Hormonal regulation of activities of 4-ene-5 beta and 5 alpha-reductases and 17 beta-ol-dehydrogenase in immature golden hamster ovary

Diethylstilbestrol (DES) pellets were implanted in female golden hamsters on day 22 after birth. Hamsters with or without the DES pellet were hypophysectomized on day 23. Starting from day 26, the hypophysectomized hamsters were injected daily with 2.3-40 micrograms NIH-LH-S19, 6 or 18 micrograms NIAMD-oFSH-13, 50 micrograms NIAMD-Rat-FSH-B-1, or saline for 3 days. Ovarian homogenates from these hamsters on day 29 were incubated with [14C]-4-androstene-3,17-dione and enzyme activity (nmol/g/h) was estimated. The 5 alpha- and 5 beta-reductase activities decreased significantly following hypophysectomy. In the hypophysectomized hamster ovary, a distinct response to LH but not to FSH or DES in the 5 alpha-reductase activity was found. On the other hand, the 17 beta-ol-dehydrogenase activity was stimulated by FSH but not by LH or DES. The 5 beta-reductase activity was stimulated by DES, FSH or 2.3 micrograms LH but not by 7-40 micrograms LH. In the DES-treated, hypophysectomized hamster ovary, LH and FSH stimulated the 5 alpha-reductase and 17 beta-ol-dehydrogenase activities, respectively, but FSH or LH treatment had no significant effect on the 5 beta-reductase activity. These results show that the 5 alpha-reductase activity is regulated by LH, while the 17 beta-ol-dehydrogenase activity is stimulated by FSH in immature golden hamster ovary. The 5 beta-reductase activity seems to be regulated predominantly by FSH but the effect of FSH is largely mediated by estrogen.     

Changes in serum and ovarian steroids during reproductive development in the female guinea pig

This study was designed to measure ovarian hormones prior to and during the first estrous cycle in guinea pigs. Blood was obtained from 12 animals throughout the first estrous cycle. Ovaries and peripheral serum were obtained from 25 additional animals at various stages of development prior to and after first ovulation. Estradiol, progesterone, androstenedione, and testosterone were measured in all sera and half of the ovaries. The remaining ovaries were fixed for histology. Serum estradiol was nondetectable until a few days before first ovulation, but was present in the ovary throughout development. Serum progesterone was nondetectable until the day of ovulation, but the luteal phase pattern was similar to that observed in adults. Serum androgens were detectable throughout development, with androstenedione higher than testosterone. The immature ovary contained more testosterone than androstenedione, but this pattern was reversed after ovulation. These results indicate that the immature ovary in the guinea pig contains minimal amounts of estradiol and progesterone, the first estrous cycle is similar to that in adults, and that the pattern of ovarian androgen content changes during the peripubertal period.     

Physiological peripubertal activation of the ovary is not reproduced by pregnant mare serum gonadotropin (PMSG) administration

During the days preceding the first ovulation the ovary of the rat exhibits a remarkable increase in estradiol (E2) and progesterone (P) release in response to gonadotropins. No such increase is observed in the case of androgens (A, testosterone + dihydrotestosterone). The present experiments were undertaken to examine the possibility of reproducing these developmental events by stimulating the ovary with a gonadotropin that has substantial FSH-like activity. In vivo administration of pregnant mare serum gonadotropin (PMSG) to juvenile 29-day-old rats greatly increased the in vitro E2 and A response to human chorionic gonadotropin (hCG) measured 2 days later in the morning. The magnitude of the A response was significantly larger than that of ovaries from juvenile animals or rats in first proestrus. The E2 response was much greater than that of juvenile ovaries but similar to that of ovaries from late proestrous rats. In contrast, the P response to hCG was not enhanced by PMSG. In fact the response was similar to that of juvenile ovaries and markedly less than that of first proestrous rats. This decreased P response was not due to a greater conversion of P to its less active metabolite 20 alpha-hydroxy-4-pregnen-3-one (20 alpha-OH-P). The results suggest that PMSG enhances the E2 and A response of immature ovaries to hCG at the expense of that of P. Treatment of immature rats with PMSG may represent a useful model to study E2 release from preovulatory ovaries, but it cannot be used to reproduce in its entirety the developmental changes in steroidal response to gonadotropins associated with normal puberty.     

Supernumerary ovarian grafts in aging C57BL/6J mice reveal complexities in the neuroendocrine impairments of acyclic mice

Determinants of the age-related acyclic state, persistent vaginal cornification (PVC), were studied in reproductively senescent mice using a 2-stage ovarian transplantation procedure, whereby ovaries from young mice were grafted to older mice without removing their autogenous ovaries until 8 wk later. In contrast to the usual ("1-stage") procedure, in which the autogenous ovaries are removed at the time of grafting, the 2-stage approach is postulated to circumvent potential effects of the reduction in steroids during the ovariprival phase prior to vascularization of the grafted ovary, which may reverse age-related hypothalamic-pituitary impairments. The 2-stage transplantation procedure was validated in young C57BL/6J mice. Estrous cycles were not disrupted by removal of the autogenous ovaries 8 wk after the grafting, indicating that grafted ovaries began functioning before or within days after ovariectomy. No difference in estrous cycle frequency or distribution was detected between the young mice with 2-stage and those with 1-stage transplants for at least 3 mo after removal of the autogenous ovaries. Most older (15- to 18-mo-old) mice with PVC (70%) remained acyclic after receiving young ovaries by either the 1-stage or the 2-stage procedure, indicating that extra-ovarian, presumably neuroendocrine, impairments are sufficient to maintain acyclicity in most older mice once it is initiated. However, 30% of the older mice from each transplantation group began cycling after receiving young ovaries by either the 1-stage or 2-stage procedure, as observed before 1-stage transplants. Therefore, cycle reactivation was not a result of the transient ovariprival phase incurred during 1-stage transplantation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ovarian contents of immunoreactive beta-endorphin and alpha-N-acetylated opioid peptides in rats

beta-Endorphin was measured by radioimmunoassay in homogenates of ovaries from immature Sprague-Dawley rats (21-29 days of age) and found to be present at levels of about 0.6-0.7 ng/ovary. After administration of PMSG there was approximately a 4-fold increase (2-3 ng/ovary) in total ovarian immunoreactive (ir) beta-endorphin 48 h after injection. Analysis of follicular fluid from similarly treated rats indicated about the same amount of ovarian ir-beta-endorphin (2-3 ng/ovary) as in ovarian homogenates, suggesting that most of the ir-beta-endorphin is localized in follicular fluid of PMSG-primed immature rats. Immature rats were made pseudopregnant by administration of hCG 48 h after PMSG, and at 24 h after injection of hCG there was a slight, but significant and reproducible, increase in the ovarian content of ir-beta-endorphin. The serum concentration of ir-beta-endorphin was in the range of 1-3 ng/ml and was unaffected by PMSG and PMSG/hCG; likewise, the pituitary content of ir-beta-endorphin did not change following administration of gonadotrophins to immature rats. In mature cyclic animals, levels of 2-4 ng ir-beta-endorphin/ovary were found, comparable to those in the ovaries of PMSG-primed immature rats, and there were only small changes during the oestrous cycle. In addition to ir-beta-endorphin, we also obtained evidence for the presence of alpha-N-acetylated opioid peptides (endorphins or enkephalins) in the ovaries of PMSG-primed immature and mature rats. The physiological role of the opioid peptides in reproductive tissue is unknown, but they are presumably acting in an autocrine or paracrine fashion.     

Prenatal exposure to antiandrogen flutamide affects androgen receptor (AR) expression in postnatal ovarian development in pig

The following study was undertaken to localize androgen receptors (ARs) in various structures of the porcine ovary after prenatal exposure to antiandrogen flutamide. In utero treatment by antiandrogens may have adverse effects on reproductive function in immature and adult animals. Flutamide was injected into pregnant swines between days 20 and 28 (GD20) or 80 to 88 (GD80) of gestation. The ovaries were collected from treated animals and from control ones (non-treated) at two different points of development: from immature and adult pigs. Immunoexpression of AR was determined for preantral and antral follicles and for stroma cells. Immunostaining showed that AR expression in immature animals was unaffected in the primary follicles, while in the preantral and antral follicles the AR level fluctuated depending on day of treatment as well as on analyzed tissue. In adult animals, the immunoexpression of AR slightly decreased in antral follicles independently on the day of flutamide treatment. Therefore, AR expression in postnatal life may be affected by in utero exposure to antiandrogen flutamide.     

Surgical transplantation of sexually immature ovaries in rainbow trout (Oncorhynchus mykiss)

Transplantation of testes between isogenic rainbow trout males has been recently demonstrated. The objective of the present investigation was to determine if ovaries detached from the body wall and removed from the abdominal cavity would reestablish themselves when autografted to an ectopic site. In the first experiment, eleven sexually immature, female rainbow trout were laparotomized midventrally, and the right ovary was removed and transplanted to the abdominal cavity and positioned along the pyloric cecae on the right side. In the second experiment, the ovary was autografted in four animals as in experiment 1 or was transferred to and allografted in four other sexually immature female trout. The animals were examined three months following surgery. At the termination of experiment 1, the autografted ovaries were present in 73% of the animals; the transplanted ovaries were smaller in size than the intact control ovaries. Histological examination did not reveal any necrotic tissue in these transplanted gonads, and oocyte development was not different between the transplanted and the intact ovary within animal. Transplanted ovaries allografted from another female were not found. Taken together, these data support the conclusion that rainbow trout ovaries detached from the body wall can reestablish their blood supply and maintain ovarian development and that female trout appear to reject gonadal tissue from other individuals of their species.     

Role of pituitary adenylate cyclase-activating peptide (PACAP) in the cyclic recruitment of immature follicles in the rat ovary

Following the midcyclic gonadotropin surge, PACAP is transiently expressed for approximately 12 h in the cyclic adult rat ovary. PACAP is observed in granulosa/lutein cells of the large mature follicles destined to ovulate and is believed to be a regulator of acute progesterone production and luteinization in these follicles. PACAP is also observed in solitary theca cells of immature follicles and in interstitial glandular cells intimately surrounding immature follicles. To examine if PACAP could be involved in the process of cyclic recruitment of such immature follicles, we primed immature granulosa cells from prepubertal ovaries with PACAP (1 nM and 100 nM) for 12 h. The treatment significantly stimulated the subsequent 24 h FSH-induced estradiol production (2.2 and 2.4 fold, respectively). The response seemed to be caused by a stimulation of aromatase activity. Estradiol production induced by testosterone was increased 2.4 and 2.6 fold, respectively, whereas functional FSH-receptors (cAMP production following FSH stimulation) or spontaneous apoptosis (immunohistochemical detection of DNA fragments) was unaffected. We conclude that PACAP priming of immature rat granulosa cells for 12 h increases subsequent FSH induced estradiol production and that PACAP could be involved in the cyclic recruitment of immature follicles in the adult rat ovary.     

The effect of LH on cyclic AMP and progesterone in rat ovaries in vivo.

LH injected into the abdominal vein of immature female rats increased ovarian cyclec AMP levels within 1 min, and the effect lasted at least 2 hr. In PMS stimulated rats, a maximal effect on cyclic AMP levels was obtained with 5 mug of LH 10 min after injection. Significant effects were obtained with as little as 0.1 mug. The minimum effective dose required to increase ovary cyclic AMP levels in proestrus rats was 0.05 mug of LH. While 0.01 mug did not affect cyclic AMP levels, an increase in ovary progesterone was found. In other experiments, the response of cyclis AMP to LH in vivo was greater in immature ovaries than in those from animals pretreated with PMS and hCG. Small increases in cyclic AMP levels were also seen with FSH in PMS and PMS + hCG treated animals and with prostaglandin E2 and prolactin in PMS treated rats. These results parallel, to some extent, previous results found in vitro, and show that very small doses of LH can stimulate ovary cyclic AMP increases in vivo.     

Restoration of fertility in light-deprived female hamsters by chronic melatonin treatment

Summary Blinding young adult female hamsters was followed by functional involution of the ovaries and uteri and by the cessation of cyclic vaginal phenomena. Light deprivation was also accompanied by elevated plasma and pituitary levels of luteinizing hormone and depressed levels of prolactin in both the blood and the pituitary gland. Only one of 15 blinded hamsters became pregnant when they were exposed to fertile males for 30 days. Both pinealectomy or chronic melatonin treatment (1 mg melatonin implanted subcutaneously per week in beeswax) prevented the changes in the reproductive organs and in pituitary hormone levels attendant on light-deprivation. Both treatment also returned vaginal cycles to normal and restored plasma prolactin titers. Unlike hamsters that were blinded only, light deprived hamsters that were either pinealectomized or melatonin treated were capable of reproducing when they were caged with fertile males. The reproductive capability (i.e., percent of animals that become pregnant and the sizes of their litters) of these animals was equivalent to that of the untreated control hamsters. This is the first report that chronic melatonin treatment restores fertility in blinded female hamsters.Supported by Grant GB-43233X from the National Science Foundation     

Follicular development in immature Djungarian hamsters (Phodopus sungorus) and the influence of exogenous gonadotropins

This study evaluated follicular development and oocyte growth in ovaries of immature Djungarian hamsters from 8 to 28 days of age and examined the influence of exogenous gonadotropins on follicular growth. An age-specific pattern of progressive follicular development was found, beginning with a compact, virtually undifferentiated ovary containing mostly small follicles on Day 8 postpartum and progressing to an ovary with mature preovulatory follicles at the end of the fourth week. Antral follicles not present on Day 12 were first detected on Day 16 postpartum. Follicles were sensitive to gonadotropins (GTH) by Day 12 postpartum, as indicated by the stimulation of follicular maturation by treatment with GTH. Ovulation, however, could be induced only when treatment with GTH was begun with females from Day 14 postpartum onwards. It was concluded that the injected GTH initiated and enhanced follicular growth in immature Djungarian hamsters.     

Studies on follicular growth in the immature rat and hamster: Effect of a single injection of gonadotropin or estrogen on the rate of3H-thymidine incorporation into ovarian DNAin vitro

Initiation of follicular growth by specific hormonal stimuli in ovaries of immature rats and hamsters was studied by determining the rate of incorporation of³H-thymidine into ovarian DNAin vitro. Incorporation was considered as an index of DNA synthesis and cell multiplication. A single injection of pregnant mare serum gonadotropin could thus maximally stimulate by 18 hr³H-thymidine incorporation into DNA of the ovary of immature hamsters. Neutralization of pregnant mare serum gonadotropin by an antiserum to ovine follicle stimulating hormone only during the initial 8–10 hr and not later could inhibit the increase in³H-thymidine incorporationin vitro observed at 18 hr, suggesting that the continued presence of gonadotropin stimulus was not necessary for this response. The other indices of follicular growth monitored such as ovarian weight, serum estradiol and uterine weight showed discernible increase at periods only after the above initial event. A single injection of estrogen (diethyl stilbesterol or estradiol-l7β) could similarly cause 18 hr later, a stimulation in the rate of incorporation of³H-thymidine into DNAin vitro in ovaries of immature rats. The presence of endogenous gonadotropins, however, was obligatory for observing this response to estrogen. Evidence in support of the above was two-fold: (i) administration of antiserum to follicle stimulating hormone or luteinizing hormone along with estrogen completely inhibited the increase in³H-thymidine incorporation into ovarian DNAin vitro; (ii) a radioimmunological measurement revealed following estrogen treatment, the presence of a higher concentration of endogenous follicle stimulating hormone in the ovary. Finally, administration of varying doses of ovine follicle stimulating hormone along with a constant dose of estrogen to immature rats produced a dose-dependent increment in the incorporation of³H-thymidine into ovarian DNAin vitro. These observations suggested the potentiality of this system for developing a sensitive bioassay for follicle stimulating hormone.     

Hepatic lipase in the rat ovary. Ovaries cannot synthesize hepatic lipase but accumulate it from the circulation

Hepatic lipase is proposed to have a role in steroidogenesis through its involvement in the metabolism of high density lipoproteins. We examined the activity, synthesis, distribution, and uptake of this enzyme and assessed the content of its mRNA in luteinized ovaries. We found that during peak steroidogenesis, ovaries of pregnant mare's serum gonadotropin-human chorionic gonadotropin-treated immature rats contained heparin-releasable hepatic lipase-like activity which was neutralized in a dose-dependent manner by purified antibodies to hepatic lipase isolated from post-heparin perfusates of rat livers. Quantitative immunoelectron microscopy revealed that ovarian hepatic lipase occurred along endothelial cells and was 3-fold more abundant in blood vessels of corpora lutea than those of stroma. However, hepatic lipase was not synthesized by the ovary since radiolabeled enzyme was not immunoisolated from the medium of dispersed luteinized granulosa cells incubated with [35S]methionine whereas it was present in the medium of control cells (hepatocytes). Similarly, hepatic lipase mRNA was detectable in liver but not ovaries or kidneys by Northern or slot blot analyses or by the polymerase chain reaction. Finally, 125I-labeled hepatic lipase injected into tail veins was quickly cleared from the systemic circulation, accumulating in liver, ovaries, kidneys, and spleen. Subsequent heparin injection caused rapid reappearance of radioactivity in the bloodstream and a marked decline of radiolabel in liver and ovaries but a modest decrease of that in kidneys and none in spleen. Exogenous 125I-bovine serum albumin also accumulated in all four organs but was not displaced from liver or ovaries by subsequent administration of heparin. Taken together, these data suggest that steroidogenically active ovaries possess but do not synthesize hepatic lipase. Instead, hepatic lipase originating elsewhere, presumably in the liver, is accumulated from the circulation at heparin-sensitive sites in ovarian blood vessels.     

Immunocytochemical localization and enzymatic distribution of rat ovarian aromatase

A rabbit antiserum directed against purified human placental aromatase was used for immunohistochemical localization of the enzyme in rat ovaries. Immunostaining was conducted on tissue from animals at various ages and in different reproductive states: immature; immature, eCG-treated; immature pseudopregnant; adult cycling; and adult pregnant. Various labeling protocols were employed (e.g. horseradish peroxidase-conjugated secondary antibody, peroxidase-antiperoxidase, and avidin-biotin-peroxidase on fresh frozen and Bouin's fixed paraffin-embedded sections), but the avidin-biotin-peroxidase method on paraffin sections proved to be superior to the others. In immature rats, most of the immunostaining, which was quite weak, was limited to the stroma. After stimulation with eCG, some of the granulosa cells of antral follicles exhibited immunostaining; in pseudopregnant rats, most staining occurred in the luteal cells. In mature animals, the corpora lutea of pregnant and cycling rats demonstrated the greatest degree of immunostaining. No significant immunoreactivity was detected in pre-antral follicles, but in early antral follicles and preovulatory follicles, both theca and granulosa cells exhibited immunostaining. Aromatase enzymatic activity was also determined on ovarian microsomal fractions of eCG-treated immature animals, pregnant animals at term, and cycling animals. Furthermore, enzyme activity and estradiol concentrations were examined after ovaries from proestrous rats were dissected into follicular, luteal, and residual components. Activity was found in all regions and correlated with immunostaining and estrogen production. These results argue against a model in which all the immunoreactive/enzymatically active protein is localized in granulosa cells of Graafian follicles and suggest that corpora lutea may be involved in estrogen synthesis during the rat estrous cycle as well as during pregnancy.     

Latent antithrombin does not affect physiological angiogenesis: an in vivo study on vascularization of grafted ovarian follicles

Latent antithrombin (L-AT), a heat-denatured form of native antithrombin (AT), is a potent inhibitor of pathological tumor angiogenesis. In the present study, we have investigated whether L-AT has comparable antiangiogenic effects on physiological angiogenesis of ovarian tissue. For this purpose, preovulatory follicles of Syrian golden hamsters were mechanically isolated and transplanted into dorsal skinfold chambers chronically implanted in L-AT- or AT-treated hamsters. Non-treated animals served as controls. Over 14 days after transplantation neovascularization of the follicular grafts was assessed in vivo by quantitative analysis of the newly developed microvascular network, its microvessel density, the diameter of the microvessels, their red blood cell velocity and volumetric blood flow as well as leukocyte-endothelial cell interaction using fluorescence microscopic techniques. In each group, all of the grafted follicles were able to induce angiogenesis. At day 3 after transplantation, sinusoidal sacculations and capillary sprouts could be observed, finally developing complete glomerulum-like microvascular networks within 5 to 7 days. Overall revascularization of grafted follicles did not differ between the groups studied. Interestingly, follicular grafts in L-AT- and AT-treated hamsters presented with higher values of microvessel diameters and volumetric blood flow, when compared to non-treated controls, which may be best interpreted as a reactive response to an increased release of vasoactive mediators. In conclusion, the present study demonstrates, that L-AT has no adverse effects on physiological angiogenesis of freely transplanted ovarian follicles. Thus, L-AT may be an effective drug in tumor therapy, which blocks tumor growth by selective suppression of tumor vascularization without affecting new vessel formation in the female reproductive system.     

In utero and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin and 2,3,4,7,8-pentachlorodibenzofuran reduces growth and disrupts reproductive parameters in female rats

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 2,3,4,7,8-pentachlorodibenzofuran (PCDF) are widespread environmental pollutants. TCDD is well known for its adverse effects on female reproduction when administered acutely to immature or adult rats. It is also known that fetal/neonatal exposure to this compound alters reproductive parameters. It is unknown whether exposure to PCDF causes similar adverse effects in offspring. The objectives of the study were to investigate the effects of in utero and lactational (IUL) exposure to TCDD and PCDF on subsequent growth, estrous cycles, and ovulation. Additionally a gonadotropin-primed immature rat model was used to investigate possible direct effects on the ovary after IUL exposure to TCDD (2.5 microg/kg) by evaluating 1) ovarian morphometrics and 2) serum estradiol concentrations. Body weights were reduced in animals with IUL exposure to TCDD and PCDF relative to those in controls at 10 days of age (P < 0.05 for each), and this difference was maintained until termination of the experiment at 125-165 days of age (P < 0.05). Exposure to TCDD or PCDF also disrupted regular estrous cycles and inhibited ovulation rate. On Day 23 (before eCG stimulation), ovaries from animals exposed to TCDD contained the same number of primordial, primary, secondary, preantral, and antral follicles as ovaries from control animals. On Day 25 (48 h after eCG stimulation), ovaries from TCDD-exposed rats had significantly fewer large preovulatory follicles when compared with ovaries from controls. The numbers of smaller follicles (both antral and small antral) were not different. Serum estradiol was significantly lower in TCDD-exposed animals 48 h after eCG stimulation.     

不同性别和年龄的大仓鼠对黄鼬气味的反应

将雌性成体和雌雄亚成体大仓鼠 (Cricetulustriton)长期 (4周 )暴露给过量的黄鼬 (Mustelasibirica)肛腺分泌物 ,观察其行为和生理状态的变化 ,并通过与我们以前有关黄鼬气味对成年雄鼠影响的研究结果进行比较 ,表明黄鼬气味对不同性别和不同年龄大仓鼠的胁迫效应和生殖抑制存在差异。发现黄鼬气味对雌性大仓鼠的影响较雄性小 ,对亚成体的影响较成体小 ,这与雌性和未成年动物对各种胁迫因素的反应更敏感的普遍现象相反。在成年鼠中 ,雌雄鼠的攻击行为都受到黄鼬气味的抑制 ;但天敌气味使雌性的胁腺膨大 ,对胁腺标记和肾上腺大小无影响 ;成年雄鼠的肾上腺膨大 ,胁腺萎缩 ,标记减少。在亚成体中 ,除了雄性胁腺受到抑制(与成年雄鼠相同 )外 ,雌雄鼠的肾上腺和雌性的胁腺未受影响。亚成体实验鼠的体重都比对照组低 ,但成年鼠的体重未受影响。另外 ,与以往对其它鼠类的研究结果一致 ,天敌气味并不影响成年鼠的生殖器官 ,却抑制了未成年雄鼠的附睾和未成年雌鼠的子宫。这些差异可能和生理基础的性二态以及可能面临的被捕食风险大小有关     

Effects of decapitation and ovariectomy on the regulation of juvenile hormone synthesis in the cockroach, Diploptera punctata

Corpora allata from Diploptera punctata females at adult ecdysis or at the end of the last-larval stadium, when implanted into decapitated females, underwent a cycle of juvenile hormone synthesis similar in timing and magnitude to that of glands implanted into control animals which had been starved and allatectomized. Starvation did not alter the cycle in rates of juvenile hormone synthesis of sham-operated animals.Decapitation of ovariectomized animals resulted in no cycle in rates of juvenile hormone synthesis by implanted adult corpora allata; however, implantation of an ovary along with the corpora allata into decapitated, ovariectomized hosts resulted in a cycle of juvenile hormone synthesis. In control animals, which retained their heads but were starved and allatectomized as well as ovariectomized, the implanted corpora allata showed a cycle of juvenile hormone synthesis only when implanted with an ovary. The maximal rates of juvenile hormone synthesis by the corpora allata in both experimental and control conditions were lower than normal, likely due to the repeated trauma of surgery. However, at no time from eclosion to the end of the first gonotrophic period was the brain necessary for the cyclic response of the corpora allata to the presence of the ovary.