The cardiovascular system is adapted to gravity, and reactions to the loss of gravity in space are presumably dependent on body size. The dependence of hematological parameters and body fluid volume on simulated microgravity have never been studied as an allometric function before. Thus, we estimated red blood cell (RBC), blood and extracellular fluid volume in hindlimb-unloaded (HLU) or control (attached) mice, rats and rabbits. RBC decrease was found to be size independent, and the allometric dependency for RBC loss in HLU and control animals shared a common power (-0.054±0.008) but a different coefficient (8.66±0.40 and 10.73±0.49, respectively,<0.05). Blood volume in HLU animals was unchanged compared with that of controls, disregarding body size. The allometric dependency of interstitial fluid volume in HLU and control mice shared (1.02±0.09) but had different powers (0.708±0.017 and 0.648±0.016, respectively, <0.05), indicating that the interstitial fluid volume increase during hindlimb unloading is more pronounced in larger animals. Our data underscore the importance of size-independent mechanisms of cardiovascular adaptation to weightlessness. Despite the fact that the use of mice hampers application of a straightforward translational approach, this species is useful for gravitational biology as a tool to investigate size-independent mechanisms of mammalian adaptation to microgravity.
Introduction Low sexual desire is a frequent sexual problem in women, with only one drug for the condition approved by the Food and Drug Administration. Aim To evaluate the ability of a novel synthetic peptide, BP101, to facilitate sexual behavior after intranasal administration or infusion into certain brain areas in female rats. Methods Bilaterally ovariectomized female rats, primed with a suboptimal combination of estradiol benzoate (EB) and progesterone, were used as a model of low sexual motivation. Sexual behavior was tested with stud male rats after acute (experiment 1) or long-term (experiment 2) intranasal administration of BP101 or peptide infusion into the olfactory bulb, medial preoptic area, ventromedial hypothalamic nucleus, or ventral tegmental area (experiment 3). Main Outcome Measures Frequency of solicitations (SF), as an indicator of sexual motivation in female rats, and lordosis frequency and ratio, as measurements of female consummatory sexual behavior. Results Acute intranasal BP101 administration moderately increased SF, with the highest tested dose of 300 μg/kg causing an 80% increase. Female rats receiving BP101 75 or 300 μg/kg daily on days 6 to 16 of the peptide administration displayed twofold higher SF compared with the placebo-treated animals, an increase comparable to optimally hormone-primed female rats. Infusion of BP101 1 and 5 μg per rat into the medial preoptic area, but not into the olfactory bulb, ventromedial hypothalamic nucleus, or ventral tegmental area, increased SF in female rats supplemented with EB 10 or 20 μg. The effect was relatively more pronounced in female rats receiving EB 10 μg (≈300%) compared with EB 20 μg (≈50%) with direct brain infusions. Conclusion BP101 displays a potent stimulatory effect on sexual motivation in the female rat, and the medial preoptic area seems to be the site of its action. BP101 is effective in female rats receiving different hormone supplementations, making the present data generalizable to pre- and postmenopausal women with hypoactive sexual desire.
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