its complications and evaluating the effectiveness of their treatment. Recently, intranasal insulin (I-I) and the drugs increasing brain serotonin level, thus effectively restoring CNS functions, have begun to be used for the treatment of type 2 DM. However, the mechanisms of their action on peripheral tissues and organs at DM are not understood. The aim of this work was to study an influence of I-I and intranasal serotonin (I-S) on the functional activity of ACS in myocardium, ovary and uterus of rats with a neonatal model of type 2 DM. In the tissues of diabetic rats the changes in the regulation of adenylate cyclase (AC) by guanine nucleotides and hormones acting on enzyme in stimulatory and inhibitory manner were found, and these changes were characterized by receptor and tissue specificity. In diabetic rats I-I restored AC-stimulating effects of isoproterenol in the myocardium, that of guanine nucleotides and gonadotropin in the ovaries and relaxin in the uterus, as well as AC-inhibiting effects of somatostatin in all tissues and norepinephrine in the myocardium. Treatment with I-S led to a partial recovery of AC-inhibiting effect of norepinephrine in the diabetic myocardium, but did not affect the regulation of AC by other hormones. These data indicate that I-I normalizes the functional activity of ACS in the myocardium and in the tissues of reproductive system of female rats with neonatal DM, whereas the effect of I-S on ACS in the studied tissues is less pronounced. These results should be considered for the design and optimization of the strategy of I-I and I-S application for the treatment of DM and its complications.     

Erratum: “Functional state of hypothalamic signaling systems in rats with type 2 diabetes mellitus treated with intranasal insulin”

On page 214, left column, the final paragraph of the text should read: Supported by the RSF grant no. 14-15-00413. Spectrophotometric studies were carried out at the Center for Collective Usage of Scientific Equipment, Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences.     

Erratum: “The brain leptin signaling system and its functional state in metabolic syndrome and type 2 diabetes mellitus”

On page 189, left column, the final line of the text should read: Supported by the RSF grant no. 14-15-00413.