Rate Of Follicular Atresia Research Articles

Foliculogênese e esteroidogênese ovarianas em ratas adultas hipertireóideas

A foliculogênese e a esteroidogênese ovarianas foram estudadas em ratas adultas hipertireóideas. O hipertireoidismo foi induzido em 27 ratas Wistar com cinco meses de idade pela administração diária de 50µg de L-tiroxina. Outras 27 ratas foram mantidas em estado eutireóideo e serviram como controle. Aos 30, 60 e 90 dias após o início do tratamento, nove ratas de cada grupo foram sacrificadas, os ovários inspecionados, pesados e processados para avaliação histomorfométrica e o plasma sangüíneo colhido para dosagem de T4-livre, estradiol e progesterona. As concentrações plasmáticas de T4-livre foram significativamente maiores nas ratas hipertireóideas aos 30, 60 e 90 dias, e o peso médio dos ovários foi significativamente maior somente aos 90 dias. Já o número de folículos secundários e terciários e de corpos lúteos foi significativamente maior aos 60 ou aos 90 dias, mas a taxa percentual de atresia folicular só foi diferente aos 90 dias. O número de folículos primários e pré-ovulatórios, assim como as concentrações plasmáticas de estradiol e progesterona, não diferiram entre grupos e entre períodos. Concluiu-se que o hipertireoidismo estimula a foliculogênese ovariana em ratas sexualmente maduras e diminui a atresia folicular.

High serum follicle stimulating hormone (FSH) during perimenopause at high altitude

The current data provide evidence that women living at high altitude may experience accelerated w x menopause than at sea level 1 , although the precise mechanisms are unknown. It has been suggested that early age at menopause may be due to high levels of serum FSH observed in regularly menstruating women at high altitude w x than at sea level 2 . The loss of ovarian oocytes, the cause of menopause, accelerates in the decade before menopause. This accelerated oocyte loss may in turn be caused by a selective elevation of w x plasma follicle-stimulating hormone 3 . Serum FSH levels increase significantly after the age of 40, and this elevation seems to be related to the high rate of follicular atresia, determining age at w x menopause 3 . It could be interesting to determine serum FSH levels in women in their forties living at high altitude.

Study of preantral follicle population in situ and after mechanical isolation from caprine ovaries at different reproductive stages

The purposes of this study were to estimate the population of caprine preantral follicles, and to evaluate quantitatively and qualitatively the efficiency of a specific mechanical method for the isolation of preantral follicles from mixed breed goats at different reproductive stages. On average, 37,646+/-4277 preantral follicles were present in goat ovaries, and 13,631+/-2399 preantral follicles were obtained after isolation. The number of preantral follicles isolated or in situ was not significantly affected by the reproductive stage. The mean recovery rate per ovary ([number of isolated follicles/number of in situ follicles] x 100) of isolated follicles was 36.2%. The distribution of follicles in situ was 67.8% primordial, 25.8% primary and 6.4% secondary; the respective distribution after isolation was 93.8%, 5.2% and 1.0%. In this study, many polyovular follicles were also observed, mainly in prepubertal goat ovaries. Histological analysis showed that few preantral follicles were atretic in situ (4.83%+/-0.35) or after the isolation procedure (4.67%+/-0.65) in the three reproductive stages. The percentage of atretic follicles was not affected either by the mechanical method or by the reproductive stage. It is concluded that a large number of preantral follicles can be successfully isolated mechanically, with a high recovery rate and a low rate of follicular atresia, irrespective of the reproductive stage of the caprine female.

RU486-treated rats show endocrine and morphological responses to therapies analogous to responses of women with polycystic ovary syndrome treated with similar therapies.

Administration of 4 mg of the antiprogestagen RU486 to 4-day-cyclic rats over 8 consecutive days starting on the day of estrus (Day 1) induced and anovulatory cystic ovarian condition with endocrine and morphological features similar to those exhibited in polycystic ovarian disease (PCO). To determine whether the RU486-treated rat responds in an analogous fashion to therapies similar to those that have been used to treat human PCO, RU486-treated rats were injection on Days 5 and 7 with 1) 1 mg of an LHRH antagonist (LHRHa), 2) 5 IU of human FSH (hFSH), 3) 2 mg of the antiandrogen flutamide (FLU), 4) 1 mg of the antiestrogen tamoxifen (TMX), or 5) 1 mg of the dopamine agonist bromocriptine (BRC). Controls were intact cyclic rats decapitated on estrus and rats injected with RU486 and the corresponding vehicles (saline or 70% ethanol) used with LHRHa, hFSH, FLU, TMX, and BRC injections. RU486-treated rats were decapitated on Day 9, and the serum concentrations of LH, FSH, prolactin (PRL), testosterone (T), and estradiol-17 beta (E2) were determined. Pituitary and ovary weight, number of follicular cysts, size of the corpora lutea, and rates of follicular growth and atresia were also noted. Finally, the ovulatory response to ovine LH (oLH) in rats treated with RU486 and injected with various doses of hFSH (5, 10, or 20 IU) was evaluated. While administration of LHRHa and of TMX decreased the serum concentrations of LH, T and E2 and the LH/FSH and T/E2, ratios, and injections of BRC and of FLU increased the serum concentration of LH and T, the administration of hFSH (10 IU) to RU486-treated rats increased only the serum levels of E2. All treatments decreased, though in different degrees, both the number of cysts and the rate of follicular atresia, and stimulated follicular growth. The positive effects on follicular growth and atresia were significantly higher in those rats injected with hFSH. Moreover, RU486-treated rats injected with different doses of hFSH ovulated in a dose-dependent manner in response to oLH. Rates deprived of the actions of progesterone through the administration of the antiprogestagen RU486 had 1) endocrine and morphologic alterations comparable to those observed in women with PCO, 2) analogous responses to therapies similar to those that have been used to treat human PCO, and 3) an ovulatory response to combined treatment with FSH and LH. These results establish the fundamental adequacy of using the RU486-treated rat as a PCO model.

1 The menopausal transition

The menopausal transition is that period beginning with the first indications of the approach of menopause and ending with the final menses. Its morphological basis is a rapidly declining number of primordial follicles within the ovary; a decline which appears to result from an increased rate of follicular atresia. The most characteristic hormonal change in the menopausal transition is a progressive, though often fluctuating, rise in the level of serum FSH. Oestradiol and inhibin levels fluctuate markedly when observed in individual subjects but remain relatively preserved during the follicular phase of the cycle, until late in the menopausal transition. The frequency of anovulatory cycles increases as the final menstrual period approaches. The rate of symptom reporting varies among different populations of women, with maximum symptom frequency being seen during the menopausal transition. There are some indications that cardiovascular and osteoporosis risk factors may change adversely during the menopausal transition and medical practitioners should be ready to offer hormonal supplementation to women at increased risk of cardiovascular disease and osteoporotic fracture.

Evidence that androgens are involved in atresia and anovulation induced by antiprogesterone RU486 in rats

Administration of antiprogesterone RU486 to female cyclic rats results in blockade of ovulation associated with both a decreased ovulatory release of LH and an increased rate of follicular atresia. These rats also exhibit increased LH:FSH and testosterone:oestradiol ratios in serum during the period of follicular development as well as an increase in serum concentrations of prolactin that can be suppressed by a dopamine agonist. The increase in either prolactin or testosterone concentrations as well as the relative deficiency in FSH might be responsible for the increase in follicular atresia. The present work evaluated the involvement of LH, FSH, prolactin and testosterone in follicular atresia and in blockade of ovulation induced by RU486 in the cyclic rat. Although bromocriptine treatment did not modify the blockade of ovulation induced by RU486, unilateral ovariectomy at metoestrus and anti-androgen flutamide treatment reversed, in part, the effects of RU486 on both follicular development and ovulation. The combined increase in FSH serum concentration during dioestrus induced by unilateral ovariectomy and the treatment with flutamide had no additive effects. Furthermore, treatment with a superovulatory amount of hFSH did not reverse the effects of RU486. Moreover, unilateral ovariectomy halved testosterone serum concentrations and flutamide treatment had no effect on LH and FSH concentrations in RU486-treated rats. It was therefore concluded that androgens play a role, at least in part, in the process of follicular atresia induced by RU486.

Ovarian development in sexual and parthenogenetic geckos of the Heteronotia binoei complex

Ovarian development in sexual and parthenogenetic geckos of the Heteronotia binoei complex was analysed quantitatively by gross and histological examination. Females were classified into one of four stages of the reproductive cycle: non‐reproductive, preovulatory, postovulatory and postoviposition. Parthenogens had significantly more developing follicles present in the ovaries than sexual females in non‐reproductive, preovulatory and postovulatory stages of the reproductive cycle. The larger number of developing follicles in parthenogenetic Heteronotia was correlated with the significantly larger body size of the parthenogenetic females at the localities examined. Maximum follicular size and rates of follicular atresia were not significantly different between sexual and parthenogenetic females. These findings raise the possibility that the reproductive output of the parthenogenetic females may be higher than that of sympatric sexual females at these localities due to an increase in follicular recruitment. Based on this evidence, we predict that at these localities parthenogenetic females produce more clutches of two eggs than sexual females. If viability is equal, this would enhance the reproductive advantage of parthenogens over the two‐fold level already present. In all other respects, the morphology of the ovaries appeared very similar between parthenogenetic and sexual females and was typical of geckos.

How does daily treatment with human chorionic gonadotropin induce superovulation in the cyclic hamster?

Daily s.c. injection of 2.0 IU hCG per day, begun on Day 1 of the cycle (estrus), results in hamsters ovulating 20.7 +/- 0.7 eggs instead of the normal number of 13.3 +/- 0.5 (SEM). This is associated with a reduced rate of follicular atresia so that more of the 10 developing follicles per ovary (large preantral stages) normally recruited on Day 1 of the cycle mature and go on to ovulate. The hCG-treated follicles were larger than control follicles, but contained similar amounts of DNA/follicle; increased size of the antral cavity accounted for their greater size. Moreover, DNA synthesis was significantly reduced in the hCG follicles on Days 2 and 4. Thecal vascularity as judged by the number of red blood cells retained in the theca or microsphere uptake by follicles indicates that on Day 2, thecal blood flow was significantly lower in the hCG-treated animals than in controls. On the other hand, after hCG treatment begun on Day 1, serum levels and in vitro incubation of individual follicles revealed that on Day 2 and beyond, androstenedione (A) and estradiol (E2) levels were elevated. After hCG treatment, the elevated serum E2 correlated with reduced serum LH on Days 3 and 4 whereas FSH was unaffected. To study in vitro steroid accumulation, the 10 largest follicles (the developing follicles) were dissected from alternate left and right ovaries from control and hCG-treated animals and incubated individually, and their histology was then compared with the steroid profiles. Accumulation of A and E2 was significantly greater in the hCG-treated follicles than in controls in a 1-h basal incubation and after the addition of 50 ng LH. Progesterone accumulation usually did not differ between the control and hCG-treated follicles. Early stage 1 atretic follicles (judged by histology) were still capable of producing A and E2 in vitro, comparable to control follicles; but, as atresia progressed, the follicles synthesized only progesterone. This is consistent with the temporal pattern previously observed in a model of induced follicular atresia in the hamster [Greenwald, Biol Reprod 1989; 40:175-181]. It is concluded that superovulation resulting from hCG injections is due to thecal production of androgens from follicles normally destined for atresia. For the untreated cyclic hamster, the critical time for thecal androgen production is the first 2 days of the cycle. The aromatizable androgens are then converted into estrogens, which in turn may maintain the microenvironment of the antral cavity, which is essential for viability of the granulosa cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of litter size and light regimen imposed during lactation on ovarian follicular population at weaning in third-parity sows.

Sixteen third-parity sows maintained under two photoperiod treatments (16 h light: 8 h dark [16 h] or 4 h light: 20 h dark [4 h]) were assigned to be unilaterally ovariectomized (left ovary) at weaning on d 28 after farrowing a small litter (12 or fewer piglets; S) or a large litter (more than 12 piglets; L). Antral follicles were classified as atretic or nonatretic and divided into six size classes. The right ovary was obtained at slaughter, 16 d after estrus was detected. Number of antral follicles in the left ovary was greater (P less than .05) for L sows (540) than for S sows (427). Sows exposed to 16 h of light with large litters had a higher number of atretic follicles than all other groups (litter size x photoperiod interaction, P less than .05). Number of nonatretic follicles were similar between groups. However, when nonatretic follicles were classed by size (1 = smallest; 6 = largest), their distribution differed. In Class 1, L sows had more follicles than S sows (P less than .05). For Classes 3 and 4, photoperiod interacted with litter size to decrease the number of follicles in L 16 h sows (litter size x photoperiod interaction, P less than .05). These lower numbers of nonatretic follicles were related to a higher rate of follicular atresia in L 16 h sows. In Classes 2, 3 and 4, L 16 h sows had more atretic follicles than any other group (litter size x photoperiod interaction, P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of alterations in pulsatile luteinizing hormone release on ovarian follicular atresia and steroid secretion on diestrus 1 in the rat estrous cycle.

This study examined the importance of pulsatile luteinizing hormone (LH) release on diestrus 1 (D1; metestrus) in the rat estrous cycle to ovarian follicular development and estradiol (E2) secretion. Single injections of a luteinizing hormone-releasing hormone (LHRH) antagonist given at -7.5 h prior to the onset of a 3-h blood sampling period on D1 reduced mean blood LH levels by decreasing LH pulse amplitude, while frequency was not altered. Sequential injections at -7.5 and -3.5 h completely eliminated pulsatile LH secretion. Neither treatment altered the total number of follicles/ovary greater than 150 mu in diameter, the number of follicles in any size group between 150 and 551 mu, or plasma E2, progesterone, or follicle-stimulating hormone (FSH) levels. However, both treatments with LHRH antagonist significantly increased the percentage of atretic follicles in the ovary. These data indicate that: 1) pulsatile LH release is an important factor in determining the rate at which follicles undergo atresia on D1; 2) reductions in LH pulse amplitude alone are sufficient to increase the rate of follicular atresia on D1; 3) an absence of pulsatile LH release for a period of up to 10 h on D1 is not sufficient to produce a decline in ovarian E2 secretion, most likely because the atretic process was in its early stages and had not yet affected a sufficient number of E2-secreting granulosa cells to reduce the follicle's capacity to secrete E2; and 4) suppression or elimination of pulsatile LH release on D1 is not associated with diminished FSH secretion.

The Comparative Anatomy of Lizard Ovaries, with Emphasis on the Number of Germinal Beds

Germinal bed (GB) number in ovaries of 26 lizard species is described. This infor- mation, along with previous data on 14 other lizards, allowed us to form the following hypotheses concerning the relationships of GB number and (1) the numbers of growing and atretic follicles in the preovulatory ovary, (2) instantaneous fecundity, (3) geographic distribution, and (4) taxonomic relationship. Germinal bed number can vary within a family, but may be consistent within other families and also within genera. The 11 species with one GB per ovary are tropical or subtropical, or are derived from a primarily tropical genus, and exhibit a relatively low instantaneous fecundity (usually 1 egg). In contrast, all but one of the 21 temperate species examined have two GBs per ovary, but some tropical or subtropical species also exhibit this ovarian condition. Presence of two GBs per ovary is related to a wide range of instantaneous fecundities. In these species, rates of follicular atresia in preovulatory ovaries are inversely proportional to instantaneous fecundity. Species with one GB per ovary have not readily evolved new forms with higher instantaneous fecundities in the past. In contrast, the condition of two (or several) GBs per ovary has been asso- ciated with greater phylogenetic flexibility of instantaneous fecundity. In the latter species, evo- lutionary changes in pituitary FSH secretion, which affect both the number of ovarian follicles and rates of follicular atresia, may have mediated changes in instantaneous fecundity. Testing of these hypotheses must await more data on the number of GBs and growing and atretic follicles in pre- ovulatory ovaries of more lizard species.

Rate of Follicular Atresia Following Hypophysectomy of the Turkey

Ovarian follicles in the turkey exhibited a differential rate of atresia following hypophysectomy which was dependent on follicle size. Atresia appeared in large follicles at 12 hr. postoperatively, in small follicles by 18 hrs., and in medium-sized follicles by 24 hr. Follicles weighing 6–12 g. remained intact as long as 36 hr. An inference is made concerning the value of the turkey hen in neuroendocrine research.