Ba2+ stimulation of luteinizing-hormone release demonstrates two mechanisms of Ca2+ entry in gonadotrope cells

Kinetic studies on gonadotropin-releasing-hormone (gonadoliberin, GnRH)-stimulated luteinizing-hormone (lutropin, LH) release in the cultured rat gonadotrope demonstrated a biphasic pattern of LH release. The first rapid phase of release was unaffected by the voltage-gated Ca2+-channel blockers methoxyverapamil (D600) and nifedipine [a dihydropyridine (DHP)], whereas the later second phase was partially inhibited by both drugs. These results suggested that the initial phase of LH release is independent of Ca2+ entry through dihydropyridine (DHP)-sensitive Ca2+ channels and might depend on entry of extracellular Ca2+ by another mechanism. These mechanisms were further studied by utilizing Ba2+ as a Ca2+ substitute. Ba2+, which freely permeates DHP-sensitive Ca2+ channels in the absence of GnRH, induced LH release which was sensitive to blockade by D600 and nifedipine. However, in the presence of the channel blockers, Ba2+-induced LH release could be elicited when GnRH was added to the system. This indicates that GnRH stimulates LH release by initially activating a DHP-insensitive Ca2+-entry mechanism and then a DHP-sensitive mechanism. The DHP-sensitive mechanism freely allows Ba2+ entry in the absence of GnRH-receptor occupancy, whereas the DHP-insensitive mechanism requires GnRH-receptor activation for Ba2+ entry.

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Role of Ca2+ and Na+ on luteinizing hormone release from the calf pituitary

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1988.255.4.e469 ◽

1988 ◽

Vol 255 (4) ◽

pp. E469-E474

Author(s):

J. P. Kile ◽

M. S. Amoss

Keyword(s):

Luteinizing Hormone ◽

Ionophore A23187 ◽

Channel Blockers ◽

Hormone Release ◽

Primary Cells ◽

Rat Pituitary ◽

Voltage Dependent ◽

Lh Release ◽

Ca2 Channels

It has been proposed that gonadotropin-releasing hormone (GnRH) stimulates Ca2+ entry by activation of voltage-independent, receptor-mediated Ca2+ channels in the rat gonadotroph. Little work has been done on the role of calcium in GnRH-induced luteinizing hormone (LH) release in species other than the rat. Therefore, this study was done to compare the effects of agents that alter Ca2+ or Na+ entry on LH release from calf anterior pituitary primary cells in culture. GnRH (100 ng/ml), Ca2+ ionophore A23187 (2.5 microM), and the depolarizing agent ouabain (0.1-10 microM) all produced significant increases (P less than 0.05) in LH release; these effects were significantly reduced when the cells were preincubated with the organic Ca2+ channel blockers nifedipine (1-10 microM) and verapamil (1-10 microM) and with Co2+ (0.01-1 mM). The effect of ouabain was inhibited by tetrodotoxin (TTX; 1-10 nM) as well as by nifedipine at 0.1-10 microM. In contrast to its effect on rat pituitary LH release, TTX significantly inhibited GnRH-stimulated LH release at 1-100 nM. These results suggest that GnRH-induced LH release may employ Ca2+ as a second messenger in bovine gonadotrophs and support recent speculation that GnRH-induced Ca2+ mobilization may in part be voltage dependent.

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Calcium antagonists and hormone release

Acta Endocrinologica ◽

10.1530/acta.0.1010005 ◽

1982 ◽

Vol 101 (1) ◽

pp. 5-9 ◽

Cited By ~ 6

Author(s):

Antonino Barbarino ◽

Laura De Marinis ◽

Antonio Mancini ◽

Ofa Makhoul

Keyword(s):

Luteinizing Hormone ◽

Calcium Antagonists ◽

Essential Role ◽

Normal Subjects ◽

Constant Infusion ◽

Second Phase ◽

Lh Release ◽

Two Phases

Abstract. Recent in vitro studies have demonstrated that Ca2+ plays an essential role in gonadotrophin-releasing hormone (GnRH)-stimulated luteinizing hormone (LH) release. In vivo, we have previously shown that verapamil, a substance known to inhibit calcium entry into cells, is capable of inhibiting basal gonadotrophin release as well as the release of luteinizing hormone and follicle-stimulating hormone (FSH) in response to an iv bolus of GnRH. We have examined the effects of calcium antagonists on the two phases of pituitary LH release in response to constant GnRH infusion in normal subjects. In 6 men, constant infusion of GnRH (0.2 μg/min × 4 h) resulted in the expected biphasic LH response, with an initial rapid release of LH during the first hour of infusion, followed by a second phase release during the subsequent 3 h. When verapamil (5 mg/h) was infused together with GnRH over a 4 h period, a significant decline of the rapid as well as delayed release of pituitary LH occurred. During the calcium antagonist infusion FSH release was also inhibited, indicating that Ca2+ is also important for the release of this hormone. Our data demonstrate that Ca2+ plays an essential role in the mechanism of GnRH action on both phases of LH release and the release of FSH in normal subjects.

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CENTRAL NERVOUS BLOCKADE OF OESTRADIOL-STIMULATED RELEASE OF LUTEINIZING HORMONE IN THE EWE

Journal of Endocrinology ◽

10.1677/joe.0.0600247 ◽

1974 ◽

Vol 60 (2) ◽

pp. 247-252 ◽

Cited By ~ 7

Author(s):

H. M. RADFORD ◽

A. L. C. WALLACE

Keyword(s):

Luteinizing Hormone ◽

Inhibitory Action ◽

Second Phase ◽

Biphasic Response ◽

Oestradiol Benzoate ◽

Site Of Action ◽

Lh Release

SUMMARY The injection of oestradiol benzoate (OB) into the ovariectomized ewe induced a biphasic response in circulating luteinizing hormone (LH). There was a fall in concentration during the first 8–12 h after injection, and then a rapid increase in concentration during the next 12 h. Sodium pentobarbitone anaesthesia, begun either at the time of injection of OB, or 8 or 16 h later, did not affect the first phase, but prevented the second phase of this response. The injection of synthetic luteinizing hormone releasing factor caused a release of LH that was similar both in anaesthetized and conscious ewes. The results indicated a non-nervous site for the inhibitory action of oestrogen on circulating LH, and a central nervous site of action of oestrogen in stimulating LH release.

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Functional characterization and kinetic studies of an ancestral lamprey GnRH-III selective type II GnRH receptor from the sea lamprey, Petromyzon marinus

Journal of Molecular Endocrinology ◽

10.1677/jme.1.02005 ◽

2006 ◽

Vol 36 (3) ◽

pp. 601-610 ◽

Cited By ~ 13

Author(s):

M R Silver ◽

S A Sower

Keyword(s):

Intact Cell ◽

Functional Characterization ◽

Kinetic Studies ◽

Receptor Activation ◽

Gnrh Receptor ◽

Type I ◽

Type Ii ◽

Binding Assays ◽

Gnrh Receptors ◽

Series Of Experiments

The recently cloned lamprey GnRH receptor was shown to have several unique features, including the longest intracellular C-terminal tail (120 amino acids (aa)) of any previously described GnRH receptor. In the current study, a series of experiments were performed examining cAMP responses, binding kinetics, whole cell competitive binding assays and internalization studies of the lamprey GnRH receptor using a series of three C-terminal tail truncations (80 aa, 40 aa and 0 aa) to better describe the functional significance of this unique vertebrate GnRH receptor. Activation of the lamprey GnRH receptor was shown to stimulate cAMP production in a dose-dependant manner when treated with either lamprey GnRH-I (LogEC50 −6.57±0.15) or lamprey GnRH-III (LogEC50 −8.29±0.09). Truncation analysis indicated that the membrane proximal 40 aa of the lamprey GnRH receptor C-terminal tail contain a motif required for cAMP accumulation. Saturation binding assays using the wild type and truncated lamprey GnRH receptors revealed that all of three truncated lamprey GnRH receptors were capable of binding lamprey GnRH-I. Competitive, intact cell-binding assays suggested that the lamprey GnRH receptor is lamprey GnRH-III selective, based on the observed pharmacological profile: lamprey GnRH-III (Inhibitory constant (Ki) 0.708±0.245 nM)=chicken GnRH-II (Ki 0.765±0.160 nM) > mammalian GnRH (Ki 12.9±1.96 nM) > dAla6Pro9NEt mammalian GnRH (Ki 21.6±9.68 nM) > lamprey GnRH-I (Ki 118.0±23.6). Finally, the lamprey GnRH receptor was shown to undergo rapid ligand-dependant internalization, which was significantly diminished in the tail-less truncated form. We have shown from our current and our previous structural studies that this unique lamprey GnRH receptor shares several characteristics of both type I and type II GnRH receptors which suggests that this receptor has retained ancestral characteristics that can provide insight into the function and evolution of the vertebrate GnRH receptor family.

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Androgenic and oestrogenic steroid participation in feedback control of luteinizing hormone secretion in male sheep

Acta Endocrinologica ◽

10.1530/acta.0.1020499 ◽

1983 ◽

Vol 102 (4) ◽

pp. 499-504 ◽

Cited By ~ 15

Author(s):

M. J. D'Occhio ◽

B. D. Schanbacher ◽

J. E. Kinder

Keyword(s):

Luteinizing Hormone ◽

Pulse Generator ◽

Hormone Secretion ◽

Pulse Interval ◽

Serum Concentrations ◽

Luteinizing Hormone Secretion ◽

Lh Release ◽

Lh Secretion ◽

Additional Feedback ◽

Male Sheep

Abstract. The acute castrate ram (wether) was used as an experimental model to investigate the site(s) of feedback on luteinizing hormone (LH) by testosterone, dihydrotestosterone and oestradiol. At the time of castration, wethers were implanted subdermally with Silastic capsules containing either crystalline testosterone (three 30 cm capsules), dihydrotestosterone (five 30 cm capsules) or oestradiol (one 6.5 cm capsule). Blood samples were taken at 10 min intervals for 6 h 2 weeks after implantation to determine serum steroid concentrations and to characterize the patterns of LH secretion. Pituitary LH response to exogenous LRH (5 ng/kg body weight) were also determined at the same time. The steroid implants produced serum concentrations of the respective hormones which were either one-third (testosterone) or two-to-four times (dihydrotestosterone, oestradiol) the levels measured in rams at the time of castration. Non-implanted wethers showed rhythmic pulses of LH (pulse interval 40–60 min) and had elevated LH levels (16.1 ± 1.6 ng/ml; mean ± se) 2 weeks after castration. All three steroids suppressed pulsatile LH release and reduced mean LH levels (to below 3 ng/ml) and pituitary LH responses to LRH. Inhibition of pulsatile LH secretion by all three steroids indicated that testosterone as well as its androgenic and oestrogenic metabolites can inhibit the LRH pulse generator in the hypothalamus. Additional feedback on the pituitary was indicated by the dampened LH responses to exogenous LRH.

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Receptor-operated Ca2+ channels in gastric parietal cells: gastrin and carbachol induce Ca2+ influx in depleting intracellular Ca2+ stores

Biochemical Journal ◽

10.1042/bj2890117 ◽

1993 ◽

Vol 289 (1) ◽

pp. 117-124 ◽

Cited By ~ 10

Author(s):

S Roche ◽

J P Bali ◽

R Magous

Keyword(s):

Steady State ◽

Receptor Activation ◽

Parietal Cells ◽

The Other ◽

Bivalent Cation ◽

Gtp Binding ◽

Gastric Parietal Cells ◽

Type Receptor ◽

Ca2 Channels ◽

Stimulation Of

The mechanism whereby gastrin-type receptor and muscarinic M3-type receptor regulate free intracellular Ca2+ concentration ([Ca2+]i) was studied in rabbit gastric parietal cells stimulated by either gastrin or carbachol. Both agonists induced a biphasic [Ca2+]i response: a transient [Ca2+]i rise, followed by a sustained steady state depending on extracellular Ca2+. Gastrin and carbachol also caused a rapid and transient increase in Mn2+ influx (a tracer for bivalent-cation entry). Pre-stimulation of cells with one agonist drastically decreased both [Ca2+]i increase and Mn2+ influx induced by the other. Neither diltiazem nor pertussistoxin treatment had any effect on agonist-stimulated Mn2+ entry. Thapsigargin, a Ca(2+)-pump inhibitor, induced a biphasic [Ca2+]i increase, and enhanced the rate of Mn2+ entry. Preincubation of cells with thapsigargin inhibits the [Ca2+]i increase as well as Mn2+ entry stimulated by gastrin or by carbachol. Thapsigargin induced a weak but significant increase in Ins(1,4,5)P3 content, but this agent had no effect on the agonist-evoked Ins(1,4,5)P3 response. In permeabilized parietal cells, Ins(1,4,5)P3 and caffeine caused an immediate Ca2+ release from intracellular pools, followed by a reloading of Ca2+ pools which can be prevented in the presence of thapsigargin. We conclude that (i) gastrin and carbachol mobilize common Ca2+ intracellular stores, (ii) Ca2+ permeability secondary to receptor activation involves neither a voltage-sensitive Ca2+ channel nor a GTP-binding protein from the G1 family, and (iii) agonists regulate common Ca2+ channels in depleting intracellular Ca2+ stores.

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RELATIONSHIP BETWEEN BLOOD LEVELS OF LUTEINIZING HORMONE AND TESTOSTERONE IN BULLS, AND THE EFFECTS OF SEXUAL STIMULATION

Journal of Endocrinology ◽

10.1677/joe.0.0500457 ◽

1971 ◽

Vol 50 (3) ◽

pp. 457-466 ◽

Cited By ~ 174

Author(s):

C. B. KATONGOLE ◽

F. NAFTOLIN ◽

R. V. SHORT

Keyword(s):

Luteinizing Hormone ◽

Immediate Release ◽

Blood Levels ◽

Testosterone Levels ◽

Peripheral Plasma ◽

Sexual Stimulation ◽

Maximal Stimulation ◽

Cyclical Pattern ◽

Lh Release ◽

Competitive Protein Binding

SUMMARY Luteinizing hormone (LH) and testosterone were measured in the peripheral plasma of two bulls by radioimmunoassay and competitive protein binding techniques. Samples were collected from an indwelling jugular catheter once an hour for 24 h, and then at more frequent intervals after a number of experimental procedures. Each bull showed its own characteristic pattern of cyclic LH changes, with 5–10 peaks during 24 h that were apparently unrelated to daylight, feeding or sleep. Each LH peak was associated with a testosterone peak; the LH concentrations ranged from 5 to 50 ng/ml, and those of testosterone from 2 to 20 ng/ml. Sexual stimulation, such as the sight of a cow, or 'teasing', or on one occasion the act of ejaculation itself, caused an immediate release of a large amount of LH. If the testosterone levels were low at the time, the LH peak was followed by a testosterone peak. But when the testosterone levels were high at the time of LH discharge, the testis seemed to be unable to respond any further. An intravenous injection of 500 i.u. human chorionic gonadotrophin was associated with LH release and caused the testosterone levels to rise to maximal values of 22 ng/ml within 1½ h. It is concluded that the cyclical pattern of LH release is due to some inherent central rhythm, and that each transient LH peak results in transient maximal stimulation of testicular testosterone secretion.

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EFFECT OF HYPOTHALAMIC DEAFFERENTATION ON THE CONTROL OF LUTEINIZING HORMONE SECRETION

Journal of Endocrinology ◽

10.1677/joe.0.0460001 ◽

1970 ◽

Vol 46 (1) ◽

pp. 1-7 ◽

Cited By ~ 30

Author(s):

S. TALEISNIK ◽

M. E. VELASCO ◽

J. J. ASTRADA

Keyword(s):

Luteinizing Hormone ◽

Negative Feedback ◽

Positive Feedback ◽

Hormone Secretion ◽

Feedback Effect ◽

Luteinizing Hormone Secretion ◽

Ovarian Steroids ◽

Medial Hypothalamus ◽

Lh Release ◽

Positive Feedback Effect

SUMMARY The influence that the interruption of the neural afferents to the hypothalamus exerts on ovulation and on the release of luteinizing hormone (LH) was studied in the rat. Animals with retrochiasmatic sections interrupting the neural connexions between the medial hypothalamus and the preoptic area (POA) showed constant oestrus and failed to ovulate. Animals in which the dorsal neural afferents to the POA were transected had oestrous cycles and ovulated normally. The positive feedback effect of progesterone on LH release in spayed animals primed either with 20 μg. oestradiol benzoate or 2·5 mg. testosterone propionate 3 days before was studied. Transection of the dorsal afferents to the POA favoured an increase in plasma LH, but in animals with retrochiasmatic sections the response was abolished. However, the negative feedback effect of ovarian steroids operated after both types of transection because an increase in plasma LH occurred after ovariectomy. It is concluded that the negative feedback effect of ovarian steroids acts on the medial hypothalamus which can maintain a tonic release of gonadotrophins in the absence of steroids. In contrast, the POA involved in the positive feedback effect of progesterone is concerned with the phasic release of LH.

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