Rate and course of atresia during follicular development in the adult cyclic rat

Abstract

Ovarian follicles (greater than or equal to 100 X 10(5) microns 3 or a mean diameter of greater than or equal to 275 microns) in adult rats were classified as non-atretic and atretic during the oestrous cycle and recorded in 5 volume classes. The atretic follicles were also categorized in several stages according to the progress of atresia. The degeneration of the entire granulosa wall until the induced changes in the oocyte took at least 24 h. Another 24 h elapsed before the oocyte became denuded. Therefore the % of atretic follicles, i.e. follicles in all stages of atresia, could not be used as indicator for the rate of atresia. The atretic portion in the follicle population greater than or equal to 100 X 10(5) microns 3 increased from early dioestrus 1 to early dioestrus 3, reached a plateau during dioestrus 3 and pro-oestrus, and declined at late oestrus to the level of early dioestrus 1. The sudden decrease in number of atretic follicles after late pro-oestrus was caused by the discard of many atretic follicles in the advanced stages due to various deformities as revealed by histological observation. By using the % of atretic follicles in the earliest stage as indicator of atretic rate, two waves of atresia were found affecting the population of antral follicles during their growth, the first at dioestrus 1 amounting to 15-20% and then at dioestrus 3, affecting 35% of the population. The present study also shows the extension of atresia in the various volume classes of follicles during the oestrous cycle. A pool of approximately 7 follicles in the smallest volume class was maintained after ovulation, grew further in the next cycle with a new cohort of 20 follicles, and seemed to provide the required number of follicles destined to ovulate. This suggests that the follicles that ovulate were already present at an antral stage in the preceding cycle and needed two cycles for their growth to ovulation.

Morphometric analysis of follicular dynamics in pregnant and pseudopregnant rats

“…They were kept in a temperature-controlled room (22-24°C) (Welschen et al, 1975 (Osman, 1985). They were classified in several volume classes as shown in Tables 1 and 2 with the corresponding mean diameters.…”

“…Since the rate of atresia, i.e. the proportion of follicles which start to degenerate within a follicle population, can be assessed and has proved to be useful in the analysis of follicular dynamics in cyclic rats (Osman, 1985), it can perhaps be used, together with follicular counts, to analyse follicular dynamics during pregnancy and pseudopregnancy. Moreover, the fate of atretic follicles can also be studied during these prolonged dioestrous states, when no rapid ovarian changes occur.…”

“…Moreover, the fate of atretic follicles can also be studied during these prolonged dioestrous states, when no rapid ovarian changes occur. These changes occurring at pro-oestrus and oestrus in cyclic animals (Osman, 1975) were assumed to be the cause of the elimination of follicles in the advanced stages of atresia by compression (Osman, 1985). It is also of interest to investigate the fate of the pool of small antral follicles from the preceding cycle which is maintained and produces the follicles destined to ovulate in the next cycle in cyclic animals (Osman, 1985).…”

“…These changes occurring at pro-oestrus and oestrus in cyclic animals (Osman, 1975) were assumed to be the cause of the elimination of follicles in the advanced stages of atresia by compression (Osman, 1985). It is also of interest to investigate the fate of the pool of small antral follicles from the preceding cycle which is maintained and produces the follicles destined to ovulate in the next cycle in cyclic animals (Osman, 1985). Since no ovulation occurs during pregnancy and pseudopregnancy, those follicles will prob¬ ably become atretic in the prolonged dioestrous period.…”

Investigation of Allium sativum’s Protective Effect on Ovarian Reserve in an Experimental Ovarian Injury Model

“…The follicles were then divided into the following four groups according to the mean diameter: primordial (<20 µm), preantral (20-220 µm), small antral (221-310 µm), and large antral (311-370 µm). Atretic follicles were defined according to the description in Osman et al (1985). The extents of follicular cell degeneration (granulosa cells), vascular congestion, hemorrhage, and presence of inflammatory cells were used as criteria to estimate ovarian damage scores using a 0-3 scale (0 = none; 1 = mild; 2 = moderate; and 3 = severe).…”