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

Abstract

BackgroundTo elucidate further from the biomechanical aspect whether microgravity-induced cerebral vascular mal-adaptation might be a contributing factor to postflight orthostatic intolerance and the underlying mechanism accounting for the potential effectiveness of intermittent artificial gravity (IAG) in preventing this adverse effect.Methodology/Principal FindingsMiddle cerebral arteries (MCAs) were isolated from 28-day SUS (tail-suspended, head-down tilt rats to simulate microgravity effect), S+D (SUS plus 1-h/d −Gx gravitation by normal standing to simulate IAG), and CON (control) rats. Vascular myogenic reactivity and circumferential stress-strain and axial force-pressure relationships and overall stiffness were examined using pressure arteriography and calculated. Acellular matrix components were quantified by electron microscopy. The results demonstrate that myogenic reactivity is susceptible to previous pressure-induced, serial constrictions. During the first-run of pressure increments, active MCAs from SUS rats can strongly stiffen their wall and maintain the vessels at very low strains, which can be prevented by the simulated IAG countermeasure. The strains are 0.03 and 0.14 respectively for SUS and S+D, while circumferential stress being kept at 0.5 (106 dyn/cm2). During the second-run pressure steps, both the myogenic reactivity and active stiffness of the three groups declined. The distensibility of passive MCAs from S+D is significantly higher than CON and SUS, which may help to attenuate the vasodilatation impairment at low levels of pressure. Collagen and elastin percentages were increased and decreased, respectively, in MCAs from SUS and S+D as compared with CON; however, elastin was higher in S+D than SUS rats.ConclusionsSusceptibility to previous myogenic constrictions seems to be a self-limiting protective mechanism in cerebral small resistance arteries to prevent undue cerebral vasoconstriction during orthostasis at 1-G environment. Alleviating of active stiffening and increasing of distensibility of cerebral resistance arteries may underlie the countermeasure effectiveness of IAG.

Sex differences in the structure and function of rat middle cerebral arteries

“…The passive mechanical properties of the MCA including wall thickness (WT), cross-sectional area (CSA), wall-to-lumen ratio, distensibility, incremental distensibility, circumferential wall strain, circumferential wall stress, and myogenic tone were calculated at each transmural pressure step using the equations (see Fig. 5 A ) described previously ( 4 , 9 , 12 , 20 , 34 , 38 , 40 , 59 ). The slopes (β-values) of the elastic modulus (stress-strain curves) were compared to determine the arterial stiffness.…”

Influence of dual‐specificity protein phosphatase 5 on mechanical properties of rat cerebral and renal arterioles

“…The following vascular mechanical properties were calculated using equations described previously (Baumbach, Heistad, & Siems, ; Briones et al, ; Cheng et al, ; Dobrin, ; Gonzalez et al, ; Hudetz, ; Izzard et al, ):where ID 0Ca 5mmHg is inner diameters obtained at the perfusion pressure of 5 mmHg in PSS 0Ca .…”

Spaceflight-Induced Intracranial Hypertension and Visual Impairment: Pathophysiology and Countermeasures

“…MCAs from IAG rats show greater distensibility in their passive state which may reduce the rightward shift of the bottom part of the cerebral autoregulatory curve. In this regard, distensibility represents compliance in a uniaxial stress state (56). However, recent findings with the basilar arteries isolated from space-flown mice are quite different from those from rats exposed to simulated microgravity on Earth (266,278).…”

“…It is worth mentioning that daily simulated IAG by -G x gravitation for 60 min, or 4% of the total unloading time, is sufficient to prevent vascular adaptation during 28 days of simulated microgravity, even though the minimum effective exposure time is yet undefined. In addition, the effectiveness of simulated IAG in preventing vascular adaptation is further demonstrated in an ex vivo study using artery culture (95) for biomechanical studies on isolated mesenteric and middle cerebral arteries (56,94) and for an integrative study with conscious rats (315). It seems that central to these mechanisms is the extracellular matrixintegrin-cytoskeletal axis, which provides anchoring mechanisms for cell-cell and cell-extracellular matrix interactions (166,193).…”