Immunohistochemical assessment of collagen types I, III, IV and VI in biopsy samples of the bovine uterine wall collected during the oestrous cycle.

Uterine biopsies were collected at cycle days 1 (oestrous), 8, 15 and 19 in six cows. Unfixed cryostat sections were used to immunolocalise collagen types I, III, IV and VI by an indirect FITC method. Collagen I was sparsely found in the endometrium where it formed a fine meshwork of thin fibres directly below the surface epithelium, clearly visible only at cycle days 8 and 15. Collagen III formed the bulk of connective tissue fibres and was arranged in fine aggregates within the superficial endometrial stroma, while in the deeper areas it consisted of many thick fibre bundles. Collagen IV was found in basement membranes underlying all endometrial epithelia. Furthermore, it surrounded smooth muscle cells of blood vessels. A few single fibrils also stained positively within the endometrial stroma, more numerous at cycle days 1 and 19 as compared to days 8 and 15. Collagen VI formed a mesh of fine and pericellularly situated fibrils within the endometrial stroma. The contribution of the collagen types studied to the connective tissue of caruncles, blood vessels, lymph follicles, and myometrium is also reported. The results of the present study indicate that the connective tissue of the bovine uterine wall is composed of different collagen types, which exhibit a characteristic distribution pattern each. The day of cycle may influence amounts and organisation of collagen types I and IV as demonstrated here at the light-microscopical level.