Serum hormone levels associated with spawning activity in the mummichog, Fundulus heteroclitus

Daily collections of the mummichog, Fundulus heteroclitus, from field populations during the first 45 days of the breeding season revealed a semilunar cycle in the sperm index. Peaks in the sperm index were preceded by 6 days with peaks in the serum testosterone concentration. Bihourly sampling of field populations during a 72-hr period at the new moon showed both diel cycling and an upward trend in serum progesterone levels in female mummichogs. Male mummichogs had 12-hr cycles in serum 17 beta-hydroxy-4-androstene-3,11-dione levels, the peaks of which preceded high tide by 4 hr. The physiological significance of these cycles are discussed.

6-Dimethylaminopurine blocks starfish oocyte maturation by inhibiting a relevant protein kinase activity

The puromycin analog N6,N6-dimethyladenine (6-dimethylaminopurine or 6-DMAP) was found to inhibit meiosis reinitiation in starfish oocytes stimulated by the natural hormone 1-methyladenine. Increasing concentrations of this agent delayed and eventually blocked germinal vesicle breakdown. They were found to be effective even when applied during the hormone-independent period, after the oocytes had been already committed to reinitiate meiosis. 6-DMAP mimics most of the effects of emetine since it induces protein dephosphorylation, inhibits polar body formation, and promotes the precocious appearance of resting nuclei. However, unlike emetine, 6-DMAP does not affect protein synthesis. The effect of this agent cannot be accounted for by a stimulation of the protease or phosphoprotein phosphatase activities since the rate and extent of protein dephosphorylation do not increase in its presence. Data from in vivo and in vitro endogenous protein phosphorylation experiments suggest rather that 6-DMAP may directly or indirectly affect the activity of a relevant c-AMP and Ca2+-independent protein kinase which is stimulated after hormone addition and seems to support starfish oocyte maturation.

Induction of maturation in follicle-enclosed oocytes: the response to gonadotropins at different stages of follicular development

Antral follicles, isolated from either nontreated or pregnant mare's serum gonadotropin (PMSG)-primed 27-day-old rats, were incubated in the absence or the presence of either luteinizing hormone (LH), follicle-stimulating hormone (FSH), or forskolin. The effect of these agents on oocyte maturation and cyclic adenosine 3',5'-monophosphate (cAMP) accumulation was studied and compared. Both gonadotropins, LH and FSH, as well as forskolin, effectively induced maturation of oocytes enclosed by large antral follicles isolated from PMSG-primed rats. On the other hand, we found that maturation of oocytes enclosed by small antral follicles, isolated from nonprimed and PMSG-primed rats, could be induced by either FSH or forskolin but not by LH. cAMP determinations revealed that, in spite of the inability of LH to induce oocyte maturation, elevated concentrations of the nucleotide were detectable in small antral follicles exposed to this gonadotropin. Since granulosa cells isolated from the large but not the small antral follicles were stimulated by LH to generate cAMP, the elevation of cAMP concentrations in the small antral follicle apparently represented the response of the theca cells to this gonadotropin. Since it is the ability of the granulosa cells to interact with the hormone that determines whether or not oocyte maturation will occur, we suggest that the granulosa, but not the theca cells, mediate LH action to induce oocyte maturation.

Effect of microtubule reactive drugs on steroid- and centrifugation-induced germinal vesicle migration during goldfish oocyte meiosis

During the process of progestogen-induced meiotic maturation in the goldfish oocyte, the oocyte nucleus (germinal vesicle, GV) migrates to the sperm entry site or micropyle at the animal pole. Following GV migration (GVM) to the micropyle, the nuclear membrane undergoes dissolution (GVD) and the cell enters metaphase I in preparation to generate the first polar body. Microtubule destabilizing drugs including colcemid, nocodazole and vinblastine were found to elicit GVM, mimicking the process which occurs just prior to the prophase I-metaphase I transition during steroid induced oocyte meiotic maturation. In addition, these drugs enhanced the induction of GVM by 17 alpha, 20 beta dihydroxy-4-pregnen-3-one, a potent, naturally occurring meiotogenic steroid in this species. By contrast, taxol, a microtubule stabilizing drug, was found to inhibit steroid induced GVM. A new assay for centrifugation induced GVM was applied to the goldfish oocyte in order to assess effects of steroids and drugs on GVM, without the complication of GVD or the restrictions imposed by the slow time course of naturally occurring GVM. The effective centrifugal force (ECF) required to elicit GVM in 50% of the oocytes (ECF50) decreased significantly after short incubations (1-5 hr) of oocytes with either 17 alpha,20 beta dihydroxy-4-pregnen-3-one or microtubule disrupting drugs (i.e., colcemid, nocodazole, or vinblastine). A working hypothesis, modeled after the effects of microtubule disrupting agents on intermediate filament arrays in somatic cells, is proposed in which a small number of microtubules or other polymeric tubulin units are responsible for maintaining a cytoskeletal array.(ABSTRACT TRUNCATED AT 250 WORDS)

Are ovarian steroids required for ovum maturation and fertilization? Effects of cyanoketone on the in vitro perfused rabbit ovary

An isolated perfused rabbit ovary preparation was used to determine the effects of cyanoketone, a potent inhibitor of 3 beta-hydroxysteroid dehydrogenase, on ovulation, ovum maturation and fertilizability, and steroid production. In the first experiment, cyanoketone (10(-4) M) was added to the perfusate of one ovary. The contralateral control ovary was perfused with medium alone. Thirty minutes after the onset of perfusion, hCG (50 IU) was added to the perfusate of both ovaries. The ovulatory efficiency of ovaries treated with cyanoketone plus hCG (82.3 +/- 4.6%) was similar to that of ovaries treated with hCG alone (84.8 +/- 4.4%). No difference was observed in the degree of ovum maturity or degeneration between control and cyanoketone-treated ovaries. Progesterone and estradiol production were significantly reduced by cyanoketone treatment; concentrations in the perfusate of ovaries treated with cyanoketone were 9.7% and 8.0% of the control values, respectively, 2 h after exposure to hCG. The concentration of 17-hydroxypregnenolone was not affected by cyanoketone treatment. Exposure to cyanoketone resulted in a significant (P less than 0.005) reduction in the fertilizability of ova ovulated and fertilized in vitro. In the second experiment, the percentage of ova that showed evidence of normal fertilization was significantly (P less than 0.025) increased in ovaries perfused with cyanoketone plus estradiol (64.5%) compared to that in ovaries perfused with cyanoketone alone (32.4%). In the third experiment, the addition of progesterone to the perfusate did not affect fertilizability of ovulated ova in ovaries perfused with cyanoketone plus estradiol. These results suggest that the presence of estradiol in the ovarian steroid environment may be essential for fertilizability of ova, but not for the processes of ovulation or meiotic maturation.

Steroid-induced final maturation in brook trout (Salvelinus fontinalis) oocytes in vitro: the effects of forskolin and phosphodiesterase inhibitors

The effects of phosphodiesterase inhibitors and forskolin on steroid-induced germinal vesicle breakdown (GVBD) were investigated in brook trout (Salvelinus fontinalis) oocytes using an in vitro incubation technique. Follicles were first treated with a collagenase solution to remove the follicle wall. Denuded oocytes were examined, using scanning electron microscopy. In all experiments GVBD was induced by the use of 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one. Cyclic adenosine 3',5'-monophosphate (cAMP) levels were measured (by protein-binding assay) in control and forskolin-treated oocytes. Collagenase treatment removed a majority of the follicle wall, as shown by scanning electron microscopy. Partially denuded (PD) oocytes were slightly more sensitive to steroid treatment than intact follicles (IF), as shown by ED50 values; but PD oocytes did not respond to gonadotropin (GTH) stimulation. Both 3-isobutyl-1-methyl-xanthine (IBMX) and SQ20,006 (Squibb) blocked GVBD, but IBMX was more inhibitory. Forskolin also blocked steroid-induced GVBD. Kinetics of inhibition studies were performed using IBMX, forskolin, and cycloheximide. IBMX and cycloheximide inhibited GVBD if added during the first 18 h following steroid stimulation, whereas forskolin blocked GVBD if added within 12 h after steroid treatment. Forskolin, at levels that block GVBD in vitro, significantly increased cAMP in both IF and PD oocytes, but the response of IF was greater than that of PD oocytes.

Cholesterol mediation of progesterone production and oocyte maturation in cultured amphibian (Rana pipiens) ovarian follicles

Treatment of isolated amphibian ovarian follicles with frog pituitary homogenate (FPH) increases follicular progesterone levels, which, in turn, initiate oocyte maturation. Recent studies have demonstrated that follicular progesterone production requires concomitant protein synthesis at some stage preceding pregnenolone formation. Experiments were carried out to determine whether cholesterol metabolism plays a role in mediating these biochemical and physiological processes. Aminoglutethimide (AGI, and inhibitor of P450 side-chain cleavage enzyme) inhibited FPH-induced intrafollicular progesterone accumulation and oocyte maturation (or germinal vesicle breakdown, GVBD) in a dose-dependent manner. Follicular progesterone accumulation and GVBD were both stimulated, in the absence of FPH, after addition of 25-OH-cholesterol, but not cholesterol, to the culture medium. Higher levels of progesterone were present in defolliculated oocytes as compared to intact ovarian follicles after incubation with 25-OH-cholesterol. The results indicate that the surface epithelium and theca layer in the follicle wall retard 25-OH-cholesterol access to steroid-producing follicle cells. AGI blocked 25-OH-cholesterol-induced accumulation of progesterone and GVBD in defolliculated oocytes, suggesting that 25-OH-cholesterol does not directly induce GVBD and is metabolized by the follicle cells. The capacity of follicles to accumulate progesterone following preincubation with FPH or 25-OH-cholesterol along with AGI was compared. Intrafollicular levels of progesterone increased after AGI- and 25-OH-cholesterol-treated follicles were washed. In contrast, progesterone levels decreased in follicles pretreated with AGI and FPH after washing. The results indicate that considerable 25-OH-cholesterol, but not endogenous cholesterol (FPH stimulation), remains available for steroidogenesis after removal of AGI. A significant, but incomplete, inhibition of progesterone accumulation occurred when follicles were incubated in the presence of 25-OH-cholesterol and cycloheximide. This partial blockage produced by the protein synthesis inhibitor indicates that some basal protein synthesis is required for progesterone accumulation from exogenous 25-OH-cholesterol. We conclude that intracellular cholesterol stores in the follicle wall are utilized to mediate FPH induction of progesterone accumulation and oocyte maturation in amphibian follicles.

Do calcium and calmodulin trigger maturation in amphibian oocytes?

In contrast to earlier reports (J. L. Maller and E. G. Krebs, 1980, Curr. Top. Cell. Regul. 16, 271-311; M. Moreau, J. P. Vilian, and P. Guerrier, 1980, Dev. Biol. 78, 201-214; W. J. Wasserman and L. D. Smith, 1981, J. Cell Biol. 89, 389-394; D. Huchon, R. Ozon, E. H. Fischer, and J. G. Demaille, 1981, Mol. Cell. Endocrinol. 22, 211-222) calmodulin preparations isolated from Xenopus laevis ovaries or obtained commercially rarely induced maturation upon microinjection into individual oocytes. Calmodulin injections did result in significant cases of maturation when oocytes were first pretreated (primed) with calcium-free (EGTA) OR-2 and then injected in regular OR-2 medium. However, under these conditions the injected buffer solution alone was sometimes found to induce maturation. Under more optimal priming conditions, cases were found where as high as 100% of the oocytes matured simply by returning them to regular OR-2 medium. To determine which divalent cations could be involved in the priming effects of EGTA pretreatment we repeated the earlier ionophore work of W. J. Wasserman and Y. Masui (1975, J. Exp. Zool. 193, 369-375), looking not just at calcium and magnesium but other divalent cations as well. Several divalent cations (10 mM) were found to induce germinal vesicle breakdown with the following tentative order of efficacy, Co2+ greater than or equal to Zn2+ greater than or equal to Mn2+ greater than Ca2+ greater than Mg2+ greater than Ba2+, regardless of whether or not ionophore A23187 was present. These results, along with other reports in the literature, are discussed with respect to the theory that a rise in free calcium and calmodulin is involved in triggering oocyte maturation; we conclude that neither is involved.

Induction of maturation in small Xenopus laevis oocytes

The competence of Xenopus laevis oocytes in various stages of growth to respond to progesterone treatment was investigated. Full-grown (stage 6) oocytes undergo nuclear membrane dissolution and resume meiosis in response to progesterone exposure, while smaller oocytes (stages 3-5; less than 1100 micron in diameter) do not. The defect which prevents 750- to 1050-micron oocytes from responding to progesterone can be overcome by microinjecting cytoplasm withdrawn from a stage 6 oocyte. Germinal vesicle breakdown in these small oocytes occurs on a timetable similar to that of stage 6 oocytes exposed to progesterone and is accompanied by a twofold increase in protein synthesis as well as the activation of MPF. The results argue that a cytoplasmic factor(s) which probably first appears at late stage 5 is required for progesterone responsiveness. The identity and role of the factor(s) in the development of maturation competence and the regulation of maternal mRNA translation are discussed.

Maintenance of meiotic arrest in isolated rat oocytes by the invasive adenylate cyclase of Bordetella pertussis

Rat oocytes resume meiosis spontaneously in vitro within 3 h after their isolation from the ovarian follicles. We report here that the spontaneous maturation of isolated rat oocytes is preceded by a drop in intracellular levels of cyclic adenosine 3',5'-monophosphate (cAMP). Further experiments were carried out to examine the possible correlation between the meiotic status and cAMP levels within the oocyte. To challenge rat cumulus-free oocytes to generate cAMP, bypassing their own adenylate cyclase, a preparation of an invasive adenylate cyclase from Bordetella pertussis was used. We found a dose-dependent elevation of cAMP levels within these oocytes that corresponded to inhibition of their spontaneous maturation. Persistent inhibition of meiosis was obtained with the continuous presence of the enzymatic preparation, whereas its removal resulted in a transient inhibition associated with a drop in cAMP. We suggest that the presence of elevated cAMP levels in the oocyte is directly responsible for the maintenance of meiotic arrest.

Inhibition of follicle-stimulating hormone-induced ovulation by indomethacin in the perfused rat ovary

In isolated, perfused ovaries of rats treated with pregnant mare's serum gonadotropin (PMSG), purified preparations of ovine follicle-stimulating hormone (FSH) (oFSH-211B) and rat FSH (rFSH-I-6), 100 ng/ml, were found to induce ovulations (4.8 +/- 0.9, n = 4, and 6.4 +/- 2.0, n = 5, ovulations per ovary, respectively). Indomethacin (5 micrograms/ml) added to the perfusate inhibited this ovulatory effect and exogenous prostaglandin F2 alpha (PGF2 alpha) (1 microgram/ml), or prostaglandin E2 (PGE2) (0.5 microgram/ml), reversed the blockade. Ovine FSH and rFSH had only a weak stimulatory effect on estradiol release, and only rFSH caused a significant increase in progesterone accumulation. Indomethacin reduced the stimulatory effect of rFSH on progesterone release, and this effect was reversed by PGE2 but not by PGF2 alpha. In a 6-h incubation experiment with preovulatory rat follicles, we tested the biological activity of gonadotropins used to induce oocyte maturation. The concentration of FSH used in the perfusion experiments induced oocyte maturation in more than 88% of the oocytes studied. The data confirm earlier findings that FSH can induce ovulations and show that prostaglandins are involved in this process. The data also indicate that prostaglandins might be involved in the FSH-induced increase of progesterone levels.

Short- and long-term effects of proallatotoxin (ethoxyprecocene II) on Rhodnius prolixus females

Oogenesis and oviposition can be inhibited in female of Rhodnius prolixus by means of short-term experiment (first reproductive cycle) of a single dose of ethoxyprecocene II given by ingestion. The inhibition is dose-dependent as measured by oocyte growth, egg maturation and egg deposition. In a long-term experiment (second and third reproductive cycles) egg production and oogenesis can be partially or totally re-established by subsequent blood meals without ethoxyprecocene II. These findings suggest that in female R. prolixus, damage caused to corpus allatum by ethoxyprecocene II, in certain cases, is not irreversible.

Induction of mouse oocyte maturation in vivo by perturbants of purine metabolism

Previous studies have suggested a critical role for purines in the maintenance of mouse oocytes in meiotic arrest. If so, then disrupting specific purine metabolic pathways in vivo might induce the resumption of oocyte maturation. To test this hypothesis, immature mice were primed with pregnant mare's serum gonadotropin and 24 h later received, by i.p. injection, one of several drugs that inhibit specific enzymes in the purine metabolic pathways. Cumulus cell-enclosed oocytes were isolated from the ovaries at varying times after drug treatment and assessed for germinal vesicle breakdown (GVBD). The inosine monophosphate dehydrogenase inhibitors, mycophenolic acid (MA) and bredinin (Br), each induced GVBD in a dose-dependent fashion, Br being the more effective agent. When the kinetics of oocyte maturation were examined, 71% of the oocytes from MA-treated mice had undergone GVBD 21-22 h after drug administration. Moreover, 100% GVBD was observed in oocytes from Br-treated mice after 6 h. The action of these drugs appeared to be a direct one and not mediated through stimulation of pituitary gonadotropin release or atresia. Azaserine, an inhibitor of de novo purine synthesis, also induced GVBD in a dose-dependent manner. However, sodium hadacidin and dl-alanosine, inhibitors of adenylosuccinate synthetase, failed to elicit a maturational response in oocytes in vivo. These data support an essential role for guanyl and/or xanthyl derivatives in the maintenance of meiotic arrest in vivo.

A Drosophila melanogaster mutant resistant to a chemical analog of juvenile hormone

Methoprene, a chemical analog of juvenile hormone, is toxic when applied to late third-instar larvae of Drosophila melanogaster. Using an ethyl methane sulfonate mutagenesis screen, we have selected two noncomplementing mutants, one of which is nearly 100 times more resistant than wild-type to either methoprene or juvenile hormone III topically applied or incorporated into the diet. The mutation, named methoprene-tolerant (Met), also confers resistance to methoprene-induced pseudotumor formation in larvae as well as to juvenile hormone III- or methoprene-induced vitellogenic oocyte development in adult females. Met adults show little or no cross-resistance to four other insecticides. The mutation was mapped by recombination to a location 35.4 on the X-chromosome and uncovered by chromosomes deficient for the region 10C2-10D4. Complementation was observed between Met and a lethal allele of the RNA polymerase II locus, which is also found in this region. Since the Met mutation also confers resistance to methoprene-induced abnormalities in adult cuticle formation, the autonomy of Met expression could be evaluated in flies mosiac for this mutation. Autonomous expression of Met was found both in abdominal cuticle as well as in external male genitalia. The characteristics of Met are consistent with those expected of a mutant having altered juvenile hormone reception in target tissue.

Müllerian inhibiting substance as oocyte meiosis inhibitor

Müllerian inhibiting substance (MIS) inhibited the resumption of meiosis in both denuded and cumulus cell-enclosed rat oocytes in vitro. Spontaneous germinal vesicle breakdown was prevented in both types of oocytes treated by a purified MIS preparation at protein concentrations of 15 micrograms to 150 pg/ml. The inhibiting effect of MIS on the resumption of meiosis was dose dependent, reversible and cyclic AMP independent. Neither follicular-stimulating hormone, luteinizing hormone, progesterone, estradiol, nor testosterone acted significantly to influence MIS-mediated inhibition of rat oocyte maturation. In contrast, MIS had no influence on meiosis in the mouse, where other protein has been reported to inhibit the cumulus cell-enclosed oocyte in a cyclic AMP-dependent fashion. Thus MIS may be yet another inhibitor of oocyte meiosis, acting in the rat by a mechanism different from those inhibitors known, in the mouse ovary, to exert their effect in a cyclic AMP-dependent manner.

Oocyte maturation in the mummichog (Fundulus heteroclitus): effects of steroids on germinal vesicle breakdown of intact follicles in vitro

The effects of several steroids on the maturation of follicle-enclosed oocytes of the mummichog Fundulus heteroclitus in vitro were examined. At a relatively high concentration (1.0 microgram/ml), a number of different steroids, including pregnenolone, 17 alpha-hydroxypregnenolone, corticosterone, cortisol, 11-deoxycorticosterone, 11-deoxycortisol, androstenedione, testosterone, progesterone, 17 alpha-hydroxyprogesterone, 20 beta-dihydroprogesterone, and 17 alpha-hydroxy-20 beta-dihydroprogesterone, were able to induce germinal vesicle breakdown (GVBD) in prematuration oocytes. Cholesterol, 17 beta-estradiol, 11-ketotestosterone, and 11 beta-hydroxytestosterone were totally ineffective. In general, 11-oxysteroids tended to be less effective than their 11-deoxysteroid counterparts. Two 20 beta-dihydroprogestins--17 alpha-hydroxy-20 beta-dihydroprogesterone and 20 beta-dihydroprogesterone--were the most potent maturation-inducing steroids, initiating 50% GVBD at 1 ng/ml in follicles obtained from ovaries containing mature or maturing follicles in vivo, or at 2.5-4.0 ng/ml in follicles from ovaries lacking mature or maturing oocytes in vivo. These results are consistent with several previous studies involving salmonids and various other teleosts, and suggest a possible physiological role for a 20 beta-dihydroprogestin in the resumption of meiotic maturation in F. heteroclitus.

Changes in gonadotropin and ovarian steroids associated with oocytes maturation during spawning induction in the carp

The present study correlates the profiles of certain ovarian steroid hormones with stages of oocyte maturation in common carp induced to spawn by classic hypophysation. Sixteen females were injected at midday with a calibrated homologous pituitary extract (cPE) containing 0.07 mg immunoreactive cGTH/kg body wt, as a priming dose. Ten of those females were injected 11 hr later with cPE containing 0.35 mg IR cGTH/kg body wt as an induction dose (Group P + IN). The other females were left without further treatment (Group P). An additional 6 fish were injected around midnight with the induction dose only (Group IN). A control group was injected with 0.7% saline (0.2 ml/kg) at midday and at midnight (Group S). Ovarian biopsies were taken at intervals and the maturational stages of individual females were recorded. Blood was sampled simultaneously with the biopsies. GTH, estradiol (E2) and 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17,20-P) were determined by specific RIAs. Germinal vesicle breakdown (GVBD) and ovulation were observed only in Group P + IN 2-4 hr after the second injection. The change in circulating ovarian steroids, in response to hypophysation, was found to depend on the maturational stage of the oocytes. Fish with oocytes showing central and eccentric GV responded to the increased GTH level by elevating E2, but not 17,20-P in the circulation. However, fish with ovaries containing peripheral GV responded by an increase in circulating 17,20-P (111 +/- 14.6 ng/ml) concomitantly with a transient decrease in E2. Only fish that showed such a shift in the steroidogenic profile exhibited GVBD in their oocytes and consequently ovulated. This finding is consonant with the hypothesis that 17,20-P is the maturational-inducing steroid in the carp.

Follicular maturation, luteinization and first meiotic division in oocytes after inhibiting mitochondrial function in mice with chloramphenicol

A significant number of diploid oocytes is ovulated from adult NMRI/Han mice treated with high doses of gonadotrophins. This inhibition of the first meiotic division is very likely caused by an altered communication between the germ cell and the surrounding somatic cells leading to a failure of the endocrine control of meiosis. The present study examined the role of mitochondria in follicular development, oocyte maturation and chromosomal segregation during first meiotic division in NMRI/Han mice. To affect mitochondrial function during the late phase of follicular maturation, chloramphenicol, a potent inhibitor of mitochondrial peptidyl transferase, was used. Adult mice were treated with chloramphenicol (CAM; 18.8 or 37.5 mg/kg b.w.) at different times after the pregnant mare serum injection. The results revealed that CAM inhibited the characteristic increase of ovarian weight, reduced the number of oocytes ovulated per female, lowered the progesterone concentration in the postovulatory ovary and increased the incidence of ovulated diploid oocytes. It was concluded that an irregular mitochondrial function may affect normal follicular development and oocyte maturation, and potentially interferes with the order chromosome segregation during the first meiotic division.

A histochemical study of the changes occurring in the protein-carbohydrate composition of the cumulus-oocyte complex and zona pellucida in immature mice in response to gonadotrophin stimulation

A histochemical account is presented of the changes that occur in the protein-carbohydrate composition of the cumulus-oocyte complex in immature mice after gonadotrophin treatment. The distribution and nature of the glycosaminoglycans (GAG) present was established by enzymic digestion of tissue sections with testicular of Streptomyces hyaluronidase prior to staining with periodic-acid Schiff (PAS) or Alcian Blue. Treatment with exogenous gonadotrophins [pregnant mare's serum and human chorionic gonadotrophin (hCG)] induced gross changes in the appearance of the zona pellucida (and in the histochemical staining of the cumulus-oocyte complex). A reduction was observed in the amount of PAS-positive material present within the zona pellucida of oocytes located in large Graafian follicles examined 40 h after stimulation with pregnant mare's serum. After the injection of hCG, the zona pellucida was further depleted of PAS-positive material. Most of the PAS-positive material became confined to the plasma membrane of the oocyte, while the oocyte itself also became increasingly PAS-positive. All the GAGs disappeared from zona pellucida within 4 h of hCG stimulation. The changes observed in the protein-carbohydrate composition of the zona pellucida in preovulatory oocytes immediately prior to ovulation may be a prerequisite for successful sperm-egg interactions.

Activators of protein kinase C stimulate meiotic maturation of rat oocytes

Agonistic analogs of gonadotropin releasing hormone can induce oocyte maturation in rat follicle-enclosed oocytes (1-5). Cyclic AMP does not rise following exposure of the ovarian follicle to GnRH (3) suggesting that cAMP-dependent protein kinase is not involved in the mechanism of GnRH action in this system. Protein kinase C, which is independent of cAMP, has recently been reported to mediate GnRH action in the pituitary (6-8). The possible involvement of this enzyme in the regulation of oocyte maturation has been tested in the present study. We report here that phospholipase C and direct activators of protein kinase C can mimic the response of rat oocytes to GnRH. These results suggest that GnRH-induced meiotic maturation of rat oocytes is mediated by the phospholipid-dependent protein kinase, protein kinase C.

Formaldehyde-induced mutagenesis: a novel mechanism for its action

A novel and unique mechanism for formaldehyde-induced mutagenesis is described which is mediated by the formation of an N6-substituted adenine ribonucleoside analogue, N6-hydroxymethyl adenosine, after an in vitro reaction of formaldehyde with adenosine. This type of ribonucleoside analogue (the deoxyribose derivative is ineffective) exhibits a powerful and remarkable germ-cell-stage-specific mutagenic effect in male Drosophila larvae, apparently by interfering with DNA repair. Circumstantial evidence is presented which indicates that the analogue most probably acts by its utilisation in the synthesis of diadenosine tetraphosphate (Ap4A) to form an antimetabolite(s) of Ap4A which subsequently interferes with Ap4A-mediated intracellular events, amongst which an effect on DNA repair would appear to be its mutagenic mechanism of action.

Effect of carp gonadotropin (cGTH) and a fraction unabsorbed on concanavalin A-Sepharose obtained from cGTH on vitellogenesis in the hypophysectomized marine teleost Gobius niger

To investigate whether a differential potency on vitellogenesis exists between the carp gonadotropin (cGTH) and fraction I-cGTH (proteins from cGTH unbound on concanavalin A-Sepharose, which represent 5% of cGTH in weight), hypophysectomized Gobius niger were treated with the two hormonal preparations at the same level. Vitellogenesis was checked for synthesis of vitellogenin and yolk incorporation in the ovary by means of immunological studies and histological techniques (light and electron microscopy). In addition, increased synthesis of vitellogenin was induced by injection of estradiol 17 beta together with each gonadotropin to assess the action of the two hormonal preparations on vitellogenin incorporation. Oogenesis was enhanced by cGTH and fraction I-cGTH, and at the same dose levels both treatments produced a similar pattern of stimulation of vitellogenesis. Vitellogenin was found in all the blood samples of animals treated by the hormones (cGTH and fraction I-cGTH) alone. Vesicles of pinocytosis were detected by electron microscopy up to Stage IIIa of oogenesis. When a high synthesis of vitellogenin was induced by exogeneous estradiol 17 beta injections, the two gonadotropic preparations had similar effects in yolk incorporation. cGTH was not less potent than fraction I-cGTH in these processes even though the cGTH preparation contains only 5% of fraction I-cGTH. The contamination of cGTH by a small amount of material unbound on concanavalin cannot be solely responsible for the vitellogenic activity of cGTH which consists of 95% glycoproteins.

Spontaneous maturation in vitro of cumulus-enclosed rat oocytes is inhibited by forskolin

We have recently reported that the adenylate cyclase activator, forskolin, induces in the rat ovarian follicle both cAMP accumulation and oocyte maturation. We demonstrate here, on the other hand, that the spontaneous maturation in vitro of isolated rat cumulus-enclosed oocytes is inhibited by forskolin. The inhibitory effect of forskolin is dose dependent with an ED50 at 15 microM. Forskolin inhibition decreases gradually with time, being completely relieved by 20 h of culture. Methylisobutylxanthine significantly prolongs the duration of the inhibitory action of forskolin. In addition to its inhibitory effect on oocyte maturation, forskolin triggers the cumulus-oocyte complex to generate cAMP. Cyclic AMP accumulation is maximally stimulated by 100 microM of forskolin with an ED50 at 60 microM. The potency of the cumulus-oocyte complex to respond to forskolin in terms of cAMP accumulation decreases with time. The pattern of the decrease in the potency of the cumulus-oocyte complexes to generate cAMP corresponds with the relief of its inhibitory influence on the oocyte. These results indicate that inhibition of maturation of the cumulus-enclosed oocyte may be coupled to elevation of cAMP levels in the cumulus-oocyte complex. As isolated cumulus-free oocytes are not inhibited by forskolin, we suggest that in the cumulus-enclosed oocyte system, cAMP generated by the cumulus cells is apparently transferred to the oocyte and maintains it in a meiotically arrested state. Maturation in this system occurs upon relief of inhibition which results from cessation of cAMP generation by the cumulus cells.

[Gametotoxic action of oxytetracycline on the early antenatal oogenesis of mice in in vivo and in vitro experiments]

Examination of the histological sections of mouse ovaries in the antenatal period following oxytetracycline treatment during proliferation of oogonia has shown the adequacy of some indicators obtained in experiments in vivo and in vitro (the index of sexual cells, the mitotic index of oogonia, the index of pathological mitoses of oogonia). The gametotoxic action of the drug manifested itself in a significant increase of the pathological mitoses of oogonia.

Morphological and cytogenetic studies of dominant lethality induced by mitomycin C and cyclophosphamide in female germ cells. The use of Robertsonian translocations as a 'marker system' to identify the zygote pronuclei

Dominant lethal tests were performed on female mice injected intraperitoneally with cyclophosphamide (200 mg/kg) or with mitomycin C (0.2 or 5 mg/kg) at the preovulatory stage of oogenesis. Complementary experiments were undertaken to clarify the results obtained. Embryo culture showed that sterility found after treatment with cyclophosphamide or with the high dose of mitomycin C was the reflection of true dominant lethal effects. Mortality after cyclophosphamide treatment occurred predominantly at the 2- and 3-cell stages, while it was reported in all preimplantation stages after treatment with the high dose of mitomycin C. Embryos treated with the low dose of mitomycin C developed normally to the blastocyst stage, confirming the absence of preimplantation effects found with this dose in the dominant lethal test. Cytogenetic analysis of female pronuclei at the first cleavage division were performed after mating treated females with males homozygous for one Robertsonian translocation. This method allowed one to distinguish easily the female pronuclei from the male ones, which exhibited one translocated 'marker' chromosome. After treatment with cyclophosphamide, most female pronuclei showed multiple chromatid exchanges or shattering of the entire genome. After treatment with the high dose of mitomycin C, various types of premature chromosome condensation were found, and they were often accompanied by important interchromosome associations. After treatment with the low dose of mitomycin C, no structural chromosome aberrations were found, and the number of numerical anomalies was not significantly different from that found in control embryos. These last results suggest that the increase in rate of postimplantation loss obtained in the dominant lethal test with the low dose of mitomycin C was not due to clastogenic effects of this compound in the female germ cells, but rather to indirect effects on the maternal organism.

Influence of calcium and magnesium deprivation on ovulation and ovum maturation in the perfused rabbit ovary

The role of calcium (Ca++) and magnesium (Mg++) in the ovulation process was studied using in vitro perfused rabbit ovaries. Ovaries were perfused with or without human chorionic gonadotropin (hCG) in Ca++/Mg++-free medium (M199) alone or combined with standard M199 to yield varying concentrations of Ca++ and/or Mg++. In all ovaries perfused with hCG, ovulatory efficiency was similar regardless of the concentration of Ca++ and/or Mg++. In ovaries perfused in Ca++/Mg++-free medium without hCG, ovulatory efficiency was similar to that in ovaries perfused with hCG. As Ca++/Mg++ levels were increased without hCG, ovulatory efficiency declined. Ovulation time was significantly accelerated in ovaries perfused in Ca++/Mg++-free medium with or without hCG. Most ovulated ova from ovaries perfused without hCG were immature. With hCG, degree of ovum maturity was directly related to ovulation time. Ovarian smooth muscle contractions were undetectable in 3 ovaries perfused in Ca++/Mg++-free M199 despite occurrence of ovulation. Smooth muscle contractions were recorded in 2 of 3 ovaries perfused in standard M199 with hCG. These results indicate: 1) Ca++/Mg++ exclusion results in rapid follicle rupture and immature ova; 2) oocyte maturation appears to be gonadotropin-dependent; 3) ovulation occurs in the absence of ovarian smooth muscle contractions during perfusion with Ca++/Mg++-free medium.

[Antenatal oogenesis in mice and its experimental modification]

The repeated (twice) intramuscular injection of oxytetracycline (5 mg per mouse) within 12 and 13 days after mating induced the increase of a relative number of pathological and atretic mitoses in the oogonia and, later on, the decrease of a relative number of diplotenes and early dictyotenes. The same dose injected within 16 and 17 days induced a higher degeneration of oocytes in pachytene and diplotene and inhibited the initiation of folliculogenesis.

Regulation of the development of meiotic competence and of the resumption of oocyte maturation in the rat

The first meiotic maturation division of mammalian oocytes is initiated in the embryo or during the early postnatal period. However, when the germ cells reach the diplotene stage the meiotic process is arrested. Meiosis is normally kept in abeyance up to a short period prior to ovulation, when the process is resumed in preovulatory follicles. Resumption of meiosis is studied in mammalian oocytes mainly in two dissimilar in vitro models, isolated oocytes maturing spontaneously in culture and hormone-induced maturation of follicle-enclosed oocytes. A third approach, namely, co-culture of oocytes with follicular constituents was adopted in order to test the role of follicular components in the control of meiosis. Such studies demonstrated an inhibitory action of granulosa cells, granulosa-cell conditioned medium and of follicular fluid (FF1) upon the spontaneous maturation of co-cultured oocytes. By contrast, theca tissue was without effect on meiosis. Addition of luteinizing hormone (LH) to co-cultures of rat granulosa cells and rat oocytes induced resumption of meiosis, as it does in vivo or in vitro in follicle-enclosed oocytes. It is therefore suggested that within antral follicles meiosis is held in abeyance by a granulosa cell product, the inhibitor of oocyte maturation (OMI). Further studies led to the conclusion that OMI is not species specific, that its production by granulosa cells is enhanced by follicle stimulating hormone (FSH) and that its concentration in FF1 is dependent upon the development of the follicle and not the stage of the oestrous cycle. OMI appears to be a peptide of less than 2000 Da. Its action on the oocyte appears to be mediated, at least partially, by cumulus cells and is potentiated by cyclic AMP. Since OMI activity has been demonstrated only in antral follicles, we examined the development of the ability of rat oocytes to undergo spontaneous maturation during their growth phase in preantral follicles. We have found that the ability of rat oocytes to resume maturation ('meiotic competence') is acquired between days 20-26 post partum. By the use of hypophysectomy on day 15 of life and by treatment with hormones and inhibitors we demonstrated that the acquisition of meiotic competence is dependent upon FSH stimulation and that it is mediated, at least partially, by ovarian oestrogen production. The findings that oocytes from preantral follicles are meiotically incompetent suggests that the physiological role of follicular OMI is limited only to antral follicles i.e. when the oocytes acquire meiotic competence.(ABSTRACT TRUNCATED AT 400 WORDS)

Immobilized methylglyoxal-bis(guanylhydrazone) induces starfish oocyte maturation

Methylglyoxal-bis(guanylhydrazone) diHCl (MGBG), an inhibitor of S-adenosylmethionine decarboxylase, was found to induce starfish oocyte maturation at concentrations above 30 microM. Among several analogs of MGBG three induce oocyte maturation and one lacks the maturation-inducing activity while possessing the S-adenosylmethionine decarboxylase-inhibiting activity. Although MGBG is required during a slightly longer period than the natural hormone 1-methyladenine (1-MeAde), the maturation kinetics are identical. MGBG-induced maturation is sensitive to the same inhibitors as 1-MeAde-induced maturation (theophylline, caffeine, procaine, nicotine, NH4Cl, dansylcadaverine, vinblastine, R24571, and trifluoperazine). Inhibition is reversed by increasing the MGBG concentration. MGBG also induces an increase of protein phosphorylation. MGBG and 1-MeAde were separated on the basis of charcoal adsorption, MgSO4 precipitation, and thin-layer chromatography. MGBG covalently linked to CH-Sepharose 4B induces maturation in oocytes whose jelly layer and vitelline coat have been removed by a moderate pronase treatment, but not in the untreated oocytes. The MGBG-CH-Sepharose 4B beads come in close contact with the plasma membrane only in the pronase-treated oocytes. The mode of action of MGBG and the implications of these results in the purification of the 1-MeAde receptor are discussed.

cAMP synthesis in the rat oocyte

cAMP synthesis by the rat oocyte and cumulus-oocyte complex was studied using direct labeling techniques. Cumulus-oocyte complexes synthesized cAMP in response to luteinizing hormone, follicle-stimulating hormone, cholera toxin, and forskolin. However, naked oocytes prepared from cumulus-oocyte complexes by mechanically removing the cumulus cells synthesized cAMP only in response to forskolin and follicle-stimulating hormone; cholera toxin and luteinizing hormone did not stimulate cAMP synthesis. Cholera toxin could augment the response of the oocytes to FSH, indicating an intact, though atypical, adenylate cyclase system. Forskolin was found to inhibit the onset of oocyte maturation in both cumulus-oocyte complexes and naked oocytes. The implications of these findings for the relationship between cAMP synthesis and oocyte maturation in the rat are discussed.

Tumor promoter TPA increases initiation of replication on DNA injected into xenopus eggs

The effect of the tumor promoter TPA on the control of DNA replication was assayed by following the regulated replication of DNA microinjected into eggs of the frog Xenopus laevis. TPA increases the amount of replication of injected DNA. Both initiation of replication on parental DNA molecules and reinitiation on previously replicated molecules are stimulated. Interaction with the external membrane appears necessary since injections of high concentrations of TPA into the egg are ineffective, whereas nM concentrations are active in the external medium. Related molecules that lack tumor promoting activity do not affect DNA replication. The effect of TPA on DNA replication was detectable only after the first cell cycle, and TPA cannot induce replication in oocytes, the quiescent stage which precedes the egg. When protein synthesis is inhibited TPA still increases initiation of replication, but does not allow detectable reinitiation cycles. The results suggest that interaction of TPA with the cell membrane is sufficient to increase the efficiency of replication initiation by a mechanism that does not require illegitimate reinitiation within a single cell cycle.

Effects of oestradiol-17 beta and testosterone on the histology of pituitary, liver, ovary and skin of previtellogenic Epinephelus akaara (Teleostei, Serranidae)

The pituitary gland of the red grouper, Epinephelus akaara, was studied by histochemical techniques, and the prolactin cells, corticotrops, somatotrops, gonadotrops, thyrotrops, pars intermedia cells and neurohypophyseal cells, were identified. Oestradiol-17 beta treatment caused PAS-positive cells in the proximal pars distalis, presumably a mixture of gonadotrops and thyrotrops, to undergo hypertrophy, vacuolation and degranulation of cytoplasmic glycoprotein granules. Disappearance of cytoplasmic granules was also evident in the PAS-positive pars intermedia cells. Oestrogen-treated fish also showed an increase in the hepatosomatic index, and hepatocytes enlarged in size, their nuclear diameter increased and large vacuoles were formed in the cytoplasm. These changes in the liver were paralleled by a secretion of vitellogenin into the serum and an increased production of mucus by the thickened skin epithelium. Testosterone injections did not affect such changes, neither in the pituitary nor liver cells, but a proliferation of skin epithelial cells was noted. Neither oestradiol-17 beta nor testosterone stimulated ovarian incorporation of vitellogenin, but treatment with high doses (5 mg/kg) of oestradiol-17 beta or testosterone brought about a slight increase in the gonadosomatic index and atresia of some of the primary oocytes. The oogonial population size decreased in response to treatment with high doses of oestradiol-17 beta.

Suppression of ribosomal gene expression in oocytes and nurse cells of a polychaete as a result of polyamine synthesis inhibition

The role of the polyamines in ribosomal gene expression was evaluated in the polychaete Ophryotrocha labronica by analyzing the effects of polyamine synthesis inhibition on RNA synthesis during oogenesis, a period characterized by intense nucleolar activity. At various stages of oogenesis adult polychaete females were blocked in their polyamine synthesis by the addition of 10 mM DL-alpha-difluoromethylornithine (DFMO) to the sea water in which they were cultivated. To monitor RNA synthesis during DFMO treatment the animals were pulse-labeled with [5-3H]uridine and processed for autoradiography. Light and electron microscope autoradiographs demonstrate that DFMO treatment suppresses incorporation of label into nucleolar RNA (rRNA) both in the oocytes and their associated nurse cells. The ultrastructural appearance of both cell types reveals interference with nucleolar and ribosomal activity; the endoplasmic reticulum is deprived of ribosomes, and the production of protein granules (vitellogenesis) is reduced. The high specificity of DFMO for polyamine synthesis and the fact that the effects of DFMO were counteracted by addition of a low concentration (10 microM) of putrescine shows that the observed interference with ribosomal gene expression is indeed due to polyamine deficiency.

Developmental regulation of Ca2+ and K+ currents during hormone-induced maturation of starfish oocytes

Changes in the electrical properties of starfish oocytes during hormone-induced maturation (the reinitiation of meiosis prior to fertilization) were studied by using the voltage-clamp technique. Three voltage-dependent ionic currents dominate the current-voltage relation of the immature oocyte: an inward Ca2+ current, a fast transient K+ current similar to the "A current" of molluscan neurons, and an inwardly rectifying K+ current. During in vitro maturation stimulated by the natural maturing hormone 1-methyladenine, gradual changes in the amplitudes of all three currents were seen: the Ca2+ currents became larger, and both K+ currents became smaller. The kinetics of the currents were not significantly altered during maturation. As a result of these changes, action potentials in the mature egg had lower thresholds, faster rates of rise, and larger overshoots than those of the immature oocyte. We also found that the total membrane capacitance decreased substantially during maturation, perhaps indicating a decrease in membrane surface area triggered by the hormone. The significance of these results is discussed in terms of the preparation of the immature oocyte for fertilization and the mechanisms of modification of ion channel properties during development.

The pattern of damage to the oogenetic series of cells after a single feeding of cis-diamminedichloroplatinum to Habrobracon females

A single meal of cis-diamminedichloroplatinum (DDP) fed to virgin braconid wasps decreased drastically the number of eggs derived from oogonia. In contrast, most of the larger oocytes completed oogenesis even after a dose which shortened average lifespan to 1/3 its normal length. Temporary infecundity resulted from the destruction of the germarial cells which produced the 32 cystocytes per follicle (1 oocyte and 31 trophocytes) by mitosis. As determined by egg hatchability, oogonia were the most vulnerable cell type to DDP in the ovariole sequence. Therefore, oogonial vulnerability to DDP was demonstrated by failure to complete both gametogenesis and embryogenesis. In combination with gamma radiation, DPP reduced egg production and hatchability below the values obtained from either agent used alone. However, the decreases were moderate, as expected from additivity of effect. A difference from the results from either radiation or several types of alkylating agents appeared in the proportion of early embryonic deaths. Deaths during cleavage predominated in every daily sample of eggs treated with DDP as oocytes. Usually only the eggs laid the first 2 days after treatment are characterized by a large number of 'stage 1' deaths.

Effects of toxic substances on female reproduction

Successful reproduction requires a complex series of interdependent physiological, cellular and molecular events. In the female many of these interdependent events are vulnerable to interruption by xenobiotic compounds. The physiological steps in the female reproductive cycle are reviewed. Selected xenobiotics which interrupt this cycle are presented and their mechanisms and site of adverse effects are discussed. Finally, a more detailed discussion of chemically induced ovarian failure in the human and an experimental animal model system is presented.

Bihormonal control of oogenesis in the freshwater prawn, Macrobrachium kistnensis

The hormonal control of oogenesis has been investigated in the freshwater prawn, Macrobrachium kistnensis. Experiments using bilateral eyestalk ablation and injection of eyestalk extract supported the presence of a gonad inhibiting factor in the eyestalk of female prawns. Injections of brain and thoracic ganglion extract in normal female prawns and in those subjected to bilateral eyestalk ablation revealed the presence of a gonad stimulating factor in the central nervous tissue.

Multiple effects of colchicine on oogenesis in Drosophila: induced sterility and switch of potential oocyte to nurse-cell developmental pathway

Adult female fruitflies exposed to colchicine admixed to the culture medium show a series of dosage-related abnormalities that affect oogenesis and may induce sterility. Among the effects observed were decreased fecundity and hatchability of laid eggs, formation of oocytes lacking chorionic appendages, abnormal distribution and diminution in number of yolk spheres, inhibition of oocyte growth and abnormally located oocyte nuclei. Potentially the most significant effect was the development of egg chambers which contained the normal complement of 16 cells but in which all the cells had the nuclear morphology of nurse cells. The approach provides for the first time an experimental means to divert a potential oocyte into the developmental pathway of the nurse cell in a wild-type fly, and hence should be helpful in the elucidation of factors which control oocyte and nurse cell differentiation. In addition, the results serve to expand the usefulness of oogenesis in Drosophila as a model system for the evaluation of drug-induced metabolic-morphologic abnormalities.

Factors controlling the ovarian cycle in a temperate zone anuran, the toad Bufo bufo: food uptake, nutritional state, and gonadotropin

The relations between nutritional state and vitellogenic growth of oocytes were studied in 87 sexually mature female toads Bufo bufo during the postbreeding season before initiation of the next annual ovarian cycle. Recruitment of small oocytes to vitellogenic growth was correlated with resumption of food uptake and the restoration of a positive energy balance in the toads that had become depleted of energy reserves during hibernation and breeding. Treatment with exogenous gonadotropin (hCG) immediately initiated vitellogenic growth, independently of the nutritional state. But the hCG-induced vitellogenic growth was faster in toads that ate more than the maintenance ration than in those that ate less. hCG also maintained rapid vitellogenic growth in toads that starved after an initial period of feeding during which vitellogenic growth had been resumed. The results support the hypothesis that the period of ovarian quiescence, which normally follows breeding in Bufo bufo, and other anurans from the northern range of distribution of the species, results from inactivation of the hypothalamic-hypophysial gonadotropic system, and that reactivation of the system depends upon reestablishment of a proper nutritional state of the organism.

Oocyte maturation in the amago salmon (Oncorhynchus rhodurus): in vitro effects of salmon gonadotropin, steroids, and cyanoketone (an inhibitor of 3 beta-hydroxy-delta 5-steroid dehydrogenase)

The effect of partially purified chinook salmon gonadotropin (SG-G100) and a number of steroids on the induction of germinal vesicle breakdown (GVBD) in amago salmon (Oncorhynchus rhodurus) oocytes (with intact follicle layers) was investigated in vitro. SG-G100 was effective only at the highest concentration tested (1 microgram/ml). 17 alpha,20 beta-Dihydroxy-4-pregnen-3-one (17 alpha,20 beta-diOHprog) was the most potent maturation-inducing steroid tested, followed by 17 alpha-hydroxyprogesterone. Testosterone or deoxycorticosterone (DOC) enhanced the rate of GVBD in response to SG-G100. DOC also enhanced the response to 17 alpha,20 beta-diOHprog but testosterone was without effect, suggesting that DOC has a direct action on the oocyte while testosterone probably acts at the level of the follicle. Estradiol-17 beta had no effect on GVBD in response to SG-G100 or 17 alpha,20 beta-diOHprog. The action of SG-G100 was shown to be dependent on the synthesis of a second delta 4 steroidal mediator of maturation since cyanoketone, a specific inhibitor of 3 beta-hydroxy-delta 5-steroid dehydrogenase, completely abolished the maturational effects of the gonadotropin and pregnenolone but not delta 4 steroids. Radioimmunoassay of media in which oocytes were induced to mature in vitro with SG-G100 revealed significantly elevated levels of progesterone and 17 alpha,20 beta-diOHprog. Estradiol-17 beta levels, high in control media, were only elevated twofold by SG-G100. Levels of the two progestogens were extremely low or nondetectable in media in which oocytes were incubated with cyanoketone, while estradiol-17 beta levels remained high. These results are discussed in relation to other evidence indicating that 17 alpha,20 beta-diOHprog is the naturally occurring maturation-inducing steroid of amago salmon. The role of other steroid hormones, particularly the possible involvement of corticosteroids, in the control of final oocyte maturation in teleosts is explored.

Behaviour of annulate lamellae during the maturation of oocytes in the newt, Cynops pyrrhogaster

The distribution of annulate lamellae, electron-dense masses, rough endoplasmic reticulum, and Golgi complexes in longitudinal sections of newt oocytes at several stages of progesterone-induced maturation was recorded with an electron microscope equipped with a drawing device. Annulate lamellae in full-grown oocytes occur in close contact with electron-dense masses and the nuclear envelope and elsewhere. Stacks of annulate lamellae increase in number for 6 h after progesterone treatment. Meanwhile, they segregate into three groups. The largest group, comprising about 75% of total stacks, forms a row parallel to and just beneath the oocytes cortex of both the animal and vegetal hemispheres, a second group is distributed in the middle area of the vegetal hemisphere, and a third group appears near the yolk-free cytoplasm formed at the vegetal side of the germinal vesicle during the maturation. About 6 h after progesterone treatment the annulate lamellae begin to disappear at their places of localization and none is found a few hours after germinal vesicle breakdown. No immediate fine-structural change in the cortical area follows the disappearance of subcortical annulate lamellae. The possible origins and fates of annulate lamellae in the maturing newt oocytes are discussed.

Progesterone and testosterone: contraceptive and immunosuppressive effects in mice

Progestin (medroxyprogesterone acetate, trade name Depo-Provera, Upjohn, Belgium) in 6 body-weight-matched doses with those used in women, i.e., 0.05 mg/mouse, given intramuscularly at 4-5-day intervals (duration of one ovulation) induced a marked reduction of fertility with precocious atresia of Graafian follicles, minimal numbers of growing follicles and an excess of corpora lutea; the lymphoid system remained morphologically and functionally normal. A combination of progestin and androgen (testosterone isobutyrate, trade name Agovirin Depot Biotika, Czechoslovakia) in a total dose of 1 mg + 0.9 mg (body-weight-matched with that used in men) or one order higher and divided into 6 doses given at 17-day intervals, i.e. roughly one half of the duration of spermatogenesis, had no inhibitory effect on spermatogenesis, whereas higher doses damaged the lymphoid system. This damage was reflected in a markedly reduced thymus weight with great depletion of cortex lymphocytes and diminished capacity for antibody formation to sheep red blood cells. The significance of the immunosuppressive effect for estimating the risks involved in the administration of sex steroids in human contraception is discussed.

Role of the polyamines in germ cell differentiation and in early embryonic development

The physiological function of the polyamines in germ cell differentiation and in early embryonic development was studied with the aid of the highly specific polyamine synthesis inhibitors DL-alpha-methylornithine (MO) and DL-alpha-difluoromethylornithine (DFMO). In the invertebrate Ophryotrocha labronica DFMO-induced polyamine deficiency severely affected nucleolar formation and activity in germ cell differentiation as revealed by RNA-labelling experiments and by ultrastructural analysis. Both in an invertebrate (Ophryotrocha labronica) and in a vertebrate (chick), inhibitor-induced polyamine deficiency caused a block of embryonic development at gastrulation. The major ultrastructural effect observed in the arrested embryos was an interference with nucleolar formation. Our data suggest that polyamine synthesis is essential for the ribosomal gene expression that is associated with oogenesis and embryogenesis.

Gonadotropin releasing hormone agonists stimulate meiotic maturation of follicle-enclosed rat oocytes in vitro

Although the principal function of gonadotropin releasing hormone (GnRH) is to stimulate the pituitary gland to release luteinizing hormone (LH) and follicle-stimulating hormone (FSH), there is evidence that agonistic analogues of GnRH directly inhibit steroidogenesis in the testis and ovary. On the other hand, Clark et al. have demonstrated that GnRH and two agonists have a marked stimulatory effect on prostaglandin synthesis by granulosa cells isolated from immature rats treated with pregnant mare's serum gonadotropin (PMSG). Stimulation by these compounds was distinct from that by LH in that no changes in cyclic AMP production were detected. Thus it seems important to investigate the effect of these peptides on other aspects of ovarian function, for example oocyte maturation. Mammalian oocytes are arrested in the dictyate stage of the first meiotic prophase, and meiosis (oocyte maturation) normally resumes in preovulatory follicles as a consequence of the surge of LH and FSH. This maturation can also be initiated in vitro by the addition of gonadotropins to isolated preovulatory follicles, and is accompanied by an increase in the production of lactate. We now report that GnRH and two potent agonists stimulate meiosis in vitro in follicle-enclosed oocytes in a dose-dependent and specific manner, and also cause an increase of lactate accumulation during incubation.

Effects of brain extracts on oocyte maturation in Helisoma (Pulmonata: Mollusca)

Normal oocyte development and the effects of brain extract injections on egg laying and on oocyte ultrastructure have been investigated in two populations of Helisoma: an egg-laying population (H. duryi) and a non-egg-laying, overwintering population (H. trivolvis). Oocyte development in H. duryi resembles that in other pulmonate molluscs. Endocytotic profiles occur in maturing oocytes but not in young (previtellogenic) oocytes. Injected horseradish peroxidase (HRP) and ferritin can be found in the follicular space and between follicle cells 2–3 h after injection. Ultrastructural evidence indicates that these tracers are taken up by maturing oocytes, but not by young oocytes or follicle cells. In non-egg-laying H. trivolvis large oocytes lack endocytotic profiles although a follicular space and many yolk granules may be present. Injection of extracts of dorsal bodies or suboesophageal ganglia from H. duryi induces egg laying in H. trivolvis within a few days. Injection of dorsal body extract into non-egg-laying animals also induces the appearance of many endocytotic profiles in large oocytes. It is suggested that endocytotic uptake of yolk components is stimulated by dorsal body extract in these animals.