Cardiac atrial natriuretic peptide (ANP) in rat dams and fetuses developed in space (NIH-R1 and NIH-R2 experiments)

NIH-R1 and R2 missions, conducted by NASA, allowed us to study the effects of the microgravitational environment 1) on cardiac ANP in pregnant rats, spaceflown for 11 days and dissected after a 2-day readaptation to Earth's gravity, after natural delivery, and 2) on maturation of cardiac ANP system in rat fetuses developed for 11 days in space and dissected on the day of landing, 2 days before birth. Immunocytochemical and electron microscopy analyses showed a typical formation of ANP-containing granules in atrial myocytes, in both dams and fetuses. Using competitive RT-PCR and radioimmunoassays, we observed that, after 2 days of readaptation to Earth's gravity, cardiac ANP biosynthesis of rat dams flown in space was increased by about twice, when compared to Synchronous and Vivarium Control rats, More obviously, rat fetuses developed in space and dissected on the day of landing displayed an altered maturation of cardiac ANP, evidenced by an increased mRNA biosynthesis (by about 6 fold, p < 0.05), whereas the cardiac ANP storage was slightly reduced (by about twice, p < 0.05) in both Flight and Synchronous Control groups, in comparison with Vivarium Control rats. These last results suggest that ANP metabolism during development is impacted by the microgravitational environment, but also by the housing conditions designed for space flight.