Calcitonin Receptor-like Receptor mRNA Research Articles

Intermedin in Paraventricular Nucleus Attenuates Sympathetic Activity and Blood Pressure via Nitric Oxide in Hypertensive Rats

Intermedin (IMD) is a member of calcitonin/calcitonin gene-related peptide family, which shares the receptor system consisting of calcitonin receptor-like receptor (CRLR) and receptor activity-modifying proteins (RAMPs). This study investigated the effects of IMD in paraventricular nucleus (PVN) on renal sympathetic nerve activity and mean arterial pressure and its downstream mechanism in hypertension. Rats were subjected to 2-kidney 1-clip (2K1C) surgery to induce renovascular hypertension or sham operation. Acute experiments were performed 4 weeks later under anesthesia. IMD mRNA and protein were downregulated in 2K1C rats. Bilateral PVN microinjection of IMD caused greater decreases in renal sympathetic nerve activity and mean arterial pressure in 2K1C rats than in sham-operated rats, which were prevented by pretreatment with adrenomedullin receptor antagonist AM22-52 or nonselective nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine methyl ester, and attenuated by selective neuronal NO synthase inhibitor N(ω)-propyl-l-arginine hydrochloride or endothelial NO synthase inhibitor N(5)-(1-iminoethyl)-l-ornithine dihydrochloride. AM22-52 increased renal sympathetic nerve activity and mean arterial pressure in 2K1C rats but not in sham-operated rats, whereas calcitonin/calcitonin gene-related peptide receptor antagonist calcitonin/calcitonin gene-related peptide 8-37 had no significant effect. CRLR and RAMP3 mRNA, as well as CRLR, RAMP2, and RAMP3 protein expressions, in the PVN were increased in 2K1C rats. Microinjection of IMD into the PVN increased the NO metabolites (NOx) level in the PVN in 2K1C rats, which was prevented by AM22-52. Chronic PVN infusion of IMD reduced, but AM22-52 increased, blood pressure in conscious 2K1C rats. These results indicate that IMD in the PVN inhibits sympathetic activity and attenuates hypertension in 2K1C rats, which are mediated by adrenomedullin receptors (CRLR/RAMP2 or CRLR/RAMP3) and its downstream NO.

RE: “The influence of RAMP1 overexpression on CGRP-induced osteogenic differentiation in MG-63 cells in vitro: An experimental study”

The aim of this study was to elucidate the influence of receptor activity modifying protein 1 (RAMP1) overexpression on the expression and distribution of calcitonin receptor-like receptor (CRLR) in MG-63 cells. Our research also focused on whether RAMP1 overexpression enhanced the promoting effect of exogenous CGRP on osteogenic differentiation in MG-63 cells. We first constructed a eukaryotic expression vector containing human RAMP1 and stably transfected it into MG-63 cells. Real-time PCR and Western blotting were used to determine the expression levels of RAMP1 and CRLR mRNA and protein, respectively. Immunofluorescence analysis was employed to compare the distribution of CRLR in transfected cells. After treatment with CGRP, the extent of osteogenic differentiation was evaluated by simultaneous monitoring of alkaline phosphatase activity, the expression patterns of osteoblastic markers and mineralisation staining. We found that RAMP1 was more highly expressed in the transfected group compared with the control groups (P < 0.01). The CRLR expression was significantly higher than that in the control groups (P < 0.05). In addition, after 7 days of CGRP treatment to induce osteogenic differentiation, the expression of collagen I mRNA was markedly increased in the transfected group (P < 0.05). The transfected group exhibited more granular precipitation in the cytoplasm with alkaline phosphatase staining after 7 and 14 days of differentiation. When stained with Alizarin Red, cells overexpressing RAMP1 were darker and formed many mineralised nodules with clear boundaries and calcium deposition typical of mineralised bone matrix structures at 28 days post-induction of differentiation. The CGRP-induced ALP activity in the RAMP1 overexpression group was significantly higher 3, 6 and 9 days after induction than that in the two control groups (P < 0.05). RAMP1 overexpression promotes CRLR expression, localisation on the cell membrane and enhanced CGRP-mediated differentiation of MG-63 cells. This study contributes to a better understanding of the molecular mechanisms governing CGRP-induced MG-63 differentiation.

Temporo-spatial expression of adrenomedullin and its receptors in the bovine placenta

BackgroundAdrenomedullin (AM) is a potent vasodilator peptide and is also involved in various physiological activities. In humans and rodents, AM is found in the uteroplacental unit and may be responsible for fetal development and maintenance of placental function. This study investigated 1) the mRNA expression patterns of AM and its receptor components (calcitonin receptor-like receptor (CRLR), receptor activity modifying protein (RAMP) 2 and RAMP3) during pregnancy and 2) mRNA and protein localization of AM, CRLR and RAMPs in the bovine placentome.MethodsFor real-time quantitative RT-PCR, bovine uteroplacental tissues were collected from Day 25, 60, 100, 150, 200 and 250 of gestation and separated into uterine caruncle (CAR), intercaruncular endometrium (ICAR), extra-embryonic membranes on Day 25 and cotyledonary villous after Day 60 (EEM-COT) and intercotyledonary chorion (ICOT). In situ hybridization and immunohistochemistry was performed to investigate the cellular localization of mRNA and protein of AM, CRLR, RAMP2 and RAMP3 in the placentome on Day 56, 150 and 230 of gestation and interplacentomal tissues on Day 56 of gestation.ResultsAM mRNA was highly expressed on Day 200 in EEM-COT, CAR and ICAR. CRLR mRNA was highly expressed on Day 60 in all portions. RAMP2 mRNA was also highly expressed on Day 60 in ICOT and ICAR. In EEM-COT, mRNA expression of CRLR and RAMP2 decreased from Day 150 to 250. RAMP3 mRNA was highly expressed on Day 150 in EEM-COT, ICOT and ICAR. A distinct AM mRNA and protein signal were only found in trophoblast binucleate cells (BNCs), whereas those of CRLR, RAMP2 and RAMP3 were detected in cotyledonary villous and caruncular epithelial cells. In interplacentomal tissues, AM was detected in BNCs of fetal membrane and a small part of luminal epithelium, endothelial lineage of blood vessels and glandular epithelium of the endometrium. Distinct signals of CRLR, RAMP2 and RAMP3 were found in trophoblast cells, luminal epithelium, stroma under the epithelium, endothelial lineage of blood vessels and glandular epithelium.ConclusionsOur results indicate that the AM system in the bovine uteroplacental unit may be activated at placentation and transition from the mid to late gestation period. Locally produced AM in the BNCs may play a crucial role in regulation of placental vascular and cellular functions during pregnancy.

The influence of RAMP1 overexpression on CGRP‐induced osteogenic differentiation in MG‐63 cells in vitro: An experimental study

The aim of this study was to elucidate the influence of receptor activity modifying protein 1 (RAMP1) overexpression on the expression and distribution of calcitonin receptor-like receptor (CRLR) in MG-63 cells. Our research also focused on whether RAMP1 overexpression enhanced the promoting effect of exogenous CGRP on osteogenic differentiation in MG-63 cells. We first constructed a eukaryotic expression vector containing human RAMP1 and stably transfected it into MG-63 cells. Real-time PCR and Western blotting were used to determine the expression levels of RAMP1 and CRLR mRNA and protein, respectively. Immunofluorescence analysis was employed to compare the distribution of CRLR in transfected cells. After treatment with CGRP, the extent of osteogenic differentiation was evaluated by simultaneous monitoring of alkaline phosphatase activity, the expression patterns of osteoblastic markers and mineralisation staining. We found that RAMP1 was more highly expressed in the transfected group compared with the control groups (P < 0.01). The CRLR expression was significantly higher than that in the control groups (P < 0.05). In addition, after 7 days of CGRP treatment to induce osteogenic differentiation, the expression of collagen I mRNA was markedly increased in the transfected group (P < 0.05). The transfected group exhibited more granular precipitation in the cytoplasm with alkaline phosphatase staining after 7 and 14 days of differentiation. When stained with Alizarin Red, cells overexpressing RAMP1 were darker and formed many mineralised nodules with clear boundaries and calcium deposition typical of mineralised bone matrix structures at 28 days post-induction of differentiation. The CGRP-induced ALP activity in the RAMP1 overexpression group was significantly higher 3, 6 and 9 days after induction than that in the two control groups (P < 0.05). RAMP1 overexpression promotes CRLR expression, localisation on the cell membrane and enhanced CGRP-mediated differentiation of MG-63 cells. This study contributes to a better understanding of the molecular mechanisms governing CGRP-induced MG-63 differentiation.

Cloning of two members of the calcitonin-family receptors from stingray, Dasyatis akajei: Possible physiological roles of the calcitonin family in osmoregulation

In cartilaginous fish, two cDNAs encoding calcitonin-family receptors were isolated for the first time from the stingray brain. The open reading frame of one receptor cDNA coded a 525-amino acid protein. The amino acid identity of this receptor to human calcitonin-receptor-like receptor (CRLR) is 64.5%, frog CRLR is 64.7%, and flounder CRLR is 61.2% and this was higher than to human calcitonin receptor (CTR) (46.1%), frog CTR (54.7%), and flounder CTR (48.9%). We strongly suggested that this receptor is a ray CRLR based on phylogenetic analysis. In case of the second receptor, amino acid identity among CRLRs (human 50.5%, frog 50.7%, flounder 48.0%) and CTRs (human 43.2%, frog 49.1%, flounder 41.8%) was similar. From phylogenetic analysis of both CRLRs and CTRs, we believe that this receptor is ray CTR. The expression of ray CRLR mRNA was predominantly detected in the nervous system (brain) and vascular system (atrium, ventricle, and gill), which reflects the similar localization of CGRP in the nervous and vascular systems as mammals. It was observed that the second receptor was expressed in several tissues, namely cartilage, brain, pituitary gland, gill, atrium, ventricle, pancreas, spleen, liver, gall bladder, intestine, rectal gland, kidney, testis and ovary. This localization pattern was very similar to flounder CTR. Both receptor mRNAs were strongly expressed in the gill. This suggests that the calcitonin-family members are involved in the osmoregulation of stingray as this fish is known to be euryhaline. When a stingray was transferred to diluted seawater (20% seawater), the expression of both receptors significantly decreased in the gill. Similar results were obtained in the kidney of the stingray. Thus, our cloning and isolation of both receptors in the stingray will be helpful for elucidation of their physiological role(s) such as osmoregulation including calcium metabolism of cartilaginous fish.

Adrenomedullin suppresses tumour necrosis factor alpha-induced CXC chemokine ligand 10 production by human gingival fibroblasts

Periodontal disease is an inflammatory disorder characterized by the involvement of chemokines that are important for the recruitment of leucocytes. Several cytokines, including tumour necrosis factor alpha (TNF-alpha), are involved in regulating levels of chemokines in periodontal disease. CXC chemokine ligand 10 (CXCL10) is a chemokine related to the migration of T helper 1 cells. In this study, we examined CXCL10 expression in human gingival fibroblasts (HGFs). Moreover, we investigated the effects of adrenomedullin (AM), which is a multi-functional regulatory peptide, on the production of CXCL10 by HGFs. We revealed that TNF-alpha stimulation induced CXCL10 production by HGFs. HGFs expressed AM and AM receptors, calcitonin-receptor-like receptor (CRLR) and receptor-activity-modifying protein (RAMP) 2, mRNAs constitutively. AM treatment supressed CXCL10 production by TNF-alpha-stimulated HGFs. Moreover, we elucidated that AM produced by HGFs inhibited CXCL10 production by HGFs, because AM antagonist enhanced CXCL10 production by HGFs. TNF-alpha treatment enhanced CRLR and RAMP2 mRNA expression in HGFs. Furthermore, AM is expressed in human periodontal tissues, including both inflamed and clinically healthy tissues. These results suggest that the CXCL10 produced by HGFs may be involved in the migration of leucocytes into inflamed tissues and related to exacerbation of periodontal disease. AM might be a therapeutic target of periodontal disease, because AM can inhibit CXCL10 production by HGFs.

Up-regulation of adrenomedullin receptor gene expression in activated local stem cells during rat adrenal regeneration

Previous studies showed that adrenomedullin (AM) gene expression was up-regulated in the regenerating rat adrenal cortex after enucleation and contra-lateral adrenalectomy, the effect being significant at day 1 after surgery and peaking between days 3 and 7. Using the same experimental model, we investigated by real time-polymerase chain reaction the mRNA expression of the AM receptor components: calcitonin receptor-like receptor (CRLR) and receptor activity-modifying proteins (RAMP)2 and 3. At time 0 (60 min after enucleation; control group), the CRLR mRNA content was approximately 2- and 5-fold higher than that of RAMP2 and RAMP3, respectively. No significant changes in CRLR mRNA expression were observed in relation to the time elapsed from enucleation. RAMP2 and RAMP3 mRNAs did not exhibit significant changes at day 1 after surgery, but underwent a marked increase between days 3 and 7. The mRNA content of the two RAMPs decreased at days 14 and 28, although remaining significantly higher than that of the controls. These findings indicate that the AM receptor subtypes AM1-R (CRLR-RAMP2) and AM2-R (CRLR-RAMP3) are up-regulated in enucleated adrenals, and the hypothesis is advanced that this effect depends on the increased local production of AM. The concerted increase in AM and its receptor expression would greatly improve the autocrine-paracrine mechanism(s) by which AM favors proliferation of zona glomerulosa stem cells during adrenal regeneration.

Expression of adrenomedullin in human epicardial adipose tissue: role of coronary status

Epicardial white adipose tissue (eWAT) is in close contact with coronary vessels and therefore could alter coronary homeostasis. Adrenomedullin (AM) is a potent vasodilatator and antioxidative peptide which has been shown to play a cytoprotective role in experimental models of acute myocardial infarction. We studied, using immunohistochemistry and qRT-PCR, the expression of AM and its receptors calcitonin receptor-like receptor (CRLR), and receptor activity-modifying protein (RAMP)2 and -3 in paired biopsies of subcutaneous WAT (sWAT) and eWAT obtained from patients with coronary artery disease (CAD) or without CAD (NCAD). In eWAT obtained from NCAD or CAD patients, immunoreactivity for AM, CRLR, and RAMP2 and -3 was detected in blood vessel walls and isolated stromal cells close to adipocytes. Some of the AM positive stromal cells colocalized CD68 immunoreactivity. eWAT from CAD patients showed increased AM immunoreactivity and AM gene expression. CRLR mRNA levels were comparable in sWAT of both groups and decreased by 40-50% in eWAT, irrespectively of the coronary status. RAMP2 mRNA concentrations did not change while RAMP3 mRNA levels increased in sWAT from CAD patients. There was a positive linear relationship between eWAT 11beta-hydroxysteroid dehydrogenase type 1 mRNA (11beta-HSD-1, the enzyme that converts inactive to active glucocorticoids) and AM mRNA. In conclusion, we demonstrate that AM and its receptors are expressed in eWAT. Our data suggest that eWAT AM, which could originate from macrophages, is related to 11beta-HSD-1 expression. AM synthesis, which is increased in eWAT during chronic CAD in humans, can play a cardioprotective role.

Adrenomedullin and its receptor components in adipose tissues: Differences between white and brown fats and the effects of adrenergic stimulation

Male Sprague–Dawley rats were subcutaneously injected with 2.5 mg/kg phenylephrine or 2.5 mg/kg isoproterenol or both (2.5 mg/kg for each drug) for 4 days, twice a day. Samples of scapular brown adipose tissue (BAT) and epididymal white adipose tissue (WAT) were collected for the measurement of adrenomedullin (AM) levels and the gene expression of preproAM, calcitonin receptor like receptor (CRLR) and its activity modifying proteins (RAMPs) by radioimmunoassay and RT-PCR. These values were compared with those in the rats that received 0.9% saline. The gene expression of AM and AM receptor components in BAT are much less than that in epididymal WAT. In BAT there were an increase in AM peptide level after a combined treatment of α 1 and β adrenoceptor agonists and increases in preproAM mRNA levels for rats treated with α 1 and β receptor agonists alone or in combination. Both CRLR and RAMP2 mRNA levels of αβ group were increased significantly. In WAT, AM peptide level, RAMP1 and RAMP2 mRNA expression levels were augmented in the α group while CRLR mRNA level was enhanced in the β group. The levels of AM, its receptor and RAMPs are much less in BAT than in WAT but adrenergic stimulation has a greater effect on the AM and its receptor components in BAT than those in WAT. AM stimulates lipolysis and increases the level of uncoupling protein-1 (UCP-1) in BAT. It may therefore enhance thermogenesis by increasing the availability of free fatty acids substrate as well as the UCP-1 level on the mitochondrial membrane.

Progesterone upregulates calcitonin gene-related peptide and adrenomedullin receptor components and cyclic adenosine 3'5'-monophosphate generation in Eker rat uterine smooth muscle cell line.

Calcitonin gene-related peptide (CGRP) and adrenomedullin (AM), two potent smooth-muscle relaxants, have been shown to cause uterine relaxation. Both CGRP- and AM-binding sites in the uterus increase during pregnancy and decrease at labor and postpartum. These changes in binding sites appear to be related to the changes in calcitonin receptor-like receptor (CRLR), receptor activity-modified protein 1 (RAMP1), RAMP2, and RAMP3 mRNA levels. It is not clear, however, whether the changes in the receptor components occur in the myometrial cells and whether the steroid hormones can directly alter these receptor components in the muscle cells. In addition, the mechanism of CGRP and AM signaling in the rat myometrium is not well understood. Therefore, we examined the mRNA expression of CGRP- and AM-receptor components, G protein Galphas, CGRP, and AM stimulation of cAMP and cGMP, and the effects of progesterone on these parameters in the Eker rat uterine myometrial smooth-muscle cell line (ELT3). ELT3 cells expressed CGRP- and AM-receptor components CRLR, RAMP1, RAMP2, and RAMP3. Expression of CRLR and RAMP1 mRNA increased with progesterone treatment and decreased with estradiol-17beta treatment. However, RAMP2 and RAMP3 mRNA expressions were unaltered by both progesterone and estradiol. Progesterone increased (P<0.05) Galphas expression and augmented CGRP- and AM-induced increases in cAMP levels. In uterine smooth-muscle cells, the antagonist to Galphas protein NF449 decreased basal as well as CGRP- and AM-stimulated cAMP levels. None of the cell treatments affected cyclic GMP production. Our results suggest that the progesterone-stimulated increases in CGRP and AM receptors, Galphas protein levels, and cAMP generation in the myometrial cells may be responsible for increased uterine relaxation sensitivity to CGRP and AM during pregnancy.

Differential gene expression of adrenomedullin receptors in pressure- and volume-overloaded heart—role of angiotensin II

Left ventricular (LV) adrenomedullin (AM) gene expression differs between pressure overload (POL) and volume overload (VOL) and angiotensin II could be a critical stimulator of AM gene expression in POL and VOL models. Calcitonin receptor-like receptor (CRLR) co-expressed with receptor activity modifying protein 2 (RAMP2) or RAMP3 functions as an AM receptor. Levels of CRLR, RAMP2 and RAMP3 mRNA that were significantly increased within 24 h returned to the basal level at 5 days after the imposition of POL in the present study. In contrast, mRNA levels of CRLR and RAMP2 gradually increased over 6 weeks after the imposition of VOL. Continuous infusion of angiotensin II stimulated LV AM gene and AM receptor gene expression independently of LV peak-systolic and LV end-diastolic pressure. The gene expression of LV AM receptors increased in different types of cardiac overload. The present study revealed an intimate association between the AM signaling system and angiotensin II.

Alterations of adrenomedullin and its receptor system components in calcified vascular smooth muscle cells

Vascular calcification is a common finding in many cardiovascular diseases. Paracrine/autocrine changes in calcified vessels, and the secreted factors participate in and play an important role in the progress of calcification. Adrenomedullin (ADM) is a potent vasodilator peptide secreted by vascular smooth muscle cells (VSMCs) and vascular endothelial cells. Recently, receptor activity-modifying proteins (RAMPs) have been shown to transport calcitonin receptor-like receptor (CRLR) to the cell surface to present either as CGRP receptor or ADM receptor. In this work, we explored the production of ADM, alterations and significance of ADM mRNA and its receptor system components—CRLR and RAMPs mRNA in calcified VSMCs. Our results showed that calcium content, 45Ca 2+ uptake and alkaline phosphatases (ALPs) activity in calcified VSMCs were increased, respectively, compared with control VSMCs. Content of ADM in medium was increased by 99% ( p<0.01). Furthermore, it was found that the levels of ADM, CRLR, RAMP2 and RAMP3 mRNA in calcified cells were elevated, respectively, compared with that of control. The elevated levels of CRLR, RAMP2 and RAMP3 mRNA were significant correlation with ADM mRNA ( r=0.83, 0.92 and 0.93, respectively, all p's<0.01) in calcified VSMCs. The results show that calcified VSMCs generate an increased amount of ADM, up-regulate gene expressions of ADM and its receptor system components—CRLR, RAMP2 and RAMP3, suggesting an important role of ADM and its receptor system in the regulation of vascular calcification.

The role of adrenomedullin and its receptor system in cardiovascular calcification of rat induced by Vitamin D 3 plus nicotine

Adrenomedullin (ADM) is a potent vasodilatory peptide which regulates blood pressure, cell growth and bone formation. Our work was aimed to explore the production of ADM, changes and pathophysiological significance of ADM mRNA and ADM receptor components—calcitonin receptor like receptor (CRLR) and receptor activity modifying proteins (RAMPs) mRNA in calcified myocardium and aorta of rats induced by Vitamin D 3 plus nicotine. Contents of ADM in plasma, myocardium and aorta were measured by radioimmunoassay (RIA). The amount of ADM, CRLR and RAMPs mRNA was determined by semi-quantitative RT-PCR. The calcium content and alkaline phosphatase activity in myocardium and aorta of rats were measured. The results showed that the contents of calcium in calcified myocardium and aorta were increased by 3.5- and 6-fold (all P<0.01), respectively, and alkaline phosphatases activity in calcified myocardium and aorta were increased by 66.5 and 82.7% (all P<0.01), respectively, compared with control. Contents of ADM in plasma, myocardium and aorta were increased by 58% ( P<0.01), 14.3% ( P<0.01) and 27.8% ( P<0.05). Furthermore, it was found that the amount of ADM, CRLR and RAMP2 mRNA in calcified myocardium was elevated by 90.6, 157.5 and 119.6% (all P<0.01), RAMP3 mRNA was decreased by 14.1% ( P<0.01), respectively, compared with control. The amount of ADM, CRLR, RAMP2 and RAMP3 mRNA in calcified aorta was elevated by 37.7% ( P<0.01), 41.4% ( P<0.01), 60.1% ( P<0.05) and 13% ( P<0.01), respectively, compared with control. The elevated level of CRLR and RAMP2 mRNA were in positive correlation with that of ADM mRNA ( r=0.992 and 0.882, respectively, P<0.01) in calcified myocardium. The elevated level of CRLR and RAMP3 mRNA were also in positive correlation with that of ADM mRNA ( r=0.727, P<0.05 and 0.816, P<0.01, respectively) in calcified aorta. These results demonstrated that calcified myocardium and aorta generated an increased amount of ADM, up-regulated gene expressions of ADM, CRLR and RAMP2 mRNA. While the alteration of RAMP3 mRNA in calcified myocardium and aorta was different. These suggested that ADM and its receptor system might involve in the regulation of calcification in heart and aorta.

Female sex steroid hormones and pregnancy regulate receptors for calcitonin gene-related peptide in rat mesenteric arteries, but not in aorta.

Calcitonin gene-related peptide (CGRP) is a potent vasodilator neuropeptide known to be involved in the regulation of vascular tone. Results of previous studies from our laboratory and others suggest that vascular sensitivity to CGRP is enhanced during pregnancy and that the female sex steroid hormones estradiol-17beta (E2) and progesterone (P4) may be involved in this process. We hypothesized that CGRP receptors in the mesenteric artery are increased during pregnancy and with sex steroid hormone treatments. In the present study, we investigated whether pregnancy and female sex steroid hormones modulate the CGRP-receptors CGRP-A and CGRP-B in the mesenteric artery in the rat. The CGRP-A receptor consists of calcitonin receptor-like receptor (CRLR) and receptor activity-modifying protein 1 (RAMP1); however, the CGRP-B receptor needs to be further characterized. Messenger RNA levels for CRLR and RAMP1 were assessed by reverse transcription-polymerase chain reaction, and CGRP-B receptor proteins levels were determined by Western blot analysis. In addition, [125I]CGRP binding was measured by Scatchard analysis. Both mRNA for CGRP-A (CRLR and RAMP1) and the protein for CGRP-B receptors in mesenteric arteries were increased with pregnancy compared to nonpregnant, diestrous animals. A P4 antagonist, RU-486, downregulated and P4 upregulated these receptors in mesenteric arteries (P < 0.05) in pregnant rats. In adult ovariectomized rats, P4 upregulated CRLR and RAMP1 mRNA levels as well as [125I]CGRP-binding sites. The CGRP-B-receptor protein levels were significantly (P < 0.05) elevated by P4 and by combined E2 and P4 treatment. Together with earlier findings, these data suggest that increases in the expression of CGRP-A (CRLR and RAMP1) and CGRP-B receptors in mesenteric arteries may be important in reducing vascular resistance and in vascular adaptations that occur during pregnancy; in addition, P4 may be involved in this process.

Receptor activity modifying protein 2 distribution in the rat central nervous system and regulation by changes in blood pressure.

The neuropeptide, adrenomedullin, acts in the central nervous system (CNS) to regulate blood pressure, at least partly through an adrenomedullin receptor which is composed of receptor activity modifying protein 2 (RAMP-2) and calcitonin receptor-like receptor (CRLR). We used in situ hybridization to localize RAMP-2 mRNA throughout the brain, and we performed reverse transcription-polymerase chain reaction to detect CRLR mRNA in the brain. We found that RAMP-2 mRNA is expressed in numerous areas, including autonomic nuclei such as the paraventricular, supraoptic, arcuate and ventromedial nuclei, as well as the nucleus of the solitary tract (NTS), area postrema and dorsal motor nucleus of the vagus. Many regions expressing RAMP-2 mRNA also express low levels of CRLR mRNA. We examined changes in the mRNA expression of RAMP-2 and preproadrenomedullin in the brain in response to blood pressure manipulations. Rats received intravenous infusions of nitroprusside or phenylephrine to decrease or increase blood pressure, respectively. Decreased blood pressure elicited an increase in RAMP-2 mRNA expression in the NTS and a decrease in preproadrenomedullin mRNA expression in the paraventricular nucleus (PVN). Increased blood pressure elicited a decrease in RAMP-2 mRNA expression in the PVN and NTS. The CNS distribution and modulation of adrenomedullin signalling components by changes in blood pressure provide anatomical and physiological evidence for a homeostatic role for adrenomedullin in the brain.

Differential expression of adrenomedullin and its receptors in newborn and adult rat thymus

Adrenomedullin (ADM) is a hypotensive peptide, which derives from the proteolytic cleavage of pro(p)ADM and acts via two main subtypes of receptors, referred to as L1-receptor (L1-R) and calcitonin-receptor-like receptor (CRLR). While L1-R is selective for ADM, CRLR may bind either calcitonin gene-related peptide (CGRP) or ADM depending on the expression of the subtype 1 or the subtypes 2 and 3 of a family of chaperones, named receptor-activity-modifying proteins (RAMPs). There is evidence that ADM, in addition to regulating blood pressure and water and electrolyte balance, may be also involved during embryogenesis in the growth and differentiation of organs and tissues, especially of those where strong mesenchymal-epithelial interactions take place. Thymus is a linfo-epithelial organ, which undergoes a very rapid prenatal and postnatal growth, playing a pivotal role in the development of immunological defense. Hence, it appeared worthwhile to investigate the expression of ADM system in the newborn (3-day-old) rat thymus as compared to adult (3-month-old) animals. Reverse transcription (RT)-polymerase chain reaction (PCR) allowed the detection of the specific mRNAs of pADM and peptidyl-glycine alpha-amidating monooxigenase (PAM), the enzyme which converts immature ADM to the mature peptide, in both newborn and adult rat thymuses. PAM expression was markedly higher in newborn animals, which accords well with the more elevated concentrations of ADM measured by RIA in newborn than adult rat thymuses. L1-R, CRLR, RAMP1 and RAMP2 mRNA were detected in both groups of rats, and with the exception of RAMP1, the expression was markedly higher in newborn than adult rat thymus. RAMP3 mRNA was present only in the thymus of newborn animals. Collectively, the present findings indicate that ADM system is up-regulated in newborn rat thymus, thereby making it likely that ADM may be involved in the thymus growth and in the development of immunological defense mechanisms.

Localization of calcitonin gene-related peptide receptors in rat gastric mucosa

The location of calcitonin gene-related peptide (CGRP) receptors in the rat stomach has not been elucidated. It was recently reported that the CGRP receptor is formed when a calcitonin-receptor-like receptor (CRLR) and receptor activity modifying protein (RAMP) 1 are co-expressed on the cell membrane. The aim of this study was to determine the location and the role of CGRP receptors in the rat gastric mucosa. Gene expressions of CRLR and RAMP1 were investigated by Northern blot analysis, reverse transcription-polymerase chain reaction (RT-PCR), and in situ hybridization. Immunohistochemical stainings for CGRP, somatostatin, gastrin, and chromogranin A were performed. Gastric endocrine cells were collected by counterflow-elutriation and their responses to CGRP were studied. CRLR and RAMP1 mRNA was expressed mainly in small gastric epithelial cells in the pyloric glands. The mRNA expression had a similar distribution to that of D cells. In cultured gastric endocrine cells, CGRP enhanced somatostatin production, while it inhibited the secretion of histamine and gastrin. Our results suggest that CGRP receptors are expressed in D cells in the rat gastric mucosa and control production and secretion of somatostatin.

Regulation and function of the CGRP receptor complex in human granulopoiesis.

Anatomic studies and animal experiments suggest that neuropeptides such as calcitonin gene-related peptide (CGRP) may be involved in hematopoiesis. Here, we examined the regulation and function of the CGRP receptor in human granulopoiesis. Expression of CGRP receptor components on CD34(+) cells, peripheral blood granulocytes, and in vitro differentiated CD34(+) cells was analyzed at the mRNA level and by measuring the signaling capacity of the receptor. The function of CGRP in human hematopoiesis was investigated by clonal colony formation assays. mRNA transcripts for the cell surface CGRP receptor subunits receptor activity-modifying protein-1 (RAMP-1) and calcitonin receptor-like receptor (CRLR) as well as for the intracellular adapter protein CGRP-receptor component protein (CGRP-RCP) were found in CD34(+) cells from 4/4 donors tested. CGRP-RCP mRNA was expressed in peripheral blood granulocytes of 8/15 donors, whereas RAMP-1 and CRLR were not detectable. CD34(+) cells, but not granulocytes, exhibited a marked elevation of cellular cAMP after CGRP stimulation, thereby confirming the mRNA expression data. Both RAMP-1 and CRLR mRNA expression and CGRP receptor signaling capacity were lost during in vitro granulocytic differentiation of CD34(+) cells. Consistent with a role of CGRP in hematopoiesis, we show that CGRP significantly enhances the formation of granulomonocytic, but not erythroid or mixed, colonies by purified human CD34(+) cells. The CGRP receptor is expressed on CD34(+) hematopoietic progenitor cells and is downregulated during granulocytic differentiation. CGRP directly acts on CD34(+) cells to promote formation of granulomonocytic colonies. Thus, CGRP may have a function in directing hematopoiesis.

Cessation of pulmonary and coronary secretion of adrenomedullin peptides in the progression of human heart failure.

In human heart failure (CHF), adrenomedullin (AM) counteracts vasoconstriction and sodium retention. We investigated circulating levels of proadrenomedullin N-20 peptide (PAMP) and AM, and left ventricular expression of preproAM and calcitonin receptor-like receptor (CRLR) mRNA. Peptide levels were determined from the left ventricle, pulmonary artery, coronary sinus, and antecubital vein in patients demonstrating severe CHF (n = 12; mean +/- SEM cardiac index, 1.9 +/- 0.2 l/min/m(2); pulmonary wedge pressure, 32 +/- 1 mmHg), moderate CHF (n = 11; cardiac index, 2.9 +/- 0.2; pulmonary wedge pressure, 14 +/- 2), and in controls (n = 11). Left ventricular mRNA was quantified using RT-PCR and Southern blot hybridization. Depending on sites of measurement, PAMP and AM in severe CHF were 1.3 - 2.0 and 1.2 - 1.9 times as high as in moderate CHF, and 3.8 - 4.6 and 2.3 - 2.8 times as high as in controls. Only patients with moderate CHF demonstrated pulmonary and coronary net release of both peptides, that is, significant step-ups in concentrations between the pulmonary artery, left ventricle, and coronary sinus. In failing ventricles, preproAM mRNA increased 2.9 times above control, but CRLR mRNA was unchanged. Altogether, the heart and the lungs release AM peptides in moderate CHF. This secretion breaks down in severe CHF: a process that may contribute to and indicate decompensation. Unlike AM, the CRLR is not transcriptionally upregulated in severe CHF.

Expression and distribution of calcitonin receptor-like receptor in human hairy skin

Calcitonin gene-related peptide and adrenomedullin exert potent effects in skin but their cellular targets are unknown. This study aimed to identify the cellular location of calcitonin receptor-like receptor (CRLR) which is pharmacolocically identical to CGRP receptor-1, a putative molecular target of CGRP and adrenomedullin. RT-PCR analysis of human hairy skin revealed the presence of CRLR mRNA and immunohistochemical analysis, employing a previously characterized polyclonal antibody raised to CRLR, provided novel evidence of the cellular distribution of CRLR. Extensive and specific CRLR-immunostaining was detected in arteriolar smooth muscle and venular endothelium and is consistent with CGRP’s putative role in neurogenic inflammation. Novel targets for CGRP and/or adrenomedullin were identified, including capillary endothelium, hair follicles and sweat glands.