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The suppressive effects of short- and long-loop negative feedback on serum levels of LH were assessed after administration of human chorionic gonadotrophin (HCG) and conjugated oestrogens.
Fourteen ovariectomized women were injected intravenously with 5 mg conjugated oestrogens, eight of these patients were also given an intramuscular injection of 10 000 i.u. HCG 8 h later, while the other six patients were given a control injection of 0·9% saline. The serum levels of LH decreased by similar amounts in both groups of women. Thirteen other ovariectomized women were initially injected with 10 000 i.u. HCG, i.m., seven of these patients were also given an i.v. injection of 5 mg conjugated oestrogens 8 h later, while the remaining six patients received a control injection of 0·9% saline. The results showed that conjugated oestrogens could further suppress the serum level of LH which had been reduced by prior HCG treatment. In six ovariectomized women who received i.m. saline injections at the start of the experiment and 8 h later, the serum levels of LH did not change significantly.
It is concluded that the suppression of the serum concentrations of LH by long-loop negative feedback after administration of 5 mg conjugated oestrogens is greater than that by short-loop negative feedback after treatment with 10 000 i.u. HCG.
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Department of Obstetrics and Gynecology, Osaka University Medical School, Osaka 553, Japan
(Received 4 March 1977)
The level of luteinizing hormone (LH) in the serum is significantly suppressed by the implantation of LH or human chorionic gonadotrophin (HCG) in the median eminence of gonadectomized rats (Corbin, 1966; Corbin & Cohen, 1966; David, Fraschini & Martini, 1966; Döcke & Glaser, 1971; Hirono, Igarashi & Matsumoto, 1971, 1972) and by the injection of LH or HCG into gonadectomized rabbits (Molitch, Edmonds, Jones & Odell, 1976) and HCG into gonadectomized women (Miyake, Tanizawa, Aono, Yasuda & Kurachi, 1976). These facts suggest that HCG as well as LH controls pituitary secretion of LH by a short-loop feedback. This investigation was designed to study the influence of HCG on the response of LH to luteinizing hormone releasing hormone (LH-RH) in gonadectomized women.
Twelve women aged between 32 and 53 years who had undergone total hysterectomy
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The effect of prostaglandin D2 (PGD2) on release of LH and LH releasing hormone (LHRH) was studied in a sequential double-chamber superfusion system using the medial basal hypothalamus (MBH) and the pituitary gland from female rats at dioestrus. Infusion of PGD2 (5·7 or 57μmol/l) caused a significant (P <0·05) increase in LH release to values 40–60% above the preinjection values from the pituitary gland superfused either alone or in series with the MBH. No release of LHRH in response to PGD2 was observed from the superfused MBH. These data demonstrate that PGD2 causes LH release from the pituitary gland not by inducing release of hypothalamic LHRH but by a direct action on the gland.
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Abstract
These studies were undertaken to characterize the exocytotic changes in purified gonadotropes by three-dimensional imaging using scanning electron microscopy. Rat gonadotropes were purified using a fluorescence-activated cell sorter and an argon laser treatment system. The purified gonadotropes were stimulated with GnRH under various conditions and fixed for scanning electron microscopy. After the GnRH stimulation, many 'hole' structures (diameter 0·1–0·5 μm) were observed on the cell surface, and notably the population of cells with 10 or more holes was clearly increased. The pattern of the time-course of the changes in this population was perfectly consistent with the LH secretory profile of pituitary cells, and their formation of the cells with 10 or more holes was completely inhibited by pretreatment with a GnRH antagonist. Our data suggest that the hole structure represents an exocytotic opening site and that regulated exocytosis in purified gonadotropes can be evaluated by scanning electron microscopy. This method may be widely applicable to other endocrine cells.
Journal of Endocrinology (1995) 144, 193–200
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Abstract
The effects of interleukin (IL)-1 and granulocytemacrophage colony stimulating factor (GM-CSF), which are present in the mouse placenta, on the secretion of mouse placental lactogen (mPL)-1 and mPL-II by placental cells were tested in vitro. IL-lα and IL-1β, 2·5 nmol/l each, significantly inhibited mPL-II secretion by cells from days 9 and 12 of pregnancy, but did not affect mPL-II secretion by cells from day 7 of pregnancy or mPL-I secretion by cells from days 7, 9 or 12 of pregnancy. GM-CSF had no effect on mPL-I and mPL-II secretion by cells from days 7, 9 or 12 of pregnancy. The inhibitory effects of IL-1α and IL-1β on mPL-II secretion were completely eliminated by the addition of antibodies to IL-1α and IL-1β respectively. Western blot analysis for mPL-II indicated that IL-1α significantly reduced the intensity of the mPL-II band. Steady-state levels of mPL-II mRNA, assessed by Northern blot analysis, were reduced by incubation of placental cells from day 12 of pregnancy with 2·5 nmol/l IL-1α for 5 days. Co-incubation of 0·25 pmol/l IL-1α, 25 pmol/l IL-6, and 25 pmol/l tumor necrosis factor-α, each of which did not significantly inhibit mPL-II secretion by itself, together inhibited mPL-II secretion. These results suggest that IL-1, but not GM-CSF, is a potent inhibitor of mPL-II secretion after mid-pregnancy, and that the combined action of cytokines can inhibit mPL-II secretion.
Journal of Endocrinology (1995) 147, 423–429
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Abstract
The synaptic membrane protein synaptosomal-associated protein (SNAP-25) has recently been implicated as one of the key proteins involved in exocytotic membrane fusion in neurons. However, the role of SNAP-25 in pituitary hormone release is not known. In this study, we determined that SNAP-25 is involved in regulated exocytosis in the clonal pituitary cell line GH4C1. SNAP-25 messenger RNA and protein were detected in GH4C1 cells by RT-PCR and immunoblot analysis, respectively. Immunofluorescence analysis indicated that SNAP-25 protein was localized in the plasma membrane. Next, to determine the function of SNAP-25 in GH4C1 cells, specific inhibitors of SNAP-25, botulinum neurotoxin (BoNT) /A or /E, and antisense SNAP-25 oligonucleotide were used. Neither BoNT/A nor BoNT/E affected thyrotropin-releasing hormone (TRH)-induced cytosolic Ca2+ increase, but both inhibited TRH-induced exocytosis. Moreover, they dose-dependently inhibited TRH-induced prolactin release. The introduction of antisense oligonucleotide into the cells also inhibited TRH-induced prolactin release. These results suggest that SNAP-25 is involved in regulated exocytosis in GH4C1 cells.
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Abstract
Glucose plays an important role in fetal development and energy metabolism. Facilitative glucose transporter-1 (GLUT1) has been found in placenta. However, little is known about GLUT1 modulation in placental cells. To examine changes in mouse placental GLUT1 levels caused by 8-bromo-cAMP, we performed 2-deoxyglucose uptake experiments, Northern blot analysis and immunoblot analysis using a primary mouse placental cell culture. Immunohistochemical analysis showed that GLUT1 was localized to the ectoplacental cone and the labyrinth zone of mouse placentas on days 7 and 11 of pregnancy respectively. Treatment of mouse placental cells with 250 μmol/l 8-bromo-cAMP resulted in a significant (P<0·01) decrease in glucose uptake on days 2–5 of culture. The inhibitory effect of 8-bromo-cAMP on glucose uptake was concentration-dependent. Glucose uptake was also inhibited by 100 μg/l cholera toxin and by 0·1 mmol/l forskolin. Northern blot and immunoblot analysis revealed that both GLUT1 mRNA and protein levels were also decreased by 8-bromo-cAMP. These findings suggest that 8-bromo-cAMP inhibits glucose transport activity in mouse placental cells in culture.
Journal of Endocrinology (1996) 150, 319–327
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Abstract
Aged mice exhibit an increase in their body weight (BW), which is associated with fat deposit increase. Epidermal growth factor (EGF) concentration in the submandibular gland also increases with aging. We examined the effects of elevated EGF on the adiposity of aged female mice. Studies were started in two groups of animals consisting of sham-operated (n=10) and sialoadenectomized (n=10, Sx; surgical removal of the submandibular glands) mice at 8 weeks of age. Body weight gain and food intake were measured throughout 78 weeks of age in these two groups. Body weight was significantly less in the Sx group throughout 78 weeks, while food intake was not changed by Sx after 12 weeks of age. To examine further if EGF plays a role in the induction of adiposity in aged female mice, sham-operated animals were given 100 μl anti-EGF rabbit antiserum (anti-EGF group, n=5) or normal rabbit serum (control group, n=5) every 3 days, and Sx animals were given 5 μg/day EGF (Sx+EGF group, n=5) or saline (Sx group, n=5) from 78 weeks of age for 3 weeks. At 81 weeks of age, all animals of these four groups were killed, and carcass fat deposition and fat cell sizes were measured. Although the relative weights (weight ratio to BW) of the liver and kidney were not changed by Sx and anti-EGF treatment, the relative weights of mesenteric and subcutaneous fat tissues and adipocyte weights were significantly decreased in Sx and anti-EGF groups compared with the control group. Moreover, both acyl-CoA synthetase (ACS) and lipoprotein lipase (LPL) mRNA levels were significantly decreased by Sx or anti-EGF administration in mesenteric and subcutaneous fat tissues. On the other hand, EGF administration to Sx animals had no effect on BW, fat tissues and adipocyte weights, and ACS and LPL mRNA levels. The results, however, were consistent with the fact that adipose tissue EGF receptors were down regulated in Sx mice. These findings suggest that EGF may play a role in the induction of adiposity in aged female mice.
Journal of Endocrinology (1995) 146, 381–393
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Abstract
The regulation of mouse placental lactogen (mPL)-I and mPL-II secretion by activin and inhibin and the expression of activin and inhibin subunit mRNAs in the mouse decidua were examined. Activin-A at a concentration of 10 nm/l significantly inhibited mPL-II secretion by placental cells from days 9 and 12 of pregnancy. However, activin-A did not affect mPL-I secretion by cells from days 7 and 9 of pregnancy nor mPL-II secretion by cells from day 7 of pregnancy. By contrast, 10 nm/l inhibin activated mPL-II secretion by cells from day 12 of pregnancy. These effects of activin and inhibin on mPL-II secretion were dose-dependent. Follistatin, which binds to activin and blocks its bioactivity, completely eliminated the inhibitory effect of activin on mPL-II secretion. Incubation of placental cells from day 12 of pregnancy with activin-A resulted in a significant reduction of the mPL-II mRNA level assessed by Northern blot analysis. Northern blot analysis using poly(A)+ RNA extracted from the decidua indicated that mouse decidua, as well as the placenta, express all activin and inhibin subunits and that their gene expressions increased during gestation. The expression of these mRNAs in the decidua was much higher than those in the placenta. These findings suggest that activin and inhibin regulate mPL-II secretion and suggest the presence of an autocrine or paracrine regulation of mPL-II secretion in mouse placenta by activin and inhibin after mid-pregnancy in vivo.
Journal of Endocrinology (1995) 146, 469–474
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Abstract
The placental members of the prolactin-GH-placental lactogen (PL) gene family of the mouse include mPL-I, mPL-II, proliferin (PLF) and proliferin-related protein (PRP). The aim of the present study was to assess the effects of tumour necrosis factor-α (TNF-α) on the secretion of these proteins in primary cultures of placental cells from days 7, 9 and 12 of pregnancy. The effects of epidermal growth factor (EGF) on the secretion of PLF and PRP were also determined. EGF has previously been shown to stimulate mPL-I and inhibit mPL-II secretion. Incubation of placental cells from day 7 of pregnancy for 5 days with 10 nmol human (h)TNF-α/1 did not affect the mPL-II concentration of the medium, but similar treatment of cells from days 9 or 12 of pregnancy resulted in a significant reduction in the mPL-II concentration of the medium by the second or third day of culture. The intracellular concentration of mPL-II, the number of cells that released mPL-II as assessed by reverse haemolytic plaque assay, and steady-state levels of mPL-II mRNA as assessed by Northern analysis were also reduced by hTNF-α treatment. The lowest concentration of hTNF-α that significantly inhibited mPL-II secretion by cells from day 12 of pregnancy was 0·01 nmol/l. hTNF-α treatment did not affect the secretion of mPL-I, PLF or PRP, as assessed by the concentrations of these proteins in the medium during a 5-day incubation. Incubation of the cells with 20 ng EGF/ml also did not affect the PLF or PRP concentration of the medium during 5 days of culture. To determine whether the effect of hTNF-α on mPL-II secretion was mediated by interleukin-6 (IL-6), the IL-6 concentration of the medium of control and hTNF-α-treated cells was determined. Bioactive and immuno-reactive IL-6 could not be detected in medium from either treatment group. The presence of binding sites for hTNF-α was assessed in cells from day 12 of pregnancy. Scatchard analysis detected a single class of binding sites having a Kd of 1·61±0·34 nmol/l, with about 1350 sites per cell. The results of this study demonstrate that hTNF-α inhibits the secretion of mPL-II by placental cells from days 9 and 12 of pregnancy, suggesting that TNF-α may be one of the factors that regulate the production of this hormone in vivo.
Journal of Endocrinology (1994) 143, 95–105
