Functional state of adenylyl cyclase signaling system in reproductive tissues of rats with experimental type-1 diabetes

Type-1 diabetes mellitus (DM) leads to numerous disturbances in the male and female reproductive systems. As was shown previously, one of the main causes of the development of complications in DM is a change in the sensitivity of the adenylyl cyclase signaling system (ACSS) to hormones. The aim of this work consisted in detection of disturbances in the hormone-regulated ACSS in reproductive system of rats with experimental type-1 DM (EDM1) caused by administration of streptozotocin. It has been shown that, in the testes of male rats with 5-day-long EDM1 the stimulating effects of human chorionic gonadotropin (HCG) and PACAP-38 on adenylyl cyclase (AC) and the GTP binding of G proteins are decreased considerably. In the uteri of female rats with EDM1 the effects of relaxin, PACAP-38, and biogenic amines are markedly decreased, whereas in ovaries only the effects of HCG are decreased. In all studied tissues of rats with EDM1 the attenuation of somatostatin inhibitory effects was observed, while in the uterus the inhibitory effects of serotonin and adrenalin were also decreased. Thus, in the reproductive tissues of rats with EDM1, the hormone regulatory effects on ACSS are decreased, especially the effect of HCG and the hormones, AC-inhibitors. We believe that the sensitivity of ACSS to hormones in EDM1 underlies the development of pathological changes in the reproductive system of diabetic rats under the conditions of hyperglycemia and insulin deficiency characteristic of type-1 DM.     

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.     

Functional state of adenylyl cyclase signaling system in rat testis and ovary under conditions of fasting

Sensitivity of the adenylyl cyclase signaling system (ACSS) to polypeptide hormones and biogenic amines is studied in testes and ovaries 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 adenylyl cyclase (AC) and of the basal level of the GTP binding of heterotrimeric G proteins. An increase in duration of fasting from 2 to 4 days led to intensification of these changes. In the fasted rats, the AC-stimulating effects of chorionic gonadotropin, PACAP-38, and isoproterenol, realized via G protein of 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 testes of the fasted rats the stimulating effect of serotonin on AC via both types of G proteins increased, whereas the inhibitory effects of the hormone decreased. Thus, under conditions of fasting, in rat testes and ovaries the ACSS sensitivity to regulatory effects of hormones is changing: their stimulatory effects are increased, while its inhibitory effects, on the contrary, are decreased. We suggest that these changes are 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.     

Intranasal insulin affects adenyl cyclase system in rat tissues in neonatal diabetes

The changes in hormone-regulated adenylyl cyclase (AC) signaling system implicated in control of the nervous, cardiovascular and reproductive systems may contribute to complications of diabetes mellitus (DM). We investigated the functional state of AC system in the brain, myocardium, ovary and uterus of rats with neonatal DM and examined the influence of intranasally administered insulin on the sensitivity of this system to biogenic amines and polypeptide hormones. The regulatory effects of somatostatin and 5-HT_1BR-agonist 5-nonyloxytryptamine acting via G_i protein-coupled receptors were significantly decreased in DM and partially restored in insulin-treated rats. The effects of hormones, activators of AC, are changed in tissue- and receptorspecific manner, and intranasal insulin restored the effects rather close to the level in control. In insulin-treated non-diabetic rats, AC stimulating effects of isoproterenol and relaxin in the myocardium and of human chorionic gonadotropin in the ovaries were decreased, while the effects of hormones, inhibitors of AC, were increased. These data indicate that with intranasal insulin, Gi protein-mediated signaling pathways continue to gain strength. The obtained data on the influence of hormones on AC system in the brain, myocardium, ovary and uterus allow looking anew into the mechanisms of therapeutic effects of intranasal insulin.     

A decrease in the sensitivity of adenylyl cyclase and heterotrimeric g proteins to chorionic gonadotrophin and peptide hormones action in the tissues of reproductive system of rats with experimental type 2 diabetes

Patients with different forms of the diabetes, particularly with insulin-independent type 2 diabetes, have a wide spectrum of the disturbances of the functions of reproductive system. It is suggested that the main reason of these disturbances is altered sensitivity of reproductive system tissues to the regulatory action of hormones. The aim of this study was the identification of the changes in functioning of adenylyl cyclase system (ACS) sensitive to human chorionic gonadotrophin (hCG) and the peptide hormones in the ovary, testes and uterus of rats with neonatal streptozotocin (STZ) diabetes that is similar to the type 2 diabetes in humans. The effects of hCG, PACAP-38 and relaxin, realizing their effects via stimulatory G proteins (G_s), and somatostatin, acting via the inhibitory G protein (G_i), on adenylyl cyclase (AC) activity and GTP binding to the G proteins were studied. In rats with STZ type 2 diabetes the regulatory effects of hCG and PACAP-38 decreased in the ovary and testes, while the effects of somatostatin decreased in all investigated tissues (especially in the uterus). This caused attenuation of the hormonal effects, stimulating (hCG and PACAP-38) or inhibiting (somatostatin) AC activity, and in the decrease of their stimulatory effect on the GTP binding. At the same time a significant decrease of ACS sensitivity to relaxin in the tissues of diabetic rats was not found. Data obtained suggest that one of the key reasons for impairments of reproductive functions in experimental type 2 diabetes is the decrease of ACS sensitivity to the hormones, hCG, PACAP-38 and somatostatin, which play an important role in the reproductive system functioning.     

A change of hormonal regulation of adenylyl cyclase in epididymal adipose tissue of rats with experimental models of diabetes mellitus

One of the key causes of diabetes mellitus (DM) and its complications are hormonal disturbances in functioning of hormonal signaling systems, including the adenylyl cyclase signaling system (ACSS). The goal of this work was to study the functional state and hormonal sensitivity of ACSS in the epididymal adipose tissue of male rats in the 7-month model of mild type 1 DM (DM1), in the 18-month neonatal model of type 2 DM (DM2), and in the taken for comparison model of the 30 day-longs acute DM1. It is shown for the first time that in adipocytes from the epididymal fat of rats with the studied DM models the basal AC activity and its stimulation by forskolin were decreased, which indicates a weakening of the catalytic functions of the enzyme adenylyl cyclase (AC). Stimulation of AC by guanine nucleotides in DM changed to the lesser extent, which argues in favor of preservation of functions of heterotrimeric Gs-proteins in the epididymal fat. In rats with DM1 the sensitivity of AC of adipocytes to agonists of β-adrenergic receptors (β-AR), activators of lipolysis, remained practically unchanged, while in animals with DM2 the AC stimulating effects of β-AR-agonists were reduced or completely blocked, like in the case of β₃-AR-agonists BRL-37344 and CL-316243. In adipocytes of rats with DM1 the AC inhibitory effect of N⁶-cyclopentyladenosine, agonist of type 1 adenosine receptors (Aden₁R), an inhibitor of lipolysis, was attenuated, whereas in DM2 this effect was completely preserved. Thus, in the epididymal adipose tissue of rats with DM1 the antilipolytic AC cascades including Aden₁R were decreased and the stimulation of AC by β-AR-agonists was preserved, whereas in rats with DM2 the β-AR-mediated AC cascades activating lipolysis were reduced, but Aden₁R-mediated AC cascades inhibiting lipolysis did not change. The changes of hormonal regulation of ACSS in adipocytes from the epididymal fat lead to disturbances of the metabolic status of animals with DM1 and DM2 and should be considered in the diagnostics and treatment of DM and its complications.     

Receptor and tissue specificity of the effects of peptides corresponding to intracellular regions of the serpentine type receptors

Proximal regions of the third intracellular loop (ICL-3) are responsible for the interaction with heterotrimeric G proteins in most of the serpentine type receptors. The peptides corresponding to these regions are able to activate G proteins in the absence of hormone and to alter the transduction of hormonal signal via the respective homologous receptor. However, the molecular mechanisms of action of the peptides, their specificity to receptors and target tissues are currently not well understood. The goal of this work was to study the receptor and tissue specificity of peptides-derivatives of C-terminal regions of the ICL-3 of luteinizing hormone receptor (LHR), type 1 relaxin receptor (RXFP1), somatostatin receptors of types 1 and 2 (Som₁R and Som₂R), and 5-hydroxytryptamine receptors of subtype 1B and type 6 (5-HT_1BR and 5-HT₆R) on the functional activity of adenylyl cyclase (AC) and GppNHp-binding of G proteins in the brain, myocardium, and testis of rats. It was shown that the influence of peptides on AC and G proteins is well detected in tissues enriched in homologous receptors. The effects stimulating AC and GppNHp-binding were most pronounced in the testes for LHR peptide, in the brain for peptide 5-HT₆R, and in all of the tested tissues (but mainly in the myocardium) for the RXFP1 peptide. The AC-inhibiting effects of peptides Som₁R, Som₂R and 5-HT_1BR, as well as the stimulation of GppNHp binding induced by these peptides, were most pronounced in the brain. In the presence of the peptides, the AC effects of hormones acting via homologous receptors were significantly attenuated, while the AC effects of other hormones changed insignificantly. The findings suggest that biological activity of the peptides depends on their interaction with complementary regions of homologous receptors, which should be taken into account when developing highly selective regulators of hormonal signaling systems on the basis of these peptides.     

Functional activity of thyroid gland in male rats with acute and mild streptozotocin diabetes

Type 1 diabetes mellitus (DM1) and dysfunction of the thyroid gland (TG) are the most common endocrine diseases, which are interrelated. However, the molecular mechanisms of thyroid dysfunction in DM1 and the role of adenylyl cyclase signaling system (ACSS) in this process remain poorly understood. Typically for studying etiology and pathogenesis of thyroid diseases in DM1 the models of acute DM1 induced by high doses of streptozotocin (STZ) are used. At the same time, a suitable model for this purpose is the model of mild DM1 initiated by moderate doses of STZ, which more closely resembles human DM1. The aim of this study was a comparative study of the functional state of the thyroid gland in rats with 30-day acute DM1 induced by injection of STZ at a dose of 65 mg/kg, and in rats with 30- and 210-day mild DM1 induced by three consecutive injections of STZ at medium doses (30–40 mg/kg). For this purpose in diabetic animals the levels of thyroid hormones and TSH and the functional activity of hormone-sensitive ACSS in membranes isolated from thyroid gland were studied. It was shown that in blood of rats with acute DM1 the levels of fT₄, fT₃, and tT₃ were decreased by 45, 23 and 19%, respectively, while the level of TSH did not change significantly. In rats with the 30-day mild DM1 the concentration of fT₄ was decreased by 32%, while the levels of tT₄, tT₃, and TSH were similar to that in control. In rats with prolonged mild DM1 after 150 and 210 days following the first treatment with STZ the levels of tT₄, fT₄, and tT₃ were significantly reduced, but the concentration of TSH in rats with 210-day mild DM1 was increased by 119%. The results obtained in the study of thyroid status and TSH levels in rats with prolonged mild DM1 are in good agreement with the data obtained in the study of thyroid diseases in patients with DM1. It was found that the AC basal activity in the membranes isolated from the thyroid gland of diabetic rats did not change, except for the rats with the prolonged mild DM1 where this activity was increased by 21%. In all groups of diabetic rats the decrease of AC stimulating effects of GppNHp (10^?5 M) and TSH (10^?8 M) was found, and in the rats with prolonged mild DM1 the AC effect of PACAP-38 (10^?6 M) was also reduced. The decrease of AC effect of TSH varied among different groups of the diabetic animals: in the rats with acute DM1 this effect was reduced by 46% and in the rats with 30- and 210-day mild DM1-by 18 and 34%. Thus, it was concluded that the key cause of the thyroid resistance to TSH under conditions of DM1 is a weakening of the signal transduction generated by TSH via the ACSS.     

The disturbance of the transduction of adenylyl cyclase inhibiting hormonal signal in myocardium and brain of rats with experimental type II diabetes

At present, the data obtained by us and other authors give evidence that disturbances in hormonal signaling systems are the main causes of development of pathological changes and complications under the diabetes. However, the molecular mechanisms of these disturbances remain obscure, especially in the case of insulin-independent type II diabetes. Using neonatal streptozotocin model of 80- and 180-days type II diabetes the changes in functional activity of hormone-regulated adenylyl cyclase (AC) signaling systems components in the myocardium and the brain striatum of diabetic rats in comparison with the control animals were found. The transduction of AC inhibitory hormonal signal meditated through Gi proteins was shown to by disturbed under diabetes. This was manifested in both the decrease of hormone inhibitory effect on AC activity and weakening of hormone stimulation of G-protein GTP-binding activity. In the case of noradrenaline (myocardium) the inhibitory pathway of AC regulation by the hormone was vanished and the stimulation pathway, in contrary, was protected. Prolongation of diabetes from 80 up to 180 days led to some weakening of Gi-protein-mediated hormonal signal transduction. Stimulating effect of biogenic amines and relaxin on the AC activity and GTP-binding in the myocardium and brain of diabetic rats were weakly changed in the case of both 80- and 180-days diabetes. To sum up, the experimental type II diabetes caused disturbances mainly in Gi-coupled signaling cascades participating in hormone inhibition of AC activity.     

The activity of receptor guanylyl cyclases in tissues of rats with neonatal streptozotocin diabetus mellitus and the influence of intranasal administration of insulin and serotonin

Functional activity of hormanal signaling systems and their sensitivity to regulatory actions of hormones in diabetes mellitus (DM) and its complications are altered. The activity of receptor forms of guanylyl cyclases (rGC) sensitive to natriuretic peptides, ANP and CNP, in tissues of female rats with 240-days neonatal streptozotocin DM and the influence of intranasal administration of insulin and serotonin (6 weeks, daily dose is 0.48 IU of insulin or 20 microg of serotonin to rat) on this activity were studied. In diabetic animals, the increase of the basal activity of rGC in the myocardium and its decrease in the uterus and ovaries were found, whereas the brain showed no differences from control animals. The treatment of diabetic rats with insulin led to a decrease in the basal activity of rGC in the myocardium and to its restoration to normal level in the ovaries. Serotonin treatment induced a less pronounced compared with insulin decrease in the basal activity of the enzyme in the myocardium and also a slight increase the activity in the brain. In the myocardium of diabetic rats, the weakening of GC stimulating effect of ANP and, on the contrary, the strengthening of CNP effect were observed. In the ovaries, GC stimulating effect of CNP and, to a lesser degree, the corresponding effect of ANP were decreased. In the uterus and the brain, the sensitivity of rGC to hormones was practically not changed. The administration of insulin to diabetic rats induced an increase in GC effect of ANP in the myocardium to its values in control animals and a decrease in CNP effect as well as in partially restored GC effect of CNP in the ovaries. Serotonin treatment led to some increase in the effects of natriuretic peptides in the brain of both control and diabetic animals. Summing up, in neonatal model of type 2 DM in the myocardium and the tissues of reproductive system of rats the functioning of natriuretic peptide-sensitive rGC is altered in the myocardium and the tissues of reproductive system of model rats with neonatal type 2 DM. Treatment of animals with insulin substantially restores rGC activity while intranasal administration of serotonin has little effect.     

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

Intranasal insulin (II) administration is widely used in the last years to treat Alzheimer’s disease and other cognitive disorders. Meanwhile, it is almost not used to treat type 2 diabetes mellitus (DM2), mainly due to insufficiently studied molecular mechanisms of its effect on the hormonal and metabolic status of the organism. The effect of II on activity of the hypothalamic signaling systems playing a key role in central regulation of energy metabolism is also poorly studied. The aim of this work was to study the effect of 5-week II treatment of male rats with the neonatal model of DM2 (0.48 ME/rat) both on the metabolic parameters and functional activity of the hypothalamic signaling systems. II treatment of diabetic rats (DI group) was shown to normalize the blood glucose level and restore glucose tolerance and utilization. In the hypothalamus of the DI group, the regulatory effects of agonists of the type 4 melanocortin receptor (MC4R), type 2 dopamine receptor (D2-DAR) and serotonin 1B receptor (S1BR) on adenylyl cyclase (AC) activity, reduced under DM2, were found to be restored; moreover, the inhibitory effect of S1BR agonists became even stronger as compared to control. In the DI group, the restoration of AC hormonal regulation was associated with a considerable increase in expression of the genes encoding S1BR and MC4R. Besides, the attenuation of the AC-stimulating effect of D2-DAR agonists against the background of decreasing expression of the Drd1 gene was found to promote the enhancement of the negative effect of dopamine on AC activity. II treatment did not have a considerable effect on expression of the genes encoding the insulin receptor and insulin receptor substrate-2, which was slightly reduced in the hypothalamus of diabetic rats. Thus, II treatment of rats with the neonatal model of DM2 partially restores the hypothalamic AC signaling pathways regulated by melanocortin, serotonin and dopamine, demonstrating thereby one of the mechanisms of the positive influence of II on energy metabolism and insulin sensitivity in peripheral tissues.     

Disturbance of transduction of adenylyl cyclase-inhibiting hormonal signaling in the myocardium and brain of rats with experimental type 2 diabetes

Presently, our work, as well as that of other authors, has produced convincing evidence in favor of the idea that disturbances in hormonal signaling systems are one of the main causes of the development of pathological alterations and complications in diabetes. However, the molecular mechanisms underlying these disturbances remain practically unstudied, particularly in insulin-independent type 2 diabetes. Using a neonatal streptozotocin model of type 2 diabetes, whose duration was either 80 or 180 days, we studied changes in the functional activity of components of the hormone-regulated adenylyl cyclase (AC) signaling system in the myocardium and brain striatum of diabetic rats as compared with control animals. In diabetes, the G_i-realized process of transduction of the hormonal signal inhibiting AC activity has been shown to be markedly impaired. This is manifested as a decrease of the inhibitory effect of hormones on AC activity and an attenuation of their stimulation of the G-protein’s GTP-binding activity. In the case of noradrenaline (myocardium), the inhibitory pathway of the AC system regulation is completely suppressed, while the stimulatory pathway is preserved. An increase in the duration of diabetes development from 80 to 180 days leads to some decrease in the transduction of hormonal signals realized via G_i-proteins. The stimulatory effects of biogenic amines and relaxin on AC activity and GTP binding in the myocardium and brain of diabetic rats change relatively little, both in the 80-and in the 180-day diabetes. Thus, in the experimental type 2 diabetes, disturbances in G_i-protein coupled signal cascades are primarily observed, through which hormones realize their inhibition of AC activity.     

Restoration of hypothalamic signaling systems as a cause of improved metabolic parameters in rats with neonatal diabetes model during treatment with bromocriptine mesylate

One approach to correction of diabetes mellitus 2 type (DM2) and its complications is the use of bromocriptine mesylate (BCM), a selective agonist of the dopamine receptor type 2 (DA₂R). However, the effectiveness and mechanisms of the action of BCM in the treatment of severe forms of DM2 forms currently not understood. The purpose of this study was to investigate the influence of 4-week treatment of male rats with neonatal DM2 model using BCM (300 mg/kg daily) on their metabolic parameters and on the activity of the adenylyl cyclase signaling system (ACSS) in the hypothalamus. Exposure to BCM restored glucose tolerance and glucose utilization by exogenous insulin, normalized lipid metabolism, and lowered triglycerides and atherogenic cholesterol levels, which are elevated in DM2. In the hypothalamus of diabetic rats treated with BCM, the regulation of ACSS by agonists of melanocortin receptors type 4 (MC₄R), DA₂R, and serotonin 1B-subtype receptors and expression of the Mc4r gene encoding MC₄R were restored. Furthermore, BCM treatment did not influence the insulin levels in the blood and its production by pancreatic β-cells. The data indicate that the use of BCM to correct severe forms of experimental DM2 holds promise and show that the therapeutic potential of this drug is based on its ability to restore signaling systems of the hypothalamus that are sensitive to monoamines and peptides of the melanocortin family, which are responsible for the control of energy metabolism and insulin sensitivity.     

Structural and functional characteristics of the adenylyl cyclase signaling system regulated by biogenic amines and peptide hormones in the muscle of a worm Lumbricus terrestris

It has been shown for the first time that biogenic amines (catecholamines and tryptophane derivatives) stimulate dose-dependently activity of adenylyl cyclase (AC) and GTP-binding of G-proteins in muscle of the cutaneous-muscle bag of the earthworm Lumbricus terrestris. By efficiency of their stimulating action on the AC activity, biogenic amines can be arranged in the following sequence: octopamine > tyramine > tryptamine = serotonin > dopamine > isoproterenol = adrenalin. The sequence of efficiency of their action on GTP-binding is somewhat different: serotonin > tryptamine > octopamine > dopamine = tyramine > adrenaline > isoproterenol. Sensitivity of AC and G-proteins in the worm muscle to biogenic amines is similar with that in smooth muscle of the molluse Anodonta cygnea (invertebrates), but differs markedly by this parameter from the rat myocardium (vertebrates). It has also been revealed that AC in the worm muscle is regulated by peptide hormones relaxin and somatostatin whose action is comparable with that in the mollusk muscle, but much weaker that the action of these hormones on the rat myocardium AC activity. Use of C-terminal peptides of alpha-subunits of G-proteins of the stimulatory (385-394 Galpha(s)) and inhibitory (346-355 Galpha(i2)) types that disrupt selectively the hormonal signal transduction realized via G(s)- and G(i)-proteins, respectively, allowed establishing that the AC-stimulating effects of relaxin, octopamine, tyramine, and dopamine in the worm muscle are realized via the receptors coupled functionally with G(s)-protein; the AC-inhibiting effect of somatostatin is realized via the receptor coupled with G(i)-protein, whereas serotonin and tryptamine activate both types of G-proteins.     

Structural-functional characteristics of the adenylyl cyclase signaling system regulated by biogenic amines and peptide hormones in muscles of the earthworm Lumbricus terrestris

It has been shown for the first time that biogenic amines (catecholamines and tryptophane derivatives) stimulate dose-dependently activity of adenylyl cyclase (AC) and GTP-binding of G-proteins in muscle of the skin-muscle sac of the earthworm Lumbricus terrestris. By efficiency of their stimulating action on the AC activity, biogenic amines can be arranged in the following sequence: octopamine > tyramine > tryptamine ≈ serotonin > dopamine > isoproterenol ≈ adrenalin. The sequence of efficiency of their action on GTP-binding is somewhat different: serotonin > tryptamine > octopamine > dopamine ≈ tyramine > adrenaline > isoproterenol. Sensitivity of AC and G-proteins in the worm muscle to biogenic amines is similar with that in smooth muscle of the mollusc Anodonta cygnea (invertebrates), but differs markedly by this parameter from the rat myocardium (vertebrates). It has also been revealed that AC in the worm muscle is regulated by peptide hormones, relaxin and somatostatin, whose action is comparable with that in the mollusc muscle, but much weaker that the action of these hormones on the rat myocardium AC activity. Use of Cterminal peptides of α-subunits of G-proteins of the stimulatory (385–394 Gαs) and inhibitory (346–355 Gαi2) types that disrupt selectively the hormonal signal transduction realized via Gsand Giproteins, respectively, allowed establishing that the AC-stimulating effects of relaxin, octopamine, tyramine, and dopamine in the worm muscle are realized via the receptors coupled functionally with Gs-protein; the AC-inhibiting effect of somatostatin is realized via the receptor coupled with Gi-protein, whereas serotonin and tryptamine activate both types of G-proteins.     

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.     

Activity of receptor guanylyl cyclases in rats with neonatal streptozotocin diabetes and effect of intranasal administration of insulin and serotonin

In diabetes mellitus (DM) and its complications the functional activity of hormonal signaling systems and their sensitivity to the regulatory action of hormones are changed. We studied the activity of receptor forms of guanylyl cyclase (rGC) sensitive to natriuretic peptides ANP and CNP in the tissues of female rats with 240 day neonatal streptozotocin DM and the effects of intranasal administration of insulin and serotonin (6 weeks, daily dose for rat is 0.48 IU insulin or 20 μg serotonin). In diabetic rats, the increase of the basal rGC activity in the myocardium and its decrease in the uterus and ovaries were found, while in the brain, there were no differences from the control. The treatment of diabetic rats with insulin led to a decrease of the basal rGC activity in the myocardium and its restoration to a normal level in the ovaries. The administration of serotonin produced a less pronounced decrease in the basal enzyme activity in the myocardium compared to insulin and an insignificant increase in the brain. In the myocardium of diabetic rats, the guanylyl cyclase (GC)-stimulating effect of ANP was attenuated, whereas the CNP effect was enhanced; in the ovaries, the GC-stimulating effect of CNP and, to a lesser degree, the effect of ANP were decreased. In the uterus and brain of a diabetic rats, the rGC sensitivity to hormones was practically did not change. The administration of insulin to diabetic rats induces an increase of GC effect of ANP in the myocardium to its values in control and a decrease of CNP effect, as well as partially restored GC effect of CNP in the ovaries under the influence of CNP. The administration of serotonin somewhat enhanced effect of natriuretic peptides in the brain of both control and diabetic animals. Thus, in the neonatal model of type-2 DM in the myocardium and the tissues of the reproductive systems of rats, the functioning of natriuretic peptide-sensitive rGC is changed. The treatment of animals by insulin substantially restores rGC activity, while the intranasal serotonin administration has a little effect.     

丝胶预处理对糖尿病大鼠睾丸IGF-1表达的影响

目的探讨丝胶预处理对2型糖尿病大鼠睾丸胰岛素样生长因子-1(insulin-like growth factor-1,IGF-1)表达的影响。方法 30只雄性SD大鼠随机分为3组(n=10):正常对照组、糖尿病模型组和丝胶预处理组。链脲佐菌素连续腹腔注射制作2型糖尿病大鼠模型,以血糖≥16.7mmol/L作为成模标准;丝胶预处理组大鼠在注射链脲佐菌素前给予丝胶灌胃(2.4g/kg/d)35d。采用葡萄糖氧化酶法检测血糖,采用ELISA方法检测大鼠血清睾酮和IGF-1水平;分别采用免疫组化染色和RT-PCR法检测睾丸IGF-1蛋白和mRNA的表达。结果丝胶预处理可明显抑制糖尿病大鼠血糖升高,血清睾酮、IGF-1水平的降低,睾丸IGF-1表达的下降(丝胶预处理组与糖尿病模型组比较:P0.01)。结果 丝胶预处理可通过阻止糖尿病大鼠睾丸IGF-1表达的下调,改善生精功能,发挥对糖尿病生殖功能损害的预防保护作用。     

Differential expression and localization of neuropeptide Y peptide in pancreatic islet of diabetic and high fat fed rats

Neuropeptide Y (NPY) inhibits insulin secretion. Increased numbers of pancreatic islet cells expressing NPY have been observed in type 1 diabetic rats. To understand the functional significance of NPY expression in islet cells, we investigated the effects of high fat feeding and diabetic conditions on the expression and location of NPY expressing cells in normal and diabetic rats. Twenty rats were maintained on either normal chow (ND) or a high fat dietary regimen (HFD) for 4 weeks. In half of each group, type 1 or type 2 diabetes (groups T1DM and T2DM, respectively) was induced by injection of streptozotocin. At 8 weeks rats were euthanized and the pancreases were processed for immunofluorescence labeling (NPY/insulin, NPY/glucagon, NPY/somatostatin, and NPY/pancreatic polypeptide). Compared with the ND group, HFD rats had significantly fewer alpha cells, but beta cells were similar, while T1DM and T2DM rats showed significant increases in the proportions of alpha, delta, and PP cells. Robust increases in NPY-positive islet cells were found in the HFD, T1DM, and T2DM rats compared with ND controls. In ND rats, 99.7% of the NPY-positive cells were PP cells. However, high fat feeding and diabetes resulted in significant increases in NPY-positive delta cells, with concomitant decreases in NPY-positive PP cells. In summary, high-fat feeding and diabetes resulted in changes in the hormonal composition of pancreatic islet and increased number of NPY-expressing islet cells. Under diabetic conditions NPY expression switched from predominantly a characteristic of PP cells to predominantly that of delta cells. This may be a factor in reduced pancreatic hormone secretion during diabetes.