To evaluate the promising effectiveness of intermittent artificial gravity (IAG) in preventing cardiovascular deconditioning (CVD) due to microgravity, particularly to elucidate its underlying mechanisms, a multi-level, mechanistic study has been conducted in our laboratory. Tail-suspended, head-down tilt rat model (SUS) was used to simulate cardiovascular effects of microgravity. Daily short-duration –Gx gravitation by standing (STD) was adopted to simulate the countermeasure effect of IAG. In the past two decades, several ground-based human studies have provided promising data demonstrating the effectiveness of daily +GZ gravitation in counteracting the post-bed rest cardiovascular deconditioning (CVD) [1]. Our previous work has shown that daily 1-h STD providing a dorso-ventral gravitation vector (-Gx) is sufficient to prevent both the myocardial contractility depression [2] and the differential adaptation changes in the structure and function of cerebral and hindquarter medium-sized arteries [3] that might occur due to a 28-d SUS alone. Recently, the surprising effectiveness of 1-h/d has been further elucidated with the large, elastic arteries.

Moreover, our recent study has suggested that conscious rats manifest post-suspension hypertension after a medium-term SUS and daily 1-h -Gx gravitation can prevent its occurrence. Regarding the mechanisms that modulate these region-specific vascular adaptations, we have revealed that, at least, vascular local renin-angiotensin system (L-RAS) and arterial smooth muscle ion channel remodeling are involved in. It has been shown that the expression of angiotensinogen (Ao) and angiotensin II receptor type 1 (AT1R) are upwards and downwards regulated, respectively, in the wall tissue of the fore-body/cerebral and hind-body arteries after a 28-d SUS. And the differential changes of the two key components of L-RAS in different vessels can be fully prevented by daily 1-h STD. However, the countermeasure effect of 1-h/d STD on arterial L-type Ca2+ channel (CaL) depends on the kind of the vessel examined. SUS for 28 d resulted in a decrease and an increase in CaL current density and protein expression in the cerebral and small mesenteric arterial myocytes (VSMCs). Daily 1-h STD prevented the downward regulation of CaL function and expression in small mesenteric arterial VSMCs due to SUS, but it was totally ineffective in the case of CaL in cerebrovascular VSMCs. The resistance of CaL of cerebral VSMCs to 1-h/d STD intervention seems to imply that the mechanism coupling increased transmural pressure to augmented myogenic tone can be dissociated from that for other functional and structural adaptations. Our recent findings on myogenic tone of small arteries and arterioles are consistent with this speculation. Refs: [1] Zhang LF. J Gravit Physiol 12: P1-P4, 2005. [2] Zhang LF, et al. J Appl Physiol 95: 207-218, 2003. [3] Sun B, et al. J Appl Physiol 97:1022-1031, 2004. [4]Xue JH, et al. Am J Physiol Heart Circ Physiol 293: 691-701, 2007.

Introduction. It has been shown that simulated weightlessness in rats induced an endothelial dysfunction. The mechanisms remain unclear. Changes in hydrostatic pressure, decrease in general hemodynamics could be involved. We hypothesized that translocation of LPS from gut could occur in simulated weightlessness models and could be associated with endothelial dysfunction.

Methods, Results. We indirectly estimated translocation of LPS by measurement of IL-6 level after LPS injection. A decreased response to LPS injection could be the result of a previous translocation of LPS. Weightlessness was modelled by head-down tilt at -45° (HDT) 4 hours per day for a week, after 2 weeks of training. In a first experiment, we measured the basal level of IL-6 (ELISA) in a control group (0,55±0,02 pg/ml, n = 5) and in the HDT group (0,59 ± 0,02 pg/ml, n = 5). In a second experiment, the response to single LPS injection was significantly increased in control group until 2,18 ±0.04 pg/ml (n = 7). A second injection of LPS in the control group 7 days later induce a significant decrease of the IL-6 response (1,99 ±0,1 pg/ml, n = 7). After 7 days of HDT, the response induced by a single injection of LPS was similar to the latter group (1,89±0.06 pg/ml, n = 7).

Discussion, conclusion. We could interpret those data by a global decrease of immune system response, or by a previous LPS translocation induced by HDT. LPS translocation could participate in endothelial dysfunction as already demonstrated. Further analysis would be necessary to confirm the last hypothesis.

Our previous works showed that there is a significant increase in nitrite and nitrate content of cerebral arteries of 3-week hindlimb unweighting (HU) rats, but HU treatment had no effect on nitric oxide synthase (NOS) expression. Nitrite and nitrate are stable metabolites of NO, and this result suggests that NOS activity and NO production may be increased by HU in the cerebrovasculature and may result in a enhanced endothelium-dependent dilatory responses in cerebral artery of hindlimb unweighting rats. But our previous work did not observe the increased endothelium mediated relaxation in cerebral arteries by 4-week HU, and on the contrary, recent works reported that HU diminished the endothelium-dependent relaxation in cerebral arteries. Increased basal tone, enhanced vasoconstriction and decreased endothelium-dependent relaxation indicated a downregulation of the NOS signal, which conflicts with increased nitrite and nitrate content of cerebrovasculature in HU rats.

The aim of this work is to investigate the effects of HU on endothelium mediated relaxation and find the possible mechanisms which may result in the conflict. Twenty male healthy SD rats, which body weight ranged from 250g to 280g, were divided into control and hindlimb unweighting simulated microgravity groups randomly. After three weeks, the basilar artery was isolated and arterial dilatory responsiveness were examined in vitro using isolated arterial rings from rats. And the Superoxide Anions Level was detected by oxidation-sensitive dye dihydroethidium and laser scanning confocal microscope.

The data showed: Dilatory responses of basilar arterial rings to Acetylcholine(10^-10~10^-4 mol/L ) was decreased in simulated microgravity rats as compared with that of controls, but dilatory responses of isolated arterial rings to Sodium Nitroprussid (10^-10~10^-4 mol/L ) was similar in both simulated Microgravity rats and control rats, and stronger superoxide anions signals were detected in basilar artery from HU rats, while compared with that of control rats. These results indicate that endothelium-dependent relaxation of basilar artery has been diminished by 3-week hindlimb unweighting, and increased superoxide anions levels may contribute to this alteration.

It is known that rats subjected to various accelerations (+G) exhibited increased plasma epinephrine (EPI) and norepinephrine (NE) levels. However, the collection of blood was performed after a centrifugation finished and therefore the levels could be affected by the process of deceleration.

The aim of this study was to evaluate plasma EPI and NE levels in blood collected directly during the centrifugation after reaching different G (2-6), using remote controlled equipment. Animals placed into the centrifuge cabins had inserted polyethylene tubing in the tail artery, which was connected to a pre-programmed device for blood withdrawals. Plasma EPI levels showed a huge, hypergravity level dependent increase. After the last blood collection was completed during hypergravity, the centrifuge was turned off and another blood sampling was performed immediately after the centrifuge stopped (10 min). In these samples plasma EPI showed significantly lower levels compared to centrifugation intervals. Plasma NE levels were increased after 6G only.

Repeated exposure to hypergravity (8 days for 60 min) eliminated the increase in plasma EPI but did not affect plasma NE levels. To explain these findings we measured changes in mRNA levels of catecholamine biosynthetic enzymes tyrosine hydroxylase (TH), dopamine-β-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT) in the adrenal medulla (AM) and stellate ganglia (SG) of rats exposed to continuous hypergravity (2G) for 6 hrs, 1, 3 and 6 days. In AM , TH, DBH and PNMT mRNA levels were significantly increased in intervals up to 3 days, however, after 6 day hypergravity exposure, no significant changes were found. In SG, no significant changes in gene expression of these enzymes were seen both after a single or repeated hypergravity exposure.

Thus, our data show that hypergravity highly activates the adrenomedullary system, whereas the sympathoneural system is not significantly activated. This statement is in a good agreement with the finding of increased gene expression of catecholamine enzymes in AM and unchanged expression in SG during hypergravity intervals up to 3 days. Gene expression of these enzymes however, did not show any significant increases after 6 day exposure to hypergravity, which correlated well with the reduced plasma EPI levels in such animals.

In conclusion, our results demonstrate that during repeated or continuous exposure of the organism to hypergravity, the adrenomedullary system is adapted, whereas sympathoneural system is not affected. Supported by Slovak grants VEGA 2/0133/08 and APVV-0148-06

The decrease of the single fiber contractile properties is usually found in m. soleus of humans and rodents exposed to spaceflight conditions [Stevens et al, 1993; Widrick et al, 1998 and others]. It is thought that the fiber size reduction and the titin and nebulin degradation might be among the main factors determining the decrease of peak Ca-induced tension and rightward shift of the "calcium-tension" curve.

We studied the effects of 12-day spaceflight aboard the satellite "Foton-M3" on soleus and tibialis anterior fibers of the Mongolian gerbils. This species is characterized by the much greater capability to urine concentration than other rodents and thus increased content of the osmotically active substances in blood. The samples were isolated after 24 hour after the landing. The skinned soleus fiber diameter in flight animals was found to be 19.7% decreased (30.5±1.6 microns vs 38.0±1.9.0 microns in controls, p<0.05). The P0 (peak isometric tension) was also significantly decreased by 21.8% in flight animals (20,8±1,2 mg vs 26,6±2,1 mg in controls, p<0.05). pCa50 was tended to be slightly decreased in flight animals, although the difference was not significant.

Thus in soleus fibers the contractility changes along with the fiber diameter were less pronounced than in rats after 14 flight aboard the biosatellite (e.g. Cosmos 2044 - Stevens et al., 1993). The same parameters in m. tibialis anterior fibers in flight animals demonstrated the insignificant changes.

At the same time the relative content of titin (T/MyHC) and nebulin (nebulin/MyHC) in soleus and m. tibialis anterior of flight animals didn't differ from the indices of the control gerbils. These data unexpectedly differ from the data obtained in rats and humans after exposure to simulated weightlessness. Many authors observed the dramatic decrease of the cytoskeletal proteins content under these conditions [Toursel et al, 2002; Shenkman, Podlubnaya et al, 2002; Shenkman et al, 2004]. Thus, the contractility losses and fiber size reduction in space-flown gerbils were less pronounced than in rats and were not accompanied with the changes in sarcomeric cytoskeletal proteins.

The work was supported by the Federal Space Agency ("Roskosmos"). The authors are grateful to the unified team involved in the preparation and performing the space mission Foton-M3.

In the 12-day flight of the Russian spacecraft Foton-M3 (September 14-26, 2007) we performed an experiment with Mongolian gerbils (that belong to the hamster family). We chose those animals due to two reasons. Firstly, gerbils can survive for a long time without drinking water; therefore, we could fly them in a housing unit containing no water supply. Secondly, we could investigate the role of water metabolism in systemic adaptation of the animal body to microgravity, taking into consideration gerbil's physiology. In both flight and control experiments we used 12 males aged 4-4.5 months weighing about 50 g at launch. In space the gerbils were housed in a self-contained facility with its own life support system. In the facility the environmental parameters were as follows: pO2 = 143-156 (mean 150) mm Hg, pCO2 - not more than 0.76 (mean 0.64) mm Hg, temperature = 23-28 (mean 26.7) 0C, and RH = 29% at the beginning and 57% at the end of flight (mean 39%).

During flight the animals were provided with food bars made of natural products and containing about 20% water. The day-night cycle was 12:12 hours. During the daytime video recording was performed continuously. Three hours after landing we removed the animals from the housing unit and delivered them to Moscow the same day by a chartered flight. The next day we performed animal dissection and tissue preparation for morphological and histochemical examinations. Based on video recordings, we can say that during the first 3 days in microgravity the animals moved in a fast and chaotic manner and never attempted to stabilize themselves by grasping the cage. During the next 3 days the animals began moving slowly and managed to eat food bars floating across the cage. Many animals spent most of the time being clustered in one of the corners of the cage holding to its mesh. Based on animals’ behavior we can conclude that their adaptation to the spacecraft environment developed slowly and became noticeable by flight day 10-12. This suggests that the vestibular system of Mongolian gerbils is highly sensitive to the gravity vector.

Skeletal muscle adapts to sustained reduced activity through the process of muscle atrophy, which results in lower mass and ultimately a decrease in strength and resistance to fatigue. For ill or injured patients requiring extended bedrest and astronauts assigned to long-duration spaceflight missions, disuse muscle atrophy can significantly threaten health and safety. Exercise, while an effective means to maintain muscle function, is not always a viable option for bedridden patients or for astronauts. Although a safe and effective pharmaceutical countermeasure to muscle loss is not currently available, such a treatment could replace or complement exercise as an effective therapeutic. Recent research has revealed the myostatin pathway as an exciting potential new target for pharmaceutical development. Myostatin is a negative regulator of skeletal muscle, and expression is increased in a number of muscle wasting disease states. An anti-myostatin peptibody developed to inhibit myostatin was evaluated in this study in combination with the mouse hindlimb suspension model. Mice were divided equally into four groups (n=18/group): Placebo control, drug treated (MD), 14-days hindlimb suspension (HS), or HS plus drug treatment (HSD). Hindlimb suspension alone significantly decreased lean body mass (LBM) by 5.0% (p<0.001) and the mass of individual hindlimb muscles (quadriceps, tibialis anterior, and gastrocnemius) by 10.5-14.4% compared to non-suspended controls. Drug treatment alone increased LBM 9.1% (p<0.001) and increased hindlimb muscles by 9.5-11.4% compared to placebo controls. For HS combined with drug treatment, there was no significant difference between the HSD and placebo control groups in LBM or tibialis anterior mass. The quadriceps and gastrocnemius in the HSD group averaged 3.0% greater mass than the equivalent muscles in the HS group. A functional strength assessment showed that HS alone caused a significant decreased in hindlimb strength, but treatment with the drug increased hindlimb strength both in the MD and HSD groups compared with their respective controls. These data demonstrate that the anti-myostatin peptibody can be an effective treatment for disuse muscle atrophy. This or a similar therapeutic targeting the myostatin pathway may benefit a number of patients and astronauts alike.