PROLIFERATIVE ACTIVITY IN THE DIFFERENT OVARIAN COMPARTMENTS IN CYCLING RATS ESTIMATED BY THE 5-BROMODEOXYURIDINE TECHNIQUE

The ovary is one of the most active proliferating tissues, and several methods for assessing cellular proliferation have been used to study follicular kinetics during the estrous cycle in the rat. In this study , we have estimated the proliferative activity of the different ovaria n tissue compartments by using the 5-bromodeoxyuridine (BrdU) techniqu e. Adult cyclic rats were studied 1 h after pulse-labeling with BrdU, Follicles were divided by size as small (mean diameter < 275 mu m) or large (mean diameter greater than or equal to 275 mu m). Small follicl es were recorded into five classes: 1) primordial follicles (formed by flattened pre-granulosa cells), 2) unilaminar primary follicles (whic h ranged from having at least one enlarged pre-granulosa cell up to ha ving a complete layer of cuboidal granulosa cells), 3) multilaminar cl ass a (having 1-2 layers of granulosa cells and measuring up to 75 mu m in diameter), 4) multilaminar class b (76-150 mu m), and 5) multilam inar class c (151-274 mu m). Large follicles were recorded into classe s 1-5 according to previous classifications [Osman P.J Reprod Fertil 1 985; 73:261-270], Primordial follicles and about 70% of unilaminar pri mary follicles were unlabeled, whereas all of the remaining classes of small and large follicles were labeled. The labeling index (percentag e of BrdU-positive cells) increased in parallel with follicle size but showed a progressive decrease in large preovulatory follicles and a c entripetal pattern of cell proliferation. Atretic follicles showed a s ignificantly lower number of labeled cells than healthy follicles of t he same size, The number of proliferating cells was not related to fol licle size but was inversely correlated with the degree of atresia. Cy clic CL showed intense proliferative activity that was well correlated with functional activity. The number of labeled cells was maximal in metestrus, decreased in the succeeding days, and was very low in proes trus. Proliferating cells seemed to correspond to vascular cells linin g blood vessels. These results indicate that the BrdU technique is a u seful, accurate, and sensitive method for assessing cellular prolifera tion in the rat ovary.