Changes in the relative contribution of endothelium-produced vasodilators to the modulation of mesenteric artery reactivity were studied in Wistar rats treated with 20% fructose for 16 and 32 weeks. Rats that consumed fructose developed symptoms of metabolic syndrome. Acetylcholine-induced relaxation of phenylephrine-precontracted mesenteric arteries was reduced in rats with metabolic syndrome. The NO-mediated component of acetylcholine-induced relaxation was reduced in these rats. At the same time, arterial relaxation mediated by endothelium-dependent hyperpolarization was increased. Endothelium-independent relaxation of mesenteric arteries to sodium nitroprusside in rats with metabolic syndrome was the same as in the arteries of control rats. These results suggest that the increased contraction of mesenteric arteries caused by phenylephrine in rats with metabolic syndrome is due to decreased NO production by the endothelium. Endothelium-dependent hyperpolarization appears to partially compensates for this dysfunction.

Inflammation accompanies most pathological processes, while the lymphatic system takes part in both the development and resolution of inflammation. We studied the contractile function of rat lymph nodes after cecal ligation and puncture (CLP). In 24 h after CLP, the mesenteric lymph nodes were removed and placed in the myograph chamber. After CLP, the lymph nodes showed lower tension than lymph nodes from sham-operated animals (control). The expression of inducible NO synthase, cyclooxygenase-2, and cystathionine-γ-lyase was observed in the lymph nodes of CLP rats. NO, prostaglandins, and H 2 S formed during inflammation inhibited contractile activity of smooth muscle cells in the capsule of the lymph nodes, which manifested itself in inhibition of phase contractions and a decrease in the tone of their capsule.

Over the past 50 years, the prevalence of obesity around the world has increased several times and has become a pandemic. The effect of obesity on the lymphatic system, which plays a key role in the regulation of fluid homeostasis, immune cell migration, antigen presentation, and resolution of inflammatory responses, is poorly understood, and there is no data on the contractile activity of the lymph nodes in obesity. The purpose of the research was to investigate the parameters and mechanisms of dysfunction of the contractile function of the mesenteric lymph nodes of rats in obesity caused by the feeding with the high-fat diet (HFD). Material and methods. The study was conducted on 50 male Sprague-Dawley rats. Rats aged 6 weeks were randomly divided into groups: a control group (n=10) fed a standard diet and a group of rats (n=40) kept on HFD (60% fat content by calorie value). Rats received food and water ad libitum for 16 weeks. Before the end of the experiment, four groups of HFD rats were formed: obesity resistant animals (HFD-OR, n=11), without additional interventions (HFD, n=10), rats which were administered dexamethasone three days before the study (HFD+Dexa, n=9), HFD followed by 8-week diet restriction (HFD+DR, n=9). At the end of the experiment, mesenteric lymph nodes (LNs) were taken from rats under anesthesia and their contractile function was studied in a myograph using 1400W, dynastat and Tempol. Results. LNs of control rats had a high level of tone and generated spontaneous high-amplitude phasic contractions. The LNs of HFD rats had a low initial tone, and rare low-amplitude phasic contractions were recorded in them. The parameters of contractile activity of the LNs of rats in HFD-OR and HFD+Dexa groups differed slightly from the corresponding parameters of the LNs of rats in the control group. Calorie restriction for 8 weeks in obese rats (HFD+DR) resulted in an increase in tone, frequency and amplitude of phasic contractions of the LNs compared to those in HFD rats. iNOS inhibition caused a significant increase in the tone, amplitude and frequency of phasic contractions of the LNs in the HFD group. An increase in the frequency of phasic contractions was observed only in the LNs of HFD+Dex and HFD+DR rats. Inhibition of cyclooxygenase 2 did not affect the contractile function of the LNs of rats of all groups, with the exception of animals from the HFD group (increase in the amplitude and frequency of phasic contractions). Tempol significantly increased the tone, frequency and amplitude of phasic contractions of the LNs in rats of the HFD group and increased the frequency of phasic contractions of the LNs of the HFD+DR rats. Conclusion. A high-fat diet leads to impaired contractile function of rat LNs and can create additional obstacles to the movement of lymph, promoting its leakage into surrounding tissues. Obesity is accompanied by the development of inflammation in the LNs and perinodal adipose tissue, which induces the expression of inducible NO synthase, cyclooxygenase-2 and the accumulation of reactive oxygen species (ROS). NO, prostaglandins and ROS have an inhibitory effect on the SMC capsules of the LNs, leading to a decrease in tonic tension and a weakening of spontaneous phasic contractions. The reason for inhibition of LN contractile function is obesity, but not consumption of food high in fat. Transferring obese rats to a calorie-restricted diet results in a decrease in body weight and visceral fat mass and an improvement in LN contractile function.

We formulate a compartmental model of the murine lymphatic system with the transfer rate parameters derived from the data on the geometric characteristics of the lymphatic system (LS) graph structure and the Hagen-Poiseuille-based values of the lymph flows through the system components, i.e., vertices and edges. It is supplemented by the physics-based model of lymph node draining-related function which considers a paradigmatic view of its geometry with one- and three-afferent lymphatic vessels and one efferent vessel, and the lymph flow described by the Darcy-Starling equations. We discuss further modelling work needed to gain a predictive understanding of the LS function in response to various perturbations including infections and therapeutic treatments.

BACKGROUND: In the treatment of diabetes mellitus (DM) for a persistent reduction in blood glucose levels it was widely used glibenclamide — a KATP channels blocker. However, its effects on cerebral circulation have been studied very little. A decrease in the functional activity of KATP channels due to their blocking by glibenclamide against the background of developed endothelial dysfunction may lead to impaired cerebral circulation (especially at the microcirculatory level) and promote remodeling of the vascular network.AIM: To evaluate the effect of glibenclamide on the reactivity of cerebral arteries in rats with streptozotocin-induced diabetes mellitus (STZ-T2DM).TASKS: 1. To study changes in the functional state of KATP channels of pial arteries in STZ-T2DM. 2. To evaluate the effect of glibenclamide on the participation of KATP channels in the formation of basal tone and endothelium-dependent dilatation of pial arteries.MATERIALS AND METHODS: The study was performed on 54 male Sprague Dawley rats. Streptozotocin-induced diabetes mellitus (STZ-T2DM) was modeled by keeping animals on a high-fat diet and administering streptozocin (35 mg/kg). Using an installation for intravital study of pial vessels reactivity, 3 months from the beginning of the experiment, the diameter of the arteries was measured when the brain surface was irrigated with Krebs-Henseleit solution, acetylcholine, glibenclamide, pinacidil and acetylcholine against the background of the action of glibenclamide or pinacidil.RESULTS: With modeling STZ-T2DM, rats developed glucose tolerance and insulin resistance. Compared to control animals, body weight was 1,3 times higher, the percentage of visceral fat was 3 times higher, and the blood glucose level was 3,2 times higher. It was shown that in STZ-T2DM the number of pial artery constrictions under the action of glibenclamide decreased by 1,3 — 1,9 times compared to intact rats. Glibenclamide did not block endothelium-dependent dilation.CONCLUSION: In rats with streptozotocin diabetes, KATP channels take part in the formation of the basal tone of the pial arteries, but the contribution of these channels is reduced on average by 1.5 times compared to healthy rats.The use of glibenclamide in STZ-T2DM does not affect endothelium-dependent dilatation of cerebral arteries.

Lymph formed in tissues necessarily passes through lymph nodes (LN), which not only perform an immune function, but also take part in lymph flow through rhythmic high-amplitude contractions. During inflammation, inducible NO synthase (iNOS) is expressed in the lymph nodes, which promotes relaxation of the LN capsule. This study examined the role of K ATP - and BK Ca -channels in sepsis-induced LN remodeling. Sepsis was induced in rats by cecal ligation-puncture surgery. After 12 and 24 hours, mesenteric LN were removed and examined in a myograph. K ATP -channels were activated by pinacidil and blocked by glibenclamide. BK Ca -channels blocked TEA and activated NS 1619. The strength of tonic contraction of the LN under the action of activators and blockers was assessed. LN of septic rats named low level of tone during standard stretching. Pinacidil led to greater relaxation of LN in septic rats compared to the control group; the effect of glibenclamide was accompanied by an increase in tone. Pinacidil combined with glibenclamide did not lead to significant changes in LN tone. The use of NS 1619 was accompanied by relaxation of the LN; in the LN of septic rats, the effect was more pronounced. TEA (3 mM) led to an increase in LN tone; the LN of septic rats responded to the use of TEA with a greater contraction. We concluded that NO produced by expressed iNOS in animals with sepsis directly or indirectly activates K ATP - and BK Ca -channels of smooth muscle cells of the capsule in the LN, which leading to hyperpolarization of the smooth muscle cell membrane and their relaxation, which that promotes relaxation of the LN capsule and their hypertrophy of LN. In the future, K ATP - and BK Ca -channels of smooth muscle cells of the lymph node LN capsule may be a potential target for therapeutic intervention to correct the immune response by slowing down or accelerating the flow of lymph through the LN.

Animal models of diseases, particularly mice, are considered to be the cornerstone for translational research in immunology. The aim of the present study is to model the geometry and analyze the network structure of the murine lymphatic system (LS). The algorithm for building the graph model of the LS makes use of anatomical data. To identify the edge directions of the graph model, a mass balance approach to lymph dynamics based on the Hagen–Poiseuille equation is applied. It is the first study in which a geometric model of the murine LS has been developed and characterized in terms of its structural organization and the lymph transfer function. Our study meets the demand for quantitative mechanistic approaches in the growing field of immunoengineering to utilize or exploit the lymphatic system for immunotherapy.

Abstract—The lymphatic system plays a critical role in immunity, going far beyond the simple transport of immune cells and antigens. The endothelial cells in the various parts of this vasculature are highly specialized to perform various specific functions. Lymphatic capillaries express chemokines and adhesion molecules that in tissues promote the recruitment and transmigration of immune cells. Signaling molecules produced by endothelial cells of lymphatic capillaries during inflammation modulate the migration of lymphocytes through venules with high endothelium from the blood into the parenchyma of lymph nodes. Lymphatic vessels provide active regulated transport of immune cells and antigens to the lymph nodes. In the lymph nodes, with their complex structure organized by stromal cells, optimal conditions are created for the contacts of antigen-presenting cells with lymphocytes. Different subpopulations of lymph node endothelial cells perform specific functions according to lymph node location and contribute to both innate and adaptive immune responses through antigen presentation, lymph node remodeling, and regulation of leukocyte entry and exit.

THE AIM: to evaluate the effect of a high-salt diet on the level of miRNA expression in urine and the mechanisms of endothelium-dependent vascular dilatation in rats. MATERIALS AND METHODS: 20 Wistar rats were divided into two equal groups. The high salt (HS) group received 8 % NaCl in the diet, the control (NS) received the standard diet (0.34 % NaCl). After 4 months, blood pressure (BP), left ventricular mass index (IMLV) were assessed in rats, and relative expression levels of miRNA-21, miRNA-133, and miRNA-203 were determined in urine. The reactivity of the rings of the aorta and the superior mesenteric artery (SMA) to acetylcholine (ACh) was assessed in vitro in isometric mode. RESULTS: there was no significant difference between the groups in terms of mean blood pressure (p> 0.05). However, in HS-rats an increase in IMLV was noted. The relative levels of expression of miRNA-21, miRNA-133, and miRNA-203 in the urine of rats fed a high-salt diet increased significantly as compared to the values of control animals. A high-salt diet resulted in a decrease in the reactivity of vascular segments precontracted with phenylephrine to ACh. A high-salt diet resulted in a decrease in the reactivity of vascular segments precontracted with phenylephrine to ACh. In the HS-group, the decrease in the amplitude of vasodilation under the action of ACh under conditions of blockade of NO-synthase (with the use of L-NIO) was less compared to the reaction in the absence of the blocker, than the NS-group: in the SMA of the HS group – by 45 %, NS group – by 69.4 %, in the aorta HS-group – by 49.4 %, NS-group – by 80.7 %. In contrast to the aorta, blockade of Ca2+-sensitive K+-channels in SMA (under the conditions of administration of tetraethylammonium, TRAM-34, or apamin) weakened ACh-induced relaxation, and in HS-rats, the decrease in vasodilation was more pronounced. CONCLUSION: consumption of a high-salt diet, without changing blood pressure, increases IMLV and the level of miRNA expression in the urine, and also reduces endothelium-dependent vascular relaxation, mediated, in particular, by impaired endothelial NO production, which is more pronounced in the aorta than in the SMA.

The efficiency of the lymph transport system affects not only the balance of the interstitial fluid, but also other aspects of homeostasis. Lymph transport from the interstitial space to the main veins is mainly provided by rhythmic contractions of the lymphatic vascular segments, lymphangions. Meanwhile, the lymphatic vascular network sequentially incorporates the lymph nodes whose role in lymph transport is poorly understood. The aims of this work were to study the length–tension ratio in the bull mesenteric lymph node capsule and to calculate the pressure the lymph nodes are able to generate, as well as to compare the active and passive mechanical characteristics of the lymph node capsule in young and aging bulls. Experiments on isolated lymph node capsules have shown that lymph nodes are highly extensible structures, which allows them to fill readily with lymph even at the peak of lymph formation. Our data show that the bull mesenteric lymph nodes share the ability to regulate lymph flow along them via the intrinsic mechanisms. Smooth muscle cells in the lymph node capsule are sensitive to stretching, as manifested in an increase in the strength of contractions with an increase in capsule stretching. Lymph nodes are able to generate high active pressure with a significant increase in volume and passive pressure. The extensibility of the lymph node capsule and the active pressure developed by the nodes during spontaneous contractions decline in aging vs. young bulls. Thus, we provide here the first measurements and analysis of the capsular length–tension and nodular diameter–pressure ratios in the mesenteric lymph nodes of young and aging bulls.

Inflammation is detected not only in infections or injuries, but also in many other pathological processes associated with tissue dysfunction, such as type 2 diabetes mellitus, atherosclerosis, myocardial infarction, etc. In the processes of development and resolution of inflammation in all cases involves the lymphatic system, and in particular the lymph nodes (LN), which receive products of tissue degradation, bacterial fragments, antigen-presenting cells and various cytokines from the focus of inflammation. The aim of the study was to investigate the mechanisms of inhibition of contractile function of the bovine mesenteric LN capsule contributing to LN remodeling at the early stage of inflammation. Isolated LN capsule strips treated with lipopolychasaride (LPS) were examined in a myograph. The data obtained show that when exposed to LPS, the extensibility of the LN capsule increases due to inhibition of the contractile function of the smooth muscle cells that make up the capsule. It was found that the action of LPS leads to the expression of inducible NO synthase, cyclooxygenase-2 and cystathionine-γ-lyase in the LN capsule cells. NO, prostaglandins and H 2 S produced by these enzymes not only inhibit the phase contractile function of capsule smooth muscle cells, but also lead to a significant decrease in tone. Produced in significant amounts NO activates the NO → sGC → cGMP → PKG → K ATP signaling pathway of smooth muscle cells, in addition, it has a direct effect on other regulatory mechanisms. For the first time, it was shown that H 2 S synthesized by cystathionine-γ-lyase in the LN capsule treated with LPS not only has a direct relaxing effect but also enhances NO-mediated relaxation of the capsule smooth muscle cells. Thus, the results of this study provide evidence that changes occur in the bovine mesenteric LN capsule at an early stage of LPS-induced inflammation, aimed at creating conditions for an increase in LN size and accumulation of immune cells.

Early changes in the cardiovascular system of young Wistar rats were studied in modeling metabolic syndrome by a fructose load. It was found that despite some weight loss in rats fed a fructose diet, as compared to control animals, these animals showed the signs of metabolic syndrome: hyperglycemia, insulin resistance, dyslipidemia, increased activity of the sympathetic nervous system, arterial hypertension. Changes in the mesenteric arteries included an increase in the reactivity to phenylephrine and a decrease in acetylcholine-induced dilation due to decreased NO production by the endothelium, which is to a certain extent compensated by an increased production of the endothelium-derived hyperpolarizing factor realizing its effects through the activation of intermediate-conductance Ca2+-activated K+-channels. Fructose load led to the inhibition of soluble guanylate cyclase in arterial smooth muscle cells. In the skin microcirculatory bed of fructose-loaded rats, perfusion remained at the level typical for control animals, while skin microvessels showed an increase in neurogenic tone and an attenuation of endothelium-dependent tone. A decreased endothelial NO production was found in microcirculatory vessels, which was compensated by the synthesis of other endothelium-derived vasodilating factors.

Lymphatic vessels are involved in a number of physiological and pathological processes and provide the uptake of fluid, immune cells, macromolecules, and lipids from the interstitial space. During solid organ transplantation surgery, the graft–recipient lymphatic vessel continuum is completely disrupted, and despite a remarkable progress in the lymphatic biology, the contribution of lymphatic drainage restoration to effective allograft function and/or rejection remains unclear. Lymphangiogenesis providing a recovery of the lymphatic drainage system after transplantation plays a central role in maintaining interstitial fluid balance in the allograft and hence in reducing tissue edema. Newly formed lymphatic vessels provide the transport of immune cells, however it is well known that a serious problem in organ transplantation is immune-mediated allograft rejection and inflammation. On the one hand, lymphatic vessels facilitate the transport of antigen-presenting cells to draining lymph nodes and the penetration of immune effector cells into the allograft, thus accelerating the induction of alloimmunity and subsequent allograft rejection. On the other hand, for lymphocytes and macrophages, they provide an exit route from the graft, thereby reducing post-transplantation inflammation. The degree of the involvement of lymphangiogenesis in the development of acute and chronic rejection varies considerably in different organs, and the knowledge of these mechanisms is necessary to develop therapeutic strategies providing successful allograft survival. This review pursues two goals. The first goal is to describe the role of lymphatic vessels in maintaining the homeostatic function of different organs under physiological conditions, to demonstrate the complexity of lymphangiogenesis and the role of diverse factors in this process during transplantation with consideration to the regional specificity. The second goal is to attract the attention of transplantation professionals to the lymphatic system, its role in the fate of transplanted organs, and the necessity to intensively investigate lymphangiogenesis in organ transplantation.

Proper functioning of lymphatic vessels (LV) is necessary for the transport of fluids, proteins, and metabolites from the interstitium via lymph nodes to the blood circulation. To achieve all these functions, lymphatic vessels use muscle cells for contractions and endothelial cells to precisely tune these contractions. Moreover, lymphatic vessels play important roles in antigen and immune cell trafficking to provide sufficient immune responses. During a solid organ transplantation, the body's immune system has a strong tendency to reject the organ transplant. Therefore, immunosuppressive drugs are used for tolerance induction to lower the activity of the immune system to accept the organ transplant. Rapamycin is a potent immunosuppressant that can disrupt cytokine signaling, which contributes to the proliferation of lymphocytes. Potential but unusual side effects of using Rapamycin include lymphatic disorders. Several cases were observed wherein transplant recipients exhibited delayed drainage of lymph, lymphatic obstruction, and complete blockage of lymphatic vessels. Cases such as these suggest that more research must be conducted to investigate the mechanism of these effects and possible prophylaxis and treatment of these complications. We investigated the effect of rapamycin on contractility of rat mesenteric lymphatic vessels and lymphatic muscle cell (LMC) metabolism. Rapamycin at 10^-5M after 1Hr of application decreased tone of LV at transmural pressure of 1cm H2O by 4.1 ± 2.9%, and decreased contractile amplitude by 7.8 ± 3.5% and 10.2 ± 4.2% at pressures 3 and 5 cm H2O respectively. Rapamycin at 10^-5M after 1Hr of application decreased LMC ATP production by 0.012 ± 0.002 pmol/min/ug, maximal oxygen consumption rate by 0.027 ± 0.006 pmol/min/ug, spare mitochondrial capacity by 0.025 ± 0.005 pmol/min/ug, coupling efficiency by 33.9 ± 6.1% and increased proton leak by 0.009 ± 0.002 pmol/min/ug. Rapamycin also increased basal extracellular acidification rate (ECAR) by 0.011 ± 0.003 pmol/min/ug. Therefore, rapamycin in high concentration could possibly lead to mitochondrial uncoupling that might reflect changes in contractility. Moreover, an increase in the ECAR can indicate shifting glucose fermentation to lactate that could progress to pathological LV remodeling in the future.

Hydrogen sulfide is involved in the functional regulation of various organs, both in physiological conditions and in pathology, and, specifically, is a major participant of the inflammatory process. In this study, we studied the role and mechanisms of action of hydrogen sulfide in lipopolysaccharide (LPS)-induced relaxation of the capsule of bovine mesenteric lymph nodes (LNs). Isolated strips of the LN capsule were incubated for 6 h in F-10 Ham medium supplemented with LPS from Escherichia coli O55:B5. At the end of incubation, LN capsule preparations were examined on a myograph setup. Contractile properties were evaluated using phenylephrine, relaxation properties—with papaverine. The involvement of H 2 S and NO in LPS-induced relaxation was determined through the use of specific inhibitors. Incubation of LN capsular strips in F-10 Ham + LPS led to a sustained inhibition of phasic contractions and a decrease in the level of tonic tension of LN capsule smooth muscles due to the effect of H 2 S synthesized by the enzymes cystathionine-γ-lyase, cystathionine-β-synthase and 3-mercaptosulfurtransferase, as well as NO produced by inducible NO-synthase. Our data show that H 2 S is one of the major compounds that are quickly produced in the LNs during inflammation. We believe that H 2 S is a key molecule that, along with NO, triggers the inflammatory remodeling of LNs, thus promoting a rapid increase in their size.

A Correction to this paper has been published: https://doi.org/10.1134/S0022093021020216

A high salt diet leads to a decrease in vascular dilatation to agonists, but the vascular mechanisms involved in this process are not extensively studied. A group of male Wistar rats at the age of 3 months was transferred to a high-salt diet containing 8% NaCl (HS) for 3 months, while the second group received a normal-salt diet with a standard salt content (0.34%) (NS). At the end of the experiment, the rats were euthanized and the abdominal aorta and superior mesenteric artery (SMA) were extracted. The vascular segments were placed into a myograph, and the acetylcholine (ACh)-induced relaxation of the phenylephrine (PHE)-precontracted vascular segments was measured. A high-salt diet led to attenuate the relaxation of the SMA in a calcium-free solution. In response to ACh and sodium nitroprusside, a pronounced relaxation of the vascular segments was observed, while the ACh-induced vascular relaxation in HS rats showed a lower amplitude. Potassium channel blockers (TEA, TRAM-34, apamine) attenuated the ACh-induced relaxation of the SMA, but not the aorta. In the SMA of HS rats, a decrease in the relaxation under the effect of K+ channel blockers was more prominent. Inhibition of the production of endogenous hydrogen sulfide (H2S) also led to attenuate the ACh-induced relaxation of SMA segments. In SMA of HS rats, the degree of attenuation of the ACh-induced relaxation against the background of propargylglycine was larger than in NS rats. The data obtained in the study show that a long-term high-salt diet leads to a decrease in agonist-induced relaxation of the aortic segments and SMA due to a decrease in the production of NO by the endothelium. In the SMA of HS rats, a decrease in NO-mediated relaxation is partially compensated by the increasing role of EDHF in ACh-induced relaxation. The results of the study also show that one of the EDHFs in the rat SMA is H2S, the role of which in SMA relaxation increases in HS rats.

A high salt diet leads to a decrease in vascular dilatation to agonists, but the vascular mechanisms involved in this process are not extensively studied. A group of male Wistar rats at the age of 3 months was transferred to a diet containing 8% NaCl (HS) for 3 months, while the second group received a diet with a standard salt content (0.34%) (NS). At the end of the experiment, the rats were euthanized and the abdominal aorta and superior mesenteric artery (SMA) were extracted. The vascular segments were placed in a myograph and the acetylcholine (ACh) -induced relaxation of the vascular segments previously contracted with phenylephrine - was measured. A high salt diet led to a weakening of the relaxation of SMA in a calcium-free solution. In response to ACh and sodium nitroprusside, a pronounced relaxation of the vascular segments was observed, while the ACh-induced vascular relaxation of HS rats had a lower amplitude. K+ -channel blockers (TEA, TRAM-34, and apamine) weakened ACh-induced relaxation of the SMA, but not the aorta. In the SMA of HS rats the decrease in relaxation under the action of K+ -channel blockers was more significant. Inhibition of production of endogenous H2S also led to a weakening of the relaxation of the SMA segments on ACh. In SMA of HS rats, the degree of weakening of ACh-induced relaxation against the background of propargylglycine was greater than in NS rats. The data obtained in the study shows that a long-term high salt diet leads to a decrease in agonist-induced relaxation of the aorta segments and SMA. The relaxation weakening of the aorta segments and SMA occurs due to a decrease in the production of NO by the endothelium. In the SMA of HS rats, the decrease in NO-mediated relaxation is partially compensated by an increased role of EDHF in ACh-induced relaxation. The results of the study also show that one of the EDHFs in rat SMA is H2S, the role of which in SMA relaxation increases in HS rats.