Gonadotropin-Releasing Hormone Receptor Gene Expression During Pubertal Development of Female Rats1

Postnatal Development and Maintenance of Functional Pituitary Gonadotrophs Is Dependent on PI4-Kinase A

Postnatal development of functional pituitary gonadotrophs is necessary for maturation of the hypothalamic-pituitary-gonadal axis, puberty, and reproduction. Here we examined the role of PI4-kinase A, which catalyzes the biosynthesis of PI4P in mouse reproduction by knocking out this enzyme in cells expressing the gonadotropin-releasing hormone (GnRH) receptor. Knockout (KO) mice were infertile, reflecting underdeveloped gonads and reproductive tracts and lack of puberty. The number and distribution of hypothalamic GnRH neurons and Gnrh1 expression in postnatal KOs were not affected, whereas Kiss1/kisspeptin expression was increased. KO of PI4-kinase A also did not alter embryonic establishment and neonatal development and function of the gonadotroph population. However, during the postnatal period, there was a progressive loss of expression of gonadotroph-specific genes, including Fshb, Lhb, and Gnrhr, accompanied by low gonadotropin synthesis. The postnatal gonadotroph population also progressively declined, reaching approximately one-third of that observed in controls at 3 months of age. In these residual gonadotrophs, GnRH-dependent calcium signaling and calcium-dependent membrane potential changes were lost, but intracellular administration of inositol-14,5-trisphosphate rescued this signaling. These results indicate a key role for PI4-kinase A in the postnatal development and maintenance of a functional gonadotroph population.

Role of aerobic physical training on cardiac autonomic and morphophysiological dysfunction in hypertensive rats subjected to ovarian hormone deprivation

Here we investigated the effects of physical training on cardiovascular autonomic control and cardiac morphofunctional parameters in spontaneously hypertensive rats (SHRs) subjected to ovarian hormone deprivation. Forty-eight 10-week-old SHRs were divided into two groups: ovariectomized (OVX, n=24) and sham (SHAM, n=24). Half of each group (n=12) was trained by swimming for 12 weeks (OVX-T and SHAM-T). Cardiac morphology and functionality were assessed using echocardiography, and autonomic parameters were assessed using double pharmacological autonomic block, baroreflex sensitivity (BRS), and analyses of heart rate variability (HRV) and blood pressure variability (BPV). Ovariectomy did not influence the cardiac autonomic tonus balance unlike physical training, which favored greater participation of the vagal autonomic tonus. Ovariectomy and aerobic physical training did not modify HRV and BRS, unlike BPV, for which both methods reduced low-frequency oscillations, suggesting a reduction in sympathetic vascular modulation. Untrained ovariectomized animals showed a reduced relative wall thickness (RWT) and increased diastolic and systolic volumes and left ventricular diameters, resulting in increased stroke volume. Trained ovariectomized animals presented reduced posterior wall thickness and RWT as well as increased final diastolic diameter, left ventricular mass, and stroke volume. Ovarian hormone deprivation in SHRs promoted morphofunctional adaptations but did not alter the evaluation of cardiac autonomic parameters. In turn, aerobic physical training contributed to a more favorable cardiac autonomic balance to the vagal autonomic component and promoted morphological adaptations but had little effect on cardiac functionality.

Translational relevance of rodent models of hypothalamic-pituitary-adrenal function and stressors in adolescence

Elevations in glucocorticoids that result from environmental stressors can have programming effects on brain structure and function when the exposure occurs during sensitive periods that involve heightened neural development. In recent years, adolescence has gained increasing attention as another sensitive period of development, a period in which pubertal transitions may increase the vulnerability to stressors. There are similarities in physical and behavioural development between humans and rats, and rats have been used effectively as an animal model of adolescence and the unique plasticity of this period of ontogeny. This review focuses on benefits and challenges of rats as a model for translational research on hypothalamic-pituitary-adrenal (HPA) function and stressors in adolescence, highlighting important parallels and contrasts between adolescent rats and humans, and we review the main stress procedures that are used in investigating HPA stress responses and their consequences in adolescence in rats. We conclude that a greater focus on timing of puberty as a factor in research in adolescent rats may increase the translational relevance of the findings.

Estradiol Restrains Prepubertal Gonadotropin Secretion in Female Mice via Activation of ERα in Kisspeptin Neurons

Elimination of estrogen receptorα (ERα) from kisspeptin (Kiss1) neurons results in premature LH release and pubertal onset, implicating these receptors in 17β-estradiol (E2)-mediated negative feedback regulation of GnRH release during the prepubertal period. Here, we tested the dependency of prepubertal negative feedback on ERα in Kiss1 neurons. Prepubertal (postnatal d 14) and peripubertal (postnatal d 34) wild-type (WT) and Kiss1 cell-specific ERα knockout (KERαKO) female mice were sham operated or ovariectomized and treated with either vehicle- or E2-containing capsules. Plasma and tissues were collected 2 days after surgery for analysis. Ovariectomy increased LH and FSH levels, and E2 treatments completely prevented these increases in WT mice of both ages. However, in prepubertal KERαKO mice, basal LH levels were elevated vs WT, and both LH and FSH levels were not further increased by ovariectomy or affected by E2 treatment. Similarly, Kiss1 mRNA levels in the medial basal hypothalamus, which includes the arcuate nucleus, were suppressed with E2 treatment in ovariectomized prepubertal WT mice but remained unaffected by any treatment in KERαKO mice. In peripubertal KERαKO mice, basal LH and FSH levels were not elevated vs WT and were unaffected by ovariectomy or E2. In contrast to our previous findings in adult animals, these results demonstrate that suppression of gonadotropins and Kiss1 mRNA by E2 in prepubertal animals depends upon ERα activation in Kiss1 neurons. Our observations are consistent with the hypothesis that these receptors play a critical role in restraining GnRH release before the onset and completion of puberty.

Cell Type-Specific Sexual Dimorphism in Rat Pituitary Gene Expression During Maturation

The most obvious functional differences between mammalian males and females are related to the control of reproductive physiology and include patterns of GnRH and gonadotropin release, the timing of puberty, sexual and social behavior, and the regulation of food intake and body weight. Using the rat as the best-studied mammalian model for maturation, we examined the expression of major anterior pituitary genes in five secretory cell types of developing males and females. Corticotrophs show comparable Pomc profiles in both sexes, with the highest expression occurring during the infantile period. Somatotrophs and lactotrophs also exhibit no difference in Gh1 and Prl profiles during embryonic to juvenile age but show the amplification of Prl expression in females and Gh1 expression in males during peripubertal and postpubertal ages. Gonadotrophs exhibit highly synchronized Lhb, Fshb, Cga, and Gnrhr expression in both sexes, but the peak of expression occurs during the infantile period in females and at the end of the juvenile period in males. Thyrotrophs also show different developmental Tshb profiles, which are synchronized with the expression of gonadotroph genes in males but not in females. These results indicate the lack of influence of sex on Pomc expression and the presence of two patterns of sexual dimorphism in the expression of other pituitary genes: a time shift in the peak expression during postnatal development, most likely reflecting the perinatal sex-specific brain differentiation, and modulation of the amplitude of expression during late development, which is secondary to the establishment of the hypothalamic-pituitary-gonadal and -thyroid axes.

Development of gonadotropin-releasing hormone secretion and pituitary response

Acquisition of a mature pattern of gonadotropin-releasing hormone (GnRH) secretion from the CNS is a hallmark of the pubertal process. Little is known about GnRH release during sexual maturation, but it is assumed to be minimal before later stages of puberty. We studied spontaneous GnRH secretion in brain slices from male mice during perinatal and postnatal development using fast-scan cyclic voltammetry (FSCV) to detect directly the oxidation of secreted GnRH. There was good correspondence between the frequency of GnRH release detected by FSCV in the median eminence of slices from adults with previous reports of in vivo luteinizing hormone (LH) pulse frequency. The frequency of GnRH release in the late embryonic stage was surprisingly high, reaching a maximum in newborns and remaining elevated in 1-week-old animals despite low LH levels. Early high-frequency GnRH release was similar in wild-type and kisspeptin knock-out mice indicating that this release is independent of kisspeptin-mediated excitation. In vivo treatment with testosterone or in vitro treatment with gonadotropin-inhibitory hormone (GnIH) reduced GnRH release frequency in slices from 1-week-old mice. RF9, a putative GnIH antagonist, restored GnRH release in slices from testosterone-treated mice, suggesting that testosterone inhibition may be GnIH-dependent. At 2-3 weeks, GnRH release is suppressed before attaining adult patterns. Reduction in early life spontaneous GnRH release frequency coincides with the onset of the ability of exogenous GnRH to induce pituitary LH secretion. These findings suggest that lack of pituitary secretory response, not lack of GnRH release, initially blocks downstream activation of the reproductive system.

Age and adolescent social stress effects on fear extinction in female rats

We previously observed that social instability stress (SS: daily 1 h isolation and change of cage partners for 16 days) in adolescence, but not in adulthood, decreased context and cue memory after fear conditioning in male rats. Effects of stress are typically sex-specific, and so here we investigated adolescent and adult SS effects in females on the strength of acquired contextual and cued fear conditioning, as well as extinction learning, beginning either the day after the stress procedure or four weeks later. For SS in adolescence, SS females spent more time freezing (fear measure) during extinction than did controls, whereas SS in adulthood had no effect on any measure of fear conditioning. The results also indicated an effect of age: females in late adolescence show more rapid extinction of cue and better memory of extinction of context compared to adult females, which may indicate resilience to acute footshock in adolescence. Thus fear circuitry continues to mature into late adolescence, which may underlie the heightened plasticity in response to chronic stressors of adolescents compared to adults.

Rat Gnrhr promoter directs species-specific gene expression in the pituitary and testes of transgenic mice

The GnRH receptor (GnRHR) is expressed in several non-pituitary tissues, notably in gonads. However, mechanisms underlying the gonad-specific expression of Gnrhr are not well understood. Here, Gnrhr expression was analysed in the developing testes and pituitaries of rats and transgenic mice bearing the human placental alkaline phosphatase reporter gene (ALPP) under the control of the rat Gnrhr promoter. We showed that the 3.3 kb, but not the pituitary-specific 1.1 kb promoter, directs ALPP expression exclusively to testis Leydig cells from embryonic day 12 onwards. Real-time PCR analysis revealed that promoter activity displayed the same biphasic profile as marker genes in Leydig cells, i.e. abrupt declines after birth followed by progressive rises after a latency phase, in coherence with the differentiation and evolution of foetal and adult Leydig cell lineages. Interestingly, the developmental profile of transgene expression showed high similarity with the endogenous Gnrhr profile in the rat testis, while mouse Gnrhr was only poorly expressed in the mouse testis. In the pituitary, both transgene and Gnrhr were co-expressed at measurable levels with similar ontogenetic profiles, which were markedly distinct from those in the testis. Castration that induced pituitary Gnrhr up-regulation in rats did not affect the mouse Gnrhr. However, it duly up-regulated the transgene. In addition, in LβT2 cells, the rat, but not mouse, Gnrhr promoter was sensitive to GnRH agonist stimulation. Collectively, our data highlight inter-species variations in the expression and regulation of Gnrhr in two different organs and reveal that the rat promoter sequence contains relevant genetic information that dictates rat-specific gene expression in the mouse context.

Steroid hormones, stress and the adolescent brain: a comparative perspective

Steroid hormones, including those produced by the gonads and the adrenal glands, are known to influence brain development during sensitive periods of life. Until recently, most brain organisation was assumed to take place during early stages of development, with relatively little neurogenesis or brain re-organisation during later stages. However, an increasing body of research has shown that the developing brain is also sensitive to steroid hormone exposure during adolescence (broadly defined as the period from nutritional independence to sexual maturity). In this review, we examine how steroid hormones that are produced by the gonads and adrenal glands vary across the lifespan in a range of mammalian and bird species, and we summarise the evidence that steroid hormone exposure influences behavioural and brain development during early stages of life and during adolescence in these two taxonomic groups. Taking a cross-species, comparative perspective reveals that the effects of early exposure to steroid hormones depend upon the stage of development at birth or hatching, as measured along the altricial-precocial dimension. We then review the evidence that exposure to stress during adolescence impacts upon the developing neuroendocrine systems, the brain and behaviour. Current research suggests that the effects of adolescent stress vary depending upon the sex of the individual and type of stressor, and the effects of stress could involve several neural systems, including the serotonergic and dopaminergic systems. Experience of stressors during adolescence could also influence brain development via the close interactions between the stress hormone and gonadal hormone axes. While sensitivity of the brain to steroid hormones during early life and adolescence potentially leaves the developing organism vulnerable to external adversities, developmental plasticity also provides an opportunity for the developing organism to respond to current circumstances and for behavioural responses to influence the future life history of the individual.

Aerobic physical training has little effect on cardiovascular autonomic control in aging rats subjected to early menopause

We investigated and compared the effects of physiological menopause (PM) and early menopause (EM) and the adaptations promoted by physical training on the cardiovascular autonomic control of aged rats. Female Wistar rats (N=72) were assigned to 3 groups: control (22 weeks old rats, undergoing sham surgery in the 10th week of life), PM (82 weeks old rats, undergoing sham surgery in the 10th week of life) and EM (82 weeks old rats, undergoing ovariectomy in the 10th week of life). In each group, half of the rats were subjected to swimming training over a period of 10 weeks. Sedentary PM and EM groups had higher basal mean arterial pressure (MAP) and heart rate (HR) and lower intrinsic HR compared to the sedentary control group. Physical training reduced MAP in PM group. All trained groups had lower basal HR; however, only control and PM-trained groups showed decreased intrinsic HR. The assessment of cardiac autonomic balance showed that PM and EM sedentary groups exhibited sympathetic predominance compared to control group. After physical training, only EM group presented sympathetic predominance. HR variability (pulse interval) was similar among all sedentary groups. However, control and PM-trained groups showed lower power in low frequency band (LF; 0.2-0.75 Hz) and higher power in high frequency band (HF; 0.75-3.0 Hz). The analysis of systolic arterial pressure variability revealed that PM and EM sedentary groups had higher LF power. However, PM group showed lower LF power following physical training. Finally, PM and EM groups had a reduction in spontaneous baroreflex sensitivity, that was attenuated by physical training. The overall results suggest that PM or EM promotes similar negative effects on MAP, HR and cardiovascular autonomic control. However, unlike the PM group, physical training was not able to mitigate all negative effects of EM on cardiovascular autonomic control.

Kisspeptin-immunoreactivity changes in a sex- and hypothalamic-region-specific manner across rat postnatal development

Kisspeptins are potent secretagogues of gonadotrophin-releasing hormone, playing a key role in puberty onset. These peptides are produced by distinct neuronal populations of the hypothalamus located in the rostral periventricular area of the third ventricle (RP3V) and arcuate nucleus (ARC). The present immunohistochemical study aimed to determine the spatiotemporal onset of kisspeptin-immunoreactivity (-IR) in the neonatal hypothalamus of male and female rats and to evaluate changes in kisspeptin-IR around puberty. Kisspeptin-IR cells and fibres could be detected from the day of birth in the ARC of both males and females. At this stage, only females displayed some kisspeptin-IR fibres in the RP3V. From postnatal day 7 to adulthood, males displayed lower levels of kisspeptin-IR than females in both regions. During infancy, kisspeptin-IR fibre density in the female decreased in the ARC, whereas it increased in the RP3V. A sex-independent decline in RP3V kisspeptin-IR fibre density was observed in the juvenile, followed by a peripubertal increase in RP3V and ARC kisspeptin-IR. These peripubertal increases in kisspeptin-IR occurred at different timings dependent on sex and region. In females specifically, the increase in kisspeptin-IR fibre density occurred first in the ARC and later in the RP3V under constant levels of circulating oestradiol. In conclusion, the present study highlights the expression of hypothalamic kisspeptins soon after birth, as well as the neonatal establishment of a strong and persisting sex difference in ARC kisspeptin-IR in rats. Moreover, a female-specific desynchronisation of the ARC and RP3V was observed with respect to the increase in kisspeptin-IR fibre density around puberty, which was not related to peripubertal variations in circulating oestradiol.

Steroid levels and the spatiotemporal expression of steroidogenic enzymes and androgen receptor in developing ovaries of immature rats

Immunoexpression of 3β-hydroxysteroid dehydrogenase (3β-HSD), cytochrome P450c17 (P450c17), androgen receptor (AR), and steroid contents were studied in the ovaries of immature female Wistar rats killed between postnatal days 1 and 30. During days 1-7, ovarian somatic structures lacked AR, 3β-HSD and P450c17, except for the surface epithelium, which featured the presence of these three proteins, suggestive of its androgen responsiveness and steroidogenic function. On day 10, AR appeared in many somatic structures, including the granulosa layers, which coincided with the P450c17 immunoexpression in some theca/interstitial cells, and an increase in ovarian androgen concentration. On the following days a further rise in ovarian androgen and progesterone contents paralleled an increase in 3β-HSD and P450c17 immunoexpression in the theca layer cells and primary interstitial cells. However, the development of the follicles constituting the first follicular wave was aberrant, since they lacked AR expression until the preantral stage and were characterized by a delayed onset and much lower expression of the thecal P450c17. They could not ovulate, since ovarian content of estradiol was too low to evoke the LH surge. The clusters of the secondary interstitial cells found on day 30 exhibited predominant expression of 3β-HSD over P450c17, suggesting more intensive progesterone than androgen synthesis in these structures.

Stanozolol regulates proliferation of growth plate chondrocytes via activation of ERalpha in GnRHa-treated adolescent rats

Improving the final adult height is one of the most important aims for treatment of central precocious puberty. Stanozolol (ST) is a synthetic derivative of androgen. In this study, we investigated the effects and the mechanisms of ST on the proliferation of growth plate chondrocytes isolated from adolescent rats treated with gonadotropin-releasing hormone analogue (GnRHa). Treatment with ST resulted in time- and concentration-dependent effects on proliferation as determined by MTT and proliferating cell nuclear antigen (PCNA) assays. Western blotting showed that ST increased the phosphorylation level of the estrogen receptor alpha (ERalpha), but not the androgen receptor (AR). Pharmacological inhibition of ERalpha and mitogen-activated protein kinase (MAPK) attenuated the effects of ST on the proliferation of growth plate chondrocytes. A molecular dynamics simulation showed hydrophobic interactions between ST and ERalpha. These results suggested that ERalpha, but not AR, partially mediates the ST-driven proliferation of growth plate chondrocytes, and that multiple pathways may be involved in the mechanism of action of ST.

Adolescent development, hypothalamic-pituitary-adrenal function, and programming of adult learning and memory

Chronic exposure to stress is known to affect learning and memory in adults through the release of glucocorticoid hormones by the hypothalamic-pituitary-adrenal (HPA) axis. In adults, glucocorticoids alter synaptic structure and function in brain regions that express high levels of glucocorticoid receptors and that mediate goal-directed behaviour and learning and memory. In contrast to relatively transient effects of stress on cognitive function in adulthood, exposure to high levels of glucocorticoids in early life can produce enduring changes through substantial remodeling of the developing nervous system. Adolescence is another time of significant brain development and maturation of the HPA axis, thereby providing another opportunity for glucocorticoids to exert programming effects on neurocircuitry involved in learning and memory. These topics are reviewed, as is the emerging research evidence in rodent models highlighting that adolescence may be a period of increased vulnerability compared to adulthood in which exposure to high levels of glucocorticoids results in enduring changes in adult cognitive function.

Expression of a gonadotropin-releasing hormone receptor-simian virus 40 T-antigen transgene has sex-specific effects on the reproductive axis

The GnRH receptor (GnRHR) responds to pulsatile GnRH signals to coordinate pituitary gonadotropin synthesis and secretion. Previously, a 1.2-kb fragment of the 5'-flanking region isolated from the mouse GnRHR gene was shown to target expression to pituitary gonadotropes in vivo. The 1.2-kb gene promoter fused to the simian virus 40 large T antigen (TAg) was used to generate transgenic mice that form gonadotrope-derived pituitary tumors at 4-5 months of age. Transgenic female mice have hypogonadotropic hypogonadism, infantile gonads, and are infertile throughout their life span, whereas males remain reproductively intact until their tumors become large. We hypothesized that the targeted TAg expression causes a sex-specific disruption of the reproductive axis at the level of the pituitary gland. To test this hypothesis, we characterized the pituitary gonadotropin beta-subunit and TAg expression patterns, and measured plasma gonadotropin and gonadal steroid levels in female and male mice before and after pituitary tumor development. TAg expression was observed in transgenic females and males 15 d of age, before tumor development. Interestingly, and in contrast to the transgenic males, pituitary LH beta and FSH beta subunit protein levels, and plasma LH and FSH levels, were reduced in transgenic females. Reproductive organs in transgenic female mice remained underdeveloped but were normal in transgenic males. We conclude that the expression of the TAg transgene driven by the GnRHR gene promoter results in female-specific infertility due to disruption of gonadotropin production and secretion even before tumor development.

GABA(A) receptors in normal development and seizures: friends or foes?

GABA(A) receptors have an age-adapted function in the brain. During early development, they mediate excitatory effects resulting in activation of calcium sensitive signaling processes that are important for the differentiation of the brain. In more mature stages of development and in adults, GABA(A) receptors transmit inhibitory signals. The maturation of GABA(A) signaling follows sex-specific patterns, which appear to also be important for the sexual differentiation of the brain. The inhibitory effects of GABA(A) receptor activation have been widely exploited in the treatment of conditions where neuronal silencing is necessary. For instance, drugs that target GABA(A) receptors are the mainstay of treatment of seizures. Recent evidence suggests however that the physiology and function of GABA(A) receptors changes in the brain of a subject that has epilepsy or status epilepticus.This review will summarize the physiology of and the developmental factors regulating the signaling and function of GABA(A) receptors; how these may change in the brain that has experienced prior seizures; what are the implications for the age and sex specific treatment of seizures and status epilepticus. Finally, the implications of these changes for the treatment of certain forms of medically refractory epilepsies and status epilepticus will be discussed.

Prepubertal changes in the synthesis, storage and release of growth hormone and luteinising hormone and in the immunoreactivity of oestrogen receptor-alpha in lamb pituitary cells. A morphofunctional study

The present study was designed to determine the changes in the synthesis, storage and release of luteinising hormone (LH) and growth hormone (GH) in the hypophyseal cells by investigating the presence of oestrogen receptor-alpha (ERalpha) in developing prepubertal female lambs. The experiment was carried out on 14 prepubertal (17-week-old) and 14 peripubertal (32-week-old) ovary-intact lambs. Morphofunctional changes in the cells of the adenohypophyseal population were assayed with immunohistochemistry (IH), in situ hybridisation (ISH), Real-time PCR and radioimmunoassay (RIA). Blood samples (n=14) were taken every 2 weeks from 17 to 32 weeks of age for estimation of GH and LH by RIA. Computer image analysis was used to determine the percent of cells exhibiting IH and/or ISH reaction. The percentage of cells stained for LHbeta and GH increased for both LH- and GH-producing cells and were higher (P<0.001) in the peripubertal than prepubertal group. The percentage of mRNA LHbeta-expressing cells decreased and were lower for the peripubertal (P<0.001) than prepubertal group. The GH mRNA in pituitaries of prepubertal lambs was higher in comparison to peripubertal ones (P<0.001). The percentage of ERalpha positive cells increased significantly (P<0.001) in peripubertal compared to prepubertal lambs and this increase was significant (P<0.001) in both LH- and GH-producing cells. Plasma LH concentrations increased from 27 weeks of age, while GH concentrations gradually decreased from 17 weeks of age (P<0.05). The histomorphological changes in the LH- and GH-producing cells reflect the increasing pattern of the regulation of secretory processes of these hormones and an escalating regulatory role of oestrogen in the physiology of these cells during the prepubertal period. These results support the involvement of both hormones in the events leading up to puberty.

The postnatal ontogeny of gonadotroph cells in the female sheep

The aim of this study was to determine the developmental changes in the synthesis, storage and release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in the hypophyseal gonadotroph cells from infancy to peripuberty of ovine ontogeny. An examination has been made in 15 infantile (12-, 15-week-old) and juvenile (22-, 30-week-old) ovary-intact sheep. Histomorphological and functional changes in the adenohypophyseal population of gonadotrophs were assayed with hybridohistochemistry, immunohistochemistry and radioimmunoassay. The percentage of the adenohypophyseal area (PAA) occupied by gonadotrophs containing LHbeta-mRNA or FSHbeta-mRNA was highest (P < 0.05) in the 15-week-old sheep compared with the other stages. The gradual increase in the PAA occupied by immunoreactive (ir)-LHbeta-cells from the 12th to 30th week of age was observed (P < 0.05) and has been interpreted as the increase in the storage of LH. This histomorphological change was accompanied by the gradual increase in the LH pulse frequency from the 15th to 30th week of age (P < 0.05). The PAA occupied by ir-FSHbeta-cells was extremely high in the infantile sheep, and subsequently, low in the juvenile sheep (P < 0.05). Altogether, similar patterns of pretranslational synthesis of the LHbeta- and FSHbeta-subunit but clearly different storage patterns of gonadotrophins were observed. The postnatal development of gonadotrophins seems to be determined by the progressive increase in the storage of LH until peripuberty and by the acute decrease in the storage of FSH during the infantile/juvenile shift. These findings imply the different intrahypophyseal regulation of LH and FSH posttranscriptional processing during the period of transition between infancy and peripuberty in female sheep.