Urinary cyclic AMP excretion during volume expansion in the rat

We have studied the effect of volume expansion with 0.9% saline solution (10% body weight in 1 h) on urinary cyclic AMP excretion in rats. In nine normal rats urinary cyclic AMP excretion (picomoles/minute) was 113.9+/-9.9 during the control period, rose significantly to 171+/-20 during the first 10 min of expansion, came back to control levels for the next 20 min, and finally decreased significantly to 48.8+/-13.2 at the end of the expansion period. In nine parathyroidectomized rats control cyclic AMP excretion was 78.0+/-4.5, did not rise during expansion, and decreased significantly (to 33.7+/-4.1) at the end of the expansion period. The transient increase in cyclic AMP excretion observed in normal rats could be due to parathyroid hormone release. Our studies do not allow us to explain the subsequent decrease noted in both groups.