Date of Award

1-1-1966

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Abstract

A morphological and histochemical study of the epithelium of the small intestine of the developing rat was performed using the following techniques: (1) hematoxylin and eosin; (2) periodic acid-Schiff; (3) Alcian blue; (4) alkaline phosphates; (5) acid phosphates; (6) non-specif esterace; and (7) leucine aminopeptidase. In addition to those listed above, other reactions were performed including: (1) dihydroxy-dinaphthyl-disulphide; (2) alloxan-Schiff; (3) nile blue sulfate; (4) Ziehl-Neelsen method for acid fastness; (5) Feulgen; and (6) succinic dehydrogenace. To provide a means of demonstrating whether swallowed amniotic fluid is absorbed by the fetal intestine, a colloidal iron preparation was injected into the amniotic cavity of fetal animals. Following this procedure, sections of the intestinal tissues of these animals were treated with the Prussian blue reaction to demonstrate the course taken by the iron containing material.

During the fetal developmental period, the intestinal epithelium consisted of a stratified layer of cells at 16 and 17 days gestation. In the 18 day old fetuses, the epithelium in the cephalic portion of the small intestine had transformed to the simple columnar type and by 20 days gestation, transition was complete along the entire small intestine. Beginning with the 19 day old fetuses, small, PAS-positive droplets accumulated in the supranuclear cytoplasm of the columnar cells. Similarly, granules or droplets containing iron were demonstrated in the same portion of these cells in animals which had received iron by the intraamniotic route.

In the postnatal animals, large supranuclear inclusion bodies were present in the columnar absorptive cells of the ileum and jejunum from 1 day to approximately 20 days of age at which time they disappeared. All of these instructures were PAS positive and Alcian blue negative and contained no succinic dehydrogenase. The largest of these bodies gave positive reactions for lipofuscins, sulfhydryl groups, and amino groups producing characteristics similar to "meconium corpuscles" described in the human fetus.

In regard to the enzyme technique, strong reactions with the acid and alkaline phosphatase and the non-specific esterase procedures were obtained in the intracellular inclusion bodies of the suckling animals. In the developmental process, non-specific esterase, acid and alkaline phosphatase and aminopeptidase enzyme activities appeared in the intestinal epithelial cells at 17, 18, and 19 days gestation, respectively. At the onset, the esterase enzyme was localized in the form of scattered deposits in the basal portions of the epithelium which was later replaced by the zone of activity in the supranuclear cytoplasm of the villus epithelium. The phosphatases and amino-peptidase were localized in the cuticular border of the columnar cells in all segments of of the small intestine by birth.

In the postnatal animals, alkaline phosphatase showed little change in activity in the striate border following birth, whereas definite decreases in the activity of acid phosphatase and aminopeptidase occurred in that portion of the cells. At weaning a transition occurred in which the pattern of distribution of all enzyme studied changed to the adult configuration.

On the basis of the results of the present study and information obtained from other studies in this area, the following con elusions were made: (1) the intestine of the fetal rat absorbs material from swallowed amniotic fluid; (2) the enzyme of the intestinal epithelium became active before birth; (3) the intrace llular inclusion bodies appeared to be related to lysosomes; (4) the morphological and histochemical characteristics of the inclusion bodies of the intestinal epithelium of the suckling rat were very similar to "meconium corpuscles" previously described in the human fetus; and (5) the inclusion bodies represented a developmental adaptation occurring during a certain period of ontogeny.

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