Daily short-period gravitation can prevent functional and structural changes in arteries of simulated microgravity rats

Abstract

This study was designed to clarify whether simulated microgravity-induced differential adaptational changes in cerebral and hindlimb arteries could be prevented by daily short-period restoration of the normal distribution of transmural pressure across arterial vasculature by either dorsoventral or footward gravitational loading. Tail suspension (Sus) for 28 days was used to simulate cardiovascular deconditioning due to microgravity. Daily standing (STD) for 1, 2, or 4 h, or +45 degrees head-up tilt (HUT) for 2 or 4 h was used to provide short-period dorsoventral or footward gravitational loading as countermeasure. Functional studies showed that Sus alone induced an enhancement and depression in vasoconstrictor responsiveness of basilar and femoral arterial rings, respectively, as previously reported. These differential functional alterations can be prevented by either of the two kinds of daily gravitational loading treatments. Surprisingly, daily STD for as short as 1 h was sufficient to prevent the differential functional changes that might occur due to Sus alone. In morphological studies, the effectiveness of daily 4-h HUT or 1-h STD in preventing the differential remodeling changes in the structure of basilar and anterior tibial arteries induced by Sus alone was examined by histomorphometry. The results showed that both the hypertrophic and atrophic changes that might occur, respectively, in cerebral and hindlimb arteries due to Sus alone were prevented not only by daily HUT for 4 h but also by daily STD even for 1 h. These data indicate that daily gravitational loading by STD for as short as 1 h is sufficient to prevent differential adaptational changes in function and structure of vessels in different anatomic regions induced by a medium-term simulated microgravity.

Role of Low Energy Expenditure and Sitting in Obesity, Metabolic Syndrome, Type 2 Diabetes, and Cardiovascular Disease

“…Application of the rat hindlimb unloading model over an 11-day period to identify mechanisms of lipid dysregulation during reduced standing/nonexercise ambulation have also had this concern (1) and thus have employed an intermittent phase each day where the rat is returned to the standing position. At least in rats, intermittent reloading was able to successfully prevent skeletal muscle atrophy (1) and adverse changes in both myocardial contractility (66) and the cerebral vasculature (67). Lipoprotein lipase function.…”

Mechanics and Composition of Middle Cerebral Arteries from Simulated Microgravity Rats with and without 1-h/d –Gx Gravitation

“…The technique of tail suspension with modification from our laboratory has been described in detail previously [22], [28]. Briefly, the rats were maintained in an about −30° head-down tilt position with their hindlimbs unloaded to simulate the cardiovascular effect of microgravity.…”

“…Nevertheless, the adaptation changes yet exhibits regional differences along different arterial segments in cerebral circulation. As we have shown, in the case of basilar artery, a large cerebral artery that also contributes importantly to cerebrovascular resistance [23], S+D can prevent both the enhanced vasoreactivity and hypertrophic remodeling that might occur due to SUS alone [22]; however, in MCA, a proximal resistance artery, it can prevent only hypertrophy but not the enhanced myogenic tone and increased vasoreactivity [21], [24]. To evaluate further the countermeasure effectiveness of IAG on cerebral small resistance arteries, it is also essential to understand their active and passive mechanical properties.…”

“…And it has also been demonstrated that these adaptation changes are triggered and maintained by a sustained increase of transmural pressure (TMP), but not increase of flow and volume, in the cerebral vessels [4], [18]–[19]. In addition, our work has shown further that 1 h/d –G x (dorsoventral) gravitation by restoring the rat's orthostatic standing posture and hence the normal TMP distribution along the arterial vasculature (S+D), which mimics the IAG countermeasure, is surprisingly effective in preventing hypertropic remodeling in cerebral arteries [20]–[22]. Nevertheless, the adaptation changes yet exhibits regional differences along different arterial segments in cerebral circulation.…”

Does Chronic Experimental Head-Down Tilt Alter Intramural Innervation Density of Limb Blood Vessels?

“…This daily free exercise might have influenced the vascular innervation density by augmenting the countermeasure effect of movement in the tilt cage. Sun et al [26] found that the depression in the vasoconstrictor responsiveness of rat femoral arterial rings induced by 4 weeks of tail suspension was prevented either by daily HUT for 4 h or by being horizontal for 1 h. In our previous head-up tilt experiments, the same 1 h grooming period was provided for the animals, and significant differences have been observed in the same parameters between control and tilted animals [2]. Contrary to tail suspension, however, the animals in our experiments were freely moving in the tilt cages throughout the whole tilting period [20,21], and we do not believe that the additional movement during the daily grooming period could substantially influence the observed innervation densities.…”