Biomedical subjects

R Limor

Publications and source records attributed to R Limor.

24 records · Page 2Linked to original sources

PubMed1988

Gonadotropin-releasing hormone-induced rise in cytosolic free Ca2+ levels: mobilization of cellular and extracellular Ca2+ pools and relationship to gonadotropin secretion.

Addition of GnRH to pituitary gonadotrophs preloaded with Quin 2 resulted in a rapid (approximately 8 s) mobilization of an ionomycin-sensitive intracellular Ca2+ pool. A second component of Ca2+ entry via voltage dependent channels contributed about 45% of the peak cytosolic free Ca2+ concentration ([Ca2+]i). Thereafter, influx of Ca2+ via voltage-sensitive and -insensitive channels is responsible for maintenance of elevated [Ca2+]i during the second phase of GnRH action. Addition of inositol 1,4,5-trisphosphate (IP3) to permeabilized pituitary cells resulted in a Ca2+ transient, released from a nonmitochondrial pool, which maintained ambient free Ca2+ concentration around 170 nM in an ATP-dependent mechanism. Successive stimulations of the cells with IP3 produced an attenuated response. Elevation of the gonadotroph [Ca2+]i by ionomycin, to levels equivalent to that induced by GnRH, resulted in LH release amounting to only 45% of the response to the neurohormone. Activation of the voltage-dependent Ca2+ channels by the dihydropyridine Ca2+-agonist [methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)-pyridine- 5-carboxylate (BAYK8644)] stimulated LH release, 36% of the GnRH (100 nM) response being reached by 10(-8) M of the drug, both [Ca2+]i elevation and GnRH-induced LH release were inhibited similarly (40-50%) by the dihydropyridine Ca2+-antagonist nifedipine. The results indicate that peak [Ca2+]i induced by GnRH in pituitary gonadotrophs is derived mainly from ionomycin-sensitive cellular stores most likely via IP3 formation.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1988

Induction of ovulation with D-Trp6-LHRH combined with purified FSH in patients with polycystic ovarian disease.

Seventeen patients with polycystic ovarian disease (PCOD) and evidence of mild or severe ovarian hyperstimulation syndrome (OHSS) during therapy with CC/hCG, FSH/hCG or hMG/hCG were treated with D-Trp6-LHRH until medical gonadectomy was attained. Under the suppressive therapy with the GnRH agonist (GnRHa) ovulation was induced with FSH/hCG. In 15 out of 17 patients, ovulatory cycles were obtained with this new modality of treatment. Seven patients conceived (3 viable pregnancies and 4 early abortions) after the 1st treatment cycle. Fourteen of the 17 patients demonstrated symptoms of mild OHSS which did not require hospitalization. Only 1 patient developed severe OHSS after the combined treatment. Our results suggest that therapy with GnRHa, especially in its delayed release formulation, is effective for the prevention of severe ovarian hyperstimulation in PCOD patients undergoing treatment with menotropins for the induction of ovulation.

Adult↗

PubMed1987

Cytosolic free calcium levels in cultured pituitary cells separated by centrifugal elutriation: effect of gonadotropin-releasing hormone.

The cytosolic concentration of free Ca2+ ([Ca2+]i) in normal rat pituitary cells separated by centrifugal elutriation was monitored with the fluorescent Ca2+ indicator Quin 2. GnRH (10(-7) M) induced a rapid rise (6-8 sec) in the gonadotroph's [Ca2+]i, followed by a plateau phase of prolonged elevated [Ca2+]i which lasted about 15 min. The stimulatory effect of GnRH was dose dependent, with an ED50 of 10(-9) M, and was blocked by the potent antagonist [Dp-Glu1,pclPhe2,DTrp3.6]GnRH. GnRH elevated [Ca2+]i only in gonadotroph-enriched cell fractions, whereas TRH and GH-releasing factor (GRF) elevated [Ca2+]i in mammotroph- and somatotroph-enriched cells fractions, respectively. A rapid increase (first phase) in [Ca2+]i induced by GnRH was observed in Ca2+-free medium containing EGTA, but this rapid phase was terminated within 2 min. Readdition of Ca2+ to the medium induced a second slower rise in [Ca2+]i (plateau phase). Addition of K+ caused a rapid rise in [Ca2+]i, which was dependent on extracellular Ca2+, but was not affected by prior stimulation with GnRH. On the other hand, stimulation of gonadotroph's [Ca2+]i response by GnRH desensitized the cells to a subsequent GnRH challenge within the time frame studied. These findings indicate an elevation of [Ca2+]i induced by GnRH, TRH, and GRF in their respective separated target cells in the rat pituitary. The rise in [Ca2+]i in GnRH-stimulated gonadotrophs originates partly from intracellular Ca2+ pools and partly from influx of Ca2+ across the cell membrane.

Aminoquinolines↗

PubMed1986

Gonadotropin-releasing hormone activates a rapid Ca2+-independent phosphodiester hydrolysis of polyphosphoinositides in pituitary gonadotrophs.

Addition of gonadotropin releasing hormone (GnRH) to pituitary cells prelabeled with [32P]Pi or with myo-[2-3H]inositol, resulted in a rapid decrease in the level of [32P]phosphatidylinositol 4,5-bisphosphate (approximately 10 s), and in [32P]phosphatidylinositol 4-phosphate (approximately 1 min), followed by increased labeling of [32P]phosphatidylinositol and [32P]phosphatidic acid (1 min). GnRH stimulated the appearance of [3H]myo-inositol 1,4,5-trisphosphate (10 s), [3H]myo-inositol 1,4-bisphosphate (15 s), and [3H]myo-inositol 1-phosphate (1 min) in the presence of Li+ (10 mM). Li+ alone stimulated the accumulation of [3H]myo-inositol 1-phosphate and [3H]myo-inositol 1,4-bisphosphate but not [3H]myo-inositol 1,4,5-trisphosphate, but had no effect on luteinizing hormone release. The effect of GnRH on inositol phosphates (Ins-P) production was dose-related (ED50 = 1-5 nM), and was blocked by a potent antagonist [D-pGlu,pClPhe,D-Trp]GnRH. Elevation of cytosolic free Ca2+ levels ([Ca2+]i), by ionomycin and A23187 from intracellular or extracellular Ca2+ pools, respectively, had no significant effect on [3H]Ins-P production. GnRH-induced [3H]Ins-P production was not dependent on extracellular Ca2+ and was noticed also after extracellular or intracellular Ca2+ mobilization by A23187 or ionomycin, respectively. The effect of GnRH on [3H]Ins-P accumulation was not affected by prior treatment of the cells with the tumor promoter phorbol ester 12-O-tetradecanoylphorbol-13-acetate or with islet-activating protein pertussis toxin. These results indicate that GnRH stimulates a rapid phosphodiester hydrolysis of polyphosphoinositides. The stimulatory effect is not mediated via an islet-activating protein-substrate, is not dependent on elevation of [Ca2+]i, neither is it negatively regulated by 12-O-tetradecanoylphorbol-13-acetate which activates Ca2+/phospholipid-dependent protein C kinase. The results are consistent with the hypothesis that GnRH-induced phosphoinositide turnover is responsible for Ca2+ mobilization followed by gonadotropin release.

Animals↗

PubMed1986

Cytochemical evidence for different routes of gonadotropin-releasing hormone processing by large gonadotropes and granulosa cells.

The route and rate of internalization of GnRH were compared in studies of dispersed ovarian granulosa cells and large pituitary gonadotropes from fractions enriched by centrifugal elutriation. GnRH receptors were localized with the use of a biotinylated [D-Lys6]GnRH analog, followed by avidin gold or avidin-biotin-peroxidase complex stains. Both target cell types bound the [biotinyl-D-Lys6]GnRH (Bio-GnRH) in 1 min, and there were multiple patches of label on microvilli and coated or uncoated pits by 3 min. Quantification of the avidin-gold stains showed a significant increase in the number of labeled sites per cell profile at 3 min, followed by a decrease 15 min after exposure. No staining was seen in cells treated with medium only or with Bio-GnRH competing with a 100-fold excess of unlabeled [D-Lys6]GnRH. Internalization of the Bio-GnRH occurred during the first 3 min in both target cell types. However, the initial sites of processing appeared to be different. In granulosa cells, label was in vesicles and receptosomes (endosomes) and a few small multivesicular bodies. No stain was seen in the Golgi region for at least 15 min, at which time the stain was of low intensity. At later times (15-30 min), most of the label appeared in large multivesicular bodies. In contrast, gonadotropes exhibited labeling in Golgi complex cisternae, condensing vesicles, and immature granules as early as 3 min after exposure. Label was also seen on a subpopulation of granules in the cytoplasm and in a few multivesicular bodies. These comparative studies of two different target cells suggest that whereas the rates of internalization of GnRH are similar, the initial sites of processing may be different. Granulosa cells may degrade or separate the ligand from its receptor in multivesicular bodies. Large pituitary gonadotropes appear to use the Golgi complex route, and the processing may be associated with the formation of granules. The staining pattern correlates with early immunocytochemical studies that showed staining for GnRH on gonadotrope granules. We hypothesize that the granules may be sites for degradation of the ligand, separation of the ligand from its receptor, recycling of the receptor to the plasma membrane, or all three.

Animals↗

PubMed1982

Paradoxical hypersecretion of growth hormone in patients with endometrial atypical hyperplasia and carcinoma. Effect of hysterectomy.

Paradoxical hypersecretion of human growth hormone (HGH) followed a glucose load in patients with endometrial cancer and atypical hyperplasia of the endometrium. All patients had normal fasting plasma glucose and serum HGH concentration with a normal glucose tolerance curve. Their urinary estrogen concentrations were within the normal postmenopausal range. 6 months after abdominal total hysterectomy and bilateral oophorectomy, the glucose load was repeated. Following surgery all patients showed a normal suppression of HGH secretion during the hyperglycemic period. These findings suggest the existence of a HGH-releasing factor in the neoplastic and preneoplastic endometrial tissue. This factor might be related to the abnormal HGH responses observed.

Aged↗