Evidence for a Permeability Barrier between Blood and Uterine Luminal Fluid in Estrogen-Treated, Immature Rats1

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Abstract
Experiments were conducted to investigate the existence of a permeability barrier between blood and the luminal fluid that accumulates in the uterus of immature rats treated with estrogen. The effect of time of autopsy after single i.v. injections of various radioactive substances on the levels of radioactivity in uterine luminal fluid (ULF), cisterna chyli lymph and serum was determined. The radioactive substances, in order of increasing molecular weight, were tritiated water, [14C]-urea, [3H]-sucrose, [3H]-inulin and [125I]-bovine serum albumin. The levels of radioactivity in serum decreased with time for all radioactive substances except tritiated water in which case they did not change. When tritiated water and [14C]-urea were injected, the levels of radioactivity did not differ significantly between ULF and serum. For [3H]-sucrose and [3H]-inulin, the levels of radioactivity in ULF were significantly lower than those in serum except at the last time studied (120 min) at which time there was no significant difference. When [3H]-sucrose was injected, the levels of radioactivity in ULF were not significantly different from 0 and, for [3H]-inulin, there was no significant change with time. For [125I]-bovine serum albumin, the levels of radioactivity in ULF were lower than those in serum even at 8 h. For all radioactive substances, the levels of radioactivity in lymph decreased with time except for tritiated water in which case there was no change. In general, the levels of radioactivity in lymph were significantly lower than those in serum and were higher than those in ULF. The results of the present experiments provide evidence for the existence of a blood-ULF permeability barrier in rats which is selective according to molecular weight.