Morphogenetic and gonadotrophic effects of a juvenile hormone analogue ((7S)-hydroprene) in last instar female larvae of Diploptera punctata

ABSTRACT. The effect of treatment of last instar female larvae of Diploptera punctata with a Juvenile Hormone (JH) analogue, (7 S )-hydroprene, has been determined with respect to the ability of the analogue to alter the duration of the stadium and the nature of the ensuing ecdysis. We have also investigated the effects of the analogue on JH release, the growth of the basal oocytes, as well as ecdysteroid titres during the fourth stadium. Analogue treatment prior to day 10 of the stadium results in prolongation of the stadium and desynchronization of ecdysteroid release. Thereafter, treatment with the analogue has little effect. Analogue treatment results also in the formation of supernumerary larvae and intermediates, in a dose-dependent fashion, provided that animals are treated on day 10 or earlier. Thus, the 'critical' period for metamorphosis in last instar D. punctata is between days 0 and 10.
Treatment with (7 S )-hydroprene produces profound effects also on both JH release, and basal oocyte growth. At a dose of 500μg administered on day 1, JH release is stimulated significantly at a time when JH release is normally undetectable. Significant growth of basal oocytes is observed in such treated animals, and appears to precede the peak in JH release. We suggest that the growth of the basal oocytes, as a result of analogue treatment, stimulates the production of JH by CA in these last instar larvae.     

Juvenile hormone biosynthesis,oocyte growth and vitellogenin accumulation in Choristoneura fumiferana and C. rosaceana: a comparative study

We assessed the effects of age and mating status on in vitro juvenile hormone (JH) biosynthesis, oocyte growth, egg production and vitellogenin (Vg) accumulation in the tortricid moths, Choristoneura fumiferana and C. rosaceana. To determine whether vitellogenesis is dependent on the presence of JH, we also examined the effects of decapitation and JH analog treatments on egg production. In both species, the corpora allata (CA) of adult females released fmol quantities of JH, with JH II being the major homolog produced. The CA began producing detectable quantities of JH around the time of emergence. Full activation of the CA was observed a few hours sooner in C. fumiferana than in C. rosaceana. In pharate adults and young virgin females of both species, growth of the basal oocyte reflected changes in CA activity. Decapitation of newly emerged females significantly reduced egg production, but treatment of decapitated females with the JH analog methoprene resulted in egg production that was similar to (C. fumiferana) or greater than (C. rosaceana) that of controls, indicating that JH is required for oocyte maturation. Vg was first observed in the hemolymph before the presumptive time of CA activation, suggesting that the synthesis of this protein is not dependent on JH. The presence of normal quantities of Vg in the hemolymph of pupae decapitated before CA activation confirmed this hypothesis. The Vg titer underwent a transient decline following CA activation and was significantly lower in mated than in virgin females of both species 3 and 5 days after copulation. Since CA activation at emergence and mating are both expected to cause a rise in the JH titer, we suggest that the declines in the levels of Vg result from JH-enhanced Vg uptake by the developing oocytes. Mating induced a significant increase in egg production but had no measurable impact on rates of JH biosynthesis in vitro.     

Endocrine regulations of ovarian maturation in the cockroach Blaberus discoidalis

The first gonotrophic cycle of oocyte maturation was defined for virgin Blaberus discoidalis cockroaches. A high correlation was found between growth of the basal oocytes and increased ovarian protein content. Allatectomy blocked ovarian protein formation, whereas JH-III administration compensated for the loss of the corpora allata. Experiments involving neuro-endocrine surgery and hormone replacement therapy indicated that JH, alone, could stimulate ovarian protein formation; however, the addition of neuroendocrine extracts enhanced the JH effects. The data suggest that both JH and neurohormones stimulate aspects of ovarian protein formation in this insect.     

The effect of enforced virginity and subsequent mating on the activity of the corpus allatum of Periplaneta americana measured in vitro, as related to changes in the rate of ovarian maturation

ABSTRACT. Female P. americana, reared with males from the time of adult emergence, mated on the 4th–5th day after metamorphosis, produced the first ootheca on the 8th or 9th day, and then produced successive oothecae at intervals of 3.0 days, whereas, only 50% of virgin females had produced their first ootheca by the 28th day after adult emergence. Examination of the ovaries indicated that oocyte development is normal in virgins until shortly after the time when they first become receptive to males. When mating was not allowed there was a dramatic reduction in the rate of vitellogenic growth of the terminal batch of oocytes which persisted until mating was allowed, and was often accompanied by resorption of a percentage of the oocytes. Short-term, in vitro, radiochemical assay of juvenile hormone (JH III) biosynthesis by corpora allata (CA) showed that, in females reared with males, the cycles of ovarian development are accompanied by regular pulses of CA activity. There is a small, possibly preparatory peak of JH III biosynthesis before vitellogenesis of the first wave of oocytes, followed by a larger peak of JH III production during vitellogenesis of this batch of eggs and one peak of CA activity between ovulation of each subsequent wave of oocytes. Activities as low as 0.25 pmol C₁₆JH/CA pair/h and as high as 48.38 pmol/CA pair/h were observed in CA from mated females after the onset of cyclic activity. Stimuli received during mating are somehow responsible for the cyclic activity of the CA, for when females were subjected to enforced virginity the first small peak was normal but the second peak was not fully realized and there was then a gradual decline in CA activity until approximately 2 weeks post-emergence. Thereafter the glands exhibited a more or less constant rate of JH biosynthesis (mean = 3.45 ± 0.32 pmol/CA pair/h.) When females were mated after 21 days of enforced virginity the activity of the CA was enhanced. By 48 h after mating the mean glandular activity was at least four times that found in virgins of the same age, and by 72 h rates as high as 40 pmol/CA pair/h were observed. This was followed by normal cyclic activity of the CA. The increase in rate of JH biosynthesis appears to result in a recommencement of oocyte development in these ‘delayed-mated’ females.     

Disinhibition of oocyte growth in adult,virgin Periplaneta americana by corpus allatum denervation: Age dependency and relatedness to mating

Unilateral section of the nervi corporis allati I (NCA-1) of isolated, starved, adult, virgin Periplaneta americana disinhibited oocyte growth during a specific period following their adult emergence. The effect required that the corpus allatum (CA) be free of NCA-1 innervation for 4 days beyond the time the females were 7–8 days old. The onset of this sensitive period corresponds to when most isolated, starved virgins become sexually receptive. The results suggest that NCA-1 inhibition of CA activity, initiated about 7 days, is relieved by mating. When done on sexually receptive, starved virgins, unilateral NCA-1 section was as effective as insemination for stimulating growth and chorionation of the first generation of oocytes. Neural inhibition of juvenile hormone (JH) secretion by the CA may also explain diminished production of oocytes by isolated, fed virgins, for during 30 days following unilateral NCA-1 section they produced 2.6 to 5 times more oothecae than did controls with a single CA removed or after the sham operation. The number of oothecae deposited by fed virgins was similarly increased after bilateral NCA-1 section, but to a lesser extent than when the operation was done on fed, inseminated females of the same age. Specificity of the response of the CA to denervation was substantiated by experiments in which the CA were extirpated and reimplanted, by topically applying C₁₆JH, and by experiments in which the nervus corporis cardiaci 1 and 2 on the right or left side were severed.     

Stimulating action of methyl 12, 12, 12-trifluorofarnesoate on in vitro juvenile hormone III biosynthesis in blattella germanica

Methyl 12, 12, 12-trifluorofarnesoate (MTFF) at a dose of 10 μM, stimulated in vitro juvenile hormone (JH) release in corpora allata (CA) from 6-day-old, freshly ecdysed, and 8-day-old (period of ootheca transport) adult virgin females of Blattella germanica. In addition, MTFF also induced intraglandular accumulation of JH and MF in treated CA. Trifluorofarnesoic acid (TFFA) and trifluorofarnesol (TFF) exhibited the same properties, although to a lesser extent than MTFF. The detection of MTFF in TFFA-treated CA suggested that TFFA and TFF were biotransformed into MTFF by the CA enzymatic system and that this ester might be responsible for the activity observed. Equivalent experiments carried out with farnesoic acid (FA) resulted in a more significant stimulation of JH production. This is not surprising, because exogenous FA is readily epoxidized at C10-C11 double bond and methylated to afford JH. Conversely, analytical data have shown that the C6-C7 double bond of MTFF is epoxidized by the CA enzymatic system, whereas that at C10-C11 remains practically unaltered.     

Influence of juvenile hormone and mating on oogenesis and oviposition in the codling moth,Cydia pomonella

Oogenesis in the codling moth, Cydia pomonella, and the role of juvenile hormones (JHs) were addressed. Rudimentary ovarian structures were recognisable in day 3–4 pupae, when haemolymph JH was still undetectable by coupled gas chromatography‐mass spectrometry in the selected ion mode (GC‐MS/SIM). The presence of developing oocytes was observed by light microscopy on day 8, coincident with very low JH titres (0.74 ± 0.05 ng/ml JH II). Chorionation was only evident upon emergence, following an increase in JH in the pharate adult (0h old: 4.71 ± 0.34 ng/ml JH II). Analysis of haemolymph from virgin and mated females indicated that JH II was predominant, with approximately equal and lower quantities of JHs I and III (3.3‐ to 5.0‐fold less). When pupae or newly emerged adults were treated with JH homologues, no alteration in ovarian protein content was apparent, but the JH mimetic, fenoxycarb, depressed the number of oocytes filling ≥ 50% follicular volume. Chorion deposition was stimulated by JHs I, II, or III (10 μg), but not by fenoxycarb (0.05 μg, 10 μg). Mating provided correct stimuli for enhanced choriogenesis and egg laying, and, since haemolymph JH titres were concomitantly elevated (approximately 2‐fold), it was postulated that the rise in JH elicited both these events. Application of JHs to virgin females, however, could not mimic mating; only increases in choriogenesis were induced: JH‐treatment of virgins (or mated insects) significantly decreased oviposition rates over 24 and 48 h and markedly reduced the life‐time total number of eggs. Arch. Insect Biochem. Physiol. 41:186–200, 1999. © 1999 Wiley‐Liss, Inc.     

Effects of chilling stress on allatal growth and juvenile hormone synthesis in the cockroach, Diploptera punctata

During the ovarian cycle of the cockroach, Diploptera punctata, a mitotic wave occurs in the corpora allata before an increase in gland volume and juvenile hormone (JH) synthesis. Previous studies have demonstrated that the brain inhibits mitosis and JH synthesis in corpus allatum (CA) cells until adult females have mated. Herein, we report that chilling stress effectively suppresses mating induced proliferation of CA cells. In mated females, chilling on melting ice for 0.5-3 hours caused a strong, dose-dependent decrease in mitotic activity. In insects chilled for 3 hours, although the mitotic wave in the CA was practically abolished, CA volume and JH synthesis finally reached peak levels typical of unchilled insects, despite a 2-day delay. Consequently, oocyte maturation and oviposition were also delayed by 2 days, yet in both chilled and unchilled insects, peak values of basal oocyte length were the same. By allowing virgin females to mate on different days after chilling, we found that the chilling effect could be retained in the insect body for at least 2 days. During this period, signals from mating could not effectively remove inhibition of CA cell proliferation. Unilaterally disconnecting the CA from the brain revealed that chilling stress mediated CA cell proliferation via the brain, and did not directly affect the CA.     

Changes in the size of corpora allata,in the juvenile hormone III titer in the hemolymph,and in the protein content of terminal oocytes throughout the first gonadotropic cycle in Aiolopus thalassinus (Insecta: Orthoptera: Acrididae)

In Aiolopus thalassinus (Fabr.), the changes in the volume of the corpora allata (CA), in the concentration of juvenile hormone III (JH III) in the hemolymph, and in protein content in the terminal (t) oocytes were studied during the first gonadotropic cycle. These parameters could be better related to the volume of t-oocytes than to age after emergence. The JH III titer curve was maximum (2.9 pmol/10 μl) at an oocyte volume of 1.2 mm³. Before oviposition (days 10–16) the JH III titer decreased to 0.65 pmol/10 μl hemolyph. The increase in JH III titer reflected a period of high protein storage in the t-oocytes. The largest volume of the CA was reached at the beginning of yolk storage in the t-oocytes. The highest JH III titer did not correspond with the largest volume of CA, which occurred much earlier. © 1993 Wiley-Liss, Inc.     

In vitro biosynthesis of JH III by the corpora allata of adult females of Blattella germanica (L)

A radiochemical assay which fulfills the required validation criteria has been used for quantification of the in vitro biosynthesis of JH III by the corpora allata of adult females of Blattella germanica throughout the 7 days of the first reproductive cycle. The presence of JH III has been independently confirmed by HPLC and mass spectrometry. Results indicate that rates of JH release increase repidly from day 3 to day 6, which is correlated with oocyte growth. The highest levels of JH release (2.58 ± 1.11 pmol/hr per pair) were obtained from day-6 females. The time course of JH production by CA from day-6 females showed that CA released JH at a linear rate for at least 9 hr. From these results, it can be concluded that titers at high production ages and linearity ranges are satisfactory enough to be used in studies on the regulation of JH production in this species.     

Endocrine regulation of female contact sex pheromone production in the German cockroach, Blattella germanica

ABSTRACT The amount of the major component of the cuticular sex pheromone, 3, 11-dimethyl-2-nonacosanone, on individual female German cockroaches, Blattella germanica (L.), as a function of age was determined by gas-liquid-chromatographic analysis. Accumulation of phermone increased with age in both virgin and mated females. During the first gono-trophic cycle, the pheromone accumulated most rapidly when oocyte growth rates were maximal (days 5–10), and least rapidly while the female carried an ootheca (days 11–32). Pheromone accumulation was similar in virgin and mated females when the same physiological stages (determined by oocyte maturation) were considered. Inhibition of Juvenile Hormone release, through allatectomy, chemicals (precocene or fluoromevalonate), or through mechanical egg case implants, suppressed or delayed pheromone production and oocyte growth. The Juvenile Hormone analogue ZR512 induced allatectomized or head-ligated females and females with chemically or mechanically inhibited corpora allata to produce pheromone and enlarge their basal oocytes. Finally, ZR512 applied to intact females stimulated pheromone production in a dose-dependent manner.     

Juvenile hormone biosynthesis and oocyte development in adult female Blattella germanica: Effects of grouping and mating

The roles of grouping and mating in modulating the activity of the corpora allata (CA) in adult female cockroaches were investigated using the in vitro radiochemical assay of juvenile hormone (JH) biosynthesis. Isolated virgin females have longer, asynchronous cycles of CA activity and oocyte maturation than do isolated females mated on day 8. Three factors were identified as the major contributors to this difference: (1) an experimental artifact of selection for sexually receptive females, (2) a positive effect of grouping on JH synthesis and oocyte maturation, and (3) a positive effect of copulation on oviposition and retention of the ootheca. Mated females constitute a subpopulation of receptive females that differ significantly from other females by having higher rates of JH synthesis prior to mating. The relative importance of such selection is substantial when the rate of mating is low, as in experiments with isolated females that are exposed to males for a short period of time. Long-term exposure of females to males introduces a grouping effect, which obscures any additional effect of mating on CA activity and oocyte development. However, mating influences ootheca formation and its retention. The effect of grouping can be mimicked in isolated females by transection of the nerves connecting the CA–corpora cardiaca complex to the brain, suggesting that in this insect isolation causes brain inhibition of the CA, and grouping provides disinhibitory stimuli that release the CA from brain inhibition.     

Growth of the male accessory gland in adult locusts: Roles of juvenile hormone,JH esterase,and JH binding proteins

The participation of juvenile hormone (JH) in the regulation of growth and protein synthesis in the accessory reproductive gland of male Locusta migratoria has been investigated. After elimination of endogenous JH with ethoxyprecocene, the accessory gland failed to grow, but growth was restored by a single application of the JH analog, pyriproxyfen. Pyriproxyfen appeared to stimulate total protein synthesis by 3 h, with a significant effect by 12 h, in contrast to 24 h observed in fat body. The dose curve for stimulation of protein synthesis 12 h after applying pyriproxyfen gave an ED₅₀ of 0.1 μg; the dose curve for gland growth at 72 h was biphasic, with steps at about 0.01 μg and 10 μg, suggesting two phases in JH action. SDS-PAGE analysis showed several components that were stimulated by pyriproxyfen, the effect being strongest in an 11 kDa band. A 5 kDa component was enhanced in the soluble and reduced in the particulate fraction after precocene treatment. The accessory gland contained JH esterase activity at levels about 100 times those in fat body or hemolymph, and was higher in precocene treated locusts. Binding activity for [³H]10R -JH III was high in cytosolic and nuclear fractions, and was identified immunologically as due to the previously described hemolymph JH binding protein. The results indicate that the mode of action of JH in the accessory gland may differ from that in the fat body. The presence of intracellular JH binding protein suggests a direct action of JH within the gland, that may be modulated by JH esterase. © 1995 Wiley-Liss, Inc.     

Mating in Heliothis virescens: Transfer of juvenile hormone during copulation by male to female and stimulation of biosynthesis of endogenous juvenile hormone

Studies were undertaken to determine whether adult males of Heliothis virescens transfer juvenile hormone (JH) to females during copulation, and an in vitro radiochemical assay was used to determine whether mating causes an allatotropic effect, i.e., stimulation of JH biosynthesis by corpora allata (CA). In vitro, CA from 3-day-old mated females synthesized and released approximately 2.5 times total JH as that of CA from comparably aged virgin females. Of the homologues, JH II exhibited significant increase in mated females; JH I also increased but not significantly. JH III remained similar to that of virgin females. This is the first demonstration of an allatotropic effect of mating in moths. In contrast to the female, CA of virgin males did not produce any JH, but accessory sex glands (ASG) in 3-day-old males synthesized small amounts of JH. Immediately after adult emergence, male ASG contained approximately 1.5 ng JH I and II, which increased by 12 h after emergence and remained at this high level up to 54 h after emergence. JH III was barely detected in ASG. JH in ASG of mated male immediately after uncoupling was depleted almost completely, and 24 h later recovered to levels comparable to that of 54-h-old virgin male. Virgin female bursa copulatrix did not contain any JH, but mated female bursa, immediately after uncoupling, had JH at levels comparable to that observed in virgin male ASG. By 6 h after uncoupling, JH levels decreased dramatically in mated female bursa. These data suggest the transfer of JH to females by the male. Arch. Insect Biochem. Physiol. 38:100–107, 1998. © 1998 Wiley-Liss, Inc.     

The fecundity of the walleye pollock, Theragra chalcogramma (Pallas), spawning in Canadian waters

The ovaries of 113 walleye pollock from a resident stock in the Strait of Georgia, British Columbia were examined for determination of fecundity. Oocytes were sized and counted in 20 μm intervals of diameter. Without exception, ovaries contained a pronounced bimodal distribution of oocyte diameters with peaks at 100 and 400–600 μm. Oocytes ≥ 180 μm diameter were undergoing trophoplasmic growth leading to hydration. 'Apparent' fecundity is defined as the estimated number of yolked oocytes ≥ 180 μm diameter, regardless of potential resorbtion. Previous workers have not shown that significant resorbtion takes place in the post-spawned ovary. Total oocyte complement (≥40μm diameter) was best expressed by a linear model where F_t = 33004 f.l. – 869627, where f.l. = fork length in cm and r = 0.86. Estimates of F_t , ranged from 117700 to 1394 100 oocytes ≥40μm. Age was weakly related to fecundity, reflecting large individual differences in annual growth after age 4 years. Apparent fecundity best suited a linear model where F_a = 23522 f.l. – 599713 and r = 0.91. Estimates of F_a fell within the range 58 379–1 151 527. Relative fecundity (eggs g⁻¹) decreased over most of the length range encountered in the sample. The average-sized female in Georgia Strait is twice as fecund as her counterparts in the north-western Pacific Ocean, containing some 390 000 to 420 000 oocytes 7ge;180 μm diameter compared to about 200 000 oocytes in a north-western female of comparable length.     

Neural influence on corpus allatum activity and egg maturation in starved virgin Periplaneta americana

ABSTRACT. Of sixty-seven adult female Periplaneta americana (L.) isolated when less than 8h old and kept without food at 25–30°C in LD 12:12, only six produced oothecae during 25–35 days. Growth of the basal oocytes was retarded, and maximal oocyte volume, only one-third of that in fed virgins, was achieved after about 12 days. By day 14, 60% of the basal oocytes were being resorbed in the starved females, and corpora lutea were usually all that remained beyond day 20. Oocyte growth was potentiated in starved, virgin females by severing either of the two nervi corporis allati 1 (NCA 1), and oothecae were then produced in 45–80% of cases. Sham-operated controls oviposited in fewer than 27% of the trials. Because oocyte maturation was prevented by extirpating both corpora allata (CA), but not when the glands were replaced, and because the juvenile hormone analogue, ZR 515, was highly effective in causing the starved cockroaches to produce oothecae, the starvation-induced reproductive failure probably reflects diminished hormone production by the CA. The most likely consequence of severing NCA 1 is de-repression of juvenile hormone production. The directness of the neural influence was shown by removing the one denervated CA, in which case stimulation of oogenesis was minimal even though the contralateral innervated gland was present. The incidence of ootheca production was not enhanced by transecting the NCA 2, which suggests that the CA of starved cockroaches are not inhibited via this pathway.     

Juvenile hormone coordinates the regulation of the hemolymph ecdysteroid titer during pupal commitment in Manduca sexta

The timing and magnitude of the pupal commitment peak in the hemolymph ecdysteroid titer of fifth instar Manduca sexta larvae are controlled by the combined effects of prothoracicotropic hormone (PTTH), a prothoracic gland-stimulating factor present in the hemolymph, and the biosynthetic competence of the prothoracic glands themselves. The present data indicate those individual effects are coordinated by juvenile hormone (JH): (1) Treatment of larvae with the JH analog (7S)-hydroprene prevents the normal precommitment drop in the titer of the stimulatory factor; (2) treatment of larvae with (7S)-hydroprene suppresses in a dose- and time-dependent manner the biosynthetic competence of the prothoracic glands; and (3) (7S)-hydroprene acts directly on the brain to inhibit the release of PTTH in vitro. Thus, during Manduca development, a drop in the JH titer early in the fifth instar results in a rapid drop in the titer of the stimulatory factor, the gradual acquisition by prothoracic glands of biosynthetic competence, and lastly, the gated release of PTTH into the hemolymph. The resulting increase in ecdysone synthesis by the prothoracic glands gives rise to the small peak in the ecdysteroid titer that drives pupal commitment.     

Injection of Dip-allatostatin or Dip-allatostatin pseudopeptides into mated female Diploptera punctata inhibits endogenous rates of JH biosynthesis and basal oocyte growth

Studies on the catabolism of allatostatins (ASTs) provided the rationale for the design of a series of Dip-allatostatin-derived pseudopeptide mimetic analogues. In vitro, the Dip-ASTs and pseudopeptides show varying degrees of resistance to catabolism and all show significant inhibition of juvenile hormone (JH) biosynthesis. This study was undertaken to determine whether potent Dip-ASTs and/or their pseudopeptide mimetic counterparts caused 'allatostatic' effects in vivo following injection into mated female Diploptera punctata. Animals injected with aqueous solvent or Dip-AST 7(1-7) N-terminal fragment, which excludes the active core region of the ASTs, were used as controls. An in vitro radiochemical assay revealed that injection of Dip-AST 5, 7 or pseudopeptide analogues 397-2 or AST(b)φ2 significantly inhibited the biosynthesis of JH (P<0.05). The results also indicate that basal oocyte growth was significantly inhibited by injection of these same compounds, with the exception of Dip-AST 7 (P<0.05). Analogues 396-1 and 419 did not significantly inhibit rates of JH biosynthesis but did significantly inhibit the growth of basal oocytes. Analyses of feeding, excretion and food absorption/utilization patterns of these same animals suggested that these compounds are not toxic to the insect; rather they directly inhibit the biosynthesis of JH by the corpora allata, and reduce the rate of growth of basal oocytes. Disruption of critical reproductive and/or developmental processes by pseudopeptide analogues of the ASTs could provide novel and selective strategies for future insect pest management.     

Juvenile Hormone biosynthesis and release during oocyte development in Phormia regina Meigen

A radiochemical assay for Juvenile Hormone (JH) biosynthesis and release by the corpus allatum (CA) was used to assess the effects of diet on CA activity of adult female Phormia regina (Meigen) fed either sugar-water or sugar-water-liver. CC-CA complexes were incubated in L-methionine-free medium 199 supplemented with ³H-L-methionine. The rate of JH release by the CC-CA complexes is linear for 3 h and declines slightly thereafter. JH III appears to be one of the major components of the isooctane-extractable product from incubated CC-CA. High pressure liquid chromatographic analysis indicates that 10% of the released radiolabelled product is JH III. Rates of JH release show a strict dependence on L-methionine concentration in the incubation medium, with optimal rates occurring between 100 and 150 μM L-methionine. JH release is at a low level (<0.02pmolh^-1 per pair of CC-CA) in flies fed only sugar-water, but increases dramatically in flies fed sugar-water-liver (average release rate of 0.2pmolh^-1 per pair of CA, 24h after a liver meal). The rate of JH release increases steadily to more than 1.2pmolh^-1 per pair at 128h of age (i.e. 56h after a liver meal) at which time oocytes are mature. Elevated rates of JH release in vitro appear to be correlated in vivo with the appearance of vitellogenin in the haemolymph and its uptake by the developing oocytes.     

Induction and Inhibition of Meiotic Maturation in Follicle-enclosed Mouse Oocytes by Forskolin

A continuous exposure of follicle-enclosed mouse oocytes to ovine luteinizing hormone (LH, 10 μg/ml) in vitro resulted in a 3-fold elevation of CAMP levels in the follicle cells, but not the oocytes, with subsequent oocyte maturation. When follicle-enclosed oocytes were exposed to forskolin (0.01–10 μM) for 2 hr and then incubated in forskolin-free medium (transient exposure group), oocytes underwent germinal vesicle breakdown in a dose-dependent manner. In contrast, a continuous exposure of the follicles to forskolin (10 μM) for up to 10 hr failed to induce resumption of meiosis. Follicle cell cAMP levels increased within 2 hr after the initial exposure to forskolin, and thereafter decreased rapidly regardless of whether forskolin treatment was transient or continuous. A similar transient increase in oocyte cAMP levels was observed after transient or continuous treatment with forskolin. It was evident, however, that at any time examined oocyte cAMP levels were consistently higher in the continuous exposure group than in the transient exposure group. Furthermore, a continuous exposure to forskolin also blocked LH-induced meiotic maturation. These findings suggest that elevated levels of cAMP in the oocyte block meiotic maturation in mouse oocytes. The present results further suggest that an increase in follicle cell cAMP levels is essential to the LH-induced meiotic maturation.