Assessment of the accuracy of quantitative urine collection in mink (Mustela vison) using osmotic pumps for continuous release of p-amino-hippuric acid and inulin

Abstract

A method is described to assess the accuracy of quantitative collection of urine in small experimental animals using implanted Alzet osmotic pumps for continuous release of specific urinary markers. The nominal pumping rate (10.00 +/- 0.15 microliters/h; mean +/- SEM) of 10 osmotic pumps was verified (9.96 +/- 0.12 microliters/h) in a 10-day in vitro assay in isotonic saline at 39.0 degrees C. Ten adult female mink (1100 +/- 34 g) had a 2-ml osmotic pump implanted intraperitoneally for 7 days while maintained in metabolic cages on a conventional mink diet. In 5 mink the pumps contained [3H]-labelled p-aminohippuric acid (PAH) only. The remaining 5 animals received a pump containing [3H]-PAH and [14C]-labelled inulin. The experiment was well tolerated by all animals. In fed animals, the amount of urine collected per day was not influenced by the osmotic pumps, whereas 24 h of fasting (water allowed) caused a dramatic fall in urinary volume. In 4 consecutive 24-h collections of urine (n = 10 animals) the recovery of [3H]-PAH was 70.8 +/- 3.6% (range: 52.0-87.2%), and urinary plus faecal water (= total) recovery of [3H]-PAH averaged 77.0 +/- 3.7% (range: 60.3%-94.3%). For [14C]-inulin (n = 5 animals) the urinary and total recoveries were 68.4 +/- 2.2% and 77.2 +/- 2.4%, respectively. In urine the 14C to 3H counts-ratio was almost identical to that of the infusion solution, indicating that metabolic decomposition of the markers was negligible. The results indicate that the daily recovery of suitable urinary markers, released by implanted osmotic pumps, provides a reproducible and valid measure of the accuracy achieved in quantitative collection of urine in mink and probably also in other animal species. Hence, this technique may be useful in future studies on animal nutrition and/or drug disposition.