Proliferative activity in the different ovarian compartments in cycling rats estimated by the 5-bromodeoxyuridine technique

Abstract

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 ovarian tissue compartments by using the 5-bromodeoxyuridine (BrdU) technique. Adult cyclic rats were studied 1 h after pulse-labeling with BrdU. Follicles were divided by size as small (mean diameter < 275 μm) or large (mean diameter ≥ 275 μm). Small follicles were recorded into five classes: 1) primordial follicles (formed by flattened pro granulosa cells), 2) unilaminar primary follicles (which ranged from having at least one enlarged pro granulosa cell up to having a complete layer of cuboidal granulosa cells), 3) multilaminar class a (having 1-2 layers of granulosa cells and measuring up to 75 μm in diameter), 4) multilaminar class b (76-150 μm), and 5) multilaminar class c (151274 μm). Large follicles were recorded into classes 1-5 according to previous classifications [Osman P. J Reprod Fertil 1985; 73:261-270]. Primordial follicles and about 70% of unilaminar primary follicles were unlabeled, whereas all of the remaining classes of small and large follicles were labeled. The labeling index (percentage of BrdU-positive cells) increased in parallel with follicle size but showed a progressive decrease in large preovulatory follicles and a centripetal pattern of cell proliferation. Atretic follicles showed a significantly lower number of labeled cells than healthy follicles of the same size. The number of proliferating cells was not related to follicle size but was inversely correlated with the degree of atresia. Cyclic 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 proestrus. Proliferating cells seemed to correspond to vascular cells lining blood vessels. These results indicate that the BrdU technique is a useful, accurate, and sensitive method for assessing cellular proliferation in the rat ovary.