Gonadotrophin storage patterns in the ewe during the oestrous cycle or after long-term treatment with a GnRH agonist

Pituitary multi-hormone cells in mammals and fish: history, origin, and roles

The vertebrate pituitary is a dynamic organ, capable of adapting its hormone secretion to different physiological demands. In this context, endocrinologists have debated for the past 40 years if endocrine cells are mono- or multi-hormonal. Since its establishment, the dominant "one cell, one hormone" model has been continuously challenged. In mammals, the use of advanced multi-staining approaches, sensitive gene expression techniques, and the analysis of tumor tissues have helped to quickly demonstrate the existence of pituitary multi-hormone cells. In fishes however, only recent advances in imaging and transcriptomics have enabled the identification of such cells. In this review, we first describe the history of the discovery of cells producing multiple hormones in mammals and fishes. We discuss the technical limitations that have led to uncertainties and debates. Then, we present the current knowledge and hypotheses regarding their origin and biological role, which provides a comprehensive review of pituitary plasticity.

Plasticity in medaka gonadotropes via cell proliferation and phenotypic conversion

Follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh) produced by the gonadotropes play a major role in control of reproduction. Contrary to mammals and birds, Lh and Fsh are mostly produced by two separate cell types in teleost. Here, we investigated gonadotrope plasticity, using transgenic lines of medaka (Oryzias latipes) where DsRed2 and hrGfpII are under the control of the fshb and lhb promotors respectively. We found that Fsh cells appear in the pituitary at 8 dpf, while Lh cells were previously shown to appear at 14 dpf. Similar to Lh cells, Fsh cells show hyperplasia from juvenile to adult stages. Hyperplasia is stimulated by estradiol. Both Fsh and Lh cells show hypertrophy during puberty with similar morphology. They also share similar behavior, using their cellular extensions to make networks. We observed bi-hormonal gonadotropes in juveniles and adults but not in larvae where only mono-hormonal cells are observed, suggesting the existence of phenotypic conversion between Fsh and Lh in later stages. This is demonstrated in cell culture, where some Fsh cells start to produce Lhβ, a phenomenon enhanced by gonadotropin-releasing hormone (Gnrh) stimulation. We have previously shown that medaka Fsh cells lack Gnrh receptors, but here we show that with time in culture, some Fsh cells start responding to Gnrh, while fshb mRNA levels are significantly reduced, both suggestive of phenotypic change. All together, these results reveal high plasticity of gonadotropes due to both estradiol-sensitive proliferation and Gnrh promoted phenotypic conversion, and moreover, show that gonadotropes lose part of their identity when kept in cell culture.

Gonadotrope plasticity at cellular, population and structural levels: A comparison between fishes and mammals

Often referred to as "the master gland", the pituitary is a key organ controlling growth, maturation, and homeostasis in vertebrates. The anterior pituitary, which contains several hormone-producing cell types, is highly plastic and thereby able to adjust the production of the hormones governing these key physiological processes according to the changing needs over the life of the animal. Hypothalamic neuroendocrine control and feedback from peripheral tissues modulate pituitary cell activity, adjusting levels of hormone production and release according to different functional or environmental requirements. However, in some physiological processes (e.g. growth, puberty, or metamorphosis), changes in cell activity may be not sufficient to meet the needs and a general reorganization of cell composition and pituitary structure may occur. Focusing on gonadotropes, this review examines plasticity at the cellular level, which allows precise and rapid control of hormone production and secretion, as well as plasticity at the population and structural levels, which allows more substantial changes in hormone production. Further, we compare current knowledge of the anterior pituitary plasticity in fishes and mammals in order to assess what has been conserved or not throughout evolution, and highlight important remaining questions.

Follicle-Stimulating Hormone Glycobiology

FSH glycosylation varies in two functionally important aspects: microheterogeneity, resulting from oligosaccharide structure variation, and macroheterogeneity, arising from partial FSHβ subunit glycosylation. Although advances in mass spectrometry permit extensive characterization of FSH glycan populations, microheterogeneity remains difficult to illustrate, and comparisons between different studies are challenging because no standard format exists for rendering oligosaccharide structures. FSH microheterogeneity is illustrated using a consistent glycan diagram format to illustrate the large array of structures associated with one hormone. This is extended to commercially available recombinant FSH preparations, which exhibit greatly reduced microheterogeneity at three of four glycosylation sites. Macroheterogeneity is demonstrated by electrophoretic mobility shifts due to the absence of FSHβ glycans that can be assessed by Western blotting of immunopurified FSH. Initially, macroheterogeneity was hoped to matter more than microheterogeneity. However, it now appears that both forms of carbohydrate heterogeneity have to be taken into consideration. FSH glycosylation can reduce its apparent affinity for its cognate receptor by delaying initial interaction with the receptor and limiting access to all of the available binding sites. This is followed by impaired cellular signaling responses that may be related to reduced receptor occupancy or biased signaling. To resolve these alternatives, well-characterized FSH glycoform preparations are necessary.

Effects of inhibition of gonadotropin releasing hormone secretion on the response to novel objects in young male and female sheep

This study investigated the actions of blocking the GnRH receptor using a specific agonist on the response of male and female sheep to a novel object placed in their pen. The study is part of a series performed on 46 same sex twin animals. One of the pair received a subcutaneous implant of the GnRH agonist Goserelin acetate every four weeks while the other remained untreated. Implantation began immediately prior to puberty; at 8 weeks in the males and 28 weeks in the females (as timing of puberty is sex specific). To determine the effects of agonist treatment on the reproductive axis blood samples were collected for measurement of testosterone in the males and progesterone in the females. In addition the volume of the scrotum was determined. The present study aimed to determine whether there are sexually differentiated behavioural responses to a novel object at different stages of brain development (8, 28 and 48 weeks of age) and whether these responses are altered by GnRHa treatment. Approach behaviour towards and interactions with the novel object were monitored as was the number of vocalisations per unit time during the test period. GnRHa treatment suppressed testosterone concentrations and testicular growth in the males and progesterone release in the females. Sheep vocalised significantly more prior to weaning (8 weeks of age) than post weaning (28 and 48 weeks of age) suggesting stress on separation from their dams. Our current study shows that males are more likely to leave their conspecifics to approach a novel object than females. As this behaviour was not altered by suppression of the reproductive axis we suggest that, although sex differences are more obviously expressed in the phenotype after puberty, these may be developed during adolescence but not primarily altered during puberty by sex hormones.

Predominant suppression of follicle-stimulating hormone β-immunoreactivity after long-term treatment of intact and castrate adult male rats with the gonadotrophin-releasing hormone agonist deslorelin

Gonadotrophin-releasing hormone (GnRH) agonists are used to treat gonadal steroid-dependent disorders in humans and to contracept animals. These agonists are considered to work by desensitising gonadotrophs to GnRH, thereby suppressing follicle-stimulating hormone (FSH) and luteinising hormone (LH) secretion. It is not known whether changes occur in the cellular composition of the pituitary gland after chronic GnRH agonist exposure. Adult male Sprague-Dawley rats were treated with a sham, deslorelin, or deslorelin plus testosterone implant for 41.0 ± 0.6 days. In a second experiment, rats were castrated and treated with deslorelin and/or testosterone. Pituitary sections were labelled immunocytochemically for FSHβ and LHβ, or gonadotrophin α subunit (αGSU). Deslorelin suppressed testis weight by two-thirds and reduced plasma FSH and LH in intact rats. Deslorelin decreased the percentage of gonadotrophs, although the effect was specific to the FSHβ-immunoreactive (-ir) cells. Testosterone did not reverse the deslorelin-induced reduction in the overall gonadotroph population. However, in the presence of testosterone, the proportion of gonadotrophs that was FSHβ-ir increased in the remaining gonadotrophs. There was no effect of treatment on the total LHβ-ir cell population, although the loss of FSHβ in bi-hormonal cells increased the proportion of mono-hormonal LHβ-ir gonadotrophs. The castration-induced plasma LH and FSH increases were suppressed by deslorelin, testosterone or both. Castration increased both LH-ir and FSH-ir without increasing the overall gonadotroph population, thus increasing the proportion of bi-hormonal cells. Deslorelin suppressed these increases. Testosterone increased FSH-ir in deslorelin-treated castrate rats. Deslorelin did not affect αGSU immunoreactivity, suggesting that the gonadotroph population per se is not eliminated by deslorelin, although the ability of gonadotrophs to synthesise FSHβ is compromised. We hypothesise that the FSH dominant suppression may be central to the long-term contraceptive efficacy of deslorelin in the male.

Insights into the mechanism by which kisspeptin stimulates a preovulatory LH surge and ovulation in seasonally acyclic ewes: potential role of estradiol

We have previously demonstrated that a constant intravenous infusion of kisspeptin (Kp) for 48 h in anestrous ewes induces a preovulatory luteinizing hormone (LH) surge followed by ovulation in approximately 75% of animals. The mechanisms underlying this effect are unknown. In this study, we investigated whether Kp-induced preovulatory LH surges in anestrous ewes were the result of the general activation of the whole gonadotropic axis or of the direct activation of central GnRH neurons required for the GnRH/LH surge. In the first experiment, a constant iv infusion of ovine kisspeptin 10 (Kp; 15.2 nmol/h) was given to 11 seasonally acyclic ewes over 43 h. Blood samples were taken every 10 min for 15 h, starting 5h before the infusion, and then hourly until the end of the infusion. We found that the infusion of Kp induced a well-synchronized LH surge (around 22 h after the start of the Kp infusion) in 82% of the animals. In all ewes with an LH surge, there was an immediate but transient increase in the plasma concentrations of LH, follicle-stimulating hormone (FSH), and growth hormone (GH) at the start of the Kp infusion. Mean (+/- SEM) concentrations for the 5-h periods preceding and following the start of the Kp infusion were, respectively, 0.33 +/- 0.09 vs 2.83 +/- 0.49 ng/mL (P = 0.004) for LH, 0.43 +/- 0.05 vs 0.55 +/- 0.03 ng/mL (P = 0.015) for FSH, and 9.34 +/- 1.01 vs 11.51 +/- 0.92 ng/mL (P = 0.004) for GH. In the first experiment, surges of LH were observed only in ewes that also had a sustained rise in plasma concentrations of estradiol (E(2)) in response to Kp. Therefore, a second experiment was undertaken to determine the minimum duration of Kp infusion necessary to induce such a pronounced and prolonged increase in plasma E(2) concentration. Kisspeptin (15.2 nmol/h) was infused for 6, 12, or 24h in seasonally acyclic ewes (N = 8), and blood samples were collected hourly for 28 h (beginning 5h before the start of infusion), then every 2h for the following 22 h. Kisspeptin infused for 24h induced LH surges in 75% of animals, and this percentage decreased with the duration of the infusion (12h = 50%; 6h = 12.5%). The plasma concentration of E(2) was greater in ewes with an LH surge compared to those without LH surges; mean (+/- SEM) concentrations for the 5-h period following the Kp infusion were, respectively, 2.23 +/- 0.16 vs 1.27 +/- 0.13 pg/mL (P < 0.001). Collectively, our results strongly suggest that the systemic delivery of Kp induced LH surges by activating E(2)-positive feedback on gonadotropin secretion in acyclic ewes.

Gene expression and secretion of LH and FSH in relation to gene expression of GnRH receptors in the brushtail possum (Trichosurus vulpecula) demonstrates highly conserved mechanisms

In eutherian mammals, the gonadotrophins (LH and FSH) are synthesized and stored in gonadotroph cells under the regulation of multiple mechanisms including GnRH. Very little is known about the regulation of gonadotrophin secretion and storage in pituitary glands of marsupials. This study revealed, using quantitative PCR and heterologous RIA techniques, thatLHBmRNA expression levels remained constant over the oestrous cycle, regardless of the presence of a preovulatory LH surge, which is characteristic of a hormone secreted under regulation. Our sampling regime was unable to detect pulses of LH during the follicular phase, althoughGNRHRmRNA levels had increased at this time. Pulses of LH were, however, detected in the luteal phase of cycling females, in anoestrus females and in males. There was a positive correlation between gene expression ofFSHBand plasma levels of FSH at different stages of the oestrous cycle and no pulses of FSH were detected at any time; all characteristics of a hormone secreted via the constitutive pathway. Usingin situhybridisation and immunohistochemistry methods, we determined that mRNA expression ofLHBandFSHB, and protein storage of gonadotrophins exhibited a similar pattern of localisation within the pituitary gland. Additionally, sexual dimorphism of gonadotroph populations was evident. In summary, these findings are similar to that reported in eutherians and considering that marsupial evolution diverged from eutherians over 100 million years ago suggests that the regulation of gonadotrophins is highly conserved indeed.

Caloric restriction: impact upon pituitary function and reproduction

Reduced energy intake, or caloric restriction (CR), is known to extend life span and to retard age-related health decline in a number of different species, including worms, flies, fish, mice and rats. CR has been shown to reduce oxidative stress, improve insulin sensitivity, and alter neuroendocrine responses and central nervous system (CNS) function in animals. CR has particularly profound and complex actions upon reproductive health. At the reductionist level the most crucial physiological function of any organism is its capacity to reproduce. For a successful species to thrive, the balance between available energy (food) and the energy expenditure required for reproduction must be tightly linked. An ability to coordinate energy balance and fecundity involves complex interactions of hormones from both the periphery and the CNS and primarily centers upon the master endocrine gland, the anterior pituitary. In this review article we review the effects of CR on pituitary gonadotrope function and on the male and female reproductive axes. A better understanding of how dietary energy intake affects reproductive axis function and endocrine pulsatility could provide novel strategies for the prevention and management of reproductive dysfunction and its associated comorbidities.

Gonadotrope and thyrotrope development in the human and mouse anterior pituitary gland

Genes and orthologous intrinsic and extrinsic factors critical for embryonic pituitary gonadotrope and thyrotrope cell differentiation have been identified mainly in rodents, but data on the human are very limited. In human fetal pituitaries examined between 14 and 19 weeks of gestation using immunofluorescent confocal microscopy, we found that most fetal gonadotropes expressed alpha-GSU, LHbeta, and FSHbeta gonadotropin subunits while almost no cells expressed alpha-GSU and LHbeta alone. Gonadotropes expressing alpha-GSU and FSHbeta only were detected in both male and female pituitaries, increasing in proportion to total gonadotropes in both males and females from 14 (approximately 4.5%) to 19 weeks (approximately 16.5%) with a peak in males of 45.5% compared with females of 16.5% at 17 weeks of gestation. When FSHbeta or LHbeta genes were expressed, gonadotropes were non-dividing. This profile of human fetal gonadotrope development differs from the current mouse model. Furthermore, while expression of alpha-GSU appears to be the lead protein in gonadotropes, in thyrotropes which ultimately express alpha-GSU with TSHbeta, we observed that most if not all thyrotropes were TSHbeta-positive but alpha-GSU-negative until around 19 weeks in human, and e15 in mouse, fetal pituitaries. Furthermore, the TSHbeta-only thyrotropes were dividing, and TSHbeta rather than alpha-GSU was the lead protein in thyrotrope development. Thus, while biologically active dimeric FSH and LH can be produced by the human fetal pituitary by 14 weeks, dimeric biologically active TSH will only be produced from around 17 weeks of gestation. The mechanism(s) responsible for the different molecular regulation of alpha-GSU gene expression in gonadotropes and thyrotropes in the developing human fetal pituitary now requires investigation.

Endocrine, morphological, and cytological effects of a depot GnRH agonist in bovine

The present study was conducted to assess effects of the gonadotropin-releasing hormone agonist (GnRHa) triptorelin in dairy heifers. The peptide was released from a commercial 4-week depot formulation (Decapeptyl Depot) administered at animals' estrus (day 0). First experiment (EXP I, n=5), which was aimed to explore the availability of peptide, detected a maximum of triptorelin concentration between day 2 and 5 after depot injection, and the peptide remained detectable by RIA in peripheral blood for about 3 weeks. In further experiments, the peptide release was terminated on day 9 (EXP II, n=16) or day 21 (EXP III, n=47). Treatment effects were studied on follicular development, the characteristics of cumulus-oocyte complexes (COCs) (EXP II; EXP IIIa) and secretions of LH and progesterone (EXP IIIb). Results showed that the occurrence of the pre-ovulatory LH surge was more uniform in treated heifers than that in controls. The duration of ovulation periods was similar amongst the heifers of EXP II, but more compact amongst those of EXP III each compared with the respective controls. Post-ovulatory, the number of LH pulses was significantly reduced by treatment, whereas both basal LH and progesterone concentrations were elevated on a few days. Follicular growth was reduced only by the prolonged influence of the GnRHa. There were increased proportions of both degenerated COCs and immature oocytes from small follicles (<3mm in diameter), and meiotic configuration and quality of oocytes isolated from follicles 3-5mm were changed after the prolonged, 21-day treatment. These results indicate that a continuous influence of a GnRHa over more than 1 week may increasingly impair the development of bovine follicles and oocytes. This may have some significance for the development of novel GnRH-based techniques in regulating the reproductive function in cattle.

The pituitary effects of GnRH

Advances in our understanding of the complexity of GnRH actions at the pituitary and the various mechanisms involved in mediating differential LH and FSH biosynthesis and secretion at the gonadotrope, are continually emerging. In this review, we summarise recent studies pertaining to GnRH and GnRH receptor phylogeny, the divergent signalling and trafficking pathways initiated and utilised by GnRH and its receptor, and the pathways that mediate gonadotropin secretion from the gonadotrope.

Luteal stage dependence of pituitary response to gonadotrophin-releasing hormone in cyclic dairy ewes subjected to synchronisation of ovulation

Possible hormonal aberrations precluding conception or maintenance of pregnancy in dairy ewes subjected to ovulation synchronisation were investigated in this study. The pituitary response to exogenous gonadotrophin-releasing hormone (GnRH) was tested at different luteal stages in 36 ewes. Oestruses were synchronised by using progestagen-impregnated sponges and the animals were randomly allotted into one of three treatment groups (A, B and C; n = 12 for each). Treatments commenced on Days 4, 9 and 14 of the new cycle (oestrus was defined as Day 0). Ewes were given two GnRH injections, 5 days before and 36 h after a prostaglandin F2α (PGF2α) injection, and the animals were inseminated 12–14 h after the second GnRH injection (modified OVSYNCH). For luteinising hormone (LH) determination blood samples were withdrawn from six ewes of each group at the time of GnRH administration, and 30, 90, 180, 270 and 360 min later. Progesterone was assayed in samples taken every other day starting from oestrus and for 17 days after the second GnRH injection, and in an additional sample collected on the day of insemination. After the first GnRH injection, the LH concentration was higher in Group C than in Groups B and A (mean ± s.d.: 64.8 ± 10.0 ng mL−1, 41.3 ± 3.7 ng mL−1 and 24.6 ± 9.0 ng mL−1, respectively; P < 0.05), whereas after the second GnRH injection a uniform LH release was found in all groups. PGF2α caused a significant decrease in progesterone (P4) concentration in all groups; however, at artificial insemination ewes that conceived had significantly lower P4 concentration in comparison with those that failed to conceive. As early as Day 5, pregnant animals had higher P4 concentrations than non-pregnant animals. Overall, 21 animals conceived (seven, nine and five ewes from Groups A, B and C, respectively). These results indicate that the proposed protocol is equally effective in inducing a preovulatory LH surge at any stage of the luteal phase, and that elevated P4 concentration along with a delayed P4 increase should be considered as a causative factor for inability to conceive.

Luteinizing Hormone and Follicle-Stimulating Hormone Exhibit Different Secretion Patterns from Cultured Madin-Darby Canine Kidney Cells

LH, FSH, and chorionic gonadotropin (CG) are comprised of a common alpha subunit and a hormone-specific beta subunit. Using Madin-Darby canine kidney (MDCK) epithelial cells to examine the polarized secretion of human CG/LH, we previously reported that CG and LH were detected in the apical and basolateral compartments, respectively, and the carboxyl terminal end of the CGbeta subunit contains a strong apical signal. Here we show that the carboxyl seven amino acids in the LHbeta subunit contribute to the basolateral secretion of LH, and an LH chimera bearing the CGbeta apical signal is redirected from the basolateral to the apical compartments. Because LH and FSH are synthesized in the same cell, we also compared the secretion polarity of LH with FSH. MDCK cells expressing the FSH dimer displayed an almost equal distribution of protein into the apical and basolateral compartments. Given that the LHbeta and CGbeta carboxy terminal sequences, which differ from that in the FSHbeta subunit, occupy a pivotal role in their polarized behavior, the results support the hypothesis that pituitary exit of LH and FSH occur via different secretion pathways, and are released spatially from the pituitary via different circulatory routes.

Developmental changes in the hormonal identity of gonadotroph cells in the rhesus monkey pituitary gland

To help elucidate the regulatory mechanism responsible for divergent gonadotrophin secretion during sexual maturation, we examined the gonadotroph population and hormonal identity of gonadotroph subtypes in pituitary glands of juvenile (age, 1.7 +/- 0.2 yr) and adult (age, 12.3 +/- 0.8 yr) male rhesus monkeys (Macacca mulatta). Serum LH and testosterone concentrations were, respectively, 3 and 7 times lower in juveniles than in adults, thus confirming the different stages of development. Immunohistochemistry revealed that the proportion of LH gonadotrophs in relation to the total pituitary cell population in the juvenile animals was significantly smaller than in the adults. In a subsequent study, double immunofluorescent labeling identified three distinct gonadotroph subtypes in both age groups: ones expressing either LH or FSH and another one expressing a combination of both gonadotrophins. Whereas the number of monohormonal LH cells per unit area was greater in the adults than in the juveniles, the number of monohormonal FSH gonadotrophs was remarkably lower. However, the proportion of FSH cells (whether mono- or bihormonal) within the gonadotroph population was similar between groups. Interestingly, the proportion and number of bihormonal gonadotrophs as well as the LH/FSH gonadotroph ratio were significantly greater in the adults than in the juveniles. Taken together, these data reveal that during the juvenile-adult transition period, not only does the pituitary gonadotroph population increase, but a large number of monohormonal FSH gonadotrophs are likely to become bihormonal. Because this morphological switch occurs when marked changes in plasma gonadotrophins are known to occur, it may represent an intrapituitary mechanism that differentially regulates gonadotrophin secretion during sexual development.

Dynamic changes in the gonadotrope cell subpopulations during an estradiol-induced surge in the ewe

Whether estradiol targets a subpopulation of gonadotrope cells was investigated in this study. Ovariectomized ewes (OVX) or OVX ewes immunized against GnRH and treated with hourly pulses of GnRH analogue (OVX-IMG) were killed at 6, 12, 16, and 24 h after administration of 50 microg of 17beta-estradiol (E(2)). Control ewes received no E(2) treatment. In OVX or OVX-IMG ewes killed 6 h after E(2) injection, a decrease in gonadotropin plasma levels was observed compared with non-E(2)-treated ewes. In contrast, a surge in gonadotropin plasma concentrations occurred in ewes killed 16 h after injection. The percentage of total immunoreactive gonadotrope cells among the pituitary cells was lower in E(2)-treated ewes compared with nontreated animals. The proportion of monohormonal LH cells was constant throughout the experiment, except at the surge peak, where it was enhanced. In the OVX ewes, the proportion of bihormonal LH/FSH cells was lower in the E(2)-treated ewes compared to the nontreated ewes (P: < 0.001), with a more pronounced decrease 16 h after E(2) injection. A slight increase occurred 12 h after E(2) injection compared with 6 h after injection (P: < 0.05). A similar pattern was observed in the OVX-IMG ewes, except at 12 h after E(2) injection, when no increase occurred. In both OVX and OVX-IMG ewes, injection of E(2) decreased FSHbeta mRNA expression but did not alter the relative levels of LHbeta mRNA. These data suggest that the negative feedback of E(2) on LH and FSH secretion mainly targets the bihormonal cells and occurs, at least in part, directly at the pituitary level. During the gonadotropin surge, the sustained FSH release from the bihormonal cells would induce a switch from bihormonal cells to monohormonal LH cells by depleting these cells of FSH.

Differential regulation of the gonadotropin storage pattern by gonadotropin-releasing hormone pulse frequency in the ewe

The differential control of gonadotropin secretion by GnRH pulse frequency may reflect changes in the storage of LH and FSH. To test this hypothesis, ovariectomized ewes passively immunized against GnRH received pulsatile injections of saline (group 1) or GnRH analogue: 1 pulse/6 h for group 2 or 1 pulse/h for group 3, during 48 h. Immunization against GnRH suppressed pulsatility of LH release and reduced mean FSH plasma levels (3.1 +/- 0.2 vs. 2.2 +/- 0.1 ng/ml before and 3 days after immunization, respectively). Pulsatile GnRH analogue replacement restored LH pulses but not FSH plasma levels. Low and high frequencies of GnRH analogue increased the percentage of LH-containing cells in a similar way (group 1 = 6.9 +/- 0.5% vs. group 2 = 10.5 +/- 0.8%, or vs. group 3 = 9.6 +/- 0.4%). In contrast, the rise of the percentage of FSH-containing cells was greater after administration of the analogue at low frequency than at high frequency (group 1 = 3.7 +/- 0.4% vs. group 2 = 8.4 +/- 0.2%, or vs. group 3 = 5.2 +/- 0.8%). Moreover, while GnRH pulse frequency had no differential effect on FSHbeta mRNA levels, LHbeta mRNA levels were higher under high than low frequency. These data showed that the frequency of GnRH pulses can modulate the gonadotropin storage pattern in the ewe. These changes may be a component of the differential regulation of LH and FSH secretion.