Atretic Antral Follicles Research Articles

Follicular Atresia and Infertility in Rats Treated with a Gonadotropin-Releasing Hormone Antagonist*

Adverse effects of the GnRH antagonist Antide on folliculogenesis and fertility were noted when we were evaluating the therapeutic value of Antide on endometriosis in a rat model. Cyclic rats with (n = 56) and without (n = 18) surgically induced endometriosis received Antide (2 mg/kg) or vehicle at noon on days 0 (proestrus), 3, 6, and 9. Rats were killed at noon on days 0, 6, 12, 18, 24, 30, 42, and 165. The number of antral follicles and the number of atretic antral follicles evaluated did not differ (P greater than 0.05) between endometriosis and control rats. Antide-treated rats had more (P less than 0.05 ) atretic antral follicles (64.7%) than vehicle-treated rats (15.3%). Antide-treated rat ovaries contained fewer corpora lutea than those of vehicle-treated rats on days 6, 12, and 18. No corpora lutea were found in Antide-treated rat ovaries after day 18. The abnormal ovarian morphology of the Antide-treated rats persisted for the duration of the project (165 days). Fertility (rats without endometriosis) was assessed by mating vehicle-and Antide-treated rats at spontaneous proestrus (n = 8) for eight posttreatment cycles as well as after follicular stimulation (n = 2). All vehicle-treated and no Antide-treated rats became pregnant. No oocytes were found in the oviducts of Antide-treated rats after eight cycles, indicating that ovulation had not occurred. The serum FSH and estradiol concentrations in the rats treated with Antide were lower (P less than 0.05) on days 6, 12, and 18, but rose to values equal to (days 24 and 30) or greater than (day 42) those in vehicle-treated rats. Serum progesterone levels in rats treated with Antide were lower (P less than 0.05) than those in vehicle-treated rats on all days tested. In conclusion, at a dosage sufficient to suppress reproductive cyclicity (and elicit the regression of endometriosis), Antide also caused long term follicular atresia and infertility.

Experimental autoimmune oophoritis. I. Inhibition of fertility in rats isoimmunized with homogenates of ovary.

Experimental autoimmune oophoritis (EAOO) induced in female Lewis rats by a single injection of isologous ovary in complete Freund's adjuvant (CFA) and concentrated pertussis vaccine resulted in a multifocal accumulation of mononuclear cells in ovaries and complete loss of fertility after 17-28 days. The time course of appearance of anti-ovary antibodies and their serum titers showed a good correlation with the reduction of litter size. Furthermore, the infertility also could be induced by passive immunization of rats with adsorbed anti-ovary serum. The contraceptive effect of the antibody does not result in permanent sterility. Besides lymphoid cell infiltrations, the most prominent histological alterations in ovaries of experimental rats were characterized by a significant increase in the number of atretic preantral and antral follicles and a decrease in the number of growing follicles of all sizes and corpora lutea. It is presumed that both the direct effect of anti-ovary antibodies and disturbance in ovarian morphology can lead to a reduction of litter size and appearance of infertile cycles in rats with oophoritis.

Effects of age at unilateral ovariectomy on compensatory responses of remaining ovary in rabbits.

Effects of age at unilateral ovariectomy (ULO) on compensatory responses of the remaining ovary were examined in rabbits. ULO was performed on 8 does for each group at 30 (group 30), 90 (group 90), 160 (group 160) and 230 days of age (group 230). Eight intact does were served as controls. Four does of each group were laparotomized and remaining ovaries were removed at first estrus (over 250 days of age). Numbers of large follicles on ovarian surface ( ?? 1.5 mm in diameter) per doe in all groups were nearly 10 and these values of ULO groups were twice as large as controls. Mean ovarian weight and volume of group 90 were the highest, and those of group 30 were second. The values in these ULO groups showed significant differences in comparison with controls. In histology of these ovaries, numbers of large, healthy follicles ( ?? 1 mm in diameter) per ovary in ULO groups were roughly double compared with those in controls. There was a tendency that the number of small, atretic antral follicles (< 1 mm in diameter) was increased in ULO animals operated at young age. The number of atretic antral follicles was closely correlated with ovarian weight and volume. To induce ovu-lation, the remaining 4 does of each group were injected with 20 IU of hCG. The num-bers of corpora lutea per doe of all groups were about 10 with no significant difference among groups. These results suggest that ULO in the immature period induces marked compensatory hypertrophy after puberty and that, regardless of age at ULO, the re-maining ovary in the ULO animal fulfills the function of both ovaries in the intact animal.

Rescue of atretic follicles in vitro and in vivo.

The purpose of this work was to determine if atretic follicles could be rescued and could return to the ovulatory pathway of development. Rats were given continuous infusions of 3H-thymidine (3H-thymidine (3H-TdR) resulting in uniform labeling of healthy antral follicles versus patchy labeling of atretic antral follicles. The infusion was then stopped and rats were subjected to experimental treatments known to stimulate follicular recruitment. Immature rats were given injections of pregnant mare's serum gonadotropin (PMSG) to provoke super-ovulation. Adult rats were hemicastrated to provoke compensatory follicular development in the remaining ovary. In addition, granulosa cells from individual follicles of adult rats were cultured in vitro. The differential labeling patterns, observed at the end of the treatment period, were used to determine, a posteriori, the condition of follicles as they had been at the start of the treatment period. Sparsely labeled cell cultures were found, indicating that some cells from atretic follicles were able to become established in tissue culture. However, there was no evidence that atretic follicles had revived in vivo. All follicles recruited for ovulation by PMSG or hemicastration were heavily and uniformly labeled. All poorly labeled follicles were clearly continuing their process of degeneration. These observations suggest that, despite continued viability of some granulosa cells in atretic follicles, once a follicle begins to degenerate in vivo, it will probably not return to the ovulatory pathway.

PRECISION OF SAMPLING TECHNIQUES IN DETERMINING MICROSCOPIC FOLLICULAR POPULATION IN GILTS

The precision of estimating populations of atretic and nonatretic antral follicles by sampling 10, 20 and 25% of follicles in serially sectioned ovaries was determined. From records on 18 374 gilt follicles (Data 1), three new data sets (Data 2, 3 and 4, generated by attributing a detection probability of 0.1, 0.2 and 0.25 to each of the follicles, were compared with Data 1. Estimates of the follicular populations obtained from Data 2, 3 or 4 differed from the values of Data 1 only when there were fewer than five follicles of a given size on the ovary. The coefficient of variation of the estimated numbers of follicles from values of Data 1 was below 32 ± 19% for Data 2 and 3 when there were more than 50 follicles in a class. For Data 4, however, it was 8 ± 2% or below except for classes containing less than five follicles. Data 4, but not Data 2 and 3, was as efficient as Data 1 in detecting differences in follicle distribution between breeds, age and type of ovary (P &lt; 0.05), except for follicular classes containing less than five follicles. Thus, follicular populations, as determined by sampling 25% of the total number of follicles, were consistent with the actual distribution if five or more follicles were present in a class. Key words: Follicles, sampling, ovary, gilts

In VitroEffects of Follicle-Stimulating Hormone, Luteinizing Hormone, and Prolactin on Follicular Deoxyribonucleic Acid Synthesis in the Hamster*

Follicles were dissected by hand or enzymatically from the ovary of the proestrous hamster at 0900 h and classified into 10 stages: stages 1-4, follicles with 1-4 layers of granulosa cells and no theca; stages 5-8, preantral follicles with 5 or more layers of granulosa cells and theca to small antral follicles; stage 9, intermediate-sized atretic antral follicles; and stage 10, healthy preovulatory antral follicles. Follicles were then incubated for 2 h with [3H]thymidine [( 3H]Tdr) in the absence or presence of gonadotropins and with incorporation of radionuclide into DNA as the end point. FSH (25 ng) significantly stimulated [3H]Tdr incorporation in all stages of follicular development with a latency of 2 h, and this effect was inhibited by 2 micrograms unlabeled Tdr. While FSH and PRL (25 and 100 ng) stimulated [3H]Tdr incorporation in all stages, LH (0.2-5 ng) action began from stage 5 onward, when definitive thecal cells and LH receptors started appearing. LH (5 ng) also suppressed 25 ng FSH-induced DNA synthesis in stages 5-10; however, stages 1-4 were unaffected. Significant increases in both intra- and extracellular cAMP levels occurred in follicles at stages 2-10 after FSH administration. In contrast, LH was active in stages 5-10, whereas PRL was ineffective. Follicular DNA synthesis increased markedly when stimulated by 8-bromo-cAMP (0.01-2 mM). These results show that gonadotropins act directly as a primary stimulus at the level of small primary and secondary follicles to regulate DNA synthesis and, thus, perhaps the growth and differentiation of granulosa and thecal cells; cAMP functions as one of the possible intracellular mediators of gonadotropin action in initiating DNA replication.

Influence of Infusion of Prostaglandin F (PGF ) and Weaning on Surface and Histologic Populations of Ovarian Follicles in Early Postpartum Beef Cows

Twenty-four beef cows were infused continuously for 11 d (d 2 to 13 after parturition) into the descending aorta with either prostaglandin F2 alpha-Tham salt (PGF2 alpha; 33.5 mg/d; n = 12) or with .9% NaCl (saline; n = 12) vehicle. Cows from each infusion treatment then were assigned to three slaughter groups (G). Cows in G1 and G2 were suckled until slaughter on d 15 and 35, respectively, whereas calves in G3 were weaned on d 31 and cows were slaughtered on d 35 after parturition. Nonatretic and atretic (greater than 4 pycnosis) antral follicles (greater than .15 mm) on ovaries ipsilateral to the previously gravid uterine horn were evaluated by histological techniques. Compared with saline infusion, PGF2 alpha increased mean diameters of the largest (F1) follicles on the ipsilateral (d 15 and 35; P less than .07) and contralateral (d 15; P less than .07) ovaries (surface evaluation) as well as mean diameters of the largest (F1, d 35; P less than .002), second- and third-largest (F2, F3 d 15 and 35; P less than .01) nonatretic follicles (histologic evaluation) in suckled cows. Compared with suckled cows slaughtered on d 35, weaning on d 31 increased the number of medium follicles (3 to 5 mm), diameters of the three largest nonatretic follicles, percentage of large nonatretic follicles (greater than 3.67 mm) and mitotic index of class 3 (.68 to 1.57 mm) follicles in saline-infused cows. In contrast, in PGF2 alpha-infused cows, weaning decreased (P less than .05 to P less than .001) all of these responses. Surface and histologic evaluations of follicular activity indicated that postpartum infusion of PGF2 alpha stimulated development of large follicles. In response to weaning, PGF2 alpha infusion favored development of those large follicles toward ovulation or atresia on nonovulated follicles.

Early short photoperiod effects in female LSH/SsLak Syrian hamsters.

Previous experiments showed that LSH/SsLak female hamsters cease ovarian cyclicity after 2-4 weeks of short photoperiod (SP) treatment. This study was designed to reveal early hormonal and histological changes on day 1 of the estrous cycle (estrus) in SP-treated animals and changes brought about by the SP-induced acyclic condition. Groups of 8-10 animals were killed on day 1 after 0, 4, 8, 12, and 16 days of SP treatment; sera and pituitaries were saved for hormone determinations, and ovaries were prepared for histological analysis. Intraatrial cannulae were inserted into anovulatory animals, and blood samples were withdrawn on the first and second postoperative days; the animals were killed on the third postoperative day. PRL levels were significantly reduced in cycling animals after 16 days of SP exposure and diminished further in acyclic animals. Pituitary PRL did not change in cycling animals, although it was highly depressed in SP-treated acyclic animals. The estrous FSH surge, serum LH levels, and pituitary gonadotropin contents were not affected by SP in cycling animals; in anovulatory animals, pituitary gonadotropin contents were significantly increased, and daily afternoon gonadotropin surges were observed. Uterine weights were reduced in cycling animals and underwent a further reduction after cyclicity ceased. Ovarian analysis revealed that all cycling animals had the same number of recruited follicles, yet significantly fewer corpora lutea and an apparent increase in atretic antral follicles were observed after 16 days of SP exposure. These results suggest that SP-induced cessation of estrous cyclicity occurs abruptly. SP does not alter the secondary FSH surge, but might adversely affect maintenance of follicular growth and depress serum PRL levels.

Rapid cessation of estrous cyclicity and depressed castration response in short photoperiod-treated, inbred LSH/SsLaK hamsters.

This study examined the effects of transfer from long photoperiod (LP) to short photoperiod (SP) on the cessation of ovarian cyclicity and the castration response in inbred LSH/SsLak golden Syrian hamsters. Forty-six 8 to 10-wk-old female hamsters were acclimatized in LP (14L:10D; lights on at 0600 h) during which time animals were monitored for regular ovarian cyclicity. Twenty-six animals were transferred to SP (8L:16D; lights on at 0600 h) and examined daily for vaginal discharges. One day after the day of the first missed ovulation, individual SP-exposed animals were bilaterally ovariectomized; concomitantly, an LP control animal in diestrus I underwent the same procedure. Thirty days after ovariectomy, the hamsters were fitted with intra-atrial silastic cannulae. On the following two postoperative days, 0.6 ml blood samples were collected at 0700, 1200, 1400, and 1600 h for SP animals and at 0700, 1400, 1600 and 1800 h for LP controls. On the third day, the animals were decapitated and sera and pituitaries saved for determination of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin (PRL) by radioimmunoassay (RIA). All SP-exposed animals displayed their last estrous discharge 14-34 days after transfer to SP (mean = 23.0 +/- 0.8 days). Their ovaries were characterized by the absence of corpora lutea, the presence of large atretic antral follicles, few growing follicles, and interstitium that was stimulated to varying degrees. Total and adjusted pituitary weights were decreased by SP exposure (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of ovarian follicular populations in the dairy cow within 35 days after parturition.

Ovaries were obtained at slaughter from 12 Holstein dairy cows at 15, 25 or 35 days after their 4th calving. Non-atretic and atretic antral follicles were separated into 6 size classes according to size and the numbers in each class were expressed as a percentage of the total for each ovary. Non-atretic follicles of diameter 0.16-0.28 mm decreased from 27.5% at Day 15 to 1.5% at Day 35 whereas those of 0.29-0.67 mm and 0.68-1.57 mm diameter increased from 37.4 to 47.2% and from 11.5 to 17.3% respectively (all P less than 0.05). The proportions of follicles measuring 1.58-3.68, 3.69-8.56 and greater than 8.56 mm remained almost constant. The atretic follicles of 0.29-3.68 mm varied significantly in number according to the post-partum interval and to whether they were in the ovary containing the CL of pregnancy. It is concluded that the CL of pregnancy and/or the conceptus have a carry-over effect on the rate of growth of the antral follicles even after parturition.

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.

125I]hCG binding to bovine thecal tissue from healthy and atretic antral follicles

[ 125I]hCG binding to thecal tissue from healthy bovine follicles was examined and compared to [ 125I]hCG binding to other bovine ovarian tissues. [ 125I]hCG bound specifically to theca interna but not to theca externa. Binding to theca interna was a time- and temperature-dependent process, the rate of association obeying second-order kinetics with calculated rate constants of 1.97 ± 0.13 × 10 5 and 0.85 ± 0.04 × 10 5 1 M −1 sec −1 at 37 and 22°C, respectively. The dissociation of [ 125I]hCG from theca interna was a slow biphasic process with only 40% of specifically bound [ 125I]hCG being liberated after 8 h at 37°C. Unlabelled hCG and LH, but not FSH, prolactin, GH, TSH or GnRH, inhibited [ 125I]hCG binding to theca interna. The specific binding of [ 125I]hCG to theca interna was saturable and equilibrium binding data produced a linear plot when fitted to the Woolf equation. The equilibrium dissociation constant ( K d ) and maximum binding capacity ( B max ) calculated from Woolf plots were 0.21 ± 0.02 nM (mean ± SEM) and 34 + 4 fmoles/mg protein, respectively. Constants for [ 125I]hCG binding to granulosa cells and lu teal tissue, respectively, were 0.29 ± 0.02 and 0.31 ± 0.04 nM for the K d values and 32 ± 6 and 116 ± 13 fmoles/mg protein for the B max values. [ 125I]hCG binding constants for small (< 8 mm dia.) and large (⩾ 8mm dia.) follicles (healthy or atretic) were not significantly different. In addition, there was no difference in the [ 125I]hCG binding constants of healthy and atretic follicles (large or small). Theca interna from large healthy follicles, but not large atretic follicles, responded steroidogenically to LH, when perifused in vitro, by increased production of androstenedione. (LH and hCG were equipotent in stimulating androstenedione production by perifused theca from healthy follicles.) These studies show that the binding characteristics of bovine theca interna LH/hCG receptors are similar to those of the LH/hCG receptors present in granulosa cells and luteal tissue. These studies also show that lack of available receptors for LH/hCG is unlikely to be the cause of the failure of large atretic follicles to produce androgen in response to LH.

Luteal and follicular populations in the ovary of the opossum (Didelphis virginiana) after ovulation.

The maximum diameters of all luteal and antral follicular structures were measured in opossum ovaries on Days 3, 7 and 11 after oestrus, and follicles were classed as developing or atretic. Ovarian weights and luteal diameters were equivalent in comparisons of pregnant and non-pregnant animals on each day. The number of CL (range 45-85) per animal per cycle indicated a very high ovulation rate for a mammal. Luteinized follicles (1-4 per ovary) were identified in all Day-3 ovaries. Ovarian weight, luteal diameter and follicular diameter were greater on Day 7 than on Days 3 or 11. More antral follicles occurred on Day 11 (120 +/- 10.7, s.e.m.) than Day 3 (77.8 +/- 8.8), although the percentage of atretic antral follicles also increased from 20% to 50 and 57% on Days 7 and 11. These increases were not accompanied by an increase in the number of developing antral follicles (58.1 +/- 4.0), thus indicating a mid-luteal increase in the rate of follicular recruitment, of growth and of atresia in the opossum.

An autoradiographic study of the binding of 125 I-labeled follicle-stimulating hormone, human chorionic gonadotropin and prolactin to the hamster ovary throughout the estrous cycle.

Specific tissue binding sites for follicle-stimulating hormone (FSH), human chorionic gonadotropin (hCG) and prolactin (Prl) were identified in the cyclic hamster ovary to provide a better understanding of the role of gonadotropins in the regulation of ovarian function. At 0800 h on Days 1–4 and at 1200 h, 1600 h and 2000 h on Day 4 (Day 1=day of ovulation and Day 4=proestrus with the LH surge occurring by 1600 h), ovaries were obtained from hamsters, frozen and serially sectioned. Selected sections were incubated with 125I-labeled FSH, hCG or FrI and processed for autoradiography. FSH binding to granulosa and oocytes of healthy follicles increased progressively with follicular size but was always notably reduced or absent in atretic follicles. Corpora lutea (CL) exhibited substantial FSH binding on Day 1; however binding was much lower on Day 2 and not detected on Day 3. hCG bound moderately to interstitial cells (IC) and thecae of all follicles. hCG binding was not detected in granulosa of preantral follicles but appeared in basal mural granulosa of growing antral follicles on Day 2 and then increased progressively to include all of the mural granulosa and became maximal at 1200 h on Day 4. This binding was slightly reduced at 1600 h and 2000 h on Day 4. hCG binding to granulosa of atretic antral follicles was always notably less than to healthy antral follicles and binding was never detected in the cumulus or oocyte of any follicle. hCG binding to CL was moderate on Day 1, sharply increased and maximal on Day 2, and then markedly reduced on Days 3 and 4. Prl binding to CL, IC and follicles followed the same pattern as for hCG on Days 1–3. On Day 4 at 0800 h, thecae of preantral follicles and IC exhibited moderate Prl binding and CL had very light binding. In addition, thecae and mural granulosa of healthy antral follicles had high Prl binding whereas binding was notably lower in atretic antral follicles. At 1600 h and 2000 h on Day 4, overall Prl binding to ovarian tissues was markedly decreased. Several new findings in the present study appear to be biologically significant: 1) the sharp reduction in Prl binding at the time of and at least 4 h after the LH and FSH surges suggests that either or both of these hormones may regulate Prl binding, and/or the loss of Fri binding may play a role in ovulation and/or luteinization: 2) FSH binding to CL suggests FSH has a role in CL function: 3) and FSH binding to the cumulus and oocyte suggests that FSH may play a role in oocyte growth and maturation.

Effects of gonadotrophins, hypophysectomy and prostaglandin F-2 alpha on corpora lutea and ovarian follicles, and evidence for the presence of PGF-2 alpha receptors in the ovarian follicles and interstitium of non-pregnant guinea-pigs.

Simultaneous administration of hCG (but not FSH or prolactin) with PGF-2 alpha prevented the luteolytic effect of PGF-2 alpha after Day 9 of the oestrous cycle both morphologically and in terms of progesterone secretion in hysterectomized guinea-pigs. Hypophysectomy on Day 5 or PGF-2 alpha administration on Days 6--9 were not luteolytic, but their combined effect resulted in an advanced state of luteolysis as early as Day 9. When PGF-2 alpha was injected simultaneously with FSH or prolactin (but not hCG), the proportion of atretic antral follicles was significantly increased, although the total number of antral follicles remained unchanged. When PGF-2 alpha receptors were measured in the membrane fractions of luteal tissue and ovarian stromal, interstitial and follicular tissue obtained from cyclic animals, the concentrations were 22.75 and 36.26, and 62.60 and 96.26 fmol/mg membrane protein on Days 5 and 12, respectively. It is concluded that (1) LH protected corpora lutea against the luteolytic action of PGF-2 alpha up to Day 9 of the cycle, (2) PGF-2 alpha receptors were present in follicles, and (3) these receptors and PGF-2 alpha were involved in the development of the normal complement of Graafian follicles.

Steroidogenesis in experimentally induced atretic follicles of the hamster: a shift from estradiol to progesterone synthesis.

The effects of phenobarbital-delayed ovulation on in vitro steroidogenesis and aromatase activity of LH-stimulated preovulatory follicles was ascertained in the cyclic hamster. After 3 days of ovulatory delay, antral follicles exhibited early signs of atresia (degenerating granulosa cells and pyknotic nuclei within oocytes). On days 2 and 3 of delay, LH-stimulated follicles produced more progesterone (P 15--20 ng P/follicle . 90 min) in vitro than control proestrous follicles (2.5 ng P/follicle . 90 min). Concomitant with the increase in LH-stimulated P production was a decline in the in vitro production of androstenedione (A) and estradiol (E2) on day 2 (A, 5 ng/follicle . 90 min; E2, 4 ng) and day 3 (1 ng A, less than 0.2 ng E2)-proestrous controls: 8 ng A or E2/follicle . 90 min. The steroidogenic profile of 1-day delayed follicles was similar to proestrous controls. A similar E2-P shift was observed in vitro when the steroidogenic profile of preovulatory follicles on the morning of proestrus (2.5 ng P, 8 ng A or E2) was compared with post-LH surge follicles (25 ng P, less than 1 ng A or E2) and with new corpora lutea (36 ng P, less than 0.2 ng A, less than 1 pg E2). A slight increase in the aromatizing activity of follicles was observed on days 1 and 2 of delay. However, atretic antral follicles (day 3 of delay) exhibited an aromatizing capacity similar to that of proestrous controls. Collectively, these results indicate that the loss of E2-synthesizing capacity in atretic antral follicles (induced by ovulatory delay) is due to the lack of A precursor. In addition, the results indicate that phenobarbital-delayed ovulation induces a shift from E2 to P synthesis in 3-day delayed follicles (early atretic). This E2-P shift is similar to that in Graafian follicles on the afternoon of proestrus but occurs at a much slower rate.

Follicular development in the adult guinea-pig and responses to human chorionic gonadotrophin.

The development of antral follicles and of atretic follicles throughout the cycle of adult guinea-pigs is a continuous process, but there are two stages when atresia is most pronounced: immediately after oestrus and in the late luteal phase. New atretic antral follicles were not found in the ovaries until around day 10 of the cycle, when an injection of HCG caused atresia of the medium-sized antral follicles within the ovary and luteinization of the largest follicles but spared the smallest antral follicles. Following the induced atresia, cycle lengths were prolonged, but the population of antral follicles could be restored to normal within 10 days of gonadotrophin treatment. It is suggested that the growth rate of antral follicles is flexible and proceeds most rapidly at the end of the luteal phase. It is not clear whether ovarian steroid play an integral part in regulating follicular growth and atresia.

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.