Luteinizing Hormone Synthesis Research Articles

Synthesis and release of luteinizing hormone in vitro: manipulations of Ca2+ environment.

We determined if luteinizing hormone (LH) synthesis is Ca2+ dependent and coupled to LH release. We monitored LH synthesis when LH release was stimulated either by specific [gonadotropin-releasing hormone (GnRH)] or nonspecific stimuli (50 mM K+ and 2 or 20 microM Ca2+ ionophore A23187) and inhibited by Ca2+-reduced medium. LH synthesis was estimated by measuring incorporation of [3H]glucosamine (glycosylation) and [14C]alanine (translation) into total (cell and medium) immunoprecipitable LH by cultured rat anterior pituitary cells. Both GnRH (1 nM) and 50 mM K+ significantly stimulated LH release and glycosylation, but had no effect on LH translation. A23187 also stimulated LH release, but significantly depressed glycosylation of LH and total protein and [14C]alanine uptake. Deletion of Ca2+ from the medium depressed both GnRH-induced LH release and glycosylation. Addition of 0.1 mM EGTA to Ca2+-free medium not only inhibited GnRH-induced release and glycosylation of LH but also uptake of precursors and glycosylation and translation of total protein. Thus glycosylation and release of LH are Ca2+ dependent. Whether parallel changes in LH release and glycosylation reflect a cause and effect relationship remains to be determined.

Inhibition of synthesis of luteinizing hormone (LH) receptors by a down-regulating dose of LH.

Although LH is known to cause down-regulation of the LH/human CG (hCG) receptor, the mechanisms underlying this process are not well understood. Here we have analyzed the effects of LH on the turnover of LH receptors in cultured granulosa cells. Down-regulation was stimulated in FSH-primed granulosa cells by exposure to LH for 1 h. By 24 h after LH exposure, the LH/hCG receptor content, as measured using [125I]iodo-hCG was 70% less than controls. To determine whether this loss of LH/hCG receptors was due to accelerated receptor degradation, turnover measurements were made using tunicamycin to inhibit LH/hCG receptor synthesis. Under these conditions, there was a small (16%) increase in the rate of degradation of LH/hCG receptors in LH-treated cells compared to controls. By contrast, the rate of LH/hCG receptor synthesis, estimated mathematically, was reduced by 75% in the LH-treated cells. LH treatment had no effect on the incorporation of [35S]methionine into total cellular protein. Withdrawing FSH from the culture medium had a similar effect, slightly enhancing LH/hCG receptor degradation while markedly reducing its synthesis. The role of lysosomes in the degradation of LH/hCG receptors was also investigated. The lysosomotropic amine NH4Cl failed to cause LH/hCG receptors to accumulate, contrary to what would be expected if LH/hCG receptors were degraded lysosomally. In contrast, NH4Cl inhibited the degradation of receptor-bound [125I]iodo-hCG, suggesting that the ligand and the receptor may be handled differently by the granulosa cell. Our results suggest that in the granulosa cell, LH down-regulates its own receptor by inhibiting the synthesis of LH/hCG receptors, possibly by interfering with the ability of FSH to stimulate the synthesis of LH/hCG receptors. Furthermore, they suggest that the degradation of LH/hCG receptors may occur by nonlysosomal mechanisms.

Influence of gonadal steroids on the time-course of release and synthesis of luteinizing hormone, follicle-stimulating hormone and prolactin from rat pituitary glands in vitro.

The effect of the gonadal steroids on the time-course of release and synthesis of LH, FSH and prolactin was studied in vitro. Pituitary glands from ovariectomized rats were incubated for four sequential periods of 1 h in the presence or absence of 1·84 μmol oestradiol-17β/l, 3·44 μmol 5a-dihydrotestosterone/l or 31·80 μmol progesterone/l. The rate of release of LH was not affected by oestradiol or dihydrotestosterone, but was enhanced by progesterone after the third period of incubation. Synthesis of LH was increased by the three steroids tested, from 1 to 4 h of incubation, the effect being more marked for oestradiol than for the other steroids. The rate of release of FSH was depressed after 3 h whereas its synthesis was increased between 1 and 2 h, only in the presence of dihydrotestosterone. Synthesis of FSH was also stimulated by oestradiol after 2 h incubation but its release was not affected. Progesterone showed no effect on either the release or the synthesis of FSH. Although oestradiol and dihydrotestosterone induced a rise in both LH and FSH synthesis, the onset, magnitude and duration of the responses were different, indicating separate regulatory mechanisms. Oestradiol stimulated the rates of both release and synthesis of prolactin. The effect was already evident after 1 h of incubation and increased thereafter. On the contrary, progesterone treatment inhibited the release and synthesis of prolactin. The rate of synthesis decreased after 1 h of incubation, whereas release was depressed after 3 h. Dihydrotestosterone had no effect on the release and synthesis of prolactin. The evidence provided by this study indicates that the effect of the steroid hormones in vitro was predominantly on the synthesis of LH, FSH and prolactin. When changes in release of LH, FSH and prolactin occurred they were always preceded by alterations in hormone synthesis.

Time-course of release and synthesis of luteinizing hormone, follicle-stimulating hormone and prolactin from rat pituitary glands in vitro.

To study the time-course of release and synthesis of LH, FSH and prolactin, anterior pituitary glands from ovariectomized rats were incubated for different time-intervals between 0 and 4 h. Comparable patterns of release and synthesis of LH and FSH as a function of the incubation time were observed. It was possible to distinguish two phases in the profiles of secretion of both gonadotrophins. During the first phase, from 0–2 h, release was associated with a corresponding decrease of the hormone concentrations within the gland but no overall changes in total LH and FSH production. During the second phase, between 2 and 4 h, a progressive reaccumulation of both gonadotrophins occurred in spite of the continuous release of hormones into the medium, reflecting formation of new immunoassayable material. These results suggest that the increased synthesis ensues as a secondary phenomenon arising from the release of the hormones from the tissue. The time-course of release and synthesis of prolactin showed different dynamics during the course of incubation. High levels of prolactin were released and synthesized when the adenohypophysis was incubated in vitro. Considerably larger amounts of this hormone were found in the medium than in the tissue from the first hour of incubation. After a lag of about 40 min synthesis of prolactin was increased in parallel with its release. This led to the assumption that both prolactin synthesizing and releasing processes occurred simultaneously from the early stages of the incubation. Comparatively, prolactin-secreting cells had a very fast and LH-secreting cells a low rate of turnover; FSH-secreting cells were intermediate between the two. These results indicate that (1) the increase in release of LH, FSH and prolactin into the medium precedes that of hormone synthesis and (2) the initial depletion of the pituitary gland as a result of hormone release could act as a stimulus for synthesis, leading to the reestablishment of hormonal storage levels.

Effects of GnRH and drugs that affect cAMP levels on LH synthesis and release.

We examined basal and gonadotropin-releasing hormone (GnRH)-stimulated luteinizing hormone (LH) release and synthesis in response to drugs that raise intracellular adenosine 3',5'-cyclic monophosphate (cAMP) levels. Anterior pituitaries from ovariectomized rats were incubated with or without drugs in the presence of GnRH and [3H]glucosamine. Neither 8-bromo-cAMP (8-Br-cAMP) (10 mM), cholera toxin (10 micrograms/ml), nor phosphodiesterase inhibitors [theophylline, 2 and 8 mM; 3-isobutyl-1-methylxanthine (MIX), 0.2 mM] had any detectable effect on release of immunoreactive LH (IR-LH) when used alone. However, 8-Br-cAMP and the inhibitors potentiated (P less than 0.01) GnRH-induced release of IR-LH. Total radiolabeled LH in the system was elevated (P less than 0.01) by either GnRH, 8-Br-cAMP for cholera toxin, but reduced (P less than 0.01) by 8 mM theophylline and unaffected by MIX or 2 mM theophylline. 8-Br-cAMP did not alter the effect of GnRH on radiolabeled LH in the total system, whereas MIX and 2 mM theophylline reduced (P less than 0.05) it. These results suggest that 1) cAMP does not effect LH release directly, but may interact with GnRH to potentiate it, 2) GnRH and cAMP have a similar mode of action on LH glycosylation, and 3) phosphodiesterase inhibitors have additional actions that interfere with LH glycosylation.

Differential effects of cyclic nucleotide analogues and GnRH on LH synthesis and release.

We compared the effects of gonadotropin-releasing hormone (GnRH) and cyclic nucleotides on biosynthesis and release of luteinizing hormone (LH) by rat anterior pituitary glands (APs). APs from ovariectomized rats were incubated in the presence of test compounds, [3H]glucosamine, and [14C]alanine. GnRH significantly (P less than 0.01) increased both incorporation of [3H]glucosamine into LH (glycosylation) and release of immunoreactive LH (IR-LH) and [3H]LH. None of the cyclic nucleotides alone at 5 mM significantly stimulated release of IR-LH. Adenosine 3',5'-cyclic monophosphate (cAMP), N6,O2'-dibutyryl cAMP (DBcAMP), and 8-bromo-adenosine 3',5'-cyclic monophosphate (8-Br-cAMP) stimulated (P less than 0.01) glycosylation, whereas 8-Br-AMP, 8-bromoguanosine 5'-monophosphate (8-Br-GMP), cGMP, and 8-Br-cGMP had no detectable effect. Release of [3H]LH was increased by GnRH, 8-Br-cAMP, and DBcAMP, but not by other nucleotides. None of the cyclic nucleotides elevated [14C]LH, whereas GnRH elevated it (P less than 0.01) in the medium. Dose-response curves for glycosylation in response to 8-Br-cAMP and GnRH were parallel. In contrast, dose-response curves for release of both [3H]LH and IR-LH were nonparallel. It appears that cAMP can mimic the action of GnRH on LH glycosylation, but may have little direct effect on LH release.

Gonadotropin secretion in rats bearing a prolactin-secreting pituitary tumor: effects of naloxone administration

In this study the effects of the implantation of the transplantable rat prolactin (PRL)-secreting pituitary tumor 7315a on gonadotropin secretion were investigated. Hyperprolactinemia was accompanied by suppressed plasma levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). The total PRL content of the host's pituitary gland was decreased, but the glands of tumor-bearing animals contained greatly increased amounts of LH and FSH. Chronic administration of naloxone to tumor-bearing rats for 5 days further diminished the already suppressed total PRL content of the pituitary gland, normalized the total LH content, and did not affect the FSH content. The pituitary glands from tumor-bearing rats given naloxone showed a higher ability to release LH in vitro. Hyperprolactinemia in rats is accompanied by an increased total gonadotropin content of the pituitary gland with lowered circulating gonadotropin levels. Some of the PRL-induced changes on LH synthesis and release are mediated by opioid receptors in the hypothalamus, as naloxone administration reversed some of these effects.

Effect of serum sex steroids on pituitary LH response to LHRH and LH synthesis

To determine the factors responsible for the sex difference in luteinizing hormone (LH) response to luteinizing hormone-releasing hormone (LHRH) observed earlier in pituitary cultures, we examined the effects of serum, 17 beta-estradiol, and testosterone on pituitary LHRH-responsiveness and LH synthesis. Cultures prepared from female rats were maintained in medium supplemented with serums. Dextran-coated charcoal (DCC) adsorption of female rat serum reduced, whereas DCC adsorption of male rat serum increased the pituitary LHRH-responsiveness, indicating the existence of stimulatory factor(s) in female rat serum and inhibitory factor(s) in male rat serum. Readdition of testosterone to DCC female rat serum significantly reduced LH release in response to LHRH (78-32% of the control) without affecting total LH content. Readdition of 17 beta-estradiol to DCC female rat serum significantly increased the LH release in response to LHRH, cellular LH content, and 3H-labeled precursor uptake and incorporation into immunoprecipitable LH. These results indicate that the sex difference in LHRH responsiveness may be attributed to the stimulatory effect of 17 beta-estradiol and the inhibitory effect of testosterone on the LH cells.

Interactions of gonadal steroids, gonadotropins and gonadotropin-releasing hormones in sexual maturation

Plasma and pituitary concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were measured in individual male rats pretreated with testosterone and its 5α-reduced metabolites for various lengths of time at various stages of sexual maturation. The degree of androgen induced inhibition of the gonadotropins depended on the maturation of the animals and the administration of synthetic LH-RH could not restore the levels to the pre-androgenblocked periods. The stimulation of LH and FSH due to LH-RH was also dependent on age and time-interval between the treatment with androgen and the collection of samples. The chronic treatment of dihydrotestosterone (DHT) and 3α, 5α-androstanediol (ADIOL) daily from day 1 after birth to day 90 demonstrated extremely variable results. Although release and synthesis of LH was inhibited due to LH, FSH was inhibited only between ages 25 and 40 days. From day 50 onwards FSH in the DHT-treated animals registered higher values. With ADIOL, although LH showed mild inhibitory effects at certain age points, FSH demonstrated stimulating values. Pituitary contents of both LH and FSH were markedly higher in the ADIOL-treated animals than the levels seen in the control group. This significant augmentation of serum and pituitary FSH as well as pituitary LH contents in the pubertal and adult animals with chronic treatment of ADIOL suggests that this metabolite may have an action not shared by the parent compound.

Ultrastructural and Functional Correlates of Increased Luteinizing Hormone Synthesis and Secretion in Castrated Male Mice*

AbstractThe changes in the ultrastructure of gonadotrops and in the plasma levels of LH were studied three, five, seven, ten, twenty and forty days after castration in adult male mice. Gonadotrops in sham operated animals contained numerous granules and moderately developed synthetic organelles. Castration induced mobilization of the secretory granules at three days, and degranulation of gonadotrops and a hypertrophy of the synthetic organelles at seven days. By ten days after castration gonadotrops were greatly enlarged, while in addition at forty days they frequently contained large cytoplasmic vesicles filled with lipid‐like material. These changes were paralleled by an initial three fold increase in serum LH three days after castration, and a further ten fold increase in the levels of the hormone forty days after castration. In conclusion, the castration‐induced morphologic changes in gonadotrops correlate well with increased release of LH. The subtle differences in the control of timing of LH secretion in mice and rats are discussed. A trans‐cytoplasmic route for rapid transport of gonadotropic hormones in the mouse is postulated, and the significance of cytoplasmic vesicles in the castrate discussed.

Effects of Estradiol on Basal and Luteinizing Hormone Releasing Hormone (LHRH)-Induced Release of Luteinizing Hormone (LH) from Bovine Pituitary Cells in Culture1

The effect of estradiol-17a(E2) in regulation of basal and luteinizing hormone releasing hormone (LHRH) mediated release of LH was studied. Bovine anterior pituitaries were dispersed and o5 X iocells in 1 ml medium were dispensed to each well of multiwell culture plates. LHRH at concentrations of 0.01, 0.1, 1 and 10 ng/ml increased LH release 3, 23, 94 and 183%, relative to controls without LHRH. In addition, experiments were conducted as 4 X 5 factorials where concentrations of E2 (0, 5, 50 or 500 ng/ml) and concentration of LHRH (0, 0.1, 1, 10 and 100 ng/ml) were main effects. Estradiol was present in media beginning 2 h (acute) or 26 h (chronic) before LHRH was added. Estradiol exposure for 2 h did not affect basal LH release. In contrast, basal LH release by pituitary cells incubated for 26 h with 5, 50 and 500 ng E2 /ml media averaged 26, 37 and 33 ng/ml, greater (P<0.005) than the 6 ng/ml average for controls. LH release increased linearly (P<0.1) with log dose of LHRH when 0, 5, or 50.ng/ml E2 was added to the media beginning 2 or 26 h before LHRH. Dose response slopes were 0.75, 1.40 and 2.12 (acute) and 1.5, 13.4 and 10.5 (chronic), respectively. Acute, but not chronic exposure of pituitary cells to 500 ng/ml E2 inhibited (P<0.01) LHRH-induced LH release. LU content in cells not exposed to E2 was 854 ng. LH content was increased 201, 360 and 542% relative to untreated controls by chronic exposure of cells to 5, 50 or 500 ng E2 /ml media. We conclude that chronic exposure of bovine pituitary cells to E2 increased basal LH release and synthesis. In addition, acute exposure of bovine pituitary cells to 5 or 50 ng/ml E2 or chronic exposure to 5, 50 or 500 ng/ml E2 increased sensi- tivity of bovine pituitary cells to LU RH.

Effect of pre-incubation with different concentrations of LH-RH on subsequent LH release caused by supramaximally active amounts of LH-RH; Role of LH-RH-induced protein synthesis

Anterior pituitary glands from intact diestrous female rats were incubated for two consecutive periods of 3 hours. During the first period various submaximally active amounts of luteinizing hormone-releasing hormone (LH-RH) were added to the media, whereas during the second period a supramaximally active concentration of LH-RH was present. When during the second incubation period protein synthesis was inhibited by cycloheximide, the amount of luteinizing hormone (LH) released during that period was positively correlated to the concentration of LH present during the first incubation period. This relationship was not seen when cycloheximide was absent, or when cycloheximide was present throughout both periods. Total LH was not affected by LH-RH; thus no effect of LH-RH on LH synthesis was observed. It is concluded that the amounts of protein synthesized by the pituitary glands in response to the different amounts of LH-RH during the first incubation period can constitute a limiting factor for the response to the supramaximally active amount of LH-RH added during the second incubation period.

Effect of in Vivo Treatment with Estrogen on Luteinizing Hormone Synthesis and Release by Rat Pituitaries in Vitro

The influence of estrogen on uptake of [3H]glucosamine and [14C]alanine and their incorporation into LH and total protein was investigated. Ovariectomized rats were sacrificed 22 h after injection with either oil or estradiol benzoate (EB, 50 microng/rat). Quartered anterior pituitary glands were incubated for 4 h with radioactive precursors in the presence or absence of 3.6 X 10-8M synthetic gonadotropin-releasing hormone (GnRH). Labeled LH was isolated by immunoprecipitation with specific anti-LH-beta serum. Both EB and GnRH significantly elevated the amount of [3H]glucosamine-LH appearing in the medium, the tissue, and the total system (medium + tissue), but they increased the amount of [14C]alanine-LH only in the medium. There was a significant positive interaction between EB and GnRH on the amounts of [3H]glucosamine-LH and [14C]alanine-LH in the medium and of [3H]glucosamine-LH in the tissue and total system. EB enhanced [3H]glucosamine uptake and incorporation into total protein, but GnRH had little or no effect on these parameters. In time course studies rats were injected with either oil or EB at 22, 11, or 5.5 h prior to sacrifice. At all times EB significantly increased synthesis and release of [3H]-glucosamine-LH and release of total immunoreactive LH (IR-LH) by pituitaries incubated with GnRH. The amounts of labeled and IR-LH released into the medium increased linearly with time after EB injection, but the amount of labeled LH in the total system plateaued at 5.5 h after EB injection. In another study, estradiol (E2, 5 microng/rat) dissolved in 1% ethanol-saline was injected at 0.5, 1.0, 2.0, or 4 h prior to sacrifice. Incorporation of [3H]glucosamine into tissue protein and release of [3H]glucosamine-LH was stimulated within 2 h after E2 injection. However, incorporation of [3H]glucosamine into LH was not stimulated until 4 h after E2 injection. These results suggest that estrogen and GnRH regulate LH synthesis at different sites, and that the effect of estrogen is non-specific compared to that of GnRH. The synthesis of the carbohydrate moiety of LH appears to be subjected to hormonal regulation more readily than the synthesis of the polypeptide moiety.

Thyroid hormone regulation of the pulsatile discharges of luteinizing hormone in ovariectomized rats.

The pulsatile discharges of luteinizing hormone (LH) were characterized in ovariectomized rats in the presence or absence of thyroid hormone. LH secretion in ovariectomized rats with intact thyroid glands and thyroidectomized-ovariectomized rats receiving daily physiological doses of thyroxine (2 mug/100 g BW/day for 8 days) showed equivalent periodic discharges with frequencies between 15 and 45 min. Though the frequency of the plasma LH rhythm in untreated athyroid-ovariectomized rats was normal, the maximum and minimum concentrations were 2- to 3-fold higher than those of euthyroid-ovariectomized animals. On the other hand, treatment of athyroid-ovariectomized rats with a daily hyperthyroid dose of thyroxine (20 mug/100 g BW) for 8 days, attenuated pulsatile discharges of LH. The LH measured in the sera of these animals each gave dose-response curves by radioimmunoassay which were identical to the authentic rat LH reference preparation. Furthermore, neither the molecular profile nor the metabolic clearance rate of LH was affected by alterations in thyroid status. These results suggest that altered thyroid status does not influence the synthesis and metabolism of LH but does exert a profound effect on the secretion of this hormone by presumably acting directly on the hypothalamo-pituitary axis.

Effect of starvation on pituitary and serum follicle-stimulating hormone and luteinizing hormone following ovariectomy in the rat.

The concentration of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in serum and pituitary glands was studied in intact female rats and rats that were ovariectomized on day 0 of the experiment and then starved or fed for 2, 4, 7, or 9 days. Ovariectomy resulted in enhanced rates of synthesis and release of FSH and LH as indicated by the significant (P &lt; 0.01) rises in the concentration of both hormones in the pituitary gland and serum.Starvation resulted in a decrease in body and pituitary weight. The concentration of FSH and LH in pituitary glands of starved rats was higher (P &lt; 0.05) than that in fed rats on days 7 and 9. The concentration of FSH and LH in serum of starved rats was increased after ovariectomy but the levels on days 7 and 9 were lower than those of fed rats.These results suggest that the synthesis of FSH and LH was enhanced in both starved and fed rats following ovariectomy while the rate of release of both hormones was decreased at 7 and 9 days of starvation in comparison with rats fed ad libitum.

Short-term effects of castration and starvation upon pituitary and serum levels of luteinizing hormone and follicle stimulating hormone in male rats.

ABSTRACT Serum and pituitary levels of luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured by radioimmunoassay in intact and castrated juvenile (21 days) and adult male rats. The effect of total starvation upon the gonadotrophin response to castration was also investigated in adult animals. In rats castrated at 21 days of age, serum and pituitary levels of LH were elevated by 7 days and increased progressively for 4 weeks. Serum concentrations of FSH also increased within 7 days and remained stable thereafter. Pituitary FSH levels initially declined and then increased. In adult animals serum LH and FSH concentrations increased after castration. Pituitary LH values also increased, while FSH levels remained stable for 14 days after operation. Serum FSH concentrations were consistently decreased in starved-intact animals. Starvation partially inhibited castration-induced release of LH without affecting pituitary LH or FSH synthesis or FSH release.

Regulation of luteinizing hormone (LH) in the fetal and neonatal lamb: effect of castration during the early postnatal period on levels of LH in sera and pituitaries of neonatal lambs.

To determine if the gonads of the immature sheep influence the secretionof luteinizing hormone (LH) during the first two weeks after birth, concentrations of LH in the peripheral blood of intact and castrated lambs of both sexes were compared. Pituitary weights, pituitary LH concentrations, and uterine weights were also compared. Neither an effect of castration nor sex was observed on the weight or LH concentration of the pituitary. The weight of the uterus was not influenced by castration. Mean levels of serum LH remained low (<0.5 ng/ml) in intact males during the age period studied. Levels of circulating LH in the castrated males were elevated significantly 8 days after orchidectomy and continued to increase in an apparently erratic pattern during the final half of the experimental period. In both intact and ovariectomized females, concentrations of LH in the blood followed a trend similar to that of castrated males. The data suggest that: (a) negative feedback of gonadal steroid hormones on the hypothalamo-hypophyseal system becomes establishedearlierin the male in the female; (b) the neonatal ovary may not be producing a sufficient amount of the proper steroid to inhibit release of LH or to influence the growth of the uterus; and (c) residual effects of the recent intrauterine environment may influence the early postnatal secretion of LH. Comparison of these data with those found in the literature indicate that the failure of early castration to increase synthesis or storage of pituitary LH may be age or species dependent.

Stimulation of release and synthesis of luteinizing hormone(LH) and follicle stimulating hormone(FSH) in tissue culture of rat pituitaries in response to natural and synthetic LH and FSH releasing hormone.

Addition of nanogram amounts of highly purified or pure porcine LH-RH/FSH-RH, once daily for 5 days to female rat anterior pituitary cultures, significantly increased the release of both LH and FSH. LH release appeared to be linearly related to the log-dose of LH-RH/FSHRH over the range of S-40 ng/ml/day. Total content of LH and of FSH in stimulated tissue and medium exceeded that of controls as measured by radioimmunoassays for LH and FSH. Synthetic LH-RH/FSH-RH also stimulated the release and synthesis of both LH and FSH in rat anterior pituitary cultures. This indicates that both LH and FSH releasing activities are intrinsic to the same molecule. When anterior pituitary tissue was incubated with tritiated glucosamine in the presence of porcine LH-RH/FSH-RH, there was a significant incorporation of radioactivity into the LH found in the incubation medium. These data indicate that de novo synthesis, as well as release of LH, occurred in tissue stimulated with porcine LH-RH/FSH-RH. (Endocrinology 90: 764,...

Stimulatory action of ovine LH releasing factor on synthesis of luteinizing hormone (LH) demonstrated by the rat intratesticular test system.

Owing to the action of the intratesticular LH release reported in the previous paper (Suzuki et al., 1970), LH content of the rat anterior pituitary implanted into the rat testis rapidly decreased to about 1/100 of the original amount at 25 hr after the implantation. By this time, once highly stimulated testosterone output from the treated testis by the action of released LH, returned to almost the intact level again.The anterior pituitary of extremely low LH content thus obtained was utilized to see whether LRF induces LH release after promoting de novo synthesis of LH, or not. An ovine LRF preparation was infused for 20 minutes into the testis bearing a pituitary implant from 28 hrs after the pituitary implantation. At the assessment of 2 hrs after the start of infusion, LH content of the implant elevated from nearly zero level to the amount surpassing the pre-implanting level by 40%. And a concommitant maximal increase of testosterone output from the testis bearing the implant was also observed.At least in the preparation used, it is reasonably concluded that the LRF possesses the dual action of release and synthesis of LH as its primary action.

Hypothalamic Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH)-Regulating Hormone: Structure, Physiology, and Clinical Studies

A new concept of a single hypothalamic releasing hormone which is capable of releasing either LH or FSH (luteinizing hormone or follicle-stimulating hormone) is presented, and studies are described which summarize its physiological and chemical properties. Porcine LH-RH (LH releasing hormone) in a high state of purity was found to stimulate in rats the release of LH and FSH; this also occurred in humans. The hormone was isolated and was found to consist of 10 amino acids; the hormone has been synthesized, and the synthetic material has been shown to possess the same properties as the natural material in rats: stimulation of the release of LH and FSH in vitro and in vivo. Addition of nanogram amounts of natural porcine LH-RH/FSH-RH or synthetic hormone is capable of stimulating both release and synthesis of LH and FSH in vitro. 12 steroids used for contraception did not block the release of LH and FSH after administration of LH-RH. There is some evidence that progesterone pretreatment blocks the response to LH-RH, while estrogen seems to increase the response to LH-Rh in rats. Clinical studies clearly demonstrated the effectiveness of porcine LH-RH in stimulating the release of LH in the human. The smallest dose which induced a significant rise (p=.01) in LH was 10mcg. LH levels were elevated in prepubertal children as well as in normal adults by the hormone. One woman with secondary amenorrhea ovulated and conceived after treatment with LH-RH. This and other clinical studies suggest LH-RH may be useful in the treatment of fertility and as a diagnostic aid in distinguishing between pituitary and hypothalamic disorders.