Spaceflight and Biohistochemical Alterations of Antigravity Soleus Musclein Spontaneously Hypertensive Rats (SHR) to Dietary Low and High-Calcium Intake

Dietary calcium supplementation has been to alter calcium metabolism and prevent hypertension in spontaneously hypertensive rats (SHR). Likewise, microgravity alters calcium metabolism. It is possible that the alteration of calcium metabolism caused by different levels of dietary calcium or microgravity change skeletal muscle properties. The purpose of this investigation was to determine whether spaceflight and/or dietary calcium causes alteration of properties in skeletal muscle from SHR. Nine-week-old male SHR, fed either high- (2.0%, HCa) or low-calcium (0.2%, LCa) diets, were flown on an 18-day shuttle flight. They were assigned to four groups (n=7/group): control (ground-based) with LCa or HCa, spaceflight with LCa, or HCa. After the spaceflight, the soleus muscle was dissected and analyzed histochemically and biochemically. Spaceflight caused a slow-to-fast fiber transition that did not differ between diet groups. Cross-sectional areas of a single muscle fiber were not modified by dietary calcium in either control or spaceflight groups. The changes of succinate dehydrogenase activity in Type I fibers in response to spaceflight was higher in the LCa diet (+23.7%) than the HCa diet group (+12.8%). Conversely, in Type IIa fibers the response to spaceflight was lower in the LCa (-9.6%) than the HCa (-19.2%) group. These findings suggest that the effect of dietary calcium on fiber type composition and fiber size may be smaller than that of spaceflight, while dietary calcium may inhibit the alteration of oxidative metabolism of muscle fibers by spaceflight in SHR.