Higher Ca2+ -sensitivity of arterial contraction in 1-week-old rats is due to a greater Rho-kinase activity.

AIM: During early post-natal development, arterial contraction depends less on Ca2+ -signalling pathways but more on changes in Ca2+ -sensitivity compared to adult animals. Whether this difference is related to Rho-kinase, one of the major players affecting Ca2+ -sensitivity, is unknown for intact vessels. Thus, we tested the hypothesis that Rho-kinase critically contributes to the higher Ca2+ -sensitivity of contraction in intact arteries of 1-week-old rats. METHODS: We studied 1-week-old, 4- to 5-week-old and 10- to 12-week-old rats performing isometric myography, Ca2+ -fluorimetry and Western blotting using intact saphenous arteries and arterial pressure measurements under urethane anaesthesia. RESULTS: In 10- to 12-week-old rats, methoxamine (MX) produced vasoconstriction associated with an increase in [Ca2+ ]i and Ca2+ -sensitivity. In contrast, in 1-week-old rats these contractions were accompanied only by an increase in Ca2+ -sensitivity. All MX-induced effects were reduced by the Rho-kinase inhibitor Y-27632; this reduction was complete only in 1-week-old rats. The Rho-kinase specific site Thr855 on MYPT1 was increasingly phosphorylated by MX in vessels of 1-week-old, but not 10- to 12-week-old rats; this effect was also inhibited completely by Y-27632. The Rho-kinase inhibitor fasudil in a dose not affecting the pressor response to MX in 4- to 5-week-old rats reduced it considerably in 1-week-old rats. CONCLUSION: Our results suggest that the higher Ca2+ -sensitivity of arterial contraction in 1-week-old compared to 10- to 12-week-old rats is due to a greater Rho-kinase activity. Constitutively active Rho-kinase contributes to MX-induced contraction in 10- to 12-week-old rats. In 1-week-old rats, additional Rho-kinase activation is involved. This remodelling of the Rho-kinase pathway is associated with its increased contribution to adrenergic arterial pressure responses.

Voluntary exercise training restores anticontractile effect of NO in coronary arteries of adult rats with antenatal/early postnatal hypothyroidism.

INTRODUCTION: Our recent study showed that NO-mediated anticontractile effect of endothelium is absent in coronary arteries of adult rats, which suffered from antenatal/early postnatal hypothyroidism. This study tested the hypothesis that exercise training would improve such detrimental consequences of early thyroid deficiency. DESIGN AND METHODS: Wistar dams received propylthiouracil (PTU, 7 ppm) in drinking water during gestation and two weeks postpartum; control dams received tap water. Six-week-old male offspring of control (CON) and PTU dams was divided into sedentary (CON-Sed, n = 12; PTU-Sed, n = 10) and trained (CON-Tr, n = 12; PTU-Tr, n = 10) groups; the latter had 24-h access to running wheels. Eight weeks later coronary arteries were studied by wire myography. Anticontractile effect of NO was assessed by the effects of NOS inhibitor L-NNA on the basal tone and contractile response to U46619. Oxidative phosphorylation complexes and eNOS were estimated by Western blotting. RESULTS: T3/T4 and TSH levels (ELISA) were normalized in the progeny of PTU-treated dams at the age of 6 weeks and were not affected by training. Total running distance did not differ between CON-Tr and PTU-Tr. The contents of oxidative phosphorylation complexes were increased post-training in triceps brachii muscle from CON-Tr and PTU-Tr and in heart from PTU-Tr. Coronary arteries of PTU-Sed compared to CON-Sed demonstrated higher basal tone and contractile response to U46619, which were not further increased by L-NNA. The effects of L-NNA on the basal tone and contractile response to U46619 did not differ in CON-Tr and PTU-Tr groups, but were elevated in PTU-Tr compared to PTU-Sed group. PTU-Tr rats in comparison to PTU-Sed group had higher eNOS content in heart. Responses of coronary arteries to DEA/NO did not differ among all experimental groups. CONCLUSIONS: Long-lasting coronary endothelial dysfunction resulted from transient thyroid deficiency during the antenatal/early postnatal period can be corrected by voluntary exercise training.

[THE INDICATORS OF GROWTH AND MYOGENESIS IN THE GLYCOLYTIC AND OXIDATIVE MUSCLES OF THE RAT AFTER INDIRECT ELECTROSTIMULATION].

A comparative analysis of the signaling pathways activity and gene expression in the red (RG) and white (WG) parts of the gastrocnemius muscle of rat after a series of short (1 s) tetanic contractions induced by motor nerve stimulation at a frequency of 100 Hz and with an amplitude that provides activation of all motor units of the muscle. WG compared to RG demonstrated a marked increase in the phosphorylation level of ERK1/2, although the increase in the phosphorylation of AMPK was not different in two muscles 2 h after the stimulation. Along with that, content of MyoD and myogenin mRNA in WG increased much higher than in RG, whereas the effect of stimulation on IGF-1, MaFbx and MuRF genes expression was weak and comparable in WG and RG. There was an increase of myostatin mRNA in RG. Thus, glycolytic muscle fibers of WG exhibit more pronounced regulatory shifts of hypertrophic character than oxidative muscle fibers of RG.

Trophic action of sympathetic nerves reduces arterial smooth muscle Ca(2+) sensitivity during early post-natal development in rats.

AIM: A decrease in the Ca(2+) sensitivity of smooth muscle contraction is a hallmark of functional remodelling of blood vessels during development. However, the responsible factors are largely unknown. Here, we tested the hypothesis that the post-natal decline of arterial Ca(2+) sensitivity is the result of trophic effects of sympathetic nerves. METHODS: Contractile responses, intracellular Ca(2+) levels and protein expression profiles were compared in saphenous arteries from young (1- and 2-week-old) and adult rats using wire myography, Ca(2+) fluorimetry and Western blotting respectively. RESULTS: We observed a lower Ca(2+) sensitivity of contractions induced by methoxamine, an agonist of α1 -adrenoceptors, and U46619, an agonist of thromboxane A2 receptors, in arteries from adult as compared to young animals. Post-natal maturation was associated with stronger expression of regulatory proteins mediating Ca(2+) -dependent contraction (myosin light chain kinase (MLCK), myosin targeting subunit (MYPT1) and h-caldesmon) and weaker expression of proteins regulating Ca(2+) -independent contraction (Rho kinase, extracellular-regulated kinases (ERK1/2) and mitogen-activated protein kinases p38 MAPK) in vessels from adult rats. To eliminate the trophic action of sympathetic nerves, we performed lumbar sympathectomy in adult rats. This resulted in higher Ca(2+) sensitivity of agonist-induced contractions in denervated as compared to control arteries. Furthermore, denervated arteries contained less MLCK, MYPT1 and h-caldesmon and more ERK1/2 and p38 MAPK. CONCLUSIONS: Sympathetic denervation reverses developmental changes both in Ca(2+) sensitivity and in the expression of regulatory proteins back to the early post-natal phenotype in the rat saphenous artery. We conclude that trophic effects of sympathetic nerves govern functional remodelling of arteries during early post-natal development.

[Functional alterations of the arterial vessels in experimental models of type 1 diabetes mellitus].

The review analyzws the literature on the pathological alterations of endothelium, smooth muscle and vasomotor innervation of arterial vessels in animal modes of type 1 diabetes mellitus. Particular attention is paid t the analysis of mechanisms of diabetic abnormalities in the light of modern knowledge on the functioning of the main components of the vascular wall.

[Dynamics of systemic and local physiological indices while changing intensity of physical load].

It is well known that metabolic, cardiovascular and respiratory indices during exercise of moderate intensity are linearly related to exercise power. After the load reaches the definite level this relationship changes for nonlinear. Different methods of evaluating the intensity of load at which this transition takes place are discussed. The methods for investigation of transient process dynamics in energy supply of muscle contractions with changing intensity of contractions is described. The dependence of dynamic characteristics of physiological indices from fitness level and in its turn from age and level of physical activity is discussed.

[The effects of aerobic exercise upon genes expression in skeletal muscle of trained and untrained men].

It is well recognized the PGC-1 alpha is a key regulator of mitochondrial biogenesis. Mechanical and metabolic perturbations in a skeletal muscle during and after aerobic exercise lead to increase PGC-1alpha expression. In addition to that an increase of PGC-1alpha expression after exercise depends on relative workload intensity and does not depend on fitness level. The aim of the study was to compare the expression of regulators of mitochondrial biogenesis PGC-1alpha, TFAM and TFB2M and of proteolysis-related genes FOXO1 and Atrogin-1 in skeletal muscle untrained and trained men after aerobic exercise with the same relative workload. The study showed that after exercise the PGC-1alpha expression did not differ between groups but TFAM and TFB2M expression was higher in untrained muscle than trained. On the contrary proteolysis-related genes FOXO1 and Atrogin-1 expression increased only in the muscle of trained men.

[Optimization of training: development of a new partial load mode of strength training].

Hypertrophic effect of strength training is known to originate from mechanical and metabolic stimuli. During exercise with restricted blood supply ofworking muscles, that is under conditions of intensified metabolic shifts, training effect may be achieved with much lower external loads (20% of one repetition maximum (1 RM)). The aim of the study was to compare the effects of 8 wks high-intensity (80-85% MVC) strength training and low-intensity (50% 1 RM) training without relaxation. The high-intensity strength training leads to somewhat higher increments in strength and size of trained muscles than training without relaxation. During high-intensity training an increase of area occupied by type II fibers at muscle cross section prevails while during training without relaxation - an increase of area occupied by type I fibers takes place. An exercise session without relaxation leads to a more pronounced increase in secretion of growth hormone, IGF-1 and cortisol. Expression of gene regulating myogenesis (Myostatin) is changed in different ways after high-intensity strength exercise session and after exercise session without relaxation. Low-intensity strength training (50% 1 RM) without relaxation is an effective way for inducing increases of strength and size of trained muscles. This low intensive type of training may be used in restorative medicine, sports and physical culture.

[Nitric oxide in vascular endothelium: control of production and mechanisms of action].

The review analyzes the literature on the regulatory role of NO in blood vessels. Particular attention is paid to the modern ideas about the regulation of expression and activity of endothelial NO-synthase, including those involoving microRNAs--a new class of small regulatory molecules. The physiological mechanisms activating NO-synthase in endothelial cells and key targets of NO-pathway in vascular smoth muscle cells are reviewed as well.

[Changes of rat respiratory and locomotory muscles during aerobic exercise training in continuous and interval regimens].

Male Wistar rats were treadmill-trained for 8 weeks using one of the two regimens: with the constant running speed or with alternating high-speed and low-speed intervals. Both training regimens led to an increase of rat aerobic capacities and to a higher citrate synthase activity in the medial head of gastrocnemius muscle. No differences between the effects of two training regimens were observed. However, in contrast to constant-speed training the interval one resulted in myocardium hypertrophy and also in less pronounced changes in diaphragm muscle, such as slow-direction shift of myosin phenotype and reduction of muscle fiber cross-sectional area. Neither of the training regimens had an effect on corticosterone and thyroid hormones levels in rat blood, whereas the interval training resulted in a higher level of testosterone. Anabolic influence of testosterone during interval aerobic training may be favorable for heart hemodynamic capacity and force characteristics of the diaphragm.

[Dynamics of heart rate changes in rats following stepwise change of treadmill running speed].

Amplitude and temporal responses of heart rate to stepwise increase or decrease of treadmill running intensity were investigated in rats. Heart rate amplitude response was shown to be connected mainly with the change of sympathetic nervous activity whereas heart rate temporal response was shown to be determined predominantly by parasympathetic cardiotrophic influences.

[Comparative analysis of gene expression in rat locomotor muscles and diaphragm].

Gene expression profile in diaphragm in comparison to three principally different hindlimb muscles (soleus, red and white gastrocnemius) was studied using quantitative PCR. Expression levels of PGC-1alpha mRNA and myogenin mRNA in diaphragm were in accordance with its myosin phenotype and citrate synthase activity. However, diaphragm was characterised by atypically high content of MyoD mRNA as well as high content of IGF-1 mRNA and low content of myostatin mRNA. The latter two findings suggest high intensity of protein synthesis in diaphragm muscle fibers, although they have smaller cross sectional area than fibers in locomotor muscles.

[Effect of strength-building training on manifestation of pressor reflex from working muscles receptors].

Ten young normal volunteers and 8 armrestlers worked with forearm muscles till refusal at 30% of maximal arbitrary force. Work was either static or rhythmic with alternation of 20-s period of contraction and relaxation and followed by post-work arterial occlusion of the forearm muscles (PWAO). Heart rate (HR), blood pressure (BP) and muscular vessels-related sympathetic activity (MRSA) were measured continuously. MRSA was registered in n. peroneus using the microneurographic technique. Static work and subsequent PWAO produced different BP and MRSA neither in sportsmen nor amateurs. On the contrary, rhythmic work followed by PWAO suppressed the muscle pressor reflex in sportsmen significantly. The authors consider possible origination of the effect by change in energy supply to working muscles, enhanced extraction of metabolites, and sensory decrement of sportsmen's muscular receptors.

[Changes in the diaphragm muscle and its feed artery after chronic respiratory airway obstruction in rats].

A chronic respiratory load was produced in Wistar rats by tracheal binding to produce a twofold increase of pleural pressure oscillation amplitude during respiration. Eight weeks after the surgery, a higher proportion of type-I muscle fibers (MFI) in the costal diaphragm along with a greater MFI cross-section area and a higher succinate dehydrogenase activity in MFII in the crural diaphragm were observed. During recording the mechanical activity of ring preparations of diaphragm arteries under isometric conditions, an increase in endothelium-dependent relaxation was found, whereas endothelium-independent relaxation and arterial reactivity to noradrenaline did not change. Tracheal binding did not produce any changes of MF in the gastrocnemius muscle, but endothelium-dependent relaxation of gastrocnemius feed arteries was reduced. We conclude that chronic respiratory load affects the endothelial function in diaphragm arteries in a manner favorable for blood flow control in the diaphragm. Functional alterations in gastrocnemius arteries may be associated with the reduced locomotor activity of operated rats.

[Myosin phosphorylation as the main way of regulating smooth muscle contractions].

Rho-kinase is a key enzyme of the receptor-dependent signal cascades and is regarded today as the most prospective target for pharmacological therapy of smooth muscle contractility disorders.

Effect of aerobic training on innervation density and neurogenic responses of skin afferent blood vessels.

We studied the effect of 8-week aerobic training (treadmill running) on neurogenic responses and density of sympathetic innervation of subcutaneous artery in rats. In trained rats, the artery response to stimulation of intramural sympathetic nerve decreased, but the sensitivity of vascular smooth muscles to norepinephrine was not changed. The density of adrenergic nerve fibers in the arterial wall after training was also lower than in the control group. This effect of training can be explained by the need in increased heat emission during physical activity.

Effects of chronic hypotension on the adrenergic nervous plexus of the saphenous artery in rats and its regeneration after femoral nerve injury.

The effects of chronic hypotension on the density and intensity of fluorescence (after treatment with glyoxylic acid) of the plexus of adrenergic fibers in the wall of the saphenous artery and on the reinnervation of this vessel were studied in Wistar rats. Regional hypotension in the vascular bed of the hind part of the rats' bodies was induced by stenosis of the abdominal part of the aorta distal to the renal arteries. After four weeks, the saphenous artery was denervated in one limb by resection of a segment of the femoral nerve. In the limb with the nerve lesion, chronic (6-7 weeks) hypotension led to a reduction in the intensity of nerve fiber fluorescence by 20% as compared with normotensive animals (controls), though the density of the nerve plexus did not change. Partial reinnervation of the vessel was observed 2-3 weeks after femoral nerve lesioning. Measures of reinnervation in normotensive and hypotensive rats were no different at two weeks, though at three weeks rats with hypotension showed more complete recovery of innervation.

[Effect of chronic hypotension on the adrenergic nerve plexus of the rat a. saphena and on its regeneration after femoral nerve injury].

The influence of chronic hypotension on density and fluorescence intensity (after glyoxylic acid treatment) of periarterial plexus of nerve fibers in saphenous artery wall and on reinnervation of this vessel was studied in Wistar rats. Regional hypotension in the rat hindquarters vascular system was created by partial occlusion of abdominal aorta distally to the renal arteries. Four weeks later, the segment of femoral nerve was resected in one of the limbs to denervate the saphenous artery. In the limb with intact nerve, chronic (6-7 weeks-long) hypotension resulted in 20% decrease of fluorescence intensity of nerve fibers, as compared to that one in normotensive (control) rats, however the density of the nerve plexus did not change. Partial reinnervation of the vessel occurred in 2-3 weeks after femoral nerve injury. After 2 weeks parameters of reinnervation were similar in hypotensive and normotensive rats, but after 3 weeks hypotensive rats demonstrated more complete restoration of the innervation.

[Ergoreflex: the essence and mechanisms].

Physical loading raises the sympathetic nervous activity which results in increased minute volume, constriction of peripheral vessels, and elevated blood pressure. These reactions are an outcome of two mechanisms: 1) the central command from cerebral structures that trigger voluntary movements to activate the vasomotor center and 2) the reflexes initiated by mechanic and metabolic changes in a working muscle. The second mechanism of the sympathetic system activation was termed ergoreflex. Ergoreflex controls hemodynamics primarily through activation of mechanosensitive afferents to first of all inhibit the tonic vagal effects on the heart manifested by a leap of heart rate during loading. Activation of chemosensitive afferents comes with some delay in pace with metabolites accumulation in muscles and leads to growth of the efferent sympathetic activity and rise of blood pressure. The metabolic reflex effect is particularly high in the event of muscle fatigue. This review deals with the mechanisms underlying the ergoreflex and their adaptation to hypodynamia, physical loading, and also some pathologies.