Large Preantral Follicles Research Articles

Reduced Ability of Rat Preantral Ovarian Follicles to Metabolize 4-Vinyl-1-cyclohexene Diepoxide in Vitro

4-Vinylcyclohexene diepoxide (1-epoxyethyl-3,4-epoxycyclohexane, VCD), an industrial chemical, is a potential health hazard because it destroys oocytes in small preantral follicles in rats. We proposed that VCD destroys oocytes in these follicles because of their reduced capacity to detoxify VCD (convert VCD to tetrol, 4-(1,2-dihydroxy)ethyl-1,2-dihydroxycyclohexane). Ovaries, livers, and adrenal glands were collected from immature and mature Fischer 344 rats. Tissues were dissociated and ovarian tissue was separated into distinct follicular fractions. Tissues were incubated with [ 14C]VCD and media were assayed for [ 14C]tetrol by HPLC. In immature rats, conversion of VCD to tetrol in large preantral follicles and hepatocytes was 1.5-fold greater than in small preantral follicles and 4-fold greater than in ovarian interstitial cells ( p < 0.05). In adults, conversion of VCD to tetrol in targe preantral follicles and hepatocytes was, respectively, 3- and 10-fold greater than in small preantral follicles and interstitial cells ( p < 0.05). Compared with immature rats, all tissues from adult rats converted more VCD to tetrol ( p < 0.05). These data demonstrate that interstitial cells and small preantral follicles from adult and immature rats have a reduced capacity to convert VCD to tetrol compared to large preantral follicles and liver cells. This may explain their increased susceptibility to VCD-induced ovotoxicity. Furthermore, adult rats may be less susceptible to VCD-induced ovotoxicity than immature rats.

Transforming Growth Factor-β Potentiation of Follicle-Stimulating Hormone-Induced Deoxyribonucleic Acid Synthesis in Hamster Preantral Follicles is Mediated by a Latent Induction of Epidermal Growth Factor1

The mechanisms of transforming growth factor-beta (TGF-beta) potentiation of FSH action on follicular DNA synthesis in the hamster were investigated by use of TGF-beta (beta 1 and beta 2) and a potent epidermal growth factor (EGF)-specific polyclonal antibody. Preantral follicles at stages 1-6 and early antral follicles at stage 7 were enzymatically and mechanically isolated from adult golden hamsters on proestrus. Follicles were incubated in Dulbecco's modified Eagle's medium with ITS+ (6.25 micrograms insulin, 6.25 micrograms transferrin, 6.25 micrograms selenium, 1.25 mg BSA, and 5.35 micrograms linoleic acid/ml) hydrocortisone, and 1 microCi/ml [3H]thymidine. Follicles were exposed for 24 h to FSH (100 ng/ml), TGF-beta 1, and TGF-beta 2 (1 and 10 ng/ml), EGF antibody (50 microliters/ml), and TGF-alpha (50 ng/ml) under various experimental conditions. Both TGF-beta 1 and TGF-beta 2 significantly potentiated FSH-induced follicular DNA synthesis; however, the effect was drastically attenuated by EGF antibody. EGF antibody also inhibited FSH-induced follicular [3H]thymidine incorporation. TGF-beta 2 potentiation of FSH action was also significantly inhibited by a second dose of TGF-beta 2 when added 6 h after the beginning of culture; however, follicles at different stages responded differently to the second dose of TGF-beta 2. For example, when the second dose of TGF-beta 2 was added 14 h after the first dose, only the large preantral follicles at stages 4-6 were affected. Interestingly, the second dose of TGF-beta 2 also inhibited TGF-beta 2-induced DNA synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphometric study of ovarian follicular growth during the estrous cycle of the laboratory-maintained Indian desert gerbil, Meriones hurrianae (Jerdon).

The pattern of changes in the population of healthy and regressing follicles in relation to the estrous cycle, was studied in the recently domesticated desert gerbil, Meriones hurrianae, which exhibits a longer cycle (proestrus: 1.5 days; estrus: 1 day; metestrus: 1.5 days; diestrus: 3 days). As the granulosa cell layers were not distinct, the follicles were classified on the basis of their morphology and size (group I: small preantral follicles; group II: large preantral follicles; group III: small antral follicles; group IV: medium-sized antral follicles; group V: large-sized follicles; group VI: Graafian follicles). Regressing follicles were classified likewise. Five animals were used for each stage of the cycle. One ovary from each gerbil was serially cut and stained with hematoxylin-eosin. Healthy and regressing follicles were found throughout the cycle. The follicular development occurred typically in a biphasic manner. In phase A, in which follicles reach the antral stage, the growth of oocytes and follicles is linearly correlated, whereas, in phase B, oocyte size remains stationary while follicle size increases due to accumulation of antral fluid. However, oocyte growth and nucleus growth are positively and linearly correlated (r = 0.74). The healthy follicles under 260 microns (groups I, II) do not fluctuate in the ovary of cyclic gerbils, whereas follicles in group III (261-350 microns) increase significantly (p < 0.05) at estrus and those of group IV in diestrus. Further, healthy group III follicles are reduced in diestrus while regressing follicles in group III increase. These findings thus suggest that the antral follicles are rescued from atresia at estrus.(ABSTRACT TRUNCATED AT 250 WORDS)

Genetic differences in Follicular DNA Synthesis between Two Strains of Hamsters

This study was designed to compare our previous results on ovarian follicular DNA synthesis by hamsters obtained from Sasco Laboratories with a different breeding colony: Harlan. Follicles from proestrous Harlan hamsters required twice as much [3H] thymidine and a minimum of 4 hr of in vitro exposure to 100 ng of ovine follicle-stimulating hormone (FSH) before a significant increase in DNA synthesis was elicited compared with 30-120 min for the Sasco breed. Peak responsiveness to FSH was observed at 8-hr incubation for the Harlan strain with significant increases in DNA per follicle at 8-12 hr. Both strains increased DNA synthesis with as little as 25 ng of ovine FSH and the response was elicited in all growing follicles, from preantral stages with one to four layers of granulosa cells, lacking theca (Stages 1-4) to mature antral follicles (Stages 8-10). A recombinant bovine FSH, devoid of luteinizing hormone activity, was not as effective as ovine FSH (which has 4% luteinizing hormone contamination) in stimulating DNA synthesis by large preantral and antral follicles. In vitro responsiveness to ovine FSH was abolished in the absence of Ca2+ in the culture medium and 0.05 mM Ca2+ was the optimal amount. For both strains of hamsters, the highest rate of DNA synthesis in response to endogenous gonadotropins was on the morning of estrus--when the second surge of FSH was in progress--and Harlan follicles in vitro also showed maximal stimulation by FSH on this day. Where the two strains differed was that the Harlan strain did not show an increase in follicular DNA synthesis on the afternoon of proestrus--when the preovulatory increase in gonadotropins commenced. When expressed as DNA per follicle, DNA approximately doubled from Stages 1 to 5 and then entered a new growth phase at Stage 6 (large preantral follicles) with a steeper increase. Collectively, these experiments show that strain characteristics can alter the latency and degree of follicular DNA replication in response to endogenous or exogenous FSH.

Deoxyribonucleic acid polymerase-α activity in hamster follicles during the estrous cycle: roles of follicle stimulating hormone and luteinizing hormone

In the hamster, DNA polymerase-a (Pol-α) in follicles at stages 1–4 (1–4 layers granulosa cells and no theca) increased significantly during the proestrous (P) gonadotropin surges, remained high on estrus (E) and then declined to low levels by 09.00 h, proestrus (P). However, Pol-a in stages 5–8 (large preantral to small antral stages) remained steady throughout the cycle. Hypophysectomy on metestrus decreased Pol-a by 17 h which was reversed by 2.5 μg follicle stimulating hormone (FSH) but not by luteinizing hormone (LH) (2.5 jug) or human chorionic gonadotropin (hCG) (1 IU). Hypophysectomy on E resulted 72 h later in a fall in Pol-α in stages 1–6; FSH (2.5 fig) or LH (2 μg) restored enzyme activity within 5 h to stages 1–6 and 5–6, respectively. Thus, Pol-α in the smallest preantral follicles is induced by FSH; however, for large preantral and antral follicles, steady levels are maintained by tonic FSH and LH resulting in no apparent change in enzyme activity during active DNA synthesis.

Quantitative autoradiographic study of FSH binding sites in prepubertal ovaries of three strains of rats.

Iodinated FSH was injected to 18- and 36-day-old rats of 3 strains (03, 04 and 12) with different sensitivity to FSH (12 less than 03 less than 04) and autoradiography was performed on histological sections of the labelled ovaries. Specific labelling was quantified by microphotometry on histological slides, on granulosa cells of individual follicles with different sizes (greater than 80 micron diameter) and qualities. In small preantral follicles (less than 160 micron diameter) the labelling was low and homogeneous within the granulosa; it increased between 18 and 36 days of age in the 3 strains. At 36 days, ovaries were characterized by the presence of large preantral and antral follicles with a higher labelling in the outer layers of granulosa (near the theca), compared to the inner layers. In definitely atretic follicles, a loss of binding sites was detected in the outer layers. In rats of Strains 03 and 04, the number of binding sites for FSH in the outer layers of granulosa of follicles with a diameter of greater than 160 micron increased with follicular size; no change was detected in follicles of Strain 12 rats. The low number of binding sites for FSH and the lack of terminal maturation which characterize the follicles of strain 12 rats can be related to the poor and delayed follicular development, the low sensitivity to exogenous FSH and the low fertility of the animals of this strain.

Stimulatory and inhibitory effects of progesterone on follicular development in the hypophysectomized follicle-stimulating hormone/luteinizing hormone-treated hamster.

Cyclic hamsters hypophysectomized at estrus (Day 1 of the cycle) and injected with 5 micrograms follicle-stimulating hormone (FSH) on Day 1 and 20 micrograms luteinizing hormone (LH) in polyvinylpyrrolidone (PVP) from Days 1-4 ovulated 15.3 ova, in response to 30 IU human chorionic gonadotropin (hCG) administered at 1500 h on Day 4 (Kim and Greenwald, 1984). When 1 mg progesterone (P4) was administered daily from Days 1-4 concurrent with the above regimen, ovulation increased to 38 ova, a clearcut superovulatory response. However, daily injection of 1, 10, or 100 micrograms P4 plus FSH and LH reduced the number of antral follicles present on the afternoon of Day 4 to 3-4 per ovary, compared to 9 per ovary after FSH-LH alone, and the ovulation rate was drastically reduced with most animals being anovulatory. Substituting 1 mg 17 alpha-hydroxyprogesterone or estradiol cyclopentylpropionate for P4 on Days 1-4 did not alter the number of antral follicles on Day 4 from FSH-LH alone, whereas 1 mg androstenedione or 1 mg testosterone cyclopentylpropionate reduced the number of antral follicles to 3 or less. Hence, the stimulatory effects of 1 mg P4 are not attributable to its conversion to other P4 derivatives. After the concurrent injection of 1 mg P4 and FSH-LH, on the afternoon of Day 3, an average of only 1.8 large preantral follicles was present per ovary. By the morning of Day 4, however, the ovary contained 14 large preantral and early antral follicles in addition to 8 large antral follicles. Injection of hCG at this time resulted in the ovulation of 14.5 ova.(ABSTRACT TRUNCATED AT 250 WORDS)

Histologic evidence for age-related differences in ovarian function in tamarins (Saguinus sp.; primates).

The ovaries of 15 tamarins (Saguinus sp.) between 2 and 16 yr of age were collected at necropsy and examined for evidence of age-related differences. As expected, there was a marked decline in the number of primary follicles with advancing age. Age and the number of primary follicles available had minimal effect on the number of follicles recruited into the preantral population; however, there were significant decreases in the number of large preantral and antral follicles with increasing age. The observed decline in follicular development with age was consistent with a reproductive decline with age observed in some tamarin females. Luteal-like masses were found in all ovaries examined and their size and appearance was unrelated to age.

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.

A species difference between hamster and rat in the effect of oestrogens on growth of large preantral follicles.

Intact or hypophysectomized 23-day-old hamsters and rats were injected s.c. with 2 mg diethylstilboestrol (DES) or 1 mg oestradiol cyclopentylpropionate (OECP) on Days 23-25 and killed on Day 26. Although serum oestradiol was elevated to the same high levels by OECP, ovarian and uterine weights were increased in the rat by OECP or DES whereas only the uterus responded in the hamster. This correlated with the ability of the oestrogens to increase significantly the number of large preantral and antral follicles in the intact rat but only the number of follicles with 2-3 layers of granulosa cells in the immature hamster. Qualitative study revealed that DES and OECP increased the number of large preantral follicles in the adult hypophysectomized rat but were ineffective in the adult hamster. It is concluded that for the immature and adult hamster oestrogens do not play a major role in the recruitment of large preantral follicles.

Is the First or Second Periovulatory Surge of FSH Responsible for Follicular Recruitment in the Hamster?

AbstractProestrous hamsters were injected at 1300 hr with phenobarbital to block ovulation. The animals were bled via cardiac puncture every 6 hr beginning at 1600 hr of proestrus until 1000 hr of estrus. The ovaries were then removed and a quantitative evaluation of follicular development carried out. In saline-injected proestrous hamsters, there was a peak of serum FSH and LH at 1600 hr followed by a second prolonged peak of FSH at 0400 and 1000 hr of estrus accompanied by low tonic levels of LH. This hormone profile was associated at 1000 hr of estrus with an average of 9.3 large preantral follicles (stage IV follicles) per ovary. In contrast, the phenobarbital-treated hamsters showed no increases in either gonadotropin at any time and the ovaries contained large antral follicles and an average of only 1.7 stage IV follicles per ovary (three of four animals). Injection of 1 mg progesterone concurrent with phenobarbital restored the first surge of LH but not FSH and partially restored the second peak of...

Induction of superovulation in the cyclic hamster by a single injection of antiluteinizing hormone serum.

Interruption of pregnancy in the hamster with equine antibovine LH (anti-LH) induces superovulation of about 30 ova at the subsequent estrus. In view of the different hormonal profiles and antral follicular development in pregnant and cyclic hamsters, the present experiments were designed to ascertain the effects of anti-LH on the serum concentrations of steroids, ovarian follicular development, and ovulation in the cyclic hamster. Hamsters injected sc on the morning of ovulation (day 1 of cycle) with 100 μl anti-LH spontaneously ovulated 31.5 eggs at the next ovulation instead of the normal number of 13 ova. The normal 4-day cycle was lengthened to 5 days after anti-LH, but subsequent cycles reverted to 4 days, and the normal number of ova was shed. Anti-LH on day 1 did not affect serum progesterone levels on day 2, but serum estradiol was depressed until day 4, whereas in the normal hamster, estradiol increases on day 3. When anti-LH was given on day 4 (proestrus), the hamsters ovulated the next day an average of 11 ova, but in the subsequent cycle (5–6 days), the mean number of ovulations was 29. Thus, anti-LH induces superovulation when injected in the periovulatory period (days 4 and 1) when serum FSH levels are high. A quantitative study of follicular development after the injection of anti-LH at 0900 h on day 1 revealed that for 12 h afterwards, follicular development was unaffected. However, by day 2, a wave of atresia destroyed the larger preantral follicles. On day 3, the ovary was repopulated with large preantral follicles, and this was followed by a greater than normal number of antral and intermediate sized follicles, thus culminating in superovulation. (Endocrinology108: 1903, 1981)

Characterization of ovarian folliculogenesis during the luteal phase of the menstrual cycle in rhesus monkeys using [3H]thymidine autoradiography.

The characteristics of the early stages of ovarian follicular maturation were investigated in rhesus monkeys during the luteal phase of the menstrual cycle using a novel procedure to supply low levels (10 microCi) of [3H]thymidine directly to ovaries in vivo. With this labeling procedure, plasma levels of [3H]thymidine did not exceed 8 cpm/microliters and labeled ovarian cells were readily identifiable by autoradiography. Results from four animals studied during the luteal phase of the cycle indicated that all sizes of preantral follicles contained granulosa cells that incorporated [3H]thymidine. There was a progressive increase in the percentage of labeled follicles in direct relationship to follicular size; 10% of the single granulosa cell layer follicles were labeled and the labeling frequency increased to greater than 60% in the large (> 6 granulosa cell layer) preantral follicles. The labeling frequency of all size classifications of preantral follicles during the luteal phase of the menstrual cycle was similar to that of an animal which was studied during the follicular phase of the menstrual cycle. The results suggest that growth of ovarian follicles to the preantral stage occurs during the luteal phase of the menstrual cycle in rhesus monkeys, and thus the cessation of preovulatory folliculogenesis during the luteal phase of the cycle is not due to a defect of growing preantral follicles.

Morphogenetic reaggregation and luteinization of mouse preantral follicle cells.

Small (60-90 micrometer) and large (100-130 micrometer) preantral follicles were isolated from adult mouse ovaries by a collagenase-dissection technique. These follicles were composed of resting oocytes surrounded either by granulosa cells, only, or by granulosa and undifferentiated theca cells. Further enzymatic dissociation of primary follicles yielded monodisperse cells characterized by abundant rough endoplasmic reticulum, microfilament-rich pseudopodia and only scant lipid droplets. These cells reaggregated, when explanted in stationary culture, forming epithelial cords and structures macroscopically reminiscent of native ovarian follicles. Anticipated association of follicular cells in epithelial-like monolayers was rare (less than or equal to 10% of all cultured cells). Formation and growth of both follicle-like (FLS) and cord-like (CLS) structures occurred within 24 hours of culture, continued for 14 days, and was inhibited by cytochalasin B, but not by neuraminidase. FLS and CLS, as well as cell monolayers, underwent luteinization, as indicated by the presence in the culture medium of radioimmunoassayable progesterone and by frequent cytological features suggestive of active steroidogenesis. The present report indicates that (a) specific cell affinities exist among immature follicular cells which may play a role in folliculogenesis; and (b) follicular cells are endowed, from their early developmental stages with intrinsic steroidogenic capabilities which become phenotypically expressed after escape from the intraovarian environment.

Ovarian Follicular Development in the Rat: Hormone Receptor Regulation by Estradiol, Follicle Stimulating Hormone and Luteinizing Hormone1

The effects of estradiol, FSH and LH on ovarian follicular development and granulosa cell differentiation were examined in the immature rat hypophysectomized on day 24 of age. Administration of estradiol to hypophysectomized rats for 4 days stimulated the growth of large preantral follicles with a concomitant 1.5-fold increase in FSH receptor content and a 4-fold decrease in LH receptor content in the granulosa cells. When highly purified hFSH was administered alone, receptor content for FSH increased progressively for 4 days while receptor for LH remained essentially unchanged. However, when rats were pretreated with estradiol, the response of follicles to FSH was markedly enhanced as indicated by the appearance of large, antral follicles and elevated receptor content for both FSH and LH. Receptor content for FSH increased markedly in response to hFSH following only one day of estradiol pretreatment, while receptor content for LH increased most rapidly in response to hFSH after 3 days of estradiol pretreatment. LH administered to rats possessing large preovulatory follicles caused luteinization of granulosa cells and a marked decline in receptor content for both gonadotropins within 24 h. Receptor content remained low even 48 h after LH administration when granulosa cells were fully luteinized. These results indicated that follicular development and granulosa cell differentiation are dependent on steroid-protein hormone regulation of hormone specific receptors.

Cytochemical Study of Interstitial Cells in the Bat Ovary

THERE are several types of glandular tissue in the mammalian ovaries and in the adjacent mesovaria, which are generally described as interstitial gland cells1. The different views regarding their origin have been reduced by Brambell1 to two comprehensive theses, namely epithelial origin and the connective tissue origin of the interstitial cells. No work has been done to compare or to contrast the cytochemical nature of these different types of cells in the ovary of the same mammal. Most of the cytochemical work has been carried out on the interstitial cells of thecal or connective tissue origin in the ovaries of a variety of mammalian species2–7. The ovaries of non-pregnant and pregnant grey bats (Myotis grisescens) show two types of interstitial cells3,8. The first type of cells are considerably developed and occupy all the ovary except the periphery which contains small follicles; they originated by the thecal hypertrophy of atretic large preantral and antral follicles and they are apparently developed to the same extent in the ovaries of pregnant and non-pregnant bats3. Mossman et al.9 have recently designated these cells of thecal origin as the interstitial gland cells in the mammalian ovary. The second type of interstitial cells in the bat ovary are in the form of cords of small epithelial cells, which are irregularly distributed among the first type of interstitial cells. The present investigation was undertaken to determine the nature of both types of interstitial cells by comparing and contrasting their cytochemical changes in the ovaries of non-pregnant and pregnant bats (Myotis grisescens) which were collected from January to June in the U.S.A. The fixing fluids and cytochemical techniques previously reported were also used in this investigation.

A HISTOCHEMICAL STUDY OF THE HAMSTER OVARY.

AbstractThe hamster ovary has been studied histochemically for various lipids. The granulosa cells of normal follicles contain lipid bodies of various sizes composed mainly of phospholipids. Some lipid bodies also contain triglycerides, cholesterol and its esters. The theca cells contain lipid granules consisting of phospholipids. At the onset of atresia, the granulosa stores lipids abundantly which consist of triglycerides, cholesterol and its esters and a slight amount of phospholipids. The theca of atretic follicles, also stores lipids consisting of phospholipids first, and then in sequence phospholipids and triglycerides and finally phospholipids, triglycerides, cholesterol and its esters. The theca hypertrophies and persists to form the interstitial gland whereas the granulosa cells, with their lipid droplets, regress and disappear. The interstitial gland in the hamster ovary occurs as patches of various sizes and these are derived from the theca of atretic preantral and antral follicles. Most of the lipid droplets of the interstitial gland, are mobilized within the preovulatory ovary. The replenishment of lipid droplets begins on day 1 of the cycle (metestrus). On day 2, the interstitial gland is again filled with lipid droplets which are rich in cholesterol and its esters, triglycerides and phospholipids.In ovaries treated with pregnant mare's serum (PMS) on each of the days of the estrous cycle, numerous large preantral follicles having 4–7 layered granulosa, are stimulated to ovulate. Normally such follicles become atretic, indicating that a lack of sufficient endogenous pituitary gonadotrophins prevents these follicles from maturing. Neutral lipids, especially cholesterol and its esters, could not be demonstrated in the normal granulosa in the PMS‐treated ovaries. The follicles, which were atretic at the time of injections, were not affected by exogenous hormones. Human chorionic gonadotrophin (HCG) did not conspicuously affect the growth of follicles. Both PMS and HCG caused mobilization of lipid droplets from the interstitial gland.

A COMPARATIVE HISTOCHEMICAL STUDY OF INTERSTITIAL TISSUE AND FOLLICULAR ATRESIA IN THE MAMMALIAN OVARY.

AbstractThe distribution and origin of interstitial tissue has been studied in various mammalian ovaries with histochemcal techniques for lipids. The interstitial tissue contains sudanophilic droplets of different sizes consisting of phospholipids, triglycerides and cholesterol and its esters; the lipids are comparatively unsaturated.The granulosa of normal follicles contains heterogeneous lipid bodies of various sizes composed of unsaturated phospholipids. With the start of atresia these lipid bodies also develop neutral fats (triglycerides). Besides the heterogeneous lipid bodies, another type of sudanophilic lipid droplets of atresia, consisting of triglycerides, cholesterol and its ester and little phospholopids, are formed in the granulosa cells. When the number of these lipid droplets is sufficiently increased, the heterogeneous lipid bodies disappear from the atretic follicles. The theca of such atretic follicles hypertrophies and persists to form the interstitial tissue whereas the granulosa cells, along with the lipid droplets, regress and disappear.In the rat ovary, the interstitial tissue occurs as scattered patches of various sizes that are derived from the theca of atretic preantral and antral follicles. Most of the lipid droplets of the interstitial tissue are mobilized from the preovulatory rat ovary. All of the bat ovary is occupied by interstitial tissue except for the cortex; the tissue is formed in the same way as in the rat. In the cat ovary, the interstitial tissue is sparsely scattered between the follicles and originates from the theca and adjacent stromal cells of normal and atretic follicles. In the dog ovary the interstitial tissue has a similar origin and also arises from invaginations of germinal epithelium. In the opossum ovary the interstitial tissue is present in the form of sparsely scattered patches of cells which arise from the theca of large preantral follicles. A few lipid bodies, consisting of unsaturated phospholipids, appear in the interstitial tissue.