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. 1972 Mar;221(2):371–387. doi: 10.1113/jphysiol.1972.sp009756

Accumulation and apparent active transport of prostaglandins by some rabbit tissues in vitro

L Z Bito
PMCID: PMC1331338  PMID: 5020982

Abstract

1. Slices or bits of rabbit tissues, not exceeding 100 mg, were incubated in tissue culture medium containing tritium-labelled prostaglandin ([3H]PG). In some experiments, incubation medium also contained saturating concentrations of an unlabelled prostaglandin (PG), or [14C]-sucrose for determination of extracellular space. At the end of the incubation period, usually 1 hr, the tissues were removed and weighed, and their 3H (and 14C) content were determined along with that of a unit volume of medium.

2. Tissues known to play a central role in PG metabolism (lung and liver) and in its excretion (kidney cortex) and tissues which have a known function in blood-brain and blood-ocular barriers (choroid plexuses and ciliary processes) show a large accumulation of 3H when incubated in a medium containing [3H]PGE1. In addition, tissues of the female reproductive tract, and the aorta of the rabbit show similar 3H accumulation. When uncorrected for tissue solid content or extracellular water volume, the extent of this accumulation is two- to sixfold. Calculated on the basis that all excess 3H is present in the free form in the intracellular water, the accumulation ratio for ciliary processes, for example, indicates an over fortysix-fold gradient of PGE1 across the cell membrane.

3. Tissues which accumulate [3H]PGE1 also accumulate [3H]PGA1, [3H]PGF1α and [3H]PGF2α. In some tissues specificity is, however, apparent; in the lung accumulation of [3H]PGA1 was significantly greater than that of [3H]PGF1α.

4. The extent of [3H]PGE1 accumulation was decreased, or in some tissues completely inhibited, by incubation at 2° C, or by addition of large concentrations of unlabelled PG.

5. Accumulation of [3H]PGE1 by the foetal liver is not apparent on the 20th day of gestation, but is fully developed by the 30th day of gestation. The foetal lung does not accumulate [3H]PGE1 at any stage of gestation.

6. In some tissues, most notably muscle, there appears to be full equilibrium of [3H]PGE1 between tissue water and medium within 1 hr of incubation.

7. PGs are partially excluded from the intracellular volume of some other tissues, most notably the spleen and subcutaneous connective tissues. This apparent exclusion cannot be blocked by incubation in the cold, or by the addition of saturating levels of unlabelled PG.

8. The simplest explanation for all observed results is that cell membranes are, in general, impermeable to PGs. However, there are specific, carrier-mediated mechanisms across some membranes which facilitate the entry of PGs. In some cells these transport mechanisms are linked to a source of metabolic energy, and/or to the counter-transport of some other substance, thus allowing net accumulation of PGs against a concentration gradient. Alternatively, 3H accumulation may represent adsorption of [3H]PGs or one of their labelled metabolites on to specific adsorption sites.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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