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PubMed2000

Influence of insulin treatment and feed restriction on follicular development in cyclic gilts.

Crossbred gilts were used to investigate whether exogenous insulin can restore normal follicular growth in feed-restricted gilts. After an 18-day altrenogest treatment, the first day of oestrous behaviour was designed as day 0. From day 0 to 13, all gilts received the same amount of feed, calculated to meet 200% of the energy requirements for maintenance. On day 14, luteolysis was induced by injection of an analogue of prostaglandin F2alpha. All gilts were slaughtered on day 19 and their ovaries removed. In Experiment 1, gilts received a high (240% of maintenance) or low (80%) level of feeding (n=10/group) from day 14 to 18. The number of large follicles (> or = 5 mm) on day 19 was reduced in feed-restricted gilts (16.9 versus 20.6, P<0.05). The same protocol of feed restriction was used in Experiment 2 (240% versus 80% of maintenance from day 14 to 18), and some gilts received daily injections of insulin (0.6 IU live weight kg(-1)). The three experimental groups were H: 240% and no insulin (n=8); H-I: 240%+insulin (n=8) and L-I: 80%+insulin (n=7). On day 18, 4 h after insulin injection, plasma insulin was higher in insulin-treated than in untreated gilts and glucose concentrations were reduced more dramatically in L-I than in H-I gilts (P<0.05). Concentrations of IGF-I were lower in L-I than in other gilts (P<0.05) and plasma IGFBPs were not significantly affected by treatments. On day 19, the number of large follicles (> or = 5 mm) was not significantly influenced by treatments (19.4, 17.6 and 15.3 for H, H-I and L-I gilts, respectively). Insulin, IGF-I and IGFBP-2 levels in follicular fluids from large follicles did not differ between females whereas IGFBP-3 levels were lower in L-I than in H gilts (P<0.05) and intermediate in H-I gilts. Intrafollicular levels of glucose were higher in feed-restricted than in well-fed gilts (P<0.05). These results suggest that exogenous insulin does not restore final follicular growth impaired by acute undernutrition.

Animals↗
PubMed2000

Intrafollicular concentrations of steroids and steroidogenic enzymes in relation to follicular development in the mare.

The objective of the present study was to determine the changes in follicular fluid steroid concentrations and in granulosa cell steroidogenic enzyme expression during the follicular phase, in relation to follicular size and physiological status in the mare. Follicular fluid and follicular cells were recovered by ultrasound-guided follicular punctures either around the time of emergence of the dominant follicle, at the end of the dominant follicle growth, or at the preovulatory stage, after injection of gonadotropin to induce ovulation. Cellular relative amounts of steroidogenic acute regulatory protein (StAR), P450-side chain cleavage (P450(scc)), 3beta-hydroxysteroid dehydrogenase (3betaHSD), 17alpha-hydroxylase, and aromatase were assessed by semiquantitative Western blot and densitometry. Follicular fluid was assayed for cholesterol concentrations by colorimetric assay and for progesterone, testosterone, and estradiol-17beta concentrations by RIA. Intrafollicular concentrations of progesterone and estradiol-17beta significantly increased in the dominant follicle during growth. After injection of gonadotropin, follicular maturation was characterized by a decrease in estradiol-17beta concentrations and a further increase in progesterone concentrations. Granulosa cells from dominant follicles had increased levels of StAR, P450(scc), 3betaHSD, and aromatase during growth, but decreased levels during maturation. Levels of StAR, P450(scc), 3betaHSD, and aromatase, as well as progesterone and estradiol-17beta, were lower in granulosa cells from subordinate than from dominant follicles. We did not observe a relationship between the steroidogenic activity of follicles and the capacity of their enclosed oocytes to complete meiosis in vitro.

3-Hydroxysteroid Dehydrogenases↗
PubMed1975

Serum luteinizing hormone, follicle-stimulating hormone, prolactin and progesterone concentrations and follicular development in the pseudopregnant rat after unilateral ovariectomy.

Serum LH, FSH, prolactin and progesterone concentrations and follicular size were measured in rats during pseudopregnancy after unilateral ovariectomy (ULO) on day 1. This operation did not affect the duration of pseudopregnancy. Following pseudopregnancy compensatory ovulation occurred. After ULO progesterone concentrations remained low as compared with control values but the progesterone secretion per ovary was increased slightly. After ULO, LH concentrations were significantly increased on days 3 and 4 of pseudopregnancy. FSH concentrations were increased 5 h after the operation and again on day 4-7 of pseudopregnancy when compared with sham-operated control animals. During pseudopregnancy prolactin secretion increased each night. Increased prolactin levels were observed 18 and 36 h after ULO. The number of medium-sized follicles had increased 24 h after ULO. From the present study it is concluded that progesterone secretion by the corpora lutea can be increased to a limited degree by the increased release of gonadotrophins. Furthermore, it is concluded that a rapid increase in FSH concentrations after ULO is responsible for the initiation of the compensatory follicular growth.

Animals↗
PubMed1987

[Endocrine, paracrine and autocrine mechanisms involved in follicular development].

Development of a single follicle during the menstrual cycle is under control of hormones stimulating follicular maturation, ovulation and luteogenesis. Several factors intervene locally to avoid other follicles developing at the same time as the dominant follicle. These other follicles remain quiescent or go on to atresia. Atresia results from the action of several endocrine, paracrine and autocrine mechanisms which synergistically inhibit aromatase activity. The subsequent lack of oestrogens reduces granulosa cell multiplication. The oocyte will not become fertilizable before the preovulatory peak of LH, after the resumption of meiosis and after reaching the metaphase of the second meiotic division. Several factors are involved in this inhibition of spontaneous resumption of meiosis: cyclic nucleotides, sex steroids, somatostatin, oocyte maturation inhibitor(s) (OMI). Ovulation is related to breakdown of connective tissue synthesized by granulosa cells under the influence of FSH. Connective tissue lysis is dependent on proteolytic enzymes which are released and activated by FSH, LH and relaxin. A paracrine control could be involved in ovulation: LH induces the production of prostaglandin and relaxin by theca cells which, in turn, stimulate collagenase and proteoglycanase secretion by granulosa cells.

Female↗
PubMed1996

Effect of preovulatory insertion of Norplant implants over luteinizing hormone secretion and follicular development.

OBJECTIVE: To determine whether the process of ovulation could be interrupted by the insertion of Norplant implants (Leiras Pharmaceuticals, Turku, Finland) in the advanced preovulatory phase. DESIGN: Prospective study. SETTING: The Department of Biomedical Research at the Family Planning Clinic of PROFAMILIA, Santo Domingo, Dominican Republic. PATIENTS: Healthy women of reproductive age, requesting Norplant implants contraception. Thirteen of 15 women volunteers who were admitted completed the study. INTERVENTIONS: Norplant implants were inserted when the dominant follicle reached a mean diameter of 16 mm, based on serial vaginal ultrasounds (US) beginning on day 10 of the cycle. Blood samples for determination of E2, P, LH, and levonorgestrel, were taken and vaginal US performed at 0, 4, 24, 48, and 72 hours after insertion. If follicle rupture had not occurred at 72 hours after insertion, blood sampling and US were done three times per week during 2 additional weeks. RESULTS: Follicle rupture occurred in 11 of 13 subjects within 72 hours after insertion, with the exception of 1 subject in whom rupture occurred between 72 and 192 hours. Two women already had an LH peak at the time of insertion. In 9 of the remaining 11 women, a shortlasting, blunted LH surge was observed at 4 hours postinsertion. In the remaining two women, who had the lowest E2 levels, ovulation was inhibited, and a persistent follicle developed without luteinization. CONCLUSIONS: The insertion of Norplant implants in the advanced follicular phase will not inhibit ovulation if sufficient E2 priming has occurred. On the contrary, the exogenous progestin may rapidly foster ovulation shortly after.

Drug Implants↗
PubMed1988

Endocrine, paracrine and autocrine control of follicular development.

Development of a single follicle during the menstrual cycle is under control of hormones stimulating follicular maturation, ovulation and luteogenesis. Several factors intervene locally to prevent other follicles from developing at the same time as dominant follicle. These other follicles remain quiescent or evaluate to atresia. Atresia results from the action of several endocrine, paracrine and autocrine mechanisms which synergistically inhibit aromatase activity. The subsequent lack of estrogens reduces granulosa cell multiplication. The oocyte will not become fertilizable before the preovulatory peak of LH, after the resumption of meiosis and after reaching metaphase of the second meiotic division. Several factors are involved in the inhibition of spontaneous resumption of meiosis: cyclic nucleotides, sex steroids, somatostatin and oocyte maturation inhibitor(s) (OMI). Ovulation is related to breakdown of connective tissue synthesized by granulosa cells under the influence of FSH. Connective tissue lysis is dependent on proteolytic enzymes which are released and activated by FSH, LH and relaxin. A paracrine control could be involved in ovulation: LH induces the production of prostaglandin and relaxin by theca cells which, in turn, stimulate collagenase and proteoglycanase secretion by granulosa cells.

Endocrine Glands↗
PubMed1981

Follicular development in the neonatal mouse ovary; effect of epidermal growth factor.

The growth of the ovary has been studied in the mouse after administration of epidermal growth factor (EGF). Newborn females injected daily with EGF for the first 5 days of life showed a retardation of ovarian development. The number of follicles in the resting pool (small follicles) was significantly greater than in control animals and there were fewer growing follicles at more advanced stages of development (types 3b and 4). The percentage of mitotic figures in the follicular and surface epithelia of the ovary and the epithelium of the extra-ovarian rete was also significantly reduced after EGF. The results indicate that EGF may inhibit rather than promote the growth of follicles in the neonatal mouse ovary in vivo.

Animals↗
PubMed1993

Follicular growth rate and lack of influence of oestradiol valerate, testosterone propionate and aminoglutethimide phosphate on ovarian follicular development in the musk shrew, Suncus murinus L.

Growth rate of follicles and effects of administration of oestradiol valerate (EV), testosterone propionate (TP) and aminoglutethemide phosphate (AGP) on the development of ovarian follicles of the adult musk shrew were investigated. The follicular growth rate was estimated by mitotic index before and 2 hr after colchicine treatment to the shrews. Mitotic index of granulosa cells increased linearly with the increase in the follicular diameter. The calculated mean duration of mitosis was 0.48 hr. The mean time taken for follicle to pass from primary follicle stage to preovulatory stage was estimated to be 12 days. Treatment of both the steroids EV and TP, failed to produce any noticeable effect on the atretic follicle of the musk shrew. The results indicate that neither EV or TP, nor the potent steroid inhibitor AGP had any influence on the growth of large follicles in this primitive eutherian mammal.

Aminoglutethimide↗
PubMed1975

The morphology of follicular development and ovulation in non-human primates.

A colony of Macaca fascicularis have been under continuous observation for the past 4 years to ascertain the follicular morphological changes that occur prior to ovulation and during the development of the corpus luteum. Of 609 experimental cycles, laparoscopy was performed at least once in 44-5% of the cycles. Of the 104 cycles where the ovulatory status was definitely known, 89-4% were deemed ovulatory and 10-6% anovulatory. The presence or absence of ovulation in the previous cycle did not have an effect on the cycle length either for the total cycles or when analysing only cycles over 28 days. Similarly, the occurrence of two consecutive ovulations (in consecutive cycles) on the same vs. opposite ovaries did not have a significant effect on the cycle length. Neither laparoscopic stress or anaesthesia effected the normal cyclicity of the animals. The characteristic changes in follicular morphology are most clearly defined in M. fascicularis. In this species the 24 of 36 hr prior to ovulation are accompanied by discrete changes which occur in a fixed sequence, allowing one to predict the time of ovulation with reasonable accuracy. In S. sciureus ovulation is preceded by extensive bulging at the follicular apex and haemorrhaging at the base of the follicle. Due to this haemorrhaging post-ovulatory follicles in S. sciureus are generally more easily discernible than in fascicularis. The formation of clear areas (stigma) is not as evident in either S. sciureus or G. senegalensis as in the macaque. Actual ovulation has been observed four times in M. fascicularis and twice in S. sciureus.

Animals↗
PubMed1991

Insulin-like growth factor I in follicular development and function in postpartum beef cows.

The objective of this study was to determine whether nutrition affects follicular growth and(or) steroid and insulin-like growth factor I (IGF-I) concentrations in follicular fluid. Beginning 6 d after calving, Hereford-cross cows (n = 28) were fed either 14 (ad libitum) or 7 (restricted) kg.animal1.d-1 of chopped alfalfa-brome hay. Half the cows in each treatment were ovariectomized on d 20 (OVX-20) and the remaining half on d 35 (OVX-35) postpartum. Cow weight and condition score were recorded weekly, and blood was collected thrice weekly for determination of insulin, IGF-I, glucose, and free fatty acid (FFA) concentrations. At ovariectomy, follicular fluid from each follicle greater than or equal to 4 mm in diameter was aspirated for determination of IGF-I, progesterone (P4), and estradiol-17 beta (E2) concentrations. Restricted cows lost more weight after calving than did ad libitum cows (P less than .0001), although all cows lost similar amounts of body condition (time postpartum, P = .008). Concentrations of FFA were elevated (P less than .0001) in restricted cows from wk 2 through 5 after calving but did not change with time in ad libitum cows. Plasma concentrations of glucose were lower in restricted than in ad libitum cows (59.6 +/- .4 vs 61.8 +/- .4 mg/dl; P = .05), but insulin and IGF-I were similar (P greater than .10) between dietary treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Androgen synthesis during follicular development: evidence that rat granulosa cell 17-ketosteroid reductase is independent of hormonal regulation.

Although androgens have been implicated in follicular atresia, ovarian follicular androgen synthesis is required for preovulatory follicular growth. To localize the site(s) of androgen biosynthesis and to obtain a better understanding of the regulation of the androgenic pathway(s) in rat ovarian follicles we examined the relative abilities of developing follicles to accumulate specific androgens [testosterone (T) and dihydrotestosterone (DHT)] using both radioimmunoassay (RIA) and 3H-substrate metabolism techniques. Small antral and preovulatory follicles were obtained from control or human chorionic gonadotropin (hCG)-primed immature rats, respectively (Richards and Bogovich, 1982). Small antral follicles, theca and granulosa cells produced little immunoassayable androgen (T + DHT) when incubated with or without 8-bromo-cAMP. In contrast, preovulatory follicles and theca produced more androgen than small antral tissues and in a manner acutely stimulable by cAMP. Granulosa cells produced little androgen under these conditions. Inclusion of [3H] androstenedione in the incubates yielded increased accumulation of [3H] T and [3H] DHT for all small antral and preovulatory tissues. Indeed, granulosa cells from both small antral and preovulatory follicles possessed a remarkable ability to accumulate [3H] T. This ability was not altered by hypophysectomy or subsequent treatment with estradiol and/or follicle-stimulating hormone (FSH). These results suggest that 17-ketosteroid reductase may be a constitutive enzyme in granulosa cells.

17-Hydroxysteroid Dehydrogenases↗
PubMed1997

A role for neurotransmitters in early follicular development: induction of functional follicle-stimulating hormone receptors in newly formed follicles of the rat ovary.

The initiation of follicular growth in the mammalian ovary is a gonadotropin-independent phenomenon. Although some of the intraovarian signaling molecules that control the later phases of this process have been recently identified, the factors involved in the acquisition of gonadotropin receptors by early growing follicles have not been fully defined. In the rat, development of the ovarian innervation precedes the onset of folliculogenesis and occurs before follicles acquire responsiveness to gonadotropins. Because vasoactive intestinal polypeptide (VIP) and norepinephrine (NE), two of the neurotransmitters contained in ovarian nerves, are present in the ovary before the gland becomes responsive to gonadotropins, we sought to determine if VIP and/or NE are able to act on early follicles to facilitate the process of molecular differentiation that leads to gonadotropin dependency. In vitro exposure of 2-day-old rat ovaries to isoproterenol (ISO), a beta-adrenoreceptor agonist, or VIP, a neurotransmitter contained in both sympathetic and sensory nerves, increased the steady state levels of the messenger RNAs encoding cytochrome P-450 aromatase (P-450arom) and FSH receptors (FSHR) within 8 h of treatment. A similar effect was observed following forskolin-induced activation of cAMP formation. In situ hybridization experiments revealed that both the P-450arom and FSHR hybridization signals were localized to follicles. The increase in FSHR messenger RNA was accompanied by formation of functional receptor molecules, as demonstrated by the ability of FSH to stimulate cAMP formation in ovaries preexposed to either ISO or VIP, but not in untreated ovaries. The stimulatory effect of ISO and VIP on the formation of FSHR coupled to the cAMP generating system was not reproduced by phenylephrine, an alpha-adrenergic agonist, or secretin, a member of the VIP family not recognized by ovarian VIP receptors. Treatment of VIP-primed ovaries with FSH resulted in follicular growth, demonstrating that exposure of the gland to the neurotransmitter led to the formation of a functional complement of FSH receptors. These results suggest that ovarian nerves, acting via neurotransmitters coupled to the cAMP generating system, contribute to the differentiation process by which newly formed primary follicles acquire FSH receptors and responsiveness to FSH. Follicles that begin to grow in more densely innervated ovarian regions, may have a selective advantage over those not exposed to neurotransmitter-activated, cAMP-dependent signals and, thus, may become more rapidly subjected to gonadotropin control.

Adrenergic beta-Agonists↗
PubMed2002

Novel signaling pathways that control ovarian follicular development, ovulation, and luteinization.

The interactions of peptide and steroid hormone signaling cascades in the ovary are critical for follicular growth, ovulation, and luteinization. Although the pituitary gonadotropins follicle-stimulating hormone (FSH) and luteinizing hormone (LH) play key regulatory roles, their actions are also dependent on other peptide signaling pathways, including those stimulated by insulin-like growth factor-1 (IGF-1), transforming growth factor-beta (TGF-beta) family members (e.g., inhibin, activin, growth differentiation factor-9, bone morphogenic proteins), fibroblast growth factor, and Wnts (via Frizzled receptors). Each of these factors is expressed and acts in a cell-specific manner at defined stages of follicular growth. IGF-1, estrogen, and FSH comprise one major regulatory system. The Wnt/Frizzled pathways define other aspects relating to ovarian embryogenesis and possibly ovulation and luteinization. Likewise, the steroid receptors as well as orphan nuclear receptors and their ligands impact ovarian cell function. The importance of these multiple signaling cascades has been documented by targeted deletion of specific genes. For example, mice null for the LH-induced genes progesterone receptor (PR) and cyclo-oxygenase-2 (COX-2) fail to ovulate. Whereas PR appears to regulate the induction of novel proteases, COX-2 appears to regulate cumulus expansion. This review summarizes some new aspects of peptide and steroid hormone signaling in the rodent ovary.

Animals↗
PubMed2000

Influence of vitamin A injection before mating on oocyte development, follicular hormones, and ovulation in gilts fed high-energy diets.

Previous research revealed that treatment with vitamin A approximately 5 d before ovulation may increase litter size in weaned sows and improve embryonal survival in gilts fed high-energy diets that reduced embryonal survival. For the current study, the hypothesis was that administration of vitamin A before ovulation would alter development of follicles and oocytes in a way favorable to enhanced embryonal survival. (Landrace x Large White) x (Duroc x Hampshire) gilts (n = 44) were fed 11.0 Mcal ME x gilt(-1) x d(-1) beginning 7 d after second estrus and given (i.m.) corn oil or 1 x 10(6) IU of vitamin A (retinyl palmitate) on d 15 after second estrus. Gilts were checked for estrus every 4 h, mated naturally at third estrus, and assigned randomly to undergo midventral laparotomy beginning at 24 to 28, 28 to 32, 32 to 36, or 36 to 40 h after onset of third estrus. At laparotomy, ovulated oocytes and early-stage embryos were recovered from oviducts, and ovaries were removed for aspiration of oocytes and granulosa cells from unovulated follicles. Oocytes and embryos were stained for assessment of stage of development. Granulosa cells were cultured to assess their ability to secrete progesterone. Follicular fluid was assayed for progesterone, estradiol-17beta, IGF-I, and PGF2alpha. Treatment with vitamin A altered development of oocytes and embryos by decreasing the percentage at the germinal vesicle stage and increasing the percentage at advanced stages. Mean stage of development was increased by vitamin A, but variation in stage was decreased. Among follicles matched by meiotic stage of oocyte, follicular fluid concentrations of progesterone, IGF-I, and PGF2alpha were greater in vitamin A-treated gilts than in controls, but treatment with vitamin A in vivo did not affect LH-stimulated or unstimulated secretion of progesterone by granulosa cells in vitro. These data provide evidence that vitamin A may influence embryonic development by advancing resumption of meiosis and altering follicular hormonal environment during follicle maturation.

Animal Feed↗
PubMed1989

Morphological and biochemical characteristics during ovarian follicular development in the pig.

Ovaries were recovered from groups of naturally cyclic pigs (N = 5) on each of Days 16, 18, 20 and 21 of the oestrous cycle. Follicular diameter, follicular fluid volume and concentrations of oestradiol, testosterone and progesterone, and granulosa cell number were determined in all follicles greater than or equal to 2 mm in diameter (n = 511). In alternate follicles either granulosa cell aromatase activity and theca testosterone content or 125I-labelled hCG binding to granulosa and theca were determined. The mean total number of follicles recovered per animal decreased as the follicular phase progressed and a strong positive relationship (P less than 0.001) existed between follicular diameter and volume on all days. The number of granulosa cells recovered per follicle was variable, and not related to oestrogenic activity of the follicles. Mean follicular fluid oestradiol, testosterone and 125I-labelled hCG binding all increased until Day 20 and decreased on Day 21, whereas mean theca testosterone content, 125I-labelled hCG binding to theca tissue and aromatase were all maximal on Day 21. On Days 20 and 21 a subset of 14-16 large follicles was readily distinguishable from the remaining smaller, less oestrogenically active population in each animal. Yet, consistently within these subsets there was a difference in follicular diameter of approximately 2.0 mm and also a considerable range of biochemical development even among follicles of equal size. These results indicate asynchrony at the time of recruitment and selection among follicles destined to ovulate and suggest that heterogeneity continues into the immediate preovulatory period.

Animals↗