The involvement of the endogenous benzodiazepine, octadecaneuropeptide (ODN), in the regulation of proopiomelanocortin (POMC) mRNA expression at the pituitary level, and the influence of adrenal and gonadal steroids, have been studied using a quantitative in situ hybridization technique. I.c.v. injection of ODN (4 micrograms/kg) in sham-operated rats induced a 17 and 7% decrease in the POMC mRNA expression in anterior and intermediate pituitary lobes respectively. To determine the reciprocal involvement of adrenal and gonadal steroids in this regulation, animals were adrenalectomized and/or castrated. Adrenalectomy significantly increased POMC mRNA expression by 48% at the anterior pituitary level, but induced a 10% decrease of hybridization signal at the intermediate pituitary lobe (vs control sham-operated). Adrenal ablation reversed the effect induced by ODN and increased POMC mRNA expression at the anterior and intermediate pituitary levels by 60 and 10% respectively, compared with control sham-operated. By contrast, castration, which produced a decrease in POMC mRNA in the anterior pituitary and an increase in the intermediate lobe, did not modify the negative influence of ODN observed in sham-operated animals. When rats were adrenalectomized and castrated, the adrenalectomy influence was predominant at the anterior pituitary level, since ODN increased significantly the hybridization signal (+68% vs control sham-operated), while the castration influence was predominant at the intermediate pituitary level, since ODN induced an 11% decrease in POMC mRNA signal compared with control sham-operated. These studies indicate that, in vivo, the decrease in POMC mRNA expression in the anterior and intermediate pituitary induced by an endogenous benzodiazepine is differently modulated by adrenal and gonadal steroids, with a predominant influence of adrenal steroids at the anterior pituitary level and gonadal steroids at the intermediate pituitary level.
You are looking at 1 - 10 of 11 items for
- Author: G Li x
- Refine by Access: All content x
G Li, Y Zhang, JT Wilsey, and PJ Scarpace
The effects of the chronic activation of the central melanocortin (MC) system by melanotan II (MTII) were assessed in chow-fed (CH) and high-fat (HF) diet-induced obese (DIO) Sprague-Dawley rats. Six-day central infusion of MTII (1 nmol/day) reduced body weight and visceral adiposity compared with ad libitum-fed control and pair-fed groups and markedly suppressed caloric intake in both CH and DIO rats. The anorexic response to MTII was similar in DIO relative to CH rats. MTII induced a sustained increase in oxygen consumption in DIO but a delayed response in CH rats. In both diet groups, MTII reduced serum insulin and cholesterol levels compared with controls. HF feeding increased brown adipose tissue (BAT) uncoupling protein 1 (UCP1) by over twofold, and UCP1 levels were further elevated in MTII-treated CH and DIO rats. MTII lowered acetyl-CoA carboxylase expression and prevented the reduction in muscle-type carnitine palmitoyltransferase I mRNA by pair-feeding in the muscle of DIO rats. Compared with CH controls, hypothalamic MC3 and MC4 receptor expression levels were reduced in DIO controls. This study has demonstrated that, despite reduced hypothalamic MC3/MC4 receptor expression, anorexic and thermogenic responses to MTII are unabated with an initial augmentation of energy expenditure in DIO versus CH rats. The HF-induced up-regulation of UCP1 in BAT may contribute to the immediate increase in MTII-stimulated thermogenesis in DIO rats. MTII also increased fat catabolism in the muscle of DIO rats and improved glucose and cholesterol metabolism in both groups.
M Stridsberg, K Öberg, Q Li, U Engström, and G Lundqvist
Chromogranins and/or secretogranins constitute a family of water-soluble acidic glycoproteins that are present in almost all endocrine, neuroendocrine and neuronal tissue. Antibodies against chromogranins have been widely used for immunohistochemical staining of endocrine tissue and tumours of neuroendocrine origin. Furthermore, measurements of circulating chromogranin A have been used as a reliable marker for neuroendocrine tumour growth. In this study, we describe the development of specific antibodies against chromogranin A, chromogranin B (secretogranin I), chromogranin C (secretogranin II) and pancreastatin. The antibodies were used for immunohistochemical staining of normal and neoplastic neuroendocrine tissue and development of reliable radioimmunoassays for chromogranin A, chromogranin B, chromogranin C and pancreastatin. In 44 patients with carcinoid tumours, 17 patients with sporadic endocrine pancreatic tumours and 11 patients with endocrine pancreatic tumours and the multiple endocrine neoplasia 1 syndrome, plasma measurements revealed elevated chromogranin A levels in 99%, elevated chromogranin B in 88%, elevated chromogranin C in 6% and elevated pancreastatin in 46% of the patients. Urinary measurements revealed elevated levels in 39%, 15%, 14% and 33% of the patients respectively. Gel permeation chromatography of plasma and urine showed that circulating chromogranin A, and immunoreactive fragments of chromogranin A, had a higher molecular weight distribution than the chromogranin A fragments excreted to the urine. Furthermore, it was noted that most of the patients excreting chromogranin A fragments to the urine had previously been treated with streptozotocin, a cytotoxic agent known to induce renal tubular dysfunction. The antibodies raised proved useful for immunohistochemical staining and visualised endocrine cells in pancreatic islets, adrenal medulla and the small intestine as well as in endocrine pancreatic tumours, pheochromocytoma and midgut carcinoid tumours. In conclusion, the antibodies raised were useful for both immunohistochemical staining of normal tissue and endocrine tumours as well as development of specific radioimmunoassays for plasma measurements of the different chromogranins. Furthermore, we show that plasma measurements of chromogranin A and B were superior to measurements of chromogranin C and pancreastatin and plasma measurements of the different chromogranins were more reliable as markers for tumour growth than the corresponding urine measurements.
Journal of Endocrinology (1995) 144, 49–59
G Pelletier, V Luu-The, S Li, and F Labrie
Androgen receptors (AR) are highly expressed in female reproductive organs. In order to define the possible involvement of estrogens in the regulation of AR expression in the uterus and vagina, we have studied the effect of short-term administration of 17beta-estradiol (E2) to ovariectomized adult mice on AR mRNA levels. Seven days after ovariectomy, the mice received a single injection of E2 (0.05 microg/mouse) 3, 12 or 24 h before they were killed. The levels of AR mRNA were measured in the different uterine and vaginal compartments using quantitative in situ hybridization. In the uterus, AR mRNA was expressed in the luminal and glandular epithelial cells, stromal cells and smooth muscle cells. In the vagina, AR mRNA was localized in both epithelial and stromal cells. In the uterus after ovariectomy, AR mRNA levels were decreased by 18% in the epithelial cells, 23% in the stromal cells and 50% in the myometrial cells. AR mRNA levels were completely restored as early as 3 h after E2 administration in the epithelium and stroma, and at the 12-h time-interval in the myometrium. In the vaginal epithelium, ovariectomy induced a 70% decrease in AR mRNA expression. No effect could be detected 3 h after E2 administration, while at the longest time-intervals (12 and 24 h) there was an increase in mRNA levels corresponding to 70% of the levels observed in intact animals. In the vaginal stroma, ovariectomy was responsible for a 55% decrease in mRNA levels. While no significant changes were observed at the 3-h time-interval, a complete restoration of AR mRNA levels in stromal cells could be recorded at the longest time-intervals after E2 administration. The data obtained indicated that, in adult mice, estrogens exert a positive regulation of AR mRNA expression in the different compartments of both the uterus and the vagina.
G Pelletier, S Li, V Luu-The, Y Tremblay, A Belanger, and F Labrie
The biosynthesis of steroid hormones in endocrine steroid-secreting glands results from a series of successive steps involving both cytochrome P450 enzymes, which are mixed-function oxidases, and steroid dehydrogenases. So far, the subcellular distribution of steroidogenic enzymes has been mostly studied following subcellular fractionation, performed in placenta and adrenal cortex. In order to determine in situ the intracellular distribution of some steroidogenic enzymes, we have investigated the ultrastructural localization of the three key enzymes: P450 side chain cleavage (scc) which converts cholesterol to pregnenolone; 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) which catalyzes the conversion of 3 beta-hydroxy-5-ene steroids to 3-oxo-4-ene steroids (progesterone and androstenedione); and P450(c17) which is responsible for the transformation of C(21) into C(19) steroids (dehydroepiandrosterone and androstenedione). Immunogold labeling was used to localize the enzymes in rat adrenal cortex and gonads. The tissues were fixed in 1% glutaraldehyde and 3% paraformaldehyde and included in LR gold resin. In the adrenal cortex, both P450(scc) and 3 beta-HSD immunoreactivities were detected in the reticular, fascicular and glomerular zones. P450(scc) was exclusively found in large mitochondria. In contrast, 3 beta-HSD antigenic sites were mostly observed in the endoplasmic reticulum (ER) with some gold particles overlying crista and outer membranes of the mitochondria. P450(c17) could not be detected in adrenocortical cells. In the testis, the three enzymes were only found in Leydig cells. Immunolabeling for P450(scc) and 3 beta-HSD was restricted to mitochondria, while P450(c17) immunoreactivity was exclusively observed in ER. In the ovary, P450(scc) and 3 beta-HSD immunoreactivities were found in granulosa, theca interna and corpus luteum cells. The subcellular localization of the two enzymes was very similar to that observed in adrenocortical cells. P450(c17) could also be detected in theca interna cells of large developing and mature follicles. As observed in Leydig cells, P450(c17) immunolabeling could only be found in the ER. These results indicate that in different endocrine steroid-secreting cells P450(scc), 3 beta-HSD and P450(c17) have the same association with cytoplasmic organelles (with the exception of 3 beta-HSD in Leydig cells), suggesting similar intracellular pathways for biosynthesis of steroid hormones.
K. M. Hua, R. Ord, S. Kirk, Q. J. Li, S. C. Hodgkinson, G. S. G. Spencer, P. C. Molan, and J. J. Bass
Tissue and plasma levels of insulin-like growth factor-I (IGF-I), and relative levels of liver IGF-I RNA, were measured in 6-month-old ewe lambs which were well fed (n = 10) or starved (n = 10) for 5 days. Half of each nutrition group was given daily (09.00 h) injections of human GH (hGH; 0·15 mg/kg body weight per day). Blood was sampled daily from 09.00 to 12.00 h at 15-min intervals through jugular vein catheters and the lambs were slaughtered 24 h after the fifth injection of hGH.
Tissue and plasma IGF-I was extracted using an acid-ethanol-cryo-precipitation technique and estimated by radioimmunoassay. Tissue IGF-I was corrected for retained plasma IGF-I using tissue and blood haemaglobin levels. Liver IGF-I RNA levels were monitored by in-situ hybridization.
Plasma IGF-I (nmol/l) was higher in both the fed group and the fed group given GH treatment. Tissue IGF-I from kidneys (nmol/kg) was also higher (P < 0·001) in the fed group. There was no significant difference in IGF-I concentrations in the muscle biceps femoris or liver between fed and starved lambs. Although GH treatment did not increase IGF-I levels in tissues significantly, IGF-I RNA levels in liver were increased (P = 0·02) in both fed and starved animals. The relative liver IGF-I RNA levels positively correlated with their corresponding tissue IGF-I levels in the fed group and the fed group given GH treatment. The lack of a significant IGF-I response to GH in tissues may be due to either the time at which tissues were sampled after the GH treatment or the dose of GH administered. However, the higher IGF-I concentrations in plasma and kidney from fed compared with starved animals and the positive correlations between liver IGF-I and IGF-I RNA levels suggest that tissue and plasma IGF-I is regulated by nutrition and GH, with nutrition playing a critical role in the regulation of tissue and plasma IGF-I in normal lambs.
Journal of Endocrinology (1993) 136, 217–224
Deborah M Sloboda, Timothy J M Moss, Shaofu Li, Stephen G Matthews, John R G Challis, and John P Newnham
To determine the expression of glucocorticoid metabolizing and action genes in the hippocampus of fetal, neonatal, and adult sheep. Pregnant ewes (or their fetuses) received intramuscular injections of saline or betamethasone (BETA, 0-5 mg/kg) at 104, 111, 118, and/or 125 days of gestation (dG). Hippocampal tissue was collected prior to (75, 84, and 101 dG), during (109 and 116 dG), or after (121, 132, and 146 dG; 6 and 12 postnatal weeks; 3.5 years of age) saline or BETA injections. Hippocampal glucocorticoid receptor (GR), mineralocorticoid receptor (MR), and 11β-hydroxysteroid dehydrogenase (11βHSD)1 and 11βHSD2 mRNA levels were determined using qRT-PCR. Control animals late in gestation demonstrated a decrease in mRNA encoding GR and 11βHSD1, whereas 11βHSD2 was undetectable, consistent with a damping of the negative feedback influence of circulating or locally produced cortisol on the hypothalamic–pituitary–adrenal (HPA) axis. BETA-administration had transient effects on fetal GR and MR, and early in postnatal life (12 weeks of age) 11βHSD1 mRNA was increased. Hippocampal MR mRNA was elevated in adult offspring exposed to either one or four doses of maternal BETA (P<0.001). Four courses of maternal BETA increased 11βHSD2 (P<0.05) but not 11βHSD1 mRNA levels. Late in gestation a reduction in hippocampal GR and 11βHSD1 mRNA suggests lessening of glucocorticoid negative feedback, facilitating increased preterm HPA activity and parturition. Adult offspring of BETA-treated mothers demonstrated increased MR and 11βHSD2 mRNA, therefore it appears that exposure of fetus to high levels of synthetic glucocorticoids may have long-lasting effects on the hippocampal expression of HPA-related genes into adulthood.
C Martel, A Sourla, G Pelletier, C Labrie, M Fournier, S Picard, S Li, M Stojanovic, and F Labrie
In order to assess the relative roles of the androgenic and/or estrogenic components in the stimulatory effect of dehydroepiandrosterone (DHEA) on bone mineral content (BMC) and density (BMD), ovariectomized (OVX) female rats received DHEA administered alone or in combination with the antiandrogen flutamide (FLU) or the antiestrogen EM-800 for 12 months. We also evaluated, for comparison, the effect of estradiol (E2) and dihydrotestosterone (DHT) constantly released by Silastic implants as well as medroxyprogesterone acetate (MPA) released from poly(lactide-co-glycolide) microspheres. Femoral BMD was decreased by 11% 1 year after OVX, but treatment of OVX animals with DHEA increased BMD to a value 8% above that of intact animals. The administration of FLU reversed by 76% the stimulatory effect of DHEA on femoral BMD and completely prevented the stimulatory effect of DHEA on total body and lumbar spine BMD. Similar results were obtained for BMC. On the other hand, treatment with the antiestrogen EM-800 did not reduce the action of DHEA on BMD or BMC. At the doses used, MPA, E2 and DHT increased femoral BMD, but to a lesser degree than observed with DHEA. Bone histomorphometry measurements were also performed. While DHEA treatment partially reversed the marked inhibitory effect of OVX on the tibial trabecular bone volume, the administration of FLU inhibited by 51% (P < 0.01) the stimulatory effect of DHEA on this parameter. The addition of EM-800 to DHEA, on the other hand, increased trabecular bone volume to a value similar to that of intact controls. DHEA administration markedly increased trabecular number while causing a marked decrease in the intertrabecular area. The above stimulatory effect of DHEA on trabecular number was reversed by 54% (P < 0.01) by the administration of FLU, which also reversed by 29% the decrease in intertrabecular area caused by DHEA administration. On the other hand, the addition of EM-800, while further decreasing the intertrabecular space achieved by DHEA treatment, also led to a further increase in trabecular number to a value not significantly different from that of intact control animals, suggesting an additional effect of EM-800 over that achieved by DHEA. Treatment with DHEA caused a 4-fold stimulation of serum alkaline phosphatase, a marker of bone formation, while the urinary excretion of hydroxyproline, a marker of bone resorption, was decreased by DHEA treatment. Treatment with DHEA and DHEA + EM-800 decreased serum cholesterol levels by 22 and 65% respectively, while the other treatments had no significant effect on this parameter. The present data indicate that the potent stimulatory effect of DHEA on bone in the rat is mainly due to the local formation of androgens in bone cells and their intracrine action in osteoblasts.
W M Lee, A S T Wong, A W K Tu, C-H Cheung, J C H Li, and G L Hammond
Sex hormone binding globulin (SHBG) is a homodimeric plasma protein found in mammals that binds sex steroids with high affinity and regulates their bioavailability. The protein is identical in structure and properties to the androgen binding protein (ABP) found in the male reproductive tract. We have isolated a 1245-base pair rabbit SHBG cDNA encoding a reading frame for a signal peptide followed by a protein of 367 amino acids, which shares 79·0, 68·1 and 63·2% amino acid identity with the corresponding human, rat and mouse proteins respectively. Northern blot and hot-nested PCR analyses indicated that rabbit SHBG is produced from a 1·6 kilobase mRNA in the liver of both sexes and in the testis. The rabbit SHBG cDNA was inserted into pGEX-1λT for expression of a glutathione S-transferase/SHBG fusion protein in Escherichia coli. The bacterial product bound 5α-dihydrotestosterone (DHT) in the same manner as the corresponding protein in serum. The dissociation constants (Kd) for rabbit and human SHBGs produced in E. coli were 11·1 ± 1·1 nm and 2·1 ± 0·6 nm respectively, and rabbit SHBG formed a less stable protein-steroid complex (t½=5 min) than human SHBG (t½>60 min). Unlike human SHBG, rabbit SHBG does not bind estradiol with high affinity. To aid in the identification of differences in the sequences of rabbit and human SHBG, which determine species differences in steroid-binding affinity and specificity, chimeras containing the 5′-terminal half of SHBG from one species and 3′-terminal half of SHBG from the other species were constructed and expressed. It was found that the chimeric proteins assumed similar steroid-binding affinity and specificity as the wild-type proteins when the amino (N)-terminal half of SHBG was derived from the same species. Replacement of the carboxyl (C)-terminal half of rabbit SHBG by the corresponding region of the human molecule increased the integrity of its steroid-protein complex. This supports the concept that amino acids within the N-terminal half of SHBG constitute the steroid-binding domain while the C-terminal half of the molecule may provide structural stability to the protein and its steroid-binding site.
Journal of Endocrinology (1997) 153, 373–384
Thorsten Braun, Shaofu Li, Timothy J M Moss, John P Newnham, John R G Challis, Peter D Gluckman, and Deborah M Sloboda
The placenta may mediate glucocorticoid-induced fetal growth restriction. Previous studies have examined effects of fetal cortisol in sheep, which reduces placental binucleate cell (BNC) number; the source of ovine placental lactogen (oPL). The effects of maternal GC are unknown. Therefore, this study examined the effects of maternal betamethasone (BET) administration on BNC number, distribution, placental oPL protein levels, and maternal and fetal plasma oPL levels. Pregnant ewes were randomized to receive injections of saline or one (104 days of gestation; dG), two (104 and 111 dG), or three (104, 111, and 118 dG) doses of BET (0.5 mg/kg). Placental tissue was collected before, during, and after the period of BET treatment. Fetal (121–146 dG) and placental (121 dG) weights were decreased after BET when compared with controls. In controls, the mean number of BNCs increased until 132 dG and decreased thereafter. Placental oPL protein levels peaked at 109 dG and remained stable thereafter. Maternal plasma oPL levels in controls increased across gestation; fetal plasma oPL levels decreased. BNCs were reduced by 24% to 47% after BET when compared with controls at all ages studied. Placental oPL protein levels, maternal, and fetal plasma oPL levels were also reduced after BET injections, but recovered to values that were not different to controls near term. BET disrupted the normal distribution of BNCs within the placentome. These data may suggest a placental role in growth restrictive effects of prenatal maternal BET exposure through alterations in placental output of oPL, a key metabolic hormone of pregnancy.