Compensatory ovarian hypertrophy in the long-term hemicastrate rat: size distribution of growing and atretic follicles

In the intact rat, on estrus, the follicle-stimulating hormone (FSH) surge recruits nearly twice the correct number of follicles for ovulation, then, on metestrus, the excess follicles undergo atresia. In contrast, in the long-term hemicastrate rat, the FSH surge recruits fewer antral follicles on estrus, but there is little atresia on metestrus. To determine if fewer follicles are recruited by the FSH surge of long-term hemicastrates because the pool of follicles capable of responding to the FSH is smaller than in intact rats, preantral, antral, atretic, and healthy follicles were counted in ovaries of rats killed on each day of the estrous cycle. In general, there were only half as many healthy preantral follicles per rat in hemicastrates compared with intacts. There were an equal number of large antral follicles per rat in hemicastrates compared with intacts. Thus, compensatory hypertrophy did not extend to preantral follicles but was evident in large preovulatory follicles. These results suggest that fewer follicles are recruited on estrus in hemicastrate rats because fewer follicles are at the appropriate stage of development to respond to the FSH surge.     

Compensatory ovulatory mechanisms operative after first ovulation in rats unilaterally ovariectomized prepubertally

Ovarian steroid contents and serum concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin were measured during the days after first ovulation in rats unilaterally ovariectomized in late prepuberty. In addition, follicle counts were made at second estrus and second metestrus. During the cycle following first ovulation, ovarian estradiol contents in unilaterally ovariectomized (ULO) rats were significantly increased as compared to intact rats on the day of metestrus, on diestrus 1 and on second estrus. Ovarian progesterone was significantly increased on the days of metestrus, on diestrus 1, second proestrus and second estrus, but no differences were seen in ovarian androgen contents. After ULO there was an indication of an augmented FSH surge at the first and the second ovulation. Follicle counts revealed that the total number of healthy as well as of atretic antral follicles on the day of second estrus was significantly increased after ULO, due to increased numbers of the smallest antral follicles. At second metestrus the number of larger antral follicles (350-500 micron 3) and the total number of healthy antral follicles was higher after ULO. It is concluded that the compensatory process after ULO involved increased recruitment of small antral follicles. Activities in the remaining ovary were not simply doubled but a new hormonal balance was established.     

Size-frequency analysis of atresia in cycling rats

The purpose of this study was to delineate when, during follicular growth, the alternative developmental pathways leading to ovulation or atresia diverge. By using computerized image analysis techniques, random samples of healthy and atretic follicles in ovaries of cycling rats were subjected to size-frequency analysis. The vast preponderance of atretic follicles were of the early antral size class (approximately 300-350 micron diameter, 800-1000 granulosa cells in the largest cross-section); atretic small follicles (less than 250 granulosa cells in the largest cross-section) were rare. Follicles in early stages of atresia were uncommon in ovaries of animals killed at estrus, but were found with great frequency in ovaries of animals killed the following day (metestrus). These results suggest that, under normal cyclic conditions, there may be only one major branching point during follicular development when growing follicles become susceptible to atresia. The alternative developmental pathways leading to ovulation and atresia may not diverge until the penultimate stage of growth, immediately preceding the final transformation into a preovulatory follicle.     

Effect of a low dose of pregnant mare's serum gonadotropin on follicular recruitment and atresia in cycling rats

Atresia appears to play a central role in selecting the correct number of follicles for ovulation in the rat. A wave of atresia, apparent by noon on metestrus, reduces the number of large healthy follicles to the appropriate quota for ovulation. The purpose of this study was to test the hypothesis that falling levels of gonadotropin on the morning of estrus precipitate the wave of atresia of large follicles seen on metestrus. Endogenous concentrations of follicle-stimulating hormone (FSH) were augmented by a single injection of pregnant mare's serum gonadotropin (PMSG; 0.025 IU/gram body weight) administered at different times during the periovulatory period. Animals given PMSG at 0800 h on estrus (when the endogenous FSH surge was waning) had a supernormal number of large healthy follicles in their ovaries at 1200 h on metestrus. This increase in large healthy follicles was accompanied by a decrease in large atretic follicles in the ovaries. The same dose of PMSG, when administered at other times during the periovulatory period, did not affect any of the parameters measured. These observations suggest that the wave of atresia normally seen in large follicles on metestrus is triggered by the decline in the concentration of FSH during the morning of estrus and can be prevented by prolonging the surge of FSH with administration of PMSG.     

Age-related alterations in follicular development and hormonal profiles in rats with 4-day estrous cycles

Two experiments were conducted to examine the hypothesis that an alteration in follicular development is associated with advancing maternal age in the absence of prolonged estrous cycles. In Experiment 1, serum and four follicles (from one ovary per rat) were collected from young and middle-aged, 4-day cycling rats on estrus or metestrus. Number and diameter of nonatretic antral follicles greater than 200 microns in diameter were determined from serial sections of the other ovary from each rat. In Experiment 2, serum and follicles (12 +/- 2) from both ovaries were collected from young and middle-aged rats on each day of a 4-day estrous cycle. All microdissected follicles were assayed for estradiol-17 beta (E2) and all sera were assayed for E2, follicle-stimulating hormone, and luteinizing hormone by radioimmunoassay. Numbers of follicles greater than 400 microns in diameter did not differ, while numbers of follicles 200-400 microns in diameter were reduced in middle-aged rats compared to young rats (Experiment 1). The mean diameter of follicles greater than 400 microns in diameter and the follicular content of E2 was greater in middle-aged than in young rats. In Experiment 2, a greater proportion of large follicles were observed in middle-aged rats than in young rats on all days, and a greater proportion of follicles with high concentrations of E2 were observed on diestrus. We interpreted these data as indicative of an early age-related change in the control of follicular recruitment, growth, and maturation.     

Ovarian follicular populations and preovulatory enlargement in Booroola and control Merino ewes

To investigate the factors contributing to the different ovulation rates observed in two strains of sheep (Booroola 5.2, Merino 1.2), in-vivo monitoring of follicular kinetics followed by histological examination of both ovaries was performed during the late luteal and follicular phases. Ewes of both strains were either ovariectomized at Day 13, or had the 3 largest follicles of each ovary ink-labelled at Day 13 and were ovariectomized at Day 15, or had the 3 largest follicles of each ovary ink-labelled at Days 13 and 15 and were ovariectomized 16 h after the beginning of oestrus (N = 6 per time per strain). In another experiment, the age effects on the follicular populations of these two strains were also studied. There were 2-4 times more primordial follicles and 1.5-2 times more preantral follicles in the ovaries of Booroola than in control Merino ewes, although the number of antral follicles was the same. The percentage of normal follicles in this population was higher in Merino than Booroola ovaries. In Booroola ewes, there was no correlation between the number of antral follicles per ovary and the ovulation rate at the previous cycle (r = 0.22). This suggests that follicle numbers do not play a key role in the high ovulation rate of the Booroola strain. The number of follicles initiating growth from the primordial pool, the number of growing follicles disappearing at the preantral stage, the pattern of antrum development, granulosa cell multiplication and appearance of atresia differed between strains. The reasons for the high ovulation rate of the Booroola strain became clear when preovulatory enlargement was followed by ink labelling. An extended period of time during which recruitment of ovulatory follicles takes place, together with a low incidence of selection and the ability of the follicles to wait for ovulation are the features involved in this high ovulation rate.     

Action of PMSG on follicular populations in the heifer

The short-term action of PMSG on the population of growing follicles in cattle was studied using histological methods. On Day 7 of a synchronized oestrous cycle 10 Friesian heifers were unilaterally ovariectomized. The remaining ovary was immediately stimulated by an injection of PMSG (2000 i.u.) and was removed 48 h after the preovulatory discharge of LH. Control animals did not receive any injection of PMSG. In all ovaries, follicles greater than 70 micron diameter were counted, measured and checked for atresia. The mitotic index in granulosa cells of follicles of different sizes was estimated in both ovaries of all the PMSG-injected animals. Unilateral ovariectomy alone had no significant effect on follicular populations. In the interval between PMSG injection and removal of the second ovary (148 +/- 22.7 h), PMSG significantly increased the number of normal preantral follicles but did not change the number of normal antral follicles. The mitotic index doubled in preantral and early antral follicles but remained unchanged in large antral follicles. PMSG stimulated slightly the growth of the antrum in large antral follicles but did not stimulate its formation in preantral follicles. The incidence of atresia among antral follicles, particularly the largest ones (diam. greater than 1.7 mm), was significantly reduced after PMSG, suggesting some 'rescue' of follicles from atresia.     

Patterns of follicular growth during the four-day estrous cycle of the rat

Female Sprague-Dawley rats underwent laporatomy during metestrus at 70 to 75 days of age or remained untreated to study the effects of surgical stress on follicular growth. Groups of rats were killed on each day of a 4-day estrous cycle, serial sections of the ovaries were prepared histologically and the number and size of follicles with one or more complete layers of cuboidal granulosa cells were determined. Since no differences due to surgery were found, the data were pooled by day of the estrous cycle (17 or 18 rats/day of cycle) for characterization and comparison of size distribution of follicles on different days of the estrous cycle. Follicles were classified as atretic or healthy and divided into groups by increments of 20 micron of diameter for graphing. Data were analyzed by analysis of variance and least squares means. Significant differences were found in the distribution of both healthy and atretic follicles among days of the estrous cycle. At least 21 follicles/ovary were recruited from less than 260 micron into greater than 260 micron in diameter between proestrus and estrus, and the follicles for ovulation were selected by diestrus. A greater number of growing follicles of 70 to 100 micron in diameter were present at diestrus. From the disappearance of follicles greater than 260 micron between estrus and proestrus, it appears that atresia is a very rapid process.     

Timing of emergence of ovulatory follicles in polyovulatory goats

The current study characterized the timing of emergence of ovulatory follicles during the follicular phase of the estrous cycle in polyovulatory does and assessed whether selection may influence ovulation rate through differences in ovarian follicular dynamics, by characterizing preovulatory follicular emergence and growth in two ecotypes of Neuquen-Criollo Argentinean goats (Short-Hair, n=11 and Long-Hair, n=9). During the breeding season, the time of estrus was synchronized in all does with two doses of a prostaglandin analogue. Ovarian laparoscopies were performed on days 17 and 19 after the induced estrus (day 0) and 7-15 h after the beginning of the subsequent estrus. Results indicate that both ecotypes of goats have common features in the ovarian follicular population and in the patterns of preovulatory follicular enlargement. In all the goats, most of the preovulatory follicles arose from the pool of follicles present in the ovary between days 17 and 19 of the estrous cycle. These follicles were all larger than 2mm at emergence, being the largest growing follicle present in the ovaries on days 17 and 19 in 56.5 and 78.6% of the does, respectively. The appearance of new follicles remained unaffected, while the mean number of small growing follicles decreased (P<0.05) during the follicular phase, indicating that preovulatory follicles do not suppress the emergence of new follicles but inhibit the growth of small follicles. A separate analysis of single and double ovulating does showed that 75% of the second ovulatory follicles in polyovulatory goats was present on the ovarian surface between days 17 and 19 of the estrous cycle, but appeared later in the other 25% of the estrous cycles. These findings support the hypothesis that follicular dominance effects are exerted during the preovulatory period, when the growth of follicles other than the ovulatory is inhibited, and that increases in ovulation rate in small ruminants are related to a reduced incidence of follicular atresia and an extended period of ovulatory follicle recruitment.     

A possible dual mechanism of the anovulatory action of antiprogesterone RU486 in the rat

The purpose of these experiments was to investigate the mechanism of the anovulatory action of antiprogesterone RU486 (RU486) in rats by studying its effects on follicular growth, secretion of gonadotropins and ovarian steroids, and ovulation. Rats with 4-day estrous cycles received injections (s.c.) of either 0.2 ml oil or 0.1, 1, or 5 mg of RU486 at 0800 and 1600 h on metestrus, diestrus, and proestrus. At the same times, they were bled by jugular venipuncture to determine serum concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), 17 beta-estradiol (E), and progesterone (P). On the morning of the day after proestrus, ovulation and histological features of the ovary were recorded. Rats from each group were killed on each day of ovarian cycle to assess follicular development. Rats treated similarly were decapitated at the time of the ovulatory LH surge and blood was collected to measure LH. The serum levels of LH increased and those of FSH decreased during diestrus in rats treated with RU486. Neither E nor P levels differed among the groups. Treatment with RU486 caused both a blockade of the ovulation and an increase in ovarian weight in a dose-dependent manner. At the time of the autopsy (the expected day of ovulation), rats treated with 1 mg RU486 had ovaries presenting both normal and post-ovulatory follicles and unruptured luteinized follicles. Rats treated with 5 mg RU486 presented post-ovulatory follicles without signs of luteinization. The number of follicles undergoing atresia increased in rats treated with RU486. Rats treated with 5 mg RU486 exhibited a significant decrease in ovulatory LH release. The mechanism by which RU486 produces the ovulatory impairment in rats seems to be dual: first, by inducing inadequate follicular development at the time of the LH surge and second, by reducing the amount of ovulatory LH released. The physiological events-decreased basal FSH secretion and follicular atresia-that result from use of RU486 cannot be elucidated from these experiments and should be investigated further.     

In vitro sensitivity of rat ovarian follicles to the direct action of various hormones applied in particular stages of sexual cycle

The direct action of various hormones on the ovary of adult rat ovaries has been investigated. The ovaries were surgically exposed at particular stages of sexual cycle i.e. in estrus, metestrus, diestrus and proestrus, and were injected with various doses of gonadotropic hormones. Injected ovaries were excised 56 hrs after injection and examined histologically. The reactivity of the ovaries to hormone applied was dependent on stage of the cycle. The considerable increase of the amount of t1 and t2 follicles was observed after injection of gonadotropins in estrus stage. In metestrus stage the influence of gonadotropins on the follicles more advanced in development was pronounced. Numerous follicles t3 appeared in diestrus under the influence of all used hormones.     

Immunocytochemical analysis of the expression of gap junction protein connexin 43 in the rat ovary

The present immunocytochemical study examines in the rat ovary the pattern of expression of connexin 43 (Cx43), a subunit of gap junctions. Using a well-characterized specific antiserum against rat Cx43, immunoreactivity was not detected in the fetal ovary, i.e., prior to follicular formation. However, in the ovary of 20-day-old, 35-day-old, and adult rats, strong Cx43-immunore-activity was associated with the cell borders of the follicular epithelium/granulosa cells of all developmental stages (primordial follicles, preantral and antral secondary follicles). In general, immunoreactivity of the granulosa cells of large antral follicles appeared more intense than the one of smaller follicles. Staining was also seen in oocytes (cytoplasmic staining). Theca cells of large antral follicles, but not of small follicles were immunoreactive. Immunoreactive interstitial cells were not seen in ovaries of 20- and 35-day-old animals, but staining in these cells was present in adult rats. In large follicles with signs of atresia, granulosa cells lacked Cx43-immunoreactivity, whereas Cx43-immunoreactivity in their theca interna strikingly increased. Corpora lutea in the cyclic adult rats were heterogeneously stained, with either no detectable immunoreactivity, staining of cell borders of most luteal cells, or with conspicuous staining of only a few cells. In the pregnant animals on gestation days (GD) 12, 14, and 17, all luteal cells stained strongly for Cx43 at the cell surface. Shortly before delivery (GD 21), however, the staining pattern vanished and only few, presumably luteal cells remained immunoreactive. In Western blots (using homogenates of whole ovaries), the Cx43 antiserum recognized a major band of approximate Mr 43 × 10³, together with minor bands, which may reflect the presence of several differently phosphorylated Cx43 forms. This is indicated by treatment with alkaline phosphatase, which reduced the banding pattern to one single band. In summary, the gap junction molecule Cx43 is abundantly expressed in all endocrine compartments of the rat ovary. The staining pattern obtained in the present study indicates that Cx43 and presumably gap-junctional communication are associated with follicular development, atresia, and the development of the interstitial gland, as well as with the development and regression of the corpus luteum. The heterogeneous staining within the ovary furthermore hints to a contribution of the local intraovarian factors in the regulation of Cx43 expression. © 1995 Wiley-Liss, Inc.     

An enzymatic method for dissociation of intact follicles from the hamster ovary: histological and quantitative aspects

An enzymatic method was developed to collect intact follicles at different stages of development from cyclic hamsters to study ovarian folliculogenesis under various circumstances. Ovaries from 6 adult hamsters on each day of the cycle (Day 1 = ovulation) were collected, corpora lutea and large preantral and antral follicles were dissected, and follicles saved. Minced ovaries were then incubated with a mixture of collagenase, DNAse and pronase at 37 degrees C for 20 min to disperse intact follicles. Histological studies with 2191 isolated follicles revealed 10 different stages of follicular development (depending on the number of granulosa cell layers surrounding the oocyte and development of the antrum). Of the total follicular population, 14% showed signs of atresia, with 50% of those having 1-3 layers of granulosa cells (Stages 1-3); a second peak of 18% was observed in antral follicles (Stages 8-10). No signs of thecal cells were evident until the follicles reached Stage 6 (7-8 layers of granulosa cells), which possibly accounts for reduced atresia in this class and beyond. Ultrastructural study revealed that there were no signs of morphological damage to the basement membrane or to other subcellular organelles in the small preantral follicles. The presence of subnuclear lipid droplets in follicles with 3 layers of granulosa cells provided evidence for potential steroidogenesis by small follicles. The number of Stage 1-10 follicles was remarkably constant throughout the estrous cycle (460 +/- 34 per animal on Day 1 vs. 492 +/- 66 on Day 4). The usefulness of this method in analyzing follicular kinetics is illustrated in experiments involving hypophysectomy and the effects of unilateral ovariectomy. This procedure offers an improved method to study the factors responsible for the growth and the differentiation of small preantral follicles in the mammalian ovary.     

Origin of the preovulatory follicle in Mouflon sheep (Ovis gmelini musimon) and effect on growth of remaining follicles during the follicular phase of oestrous cycle

Daily transrectal ultrasonographies were conducted to study development of all follicles with antral diameters > or = 2mm during the follicular phase of oestrous cycle in Mouflon, a strictly monovular wild-sheep. A total of 14 follicular phases was studied after oestrus synchronization with two cloprostenol doses, 9 days apart, in five cyclic Mouflon ewes. In 13 cycles (92.8%), the ovulatory follicle arose from those antral follicles present in both ovaries when luteolysis was induced, being the largest one with a mean size of 4.4+/- 0.3mm at that moment in 10 cycles (76.9%). The remaining cycles had a larger follicle, but it was decreasing in size. Appearance of new follicles > or =2mm in size remained unaffected during the follicular phase (3.7+/- 0.2), but there was found a linear decrease in the number of those growing to > or =3mm (2.5+/- 0.4 to 1.1+/- 0.2, P < 0.05) and > or = 4mm (0.6+/- 0.2 to 0.1+/- 0.1, P < 0.005), detection of new follicles growing to > or = 5mm was negligible. Then, number of medium (4-5mm) growing follicles present in both ovaries decreased from 1.5+/- 0.3 at 0 h to 0.3+/- 0.1 at 72 h (P<0.005). In conclusion, the single ovulatory follicle is the largest growing follicle present in both ovaries at the moment of luteolysis. This follicle is selected to grow and ovulate while development of other follicles is inhibited.     

Imminent oocyte exhaustion and reduced follicular recruitment mark the transition to acyclicity in aging C57BL/6J mice

Quantitative cytological analyses of aging C57BL/6J mouse ovaries revealed that the populations of primordial and growing follicles were nearly exhausted by 13-14 months, the average age of ovulatory failure. Anovulatory animals of this age had, on the average, half the follicle number of their counterparts which were still ovulating. This result suggests that follicular depletion is a factor which contributes to the loss of ovarian cyclicity during aging. However, the considerable overlap of follicle number between the two groups suggests that other, possibly extraovarian, factors also influence the loss of ovulatory function. Although the numbers of follicles recruited for growth was much lower in ovaries from old cycling animals, the number of ova shed cyclically was generally within the range of younger individuals. The observed reduction in incidence of morphological atresia among medium-sized follicles may explain how ovulatory constancy is maintained virtually throughout the cyclical life of the ovary.     

A role for the androgen receptor in follicular atresia of estrogen receptor beta knockout mouse ovary.

Estrogen receptor beta (ERbeta) is highly expressed, but ERalpha is not detectable in granulosa cells in the mouse ovary. In ERbeta knockout (BERKO) mice, there is abnormal follicular development and very reduced fertility. At 3 wk of age, no significant morphologic differences were discernable between wild type (WT) and BERKO mouse ovaries, but by 5 mo of age, atretic follicles were abundant in BERKO mice and there were very few healthy late antral follicles or corpora lutea. At 2 yr of age, unlike the ovaries of their WT littermates, BERKO mouse ovaries were devoid of healthy follicles but had numerous large, foamy lipid-filled stromal cells. The late antral and atretic follicles in BERKO mice were characterized by a high level of expression of the androgen receptor (AR) and IGF-1 receptor. These proteins were abundantly expressed in granulosa cells of preantral and early antral follicles in both genotypes, but their expression was extinguished in late antral follicles of WT mice. Healthy late antral follicles and corpora lutea were restored in BERKO ovaries after 15 days of treatment of mice with the antiandrogen flutamide. The results suggest that in the absence of ERbeta there was a loss of regulation of AR. Because androgens enhance recruitment of primordial follicles into the growth pool and cause atresia of late antral follicles, the inappropriately high level of AR probably is related to the follicular atresia and to the early exhaustion of follicles in BERKO mice.     

Effect of buffalo follicular fluid treatment on follicle population and ovulation rate in guinea pigs

A number of workers have studied the effect of follicular fluid (FF) on the secretion of follicular stimulating hormone (FSH) but little is known about its potential as a regulator of ovarian activity, including ovulation rate. This paper describes the effect of charcoal treated-buffalo follicular fluid (buFF) treatment on follicular growth and ovulation rate in guinea pigs. Eighteen guinea pigs in three groups of 6 each were given 0.2 ml buFF at 12 hr interval for 3 days at different stages of estrous cycle viz., early-luteal, mid-luteal or follicular phase. One control group received equal volume of saline. Estrus was monitored every morning and evening by inspection of the opening of vaginal membrane and its cytology. All animals were sacrificed at 24 hr after the onset of estrus. Both the ovaries were dissected out, weighed and number of ovulation points recorded. One ovary from each animal was processed for histological examination to determine the population of healthy and atretic follicles. In early-luteal and follicular phase-treated animals the onset of estrus was delayed (P < 0.01) and ovulation rate was not affected. However, estrus occurred at normal when the treatment was initiated at midluteal stage and 50% animals failed to ovulate in this group. The total follicle population at metestrus increased significantly in all treated animals because of increase in number of follicles of size class II (400 to < 600 microns diam.). Atresia was also declined due to treatment. These results demonstrated that the buFF contained some inhibitory substances that delayed the onset of estrus in guinea pigs.     

Cessation of transition-phase follicle growth in the guinea pig by follicle-regulatory protein

The granulosa cell produces a protein inhibitor of aromatase activity (follicle-regulatory protein: FRP), which recently was purified to homogeneity. To determine the possible involvement of FRP in follicular maturation, we examined the size distribution of follicles and their morphological patterns as well as serum steroid levels after the systemic administration of FRP and/or gonadotropin to guinea pigs, which have 5-6 days between luteolysis and ovulation in a 16-day cycle. FRP was partially purified from porcine follicular fluid by ammonium sulfate precipitation (0-35%), Dye Matrex Orange A Chromatography, dialysis, and lyophylization. To investigate the effect of pregnant mare's serum (PMS) during the periovulatory period in follicular development, adult guinea pigs underwent unilateral ovariectomy on Days 10, 12, and 14 of the estrous cycle (N = 6 each). Guinea pigs were injected twice daily with vehicle or PMS (5 IU) and 2 days thereafter the remaining ovaries were removed. Another group of guinea pigs received, in addition, intraperitoneal injections of FRP (1 mg) each morning from Day 8 of estrus until they were killed. The resected ovaries were fixed, embedded in paraffin, serially sectioned (7 micron), and stained with Azan for comparative study via light microscopy. All follicles greater than 400 micron were classified by size, and the atretic pattern was determined by mural granulosa cell pyknosis and antral sloughing. The distribution of follicular size was not affected by hemicastration at Day 10, although the percentage of total atretic follicles decreased. In the PMS-treated group, there was a significant decrease in the number of viable follicles (700-899 micron) after hemicastration. Also pronounced in follicles of this size was the lack of mid-atretic follicles. After injections of FRP for 3 or 5 days, the overall number of follicles was almost doubled as compared to the number found in the normal ovary. Additionally, there was a significant increase in the percentage of follicles that were recently atretic, although the total percentage of atretic follicles was unchanged. After hemicastration at Day 10 followed by FRP treatment for 2 days, the total percentage of atretic follicles in the remaining ovary decreased to 18% compared with 35% in the normal ovary, 46% in the hemicastrated plus PMS-treated group, and 38% in the hemicastrated and PMS- and FRP-treated group (all p less than 0.01). Treating the hemicastrated animal with PMS increased the percentage of atretic follicles in all groups.(ABSTRACT TRUNCATED AT 400 WORDS)