Influence of progesterone on the sodium and potassium concentrations of rat uterine fluid investigated by microdialysis.

Currently used techniques to measure the chemical composition of the rat uterine fluid are accompanied by interference with the physiology of the uterus, and the sampling procedure creates a methodological problem as the amount of uterine fluid is small. The aim of the present study was to investigate the utility of a new in vivo technique, microdialysis. A microdialysis probe, which functions as an 'artificial blood vessel' was implanted into the uterine lumen and perfused with a Ringer solution. This perfusion technique makes it possible to study ions and other components in the uterine fluid without withdrawal of any liquid. Compared to previous techniques it offers the advantage of continuous monitoring of the chemical composition of the uterine fluid over time. The sodium and potassium concentrations in the uterine fluid of 10 rats were monitored during oestrous. After 1-2 h of baseline perfusion an intramuscular injection of progesterone was given. The mean sodium concentration was 124.9 +/- 2.4 mEq/l before and increased in all 10 rats to 133.9 +/- 2.3 mEq/l (p less than 0.001) after injection. The mean potassium concentration was 22.3 +/- 2.4 mEq/l before and decreased to 17.9 +/- 2.1 mEq/l (p less than 0.001) after injection. This study proves the validity and applicability of microdialysis to the monitoring of chemicals in uterine fluid and especially to follow dynamic changes.