IN VITRO ABSORPTION AND METABOLISM OF SOME NATURAL ESTROGENS IN RAT INTESTINE

Abstract

In vitro intestinal absorption and metabolism of two natural estrogens, estradiol and estrone sulphate,were studied and compared using uneverted sacs from different segments of the rat intestine. Absorption was measured by determining the amount of radioactive steroid transported across (from the mucosal to serosal media) the sacs after an incubation period of 3 hours at 37°C. The serosal and mucosal fluids were extracted with di-ethyl other to separate the free from the conjugated steroids. Qualitative analysis of the other extract was carried out by thin layer chromatography while the aqueous conjugate fractions were similarly analysed after specific hydrolysis using β-glucuronidase and solvolysis. The effects of pH variation, temperature and metabolic inhibitors on estrogen transport were investigated. The effects of chloroquine phosphate, piporazine citrate, acetyl-selicylic acid and sodium phonobarbitone, drugs commonly prescribed in this environment and also alcohol, on the intestinal transport and metabolism of ostradiol and oetrone sulphate were studied. The test results were compared with control in the various experimental groups and the following observations were made:

The entire length of the small intestine is capable of absorbing both estradiol and estrone sulphate. Transport of the estrogens was by an active process and the optimum pH for estradiol was 7.4 and 8.0 for estrone sulphate. The rate of absorption of estradiol was higher than that of estrone sulphate. The transported products of estradiol absorption in the serosal fluid was found to contain a mixture of free and conjugated estrogens in the proportion of approximately 1:2. Up to 70% of the free was found to chromatograph with the mobility of standard estradiol but the conjugates were found to be exclusively glucuronides and largely those of estrone. Between 45-50% of the incubated estradiol was bound to Intestinal tissue but specific estradiol receptors wore not observed in the intestinal tissue. Transport of estrono sulphate into the serosal medium was accompanied by hydrolysis of the estrogen. Approximately 40% of the transported radioactivity was associated with free estrone while unchanged estrone sulphate accounted for the bulk of the radioactivity in the aqueous fraction. At the pharmacologically administered doses, chloroquine phosphate and piporazine citrate stimulated the transport of both estradiol and estrone sulphate and also decreased the proportion of the transported ostrogens present in the serosal fluid as conjugates. In contrast to the above, acetyl-salicylic acid and phenobarbitone (at pharmacologically administered doses) produced inhibitory effects on the absorption of estradiol and estrone sulphate. Acetyl-salicylic acid produced a reduction in the proportion of the transported estrogens present as conjugates while phenobarbitone increased the level of conjugation. Alcohol increased the absorption of estradiol and this was accompanied by a decrease in the conjugated fraction. Absorption of estrone sulphate was however significantly inhibited by alcohol. These results indicate that the simultaneous presence of estrogen and other medications in the gastrointestinal tract may lead to quantitative effects (i.e. on the level of absorption) as well as qualitative ones (i.e. on the nature of metabolites produced) on the absorption and general metabolism of these compounds. It is suggested that since similar modifications may occur during the intestinal absorption of progestagens, these results may have significant extrapolations to the situation occurring in the use of oral contraceptive drugs in man.