Dopamine receptor agonist bromocriptine restrains the follicular development,hatchling success and puberty in Gambusia affinis

The present investigation was conducted to determine the influence of dopamine (DA) receptor agonist bromocriptine (BRO) on reproduction and onset of puberty in the viviparous fish Gambusia affinis. In the first experiment, the mean number of stage I and II follicles (previtellogenic) in 0.8 or 5 mg BRO treated fish did not show significant difference compared to those of experimental controls, whereas the mean number of stage III follicles were significantly lower in 5 mg BRO treated fish compared to experimental controls. However, treatment of 0.8 or 5 mg BRO resulted in significantly lower numbers of stage IV (early vitellogenic) and V (late vitellogenic) follicles compared to those of experimental controls. There was decrease in the percent occurrence of pregnancy and different stages of embryos in BRO treated fish compared with the experimental controls. Concomitant with this, sparsely distributed gonadotropin releasing hormone immunoreactive (GnRH‐ir) fibres were observed in the proximal pars distalis (PPD) region of the pituitary gland in BRO treated fish compared to those of dense accumulations of these fibres in the PPD region of the pituitary gland in experimental controls. In the second experiment, exposure of juveniles (25 DPH) to same doses of BRO for 45 days resulted in complete absence of vitellogenic follicles and presence of few GnRH‐ir fibres in 5 mg BRO treated juvenile in contrast to presence of vitellogenic follicles and dense aggregation of GnRH fibres in treatment controls. Overall, the results of the present investigation suggest that DA affects ovarian follicular and embryonic development and onset of puberty in viviparous species.     

Influence of cortisol along the pituitary‐ovary axis in the cichlid fish Oreochromis mossambicus

Cortisol is the principal glucocorticoid released due to various forms of environmental as well as aquacultural stressors in fish. The aim of the present investigation was to determine cortisol‐induced alterations along the luteinizing hormone (LH)‐secreting cells–ovary axis in the tilapia Oreochromis mossambicus. Administration of cortisol to stripped O. mossambicus for a period of 22 days during the ovarian cycle caused significantly higher number of follicles with chromatin nucleoli (stage I) compared to those of initial controls and controls. Whereas the number of follicles at perinucleolar (stage II) and vitellogenic (stage IV) stages did not differ significantly between controls and cortisol‐treated fish, the number of follicles at cortical alveolar stage (stage III) was significantly lower in cortisol‐treated fish than in controls. While the stage V follicles (maturation stage) were absent in initial controls, their presence in controls was concomitant with intensely labelled LH‐secreting cells in the proximal pars distalis (PPD) region of the pituitary gland during prespawning phase. However, cortisol‐treatment resulted in complete absence of stage V follicles associated with weakly immunoreactive LH‐content in the PPD region of the pituitary gland during prespawning phase. These results suggest that chronic cortisol‐ treatment causes suppression of LH‐secreting cells activity and blocks progression of vitellogenic follicular development process in O. mossambicus.     

The fate of follicles after a blood meal is dependent on previtellogenic nutrition and juvenile hormone in Aedes aegypti

Juvenile hormone (JH) mediates the relationship between fecundity and nutrition during the gonotrophic cycle of the mosquito in three ways: (1) by regulating initial previtellogenic development, (2) by mediating previtellogenic resorption of follicles and (3) by altering intrinsic previtellogenic follicle “quality”, physiology, and competitiveness thereby predetermining the fate of follicles after a blood meal. To support a role for JH in mediating the response of ovarian follicles after a blood meal, we explored three main questions: (1) Do changes in nutrition during the previtellogenic resting stage lead to relevant biochemical and molecular changes in the previtellogenic ovary? (2) Do hormonal manipulations during the previtellogenic resting stage lead to the same biochemical and molecular changes? (3) Does nutrition and hormones during the previtellogenic resting stage affect vitellogenic resorption and reproductive output? We examined the accumulation of neutral lipids in the previtellogenic ovary as well as the previtellogenic expression of genes integral to endocytosis and oocyte development such as the: vitellogenin receptor (AaVgR), lipophorin receptor (AaLpRov), heavy-chain clathrin (AaCHC), and ribosomal protein L32 (rpL32) under various previtellogenic nutritional and hormonal conditions. mRNA abundance and neutral lipid content increased within the previtellogenic ovary as previtellogenic mosquitoes were offered increasing sucrose concentrations. Methoprene application mimicked the effect of offering the highest sucrose concentrations on mRNA abundance and lipid accumulation in the previtellogenic ovary. These same nutritional and hormonal manipulations altered the extent of vitellogenic resorption. Mosquitoes offered 20% sucrose during the previtellogenic resting stage had nearly 3 times less vitellogenic resorption than mosquitoes offered 3% sucrose despite taking smaller blood meals and developed ～10% more eggs during the first gonotrophic cycle. Mosquitoes treated with JH III during the previtellogenic resting stage and then offered a blood meal had a ～40% reduction in the amount of vitellogenic resorption and developed ～12% more eggs. Taken together, these results suggest that previtellogenic nutrition alters the extent and pattern of resorption after a blood meal through the effect of JH on mRNA abundance and lipid accumulation in previtellogenic follicles.     

Stress inhibits seasonal and FSH-induced ovarian recrudescence in the lizard,Mabuya carinata

Stressors (handling, chasing, and noise) applied randomly five times per day for one month to lizards during the recrudescence phase of the ovarian cycle caused a significant reduction in mean number of oocytes and primordial follicles when compared to those of controls. Further, vitellogenic follicles were absent in the ovary of lizards subjected to stressors. Administration of bovine FSH during post-breeding regression phase of the ovarian cycle induced ovarian recrudescence as shown by significant increases in the mean number of oogonia, oocytes, and primordial follicles compared to controls, as well as vitellogenic growth of follicles. However, lizards treated with FSH and exposed to stressors did not exhibit ovarian recrudescence. Furthermore, FSH administration during the post-breeding regression phase caused a significant increase in serum levels of estradiol compared to controls, which was accompanied by significant increases in the relative weight of the liver and oviduct, as well as vitellogenic growth of follicles. Despite administration of FSH to lizards subjected to stressors, there was neither any increase in serum levels of estradiol and weight of the liver nor vitellogenic growth of follicles. The results indicate that repeated application of stressors inhibits vitellogenic growth of follicles by suppression of steroidogenic activity in M. carinata. This is the first report revealing that the ovary does not respond to gonadotrophin treatment under stressful conditions in reptiles.     

Developmental profiles of PERIOD and DOUBLETIME in Drosophila melanogaster ovary

The clock protein PERIOD (PER) displays circadian cycles of accumulation, phosphorylation, nuclear translocation and degradation in Drosophila melanogaster clock cells. One exception to this pattern is in follicular cells enclosing previtellogenic ovarian egg chambers. In these cells, PER remains high and cytoplasmic at all times of day. Genetic evidence suggest that PER and its clock partner TIMELESS (TIM) interact in these cells, yet, they do not translocate to the nucleus. Here, we investigated the levels and subcellular localization of PER in older vitellogenic follicles. Cytoplasmic PER levels decreased in the follicular cells at the onset of vitellogenesis (stage 9). Interestingly, PER was observed in the nuclei of some follicular cells at this stage. PER signal disappeared in more advanced (stage 10) vitellogenic follicles. Since the phosphorylation state of PER is critical for the progression of circadian cycle, we investigated the status of PER phosphorylation in the ovary and the expression patterns of DOUBLETIME (DBT), a kinase known to affect PER in the clock cells. DBT was absent in previtellogenic follicular cells, but present in the cytoplasm of some stage 9 follicular cells. DBT was not distributed uniformly but was present in patches of adjacent cells, in a pattern resembling PER distribution at the same stage. Our data suggest that the absence of dbt expression in the follicular cells of previtellogenic egg chambers may be related to stable and cytoplasmic expression of PER in these cells. Onset of dbt expression in vitellogenic follicles coincides with nuclear localization of PER protein.     

The development of responsiveness to juvenile hormone in the follicle cells of Rhodnius prolixus

During the previtellogenic phase of the development of the follicle in Rhodnius, the JH-sensitive Na/K ATPase in the membranes of the follicle cells displays display a rapid increase in activity, so that the level in vitellogenic follicle cells is about six times that in early previtellogenic cells. The sharp increase in activity during the development of previtellogenic cells is abolished in an allatectomized female. Topical application of JH I early in development restores the level in previtellogenic cells and produces a nearly normal level in vitellogenic cells. Treatment with JH I later in the cycle fails to yield an increase in the activity of the JH-sensitive Na/K ATPase in the previtellogenic cell and leads to only partial restoration of the activity in vitellogenic follicles. These effects of allatectomy and early and late hormone replacement are duplicated by effects on the maximal binding capacity for [³H]JH I of the membranes of follicle cells. These results are interpreted in the light of “activation”, the JH-mediated process by which follicles acquire the competence to respond to JH by becoming patent.     

Domperidone treatment attenuates stress-induced suppression of reproduction in viviparous mosquitofish Gambusia affinis

The aim of this study was to determine the effect of stress on reproduction and the possible involvement of dopaminergic systems in the reproductive stress response in the mosquitofish Gambusia affinis. Exposure of fish to aquaculture stressors (four 10 min episodes of stress, each corresponding to a different stressor such as handling, chasing, frequent netting and low water levels), for a period of 30 days caused reduction in the mean numbers of stage I–IV follicles associated with lower number of pregnant females and embryos in most of the developmental stages compared with experimental controls. Besides, increase in the intensity of labelling and the per cent area of tyrosine hydroxylase (TH; a rate-limiting enzyme in the biosynthetic pathway of catecholamines)- immunoreactive (ir) neurons was observed in the preoptic area (POA) and the nucleus preopticus (NPO) regions of the brain concomitant with reduction in the labelling of gonadotropin releasing hormone–immunoreactive (GnRH-ir) fibres in the proximal pars distalis (PPD) of the pituitary gland in stressed fish compared with experimental controls. Treatment of domperidone (DOM) caused an increase in the number of stage II and V follicles and promoted pregnancy rate concomitant with an increase in the number of embryos at various developmental stages compared with those of experimental controls. Similar treatment to stressed fish caused an increase in the number of stages I–V follicles compared with those in stress alone group. The GnRH fibres showed increased immunolabelling in stress + DOM treated fish compared with stress alone fish. On the other hand, TH-immunoreactivity in the POA and the NPO regions was reduced in stress + DOM treated fish compared with stress-alone group. These results suggest that stress inhibits follicular development and subsequent hatching success through the suppression of GnRH and that the inhibition appears to be mediated through dopamine, for the first time in a viviparous fish.     

Fat body ovarian relationship in the garden lizard, Calotes versicolor (Daud.).

Abdominal fat body mass of Calotes versicolor showed annual changes that were universal related to the changes in ovarian somatic (GSI) and hepatosomatic (HSI) indices. Fat bodies were absent in late breeding phase (June-August). Thirty day fatectomy (FBX) during prebreeding phase significantly reduced GSI, HSI, and total number of extrastromal follicles; also, recruitment of vitellogenic follicles was arrested and ateretic follicles increased. The FBX during postbreeding phase had no such effect, whereas in 30 day ovariectomised (OvX) lizards in prebreeding phase fat body mass significantly increased but HSI decreased. However, in lizards in prebreeding phase, E2 caused a significant decrease in fat body mass and an increase in HSI, while during the postbreeding phase there was a significant increase in HSI but the fat bodies were not affected. The above findings suggest that the development of the first clutch of vitellogenic follicles in the lizard utilises lipids stored in the fat bodies and that the growth of the subsequent clutches of vitellogenic follicles is met through the intake of food, which is abundant in the latter part of the breeding phase. The fat bodies are not needed for the growth of previtellogenic follicles. The fact that lipolytic action of E2 occurs only during the breeding phase suggests that responsiveness of the fat bodies to the steroid is related to the reproductive phase and that during postbreeding phase of the lizard they become refractory to E2.     

Unilateral ovariectomy increases egg size and reduces follicular atresia in the semelparous coho salmon, Oncorhynchus kisutch

Unilateral ovariectomy (ULO, removal of one ovary) is a powerful technique for studying aspects of reproductive physiology, including follicular recruitment and growth. To examine effects of ULO for the first time in a semelparous species, coho salmon (Oncorhynchus kisutch) were unilaterally ovariectomized during mid-vitellogenesis approximately 3 months before spawning. At termination of the study (79 days post-surgery), single ovaries of ULO fish were gravimetrically equivalent to paired ovaries of sham surgery, control fish. There was no evidence of recruitment of new vitellogenic follicles. Instead, the dramatic increase in ovary mass was attributable to hypertrophy of existing vitellogenic follicles (33% increase in volume) and increased fecundity achieved through a greater than two-fold reduction in follicular atresia. The composition of whole ovaries on a dry weight basis from ULO fish was greater in protein, but lower in lipid than that of control fish. Expressing the data on a per follicle basis, however, showed that follicles of ULO fish contained more protein, ash, water, and lipid. The results indicate that ULO of coho salmon induces compensatory hypertrophy of existing vitellogenic follicles, while maximizing fecundity through reduction of atresia. Thus, 3 months before spawning, coho salmon exhibit the ability to adjust final egg size and number when faced with significant depletion of ovarian follicles. This in vivo system provides a platform for further study of physiological mechanisms regulating follicular growth and atresia, and the trade-off between egg size and egg number. J. Exp. Zool. 309A:468-476, 2008. (c) 2008 Wiley-Liss, Inc.     

Steroidogenic and maturation-inducing potency of native gonadotropic hormones in female chub mackerel, Scomber japonicus

ABSTRACT: BACKGROUND: The gonadotropins (GtHs), follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are produced in the pituitary gland and regulates gametogenesis through production of gonadal steroids. However, respective roles of two GtHs in the teleosts are still incompletely characterized due to technical difficulties in the purification of native GtHs. METHODS: Native FSH and LH were purified from the pituitaries of adult chub mackerel, Scomber japonicus by anion-exchange chromatography and immunoblotting using specific antisera. The steroidogenic potency of the intact chub mackerel FSH (cmFSH) and LH (cmLH) were evaluated in mid- and late-vitellogenic stage follicles by measuring the level of gonadal steroids, estradiol-17beta (Epsilon2) and 17,20beta-dihydroxy-4-pregnen-3-one (17,20beta-P). In addition, we evaluated the maturation-inducing potency of the GtHs on same stage follicles. RESULTS: Both cmFSH and cmLH significantly stimulated E2 production in mid-vitellogenic stage follicles. In contrast, only LH significantly stimulated the production of 17,20beta-P in late-vitellogenic stage follicles. Similarly, cmLH induced final oocyte maturation (FOM) in late-vitellogenic stage follicles. CONCLUSIONS: Present results indicate that both FSH and LH may regulate vitellogenic processes, whereas only LH initiates FOM in chub mackerel.     

Melatonin Effects on Steroid Production by Rainbow Trout Ovarian Follicles In Vitro: Influence of Stage of Follicle Maturation

Rainbow trout ovarian follicles at four different stages of maturation (very early vitellogenesis, early vitellogenesis, peak vitellogenesis, and pre-ovulatory) were incubated either in Cortland's medium alone, or medium containing melatonin at one of five concentrations (1 × 10^-10, 1 × 10^-8, 1 × 10^-6, 1 × 10^-4 or 1 × 10^-2M) to assess the direct actions of melatonin on basal (non-gonadotrophin stimulated) secretion of 17β-estradiol and testosterone. Testosterone secretion by peak vitellogenic phase follicles was significantly (p < 0.01) reduced by melatonin at 1 × 10^-4 or 1 × 10^-2 M, but there were no other significant effects of melatonin on T secretion. There were no significant effects of melatonin at concentrations of 1 × 10^-10 or 1 × 10^-8 M on 17β-estradiol secretion for any stage of follicular maturation, although for follicles at the peak vitellogenesis stage, melatonin at 1 × 10^-6 M had a significant (p < 0.05) stimulatory effect compared with the controls. Melatonin also stimulated 17β-estradiol secretion by very early vitellogenic stage follicles (1 × 10^-2 M concentration; p < 0.05). At concentrations of 1 × 10^-4 and 1 × 10^-2 M, melatonin significantly (p < 0.01) inhibited 17β-estradiol secretion of peak vitellogenic and preovulatory stage follicles. The findings suggest a stimulatory action of melatonin on steroidogenesis of early stage ovarian follicles, a shift to an inhibitory action of the higher concentrations of melatonin in later stages of development, but with a bimodal action of melatonin (related to hormone concentration) being present during the time of maximum follicular growth.     

Inhibition of spawning and associated suppression of sex steroid levels during confinement in the substrate-spawning Tilapia zillii

Substrate-spawning Tilapia zillii failed to spawn in crowded holding tanks but exhibited a marked tendency to spawn soon after transfer to individually partitioned aquaria. Confined conditions suppressed the levels of serum 17 β -oestradiol (E₂) and testosterone (T) in females, which remained low throughout the period of confinement. Levels of both steroids rose significantly following transfer of fish to individual aquaria and were maintained at consistently higher levels than those of fish which remained confined. Proportions of stage 3 (late perinucleolar) oocytes were significantly lower ( P <0.001) in individual fish 21–30 days after transfer, coincident with significantly higher ( P <0.01) proportions of stage 6 or 7 oocytes (late vitellogenic or maturing oocytes). However, no significant differences ( P ≥0.05) were detected between individual or confined groups of fish in the relative proportions of stage 2 (early perinucleolar), stage 4 (cortical alveolar) or stage 5 (early vitellogenic) oocytes. Atresia increased as the period of confinement increased. Following return of individual fish to confined conditions, blood steroids fell rapidly to levels seen in fish that had remained confined throughout. It is suggested that the reduced sex steroid levels detected during confinement were insufficient to allow developing oocytes to complete oocyte growth and maturation. The detection of significantly lower proportions of stage 3 and significantly higher proportions of stage 6/7 oocytes soon after transfer suggest that fish were preparing one batch of oocytes for spawning (stage 6/7 oocytes) whilst recruiting from a pool of previtellogenic oocytes (stage 3) for the ensuing spawning cycle.     

Expression of vitellogenin receptor in the ovarian follicles during the reproductive cycle of the spotted ray Torpedo marmorata Risso 1880

The aim of this investigation was to identify the encoding sequence of vitellogenin receptor gene (vtgr), and its expression during the oogenesis in the spotted ray, Torpedo marmorata, in different phases of reproductive cycle. From an ovarian cDNA of vitellogenic female, we obtained a fragment of 581?bp, which corresponds to a partial sequence encoding the vitellogenin receptor (VTGR) in Torpedo (accession number: gi/193244760). This sequence shows a high identity with the VTGR of other vertebrates, particularly Leucoraja erinacea (89% identity) and Squalus acanthias (84% identity). We also showed that vtgr mRNA expression in the ovary modifies during the oogenesis and throughout the reproductive cycle. Indeed, in immature females, whose ovary contains only previtellogenic follicles, vtgr mRNA occurred in the oocyte cortex as well as within intermediate and pyriform cells. In mature females, whose ovary contains pre- and vitellogenic follicles, vtgr mRNA was detectable not only in the oocyte cortex and in intermediate and pyriform cells but also in small follicle cells present in the follicular epithelium of vitellogenic follicles. In ovulating females, that, as pregnant ones, show pre-and vitellogenic follicles, vtgr mRNA was evident in the oocyte cortex only, whereas in pregnant females, no vtgr mRNA was evident. The role of VTGR in the control of Torpedo vitellogenesis is discussed.     

Effects of 17 beta-estradiol on the vitellogenin synthesis and oocyte development in the ovary of kuruma prawn (Marsupenaeus japonicus)

The effects of 17 beta-estradiol on induction of vitellogenin synthesis and oocyte development were investigated in previtellogenic ovary of immature kuruma prawn (Marsupenaeus japonicus) incubated with Medium 199. After three days incubation of previtellogenic ovary, Vg concentrations in media containing 3.6 nM, 36.7 nM, 367 nm and 3671 nM 17 beta-estradiol were significantly (p<0.01) greater than that of Ringer solution or the pure ethanol vehicle. Furthermore, a more advanced stage of oocyte development at oil globule stage (primary vitellogenic stage), which is surrounded by round and greatly expanded follicle cells, was observed in previtellogenic ovarian pieces incubated in media containing 3.6, 36.7, 367 and 3671 nM 17 beta-estradiol. The results of these studies show that 17 beta-estradiol induces Vg synthesis and appearance of primary vitellogenic oocyte in the ovary of immature prawns.     

IGF1 stimulates differentiation of primary follicles and their growth in ovarian explants of zebrafish (<Emphasis Type="Italic">Danio rerio)</Emphasis> cultured <Emphasis Type="Italic">in vitro</Emphasis>

The present study is an attempt to elucidate the involvement of insulin-like growth factor (IGF1) in the differentiation and growth of primary follicles in ovarian explant cultures of zebrafish. Ovaries from adult females were cultured in triplicate sets/treatment group for 15 days at 22°C in the laboratory. Culture medium was supplemented with either insulin (1 ng/mL) or IGF1 (1 ng/mL) or insulin + IGF1 (Experiment 1) or 0.1 or 1.0 or 10 ng/mL of IGF1 (Experiment 2). Ovaries cultured in medium alone served as controls and those fixed at the beginning of the culture as initial controls. Experiments were repeated. On the 16th day ovarian explants were fixed in Bouin’s fluid and processed for paraffin embedding, sections (3 µm) were cut and stained with hematoxylin-eosin. Follicles were classified into 6 stages and atretic follicles (AF). Previtellogenic, vitellogenic and total follicle number was calculated. At the start of the culture, ovaries contained all stages of growing and degenerating follicles. In in vitro cultured control ovaries, vitellogenic follicles underwent atresia, while, primary follicles remained unaffected. Insulin or insulin + IGF1 treated ovaries did not differ significantly while IGF1 exposed ovarian explants had greater (P < 0.05) number of primary follicles compared to controls. IGF1 also caused an increase in the number and growth of primary follicles in a dose dependent manner although; cultures were not supplemented with gonadotrophic hormones. Results suggest that locally derived intra-ovarian IGF1 may have a role in the differentiation and growth of primary follicles in zebrafish ovary.     

Disrupted oogenesis in the frog Xenopus tropicalis after exposure to environmental progestin concentrations

Levonorgestrel is a synthetic progesterone commonly used in pharmaceuticals (e.g., in contraceptives). It is found in sewage treatment plant effluents at concentrations up to 30 ng/L and was recently shown to pose a threat to egg laying in fish. Information on the susceptibility of adult amphibians to progestin toxicity is lacking. The present study aimed to 1) characterize progestogenic effects on the full cycle of oogenesis (egg development) in frogs and 2) determine female amphibians' susceptibility to reproductive impacts from progestogenic compounds in the environment. Sexually mature female Xenopus tropicalis were exposed to levonorgestrel via the surrounding water for 7 days (0, 51, or 307 ng/L) or 28 days (0, 1.3, 18, 160, or 1240 ng/L). Their ovaries were analyzed histologically with respect to frequencies of immature (in early meiotic prophase I), previtellogenic, vitellogenic, mature, and atretic oocytes. The 28-day exposure caused reduced proportions of oocytes at immature, vitellogenic, and mature stages, and increased proportions of previtellogenic oocytes compared with the control. The lowest tested concentration, 1.3 ng/L, increased the proportions of previtellogenic oocytes and reduced the proportions of vitellogenic oocytes, indicating inhibited vitellogenesis. The present study shows that progestin concentrations found in the aquatic environment impaired oogenesis in adult frogs. Our results indicate that progestogenic effects on oocyte development include interrupted germ cell progression into meiosis and inhibited vitellogenesis. Considering the crucial role of oogenesis in female fertility, our results indicate that progestogenic pollutants may pose a threat to reproduction in wild amphibian populations.     

Endocrine control of clutch size in reptiles. VIII. antiestrogenic effects of clomiphene citrate in the lizard Anolis carolinensis

The influence of clomiphene citrate on follicle-stimulating-hormone (FSH) and estradiol-induced growth of ovarian follicles and oviducts in the lizard A. carolinensis was studies. In Experiment 1 lizards received 14 daily injections of either saline, clomiphene (1, 10 or 20 mcg), or FSH (1 or 10 mcg) or combined clomiphene-FSH treatment. In Experiment 2, adult lizards with hypertrophied, vitellogenic ovaries, and enlarged oviducts, weres adenohypophysectomized and treated with a daily dose of .05 ml of either saline, saline plus 5 mcg clomiphene, saline plus 10 mcg FSH, saline plus 10 mcg estradiol-17beta, or FSH plus clomiphene or estradiol plus clomiphene. FSH increased follicle size in previtellogenic ovaries. Injection of 1 mcg clomiphene reduces the effects of FSH. 20 mcg clomiphene given alone stimulated the growth of larger follicles. Clomiphene blocked FSH-induced appearance or maintenance of large (less than 2.0 mm) vitellogenic follicles. It blocked FSH gains in oviductal weight and well as stimulated growth of small previtellic follicles. Estradiol-induced follicular and oviductal growth was uneffected by clomiphene. While low doses of clomiphene are antiestrogenic they are unable to combat the effects of high dose estradiol.