The microsphere technique in anaesthetized and awake pregnant guinea-pigs: reproducibility of repeated blood flow measurements.

Repeated microsphere injections are extensively employed for measurements of uteroplacental blood flows in experimental animals. However, this technique has not been systematically validated in pregnancy. In the present series of experiments the effects of three consecutive microsphere injections on central haemodynamics and regional blood flows were studied in 43 late pregnant guinea-pigs. In group A (n = 13) experiments were carried out in the awake chronically catheterized animal. In group B (n = 8) animals were studied under anaesthesia. In two additional anaesthetized groups reference withdrawal rate (C, n = 7) and the amount of injected spheres (D, n = 7) were increased 2-3 fold. Cardiac output, mean arterial blood pressure, heart rate as well as regional blood flows to placenta, ovaries, kidneys, heart, liver and carcass remained unaltered in all protocols. Myoendometrial blood flow increased in group A and C and a similar pattern could be demonstrated in group B and D but was not statistically significant. Adrenal blood flow was enhanced in groups A and C and brain blood flow increased in group C and D. The gastrointestinal tract especially the stomach was sensitive to repeated microsphere injections since blood flow reductions were apparent in all groups but were statistically significant only for groups A and D. In group E (n = 8), the three microsphere labels were injected simultaneously. The coefficients of variability for these blood flow measurements were in the range of 3.6-6.8% for different organs. It is concluded that repeated microsphere injection in an ideal method to measure placental blood flow. However, the technique may provide inaccurate results with respect to the myoendometrium and gastrointestinal tract.