Urea and osmotic excretion in rats exposed to chronic centrifugation

Background: A reduction in vasopressin was attributed to the initial diures is reported in rats exposed to chronic centrifugation. However, it was sugg ested that urea may also contribute an osmotic component to this observed d iuresis. Hypothesis: increased urea excretion will contribute to osmotic ex cretion during chronic centrifugation, which may be partly responsible for the initial diuresis previously observed. Methods: Eight Sprague-Dawley rat s were centrifuged (12 d at -2Gx) and eight were used as a control group. D aily urine samples were collected and an aliquot measured for excreted solu tes and aldosterone. Results: Urine volume was elevated over the first 7 d of centrifugation with a peak on day 4. Urea and osmotic excretion were ele vated over the first 5 d. Excreted Na+ was elevated on days 1 and 2, which coincided with an increase in excreted aldosterone over the first 3 d of ce ntrifugation. Urea excretion accounted for up to 54% of the increase in osm otic excretion during the initial portion of centrifugation suggesting that urea was, in part, responsible for the observed increase in urine output d espite a reduction in water consumption. Following the first day of centrif ugation, aldosterone appears to regulate Na+ as suggested by the reduction in Na+ excretion between days 2 and 3 when aldosterone excretion was elevat ed. Conclusions: It would appear that centrifugation induced an acute incre ase in protein catabolism as indicated by the increase in urea excretion wh ich resulted in an increase in obligatory water loss. This increased diures is may have acute consequences on the hydration state of centrifuged rats.