H2 gas clearance technique for separating rat uterine blood flow into endometrial and myometrial components

The H2 gas clearance technique was employed to measure uterine blood flow (UBF) in ovariectomized rats. A needle-type platinum electrode (125 microns diam) was inserted into the rat uterine wall to measure the tissue blood flow surrounding the electrode. The electrode can be placed in individual layers of the uterus to measure the endometrial blood flow (EBF) or the myometrial blood flow (MBF). By use of this technique, baseline EBF and MBF were 37.8 +/- 3.53 (n = 21) and 47.2 +/- 4.56 (n = 5) ml.min-1.100 g-1, respectively, with an EBF/MBF ratio of 0.8. Intravenous bolus injection of 17 beta-estradiol (1 microgram/kg) induced a significant increase in UBF. Phenylephrine, an alpha-adrenergic receptor agonist, reduced UBF. In some animals, a second platinum electrode was used to measure gastric mucosal blood flow simultaneously with UBF. While 17 beta-estradiol selectively increased UBF, pentagastrin selectively increased gastric mucosal blood flow. To further validate the baseline UBF distribution between endometrial and myometrial layers, iodo[14C]antipyrine autoradiography was employed. With the iodo[14C]antipyrine technique, the EBF/MBF ratio was 0.91 +/- 0.07 (n = 5), which is similar to that obtained with the H2 gas clearance technique.