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Z Naor

Publications and source records attributed to Z Naor.

At least 109 records · Page 6Linked to original sources
PubMed1984

Regulation of prostaglandin E, progesterone, and cyclic adenosine monophosphate production in ovarian granulosa cells by luteinizing hormone and gonadotropin-releasing hormone agonist: comparative studies.

The early direct effects of GnRH on the ovary were investigated using cultured granulosa cells from preovulatory rat follicles, and compared to the known stimulatory effects of LH. Stimulation of ovarian functions by a GnRH agonist include a rapid receptor-mediated phosphatidylinositol turnover (approximately 5 min). On the other hand, LH action on granulosa cells is initiated by increased cAMP production (approximately 10-15 min), consisting of an indomethacin-resistant and indomethacin-sensitive pools (40% and 60%, respectively). The GnRH agonist [D-Ala6] des-Gly10 N-ethylamide (GnRHa) at concentrations of 10(-12)-10(-8) M had no effect on basal or LH-stimulated cAMP production during a 4-h incubation test. Both LH and GnRHa increase progesterone formation (30 and 120 min, respectively) with ED50 values of 2.5 ng/ml and 10(-9) M, respectively and the stimulatory effect is not blocked by indomethacin. LH and GnRHa increase also prostaglandin E (PGE) formation (180 and 120 min, respectively) and the ED50 values were 0.1 microgram/ml and 10(-9) M, respectively. No inhibitory effect of GnRHa on LH actions was observed during 4 h of incubation. It is concluded that: 1) GnRH mimicks LH stimulation of ovarian PGE and progesterone production; 2) cAMP does not play a role in mediating the direct stimulatory effects of GnRH agonists on ovarian PGE and progesterone production; 3) PGE is not involved in mediating GnRH and LH stimulation of progesterone formation. 4) LH-induced cAMP production consists of indomethacin-sensitive and indomethacin-resistant pools.

Animals↗
PubMed1984

Stimulation of prostaglandin E and testosterone production in rat interstitial cells by a gonadotropin-releasing hormone agonist.

The early direct effects of a GnRH agonist analog [D-Ala6]des-Gly10-GnRH N ethylamide (GnRHa) on rat testicular interstitial cells include increased production of prostaglandin E (PGE) and testosterone (T) at 3 h (ED50 values of 0.5 and 0.75 nM, respectively). On the other hand, LH action on testicular function, which is mediated by increased cAMP, involves an increase in T production at 30 min followed by increased PGE formation at 3 h. GnRHa at concentrations of 10(-12)-10(-8) M had no effect on basal or LH-stimulated cAMP production during a 4-h incubation test. The stimulatory effect of GnRHa on PGE, but not on T production, was abolished by the prostaglandin synthesis inhibitor indomethacin (1.5 microns). We conclude that cAMP does not play a role in mediating the direct testicular effects of GnRH on PGE and T production; that PGE is not involved in mediating GnRH-induced T production; and, finally, that increased PGE and T production might be involved in mediating the direct inhibitory and stimulatory testicular effects of GnRH and its agonist analogs.

Animals↗
PubMed1983

Coincidence of down-regulation and desensitization in pituitary gonadotrophs stimulated by gonadotropin releasing hormone.

The dynamics of gonadotropin releasing hormone (GnRH) induced luteinizing hormone (LH) release was studied in vitro by superfusion of cultured pituitary cells. Continuous exposure of the cells to GnRH resulted in desensitization of the gonadotroph responsiveness to further stimulation by the hormone. The refractory state was achieved within 4 hr of hormone introduction (10(-7) M) and was accompanied by down-regulation of GnRH receptors (50%) assayed by equilibration with [125I]iodo-[D-Ala6]des-Gly10-GnRH N-ethylamide. The data indicate that GnRH can regulate the number of its own receptors, and that desensitization is accompanied by down-regulation.

Animals↗
PubMed1983

Possible involvement of lipoxygenase products of arachidonic acid pathway in ovulation.

The possible involvement of products of the lipoxygenase pathway of arachidonic acid cascade in ovulation was tested by intrabursal injection of nordihydroguaiaretic acid (NDGA); 5, 8, 11-eicosatriynoic acid (5, 8, 11-ETYA), 3 amino-1-(3 trifluromethyphenyl)-2-pyrazoline hydrochloride (BW755c) and (FPL 55712). All these drugs reduced the number of ova released from the treated ovaries in a dose-dependent manner, without affecting ovulation from contralateral ovaries. NDGA was most potent since it completely blocked ovulation from the treated ovaries in 17/38 rats receiving a dose higher than 0.15 mg/bursa. This effect of NDGA cannot be ascribed to its inhibition of ovarian PGE synthesis. Conversion of labeled arachidonic acid via the lipoxygenase pathway by preovulatory rat follicles was demonstrated by TLC chromatography. Collectively, these results suggest the involvement of products of lipoxygenase pathway of arachidonic acid in ovulation in the rat.

4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyraz↗
PubMed1983

Dissociation between the direct stimulatory and inhibitory effects of a gonadotropin-releasing hormone analog on ovarian functions.

The paradoxical effects of gonadotropin-releasing hormone (GnRH) on the ovary have hitherto been believed to result from different regimens of administration; an acute treatment was shown to stimulate the ovary while chronic administration of the hormone inhibited LH-induced responses. In the present report we demonstrate that a single injection of a GnRH analog (D-Ala6)des-Gly10-GnRH-N-ethylamide (GnRHa, 2 micrograms/rat) is sufficient to obtain a significant inhibition (75%) of hCG-induced ovulation in PMSG-primed, either intact or hypophysectomized, immature rats. Inhibition of ovarian development, in terms of growth and ovulation, by multiple injections with GnRHa (2 micrograms/rat, twice daily for 3 days) could be obtained only upon administration of the hormone at early stages of follicular development, i.e. concomitantly with the PMSG injection. When administered after PMSG, GnRHa could not inhibit the ovary but rather induced ovulation by itself in the absence of hCG. A 12-24 h delay in initiation of GnRHa treatment triggered 65% of the rats to ovulate while a delay of 48 h resulted in 100% ovulation. Under both regimes of GnRHa administration, either the inhibitory or the stimulatory, the oocytes of the treated rats were induced to resume meiotic maturation. Since under the inhibitory regime ovulation did not occur, maturation was followed by a massive degeneration of the oocytes trapped within their follicles. These findings demonstrate that the follicular stage of development rather than the dose and/or duration of GnRHa administration determines whether GnRHa inhibits ovarian growth and ovulation, while the competence of the oocytes to respond to the GnRHa stimulus and mature is independent of hormonal priming.

Animals↗
PubMed1983

Monoclonal antibodies against epidermal growth factor receptor induce prolactin synthesis in cultured rat pituitary cells (GH3).

The addition of epidermal growth factor (EGF) to cultured rat pituitary cells (GH3) leads to increased synthesis of prolactin and to partial inhibition of cell proliferation. Monoclonal antibodies generated against EGF receptor from human epidermoid carcinoma (A-431) cells were used to characterize the EGF receptor kinase system of GH3 cells and to investigate the role of the hormone-receptor complex in the expression of the prolactin gene in these cells. The EGF receptor of GH3 cells is a 170,000-dalton protein associated with a protein kinase. It is similar but not identical to the EGF receptor identified in other tissues. The immunoprecipitated membrane receptor is phosphorylated on both serine and tyrosine residues. The monoclonal antibody denoted 2G2-IgM binds to EGF receptor on GH3 cells. Like EGF, the monoclonal antibody induced the synthesis of prolactin and morphological changes in these cells. Hence, EGF receptor in GH3 cells, when properly triggered, contains all of the biological attributes necessary for the induction of EGF-induced gene expression and morphological changes in GH3 cells.

Animals↗
PubMed1983

A comparative study of the mechanism of action of luteinizing hormone and a gonadotropin releasing hormone analog on the ovary.

The mechanism of action of a gonadotropin releasing hormone (GnRH) agonistic analog ([D-Ala6]GnRH) on the rat ovary has been studied in comparison to similar effects of luteinizing hormone (LH). Stimulation of meiosis resumption in vitro in follicle-enclosed oocytes by both LH and [D-Ala6] GnRH, was blocked by elevated levels of cAMP as demonstrated when either dibutyryl cAMP or the phosphodiesterase inhibitor methylisobutylxanthine was present in the culture medium. In vivo, the prostaglandin synthase inhibitor indomethacin, which blocks LH-induced ovulation, also inhibited ovulation induced by the GnRH analog in hypophysectomized rats. On the other hand, the potent GnRH-antagonist [D-pGlu1, pClPhe2, D-Trp3,6] GnRH which blocked the stimulatory effect of the agonist on oocyte maturation and ovulation had no effect on LH action. It is concluded that while a GnRH-like peptide does not seem to mediate LH action on the ovarian follicles, both LH and GnRH agonist share some common mechanistic pathways at a post-receptor locus.

Animals↗
PubMed1983

Localization of biotinylated gonadotropin releasing hormone on pituitary monolayer cells with avidin-biotin-peroxidase complexes.

The new avidin-biotin-peroxidase complex (ABC) technique was used to localize the [D-Lys6] analog of gonadotropin releasing hormone (GnRH), labeled with biotin, on pituitary monolayer cultures from female rats. Staining was diffuse, or in patches, on the surface of 10-17% of the cells 30 sec-3 min after the addition of 10(-10)-10(-12) M biotin-labeled GnRH. In parallel studies, double stains for gonadotropins showed label on 16.3 +/- 2% of the monolayers. Capping was evident by 3 min after exposure and the stain appeared in dense patches, vesicles, or granules 10-30 min after exposure. The stain was abolished by the addition of a 10- to 100-fold excess of unlabeled [D-Lys6] GnRH. Biotinylated GnRH released luteinizing hormone (LH) and follicle stimulating hormone (FSH) and was either equipotent or 10 times more potent than the unlabeled analog in multiple dose-response tests. The ED50 of the 4 hr release was 0.075 nM for LH and 0.02 nM for FSH. Competitive binding assays showed that the binding affinity of the biotinylated GnRH was within the range found for the unlabeled analog (0.7 nM-IC50). This report describes the localization of biotinylated GnRH on the surfaces of cells exposed to low concentrations of the analog with a technique that requires minimal manipulation of the cells, and is performed in less than one day.

Animals↗
PubMed1983

Morphometric analysis of thyrotropes in developing and cycling female rats: studies of intact pituitaries and cell fractions separated by centrifugal elutriation.

The development and morphology of immunocytochemically stained thyrotropes were studied in sections of intact pituitaries and dissociated cell fractions separated by centrifugal elutriation. In the initial cell suspension from six elutriation experiments, adult female rat thyrotropes were 4.8 +/- 0.5% (+/- SE) of the cell population. Correlative morphometric studies of Araldite- or glycol methacrylate-embedded pituitaries showed that there were no changes in the percentage of thyrotropes with the stage of the estrous cycle and that the percentage of thyrotropes (5.14 +/- 0.4%) was not significantly different from the percentages in the initial cell suspension. TSH cell area fraction (a) measurements (with a 10,000-microns 2 ocular grid) showed that adult rat thyrotropes covered 171 +/- 5 microns 2 of the grid area and averaged 15 microns in diameter. In neonatal rats, thyrotropes were half the a of those in the adult for the first 9 days of life. Thereafter, they expanded, and the a reached adult levels by 20-21 days of development. TSH cell percentages remained 2-3 times adult levels throughout postnatal development (2-22 days). This developmental pattern contrasted with that in the male, which showed adult percentages of thyrotropes by 15 days of age. In the elutriation experiments from adult rats, thyrotropes were 2- to 4-fold more concentrated in the fractions eluted at 37.0 ml/min or greater, which contained the largest cells. Fraction 7 (39.5 ml/min) showed a 2-fold enrichment of thyrotropes to 11.6 +/- 1.4%, and fraction 8 showed a 4-fold enrichment to 19.6 +/- 2.7%. A few small TSH cells were found in the fractions 1-3, eluted at 11.8-19.5 ml/min. Electron microscopic studies showed that some of these small TSH cells were poorly granulated and difficult to distinguish from small gonadotropes, whereas the large thyrotropes resembled those described previously in the adult or developing male rat. These studies, thus, combine techniques of immunocytochemistry, morphometrics, and cell separation by elutriation to describe TSH cells in the female rat pituitary. Our findings agree with those reported by Denef et al., who showed that thyrotropes in the adult male rat are among the largest cells in the pituitary. The few small thyrotropes in the female rat may be equivalent to the prolific cells described by Leuschen et al. in the male rat that enrich monolayers from these fractions after 7 days in culture.

Age Factors↗
PubMed1983

Heterogeneous luteinizing hormone and follicle-stimulating hormone storage patterns in subtypes of gonadotropes separated by centrifugal elutriation.

The application of centrifugal elutriation to the separation of pituitary cells has produced a fraction that is enriched with LH and FSH gonadotropes. In this study, stains were performed on serial sections of fractions taken from six elutriation experiments with 1:10,000-1:30,000 anti-bLH beta or 1:2,000-1:8,000 anti-hFSH beta and the avidin-biotin-peroxidase complex technique. Over 900 serially sectioned gonadotropes were analyzed. In the initial cell suspensions, 59.6% of the gonadotropes contained both LH and FSH; 18% contained LH, and 23% contained FSH. Fewer than 3% contained ACTH. The elutriation fractions contained several subtypes of gonadotropes. A few small (8 micron), poorly granulated LH or FSH cells were eluted with the smallest cells (10-12%) at flow rates of 15.7 ml/min. Medium sized gonadotropes (10-10.5 micron) that eluted at flow rates of 19.8-30.5 ml/min were infrequent (3-6%) and resembled the larger gonadotrope. An analysis of serially sectioned fields showed that only 15.2%-22% of the small and medium sized gonadotropes contained both LH and FSH, whereas 30-40% contained only LH and 46-50% stored only FSH. The gonadotrope-enriched fraction was eluted at 37-39.5 ml/min; 78% of these gonadotropes (diameter, 14-15 micron) contained both LH and FSH, 10% contained only LH, and 12% contained FSH. Finally, large cells (diameter, 15-16 micron) that contained FSH only were found in the Wash fraction. These studies demonstrate that smaller gonadotropes tend to store only one of the hormones whereas most of the larger cells either store LH and FSH together or FSH alone. These heterogeneous storage patterns may correlate with studies by others who measured different responses to GnRH in gonadotropes separated by size on a unit gravity sedimentation gradient. They may also reflect different secretory phases of gonadotropes from the mixed group of cycling female rats.

Adrenocorticotropic Hormone↗
PubMed1982

Compartmentalization of luteinizing hormone pools: dynamics of gonadotropin releasing hormone action in superfused pituitary cells.

Cultured rat anterior pituitary cells were continuously perfused with medium 199, and exposed to short (5 min), intermediate (30 min), or long (6 h) pulses of a maximally effective concentration of gonadotropin-releasing hormone (GnRH). Assay of the effluent by radioimmunoassay and interstitial-cell bioassay revealed a biphasic response to GnRH, and indicated that 3 pools of luteinizing hormone (LH) are present in the gonadotroph. A rapidly releasable peak of bioactive LH comprising about 2% of the total cellular LH was mobilized within 1 min of GnRH addition, lasted for 3-4 min, and was independent of the duration of stimulation. The second, larger pool of bioactive LH varied from 15 to 50% of the total LH as the duration of exposure to GnRH was increased from 5 min to 6 h. A third LH pool comprising up to 50% of the total LH could be mobilized by 50 mM potassium but not by continuous GnRH treatment, due to refractoriness of the cells to prolonged stimulation by the decapeptide. In contrast, repeated pulses of GnRH evoked a series of biphasic LH peaks with profiles similar to that observed during a single response to GnRH, indicating that continuous exposure to GnRH is necessary for densensitization. Release of LH from the perfused cells was calcium-dependent, and the bio-immuno ratio of the first and second pools of LH was similar. The in vitro secretion profile of cultured rat cells is comparable with the early and late phases of LH release observed in GnRH-infused man, but occurs much more rapidly, and demonstrates heterogeneity of the LH release process at the level of the gonadotroph. The superfusion technique provides a powerful tool to further investigate the bioactivity of GnRH and its analogs for use in fertility control.

Animals↗
PubMed1982

Gonadotropin-releasing hormone binding and activation of enriched population of pituitary gonadotrophs.

The properties of GnRH receptors were analyzed in isolated rat pituitary cells by binding studies with the labeled GnRH agonist, [125I]iodo-[D-Ser(tBu)6]des-Gly10-GnRH-N-ethylamide. The concentration of GnRH-binding sites in pituitary cells from immature female rats was twice as high as in cells from adult females. Electron-microscopic immunocytochemistry revealed twice as many gonadotrophs in the immature rat pituitary, indicating that gonadotrophs from immature and mature female rats contain the same number of binding sites. An enriched population of gonadotrophs prepared from immature female rat pituitaries by velocity sedimentation at unit gravity contained 77% of the total radioimmunoassayable LH, and 71% of the total GnRH receptors. A second population of small, poorly granulated gonadotrophs was distributed among the cells of other fractions of the gradient, and could be detected only by immunocytochemistry. The smaller, possibly immature, gonadotrophs did not contain a measurable number of GnRH receptors. When incubated with the cells recovered from the gradient, GnRH stimulated LH release only in the mature gonadotroph-enriched fraction, and not in other regions of the gradient. These results indicate that GnRH interacts preferentially with gonadotrophs in the pituitary. The findings also suggest that functional heterogeneity exists among pituitary gonadotrophs, and that GnRH binds to and activates only the mature gonadotrophs which exhibit the highest LH-storage capacity.

Animals↗
PubMed1982

Binding affinity and biological activity of gonadotropin releasing hormone agonists in isolated pituitary cells.

The relationships between binding affinity and the biological potency of eight GnRH agonist analogs were evaluated in isolated rat pituitary cells. For this purpose, binding affinity and biological activity were assayed under similar physiological conditions in medium 199, pH 7.4, and binding affinity was also measured under the standard conditions in hypotonic buffer at low temperature. Under physiological conditions, receptor binding affinity was consistently lower than when measured in the hypotonic Tris buffer usually employed for GnRH receptor studies. In the low temperature binding assay at 0 C, which provided a measure of the affinity constant without degradation, a difference of 20- to 30-fold was observed between native GnRH and its most potent analog, [D-Ser(t-Bu)6]des-Gly10-GnRH N-ethylamide. Modifications of the amino acid residues at both positions 6 and 10 of the decapeptide increased the binding affinity of GnRH analogs. When the receptor binding assay was performed at 37 C, the range of the apparent affinity constants was extended up to 60-fold. The affinity constants derived at 37 C were closely correlated with the biological potencies of the individual analogs measured in the same cell system. The effect of temperature on binding affinity was not significantly influenced by peptide metabolism, which was minor in the absence of horse serum from the incubation medium. At the pituitary level, the biological potency of the GnRH agonist analogs is predominantly determined by their higher receptor affinity, and reduced degradation is a less important aspect of the high biological activity of the superagonist analogs.

Animals↗
PubMed1982

Gonadotropin-releasing hormone stimulates phospholipid labeling in cultured granulosa cells.

Cultured ovarian granulosa cells from preantral and preovulatory follicles were incubated with [32P]Pi to label endogenous phospholipids. Labeled cells were then incubated with FSH, GnRH, or a GnRH agonist analog [D-Ala6]GnRH (GnRHa), cellular phospholipids were separated by two-dimensional thin layer chromatography, and the radioactivity was determined. Phosphatidylcholine was the major labeled phospholipid accounting for 64% of the total radioactivity. The remaining labeling was distributed among choline plasmalogen (8.4%), phosphatidylinositol (6.3%), lyso phosphatidylcholine (3.7%), phosphatidylethanolamine (3.4%), phosphatidic acid (1.75%), phosphatidylserine (1.65%), and cardiolipin (1.3%). GnRH and its agonist analog GnRHa, but not FSH, increased 32P incorporation into phospholipids by 2-fold. Analysis of the several phospholipids revealed that GnRHa (10(-7) M) increased 32P labeling of phosphatidylcholine and lyso phosphatidylcholine by 1.5- and 2.5-fold respectively, and that of phosphatidic acid and phosphatidylinositol by 5- and 7-fold, respectively, during 60 min of incubation. The natural decapeptide GnRH was 30 times less potent than its agonist analog. Labeling of other phospholipids was not affected by GnRHa treatment, and FSH had no effect on 32P incorporation under similar conditions. The stimulatory effect of GnRHa was blocked by the potent GnRH antagonist [D-pGlu1,pClPhe2, D-Trp3,6]GnRH. The minimal stimulating dose of GnRHa was 10(-12) M, and increased phospholipid labeling could be detected after 10 min of incubation with the analog. These results indicate that phospholipids, in particular phosphatidylinositol and phosphatidic acid, might be involved in the mechanism by which GnRH exerts its gonadal effects.

Animals↗