Secretion and clearance of the mature form of adrenomedullin in humans.

In the biosynthesis of adrenomedullin (AM), glycine-extended AM, an intermediate form (iAM) processed from proAM is converted to AM[1-52]-NH2, the bioactive mature form of AM (mAM), by enzymatic amidation. We earlier showed that both molecular forms of AM circulate in human plasma. In the present study, to investigate the secretion and clearance sites of mAM and iAM in humans, we examined the plasma mAM and iAM concentrations in the femoral artery and vein (FA and FV), the aortic root and coronary sinus (AO and CS), and the pulmonary artery and capillary (PA and PC) of patients with ischemic heart disease. Plasma mAM in FV was significantly (p<0.001) higher than in FA. There also was a significant (p<0.001) step-up in the plasma mAM of the CS as compared to the AO. In contrast, plasma mAM was significantly (p<0.001) reduced in the PC as compared to the PA. However, such differences were not observed in plasma iAM levels. These findings suggest that in humans the vasculature of the lower extremities and the heart produce and secrete mAM and that the lung is a clearance site of circulating mAM.     

The role of endogenous lung neuropeptides in regulation of the pulmonary circulation

Vascular resistance in the mammalian pulmonary circulation is affected by many endogenous agents that influence vascular smooth muscle, right ventricular myocardium, endothelial function, collagen and elastin deposition, and fluid balance. When the balance of these agents is disturbed, e.g. by airway hypoxia from high altitude or pulmonary obstructive disorders, pulmonary hypertension ensues, as characterized by elevated pulmonary artery pressure (P(PA)). Among neuropeptides with local pulmonary artery pressor effects are endothelin-1 (ET-1), angiotensin II (AII), and substance P, and among mitigating peptides are calcitonin gene-related peptide (CGRP), adrenomedullin (ADM), atrial natriuretic peptide (ANP), vasoactive intestinal peptide (VIP) and ET-3. Moreover, somatostatin28 (SOM28) exacerbates, whereas SOM14 decreases P(PA) in hypoxic rats, with lowering and increasing of lung CGRP levels, respectively. Pressure can also be modulated by increasing or decreasing plasma volume (VIP and ANP, respectively), or by induction or suppression of vascular tissue remodeling (ET-1 and CGRP, respectively). Peptide bioavailability and potency can be regulated through hypoxic up- and down- regulation of synthesis or release, activation by converting enzymes (ACE for AII and ECE for ET-1), inactivation by neutral endopeptidase and proteases, or by interaction with nitric oxide (NO). Moreover, altered receptor density and affinity can account for changed peptide efficacy. For example, upregulation of ET(A) receptors and ET-1 synthesis occurs in the hypoxic lung concomitantly with reduced CGRP release. Also, receptor activity modifying protein 2 (RAMP2) has been shown to confer ADM affinity to the pulmonary calcitonin-receptor-like receptor (CRLR). We recently detected the mRNA encoding for RAMP2, CRLR, and the CGRP receptor RDC-1 in rat lung. The search for an effective, lung selective treatment of pulmonary hypertension will likely benefit from exploring the imbalance and restoring the balance between these native modulators of intrapulmonary pressure. For example, blocking of the ET-1 receptor ET(A) and vasodilation by supplemental CGRP delivered i. v. or via airway gene transfer, have proven to be useful experimentally.     

Increased plasma levels of the mature and intermediate forms of adrenomedullin in obesity

Adrenomedullin (AM) is a cardiovascular protective peptide produced in various organs and tissues including adipose tissue. In the present study, we measured the plasma AM levels of subjects with or without obesity by two assay methods to separately evaluate the biologically active AM–NH₂ and the intermediate form of AM–glycine (AM–Gly). We measured the total AM and AM–NH₂ levels of plasma in 52 obese and 172 non-obese residents of a Japanese community, who received regular health check-ups and had no overt cardiovascular disease. AM–Gly values were obtained by subtracting AM–NH₂ levels from those of total AM. Both the AM–NH₂ and AM–Gly levels of the subjects with obesity were higher than those without obesity, and significant relationships were noted between body mass index (BMI) and the plasma levels of the two molecular forms of AM in a simple regression analysis. Moreover, the significant factors identified by multivariate analyses were BMI and serum triglyceride for AM–NH₂ and diastolic blood pressure, insulin, high-density lipoprotein-cholesterol, and plasma renin activity for AM–Gly. These results suggest active roles for the two molecular forms of AM in metabolic disorders associated with obesity in subjects without overt cardiovascular disease.     

Possible role of prolactin in growth regulation

To study the possible role of prolactin on growth regulation pituitary grafted rats of different ages and their sham-operated controls have been used. After the transplant operation of one pituitary gland from a litter-mate donor on day 5 or on day 30 of life, a marked prolactin increase has been observed. This increase has been immediate in 30 day-old rats and delayed in 5 day-old rats in which the elevation starts being significant on day 20 for females and on day 25 for male rats. Pituitary grafting on day 5 of life, with an adult donor gland, resulted in an immediate and marked increase of prolactin values in both sexes. Litter-mate donor pituitary grafting, on day 5 of life, resulted in an increase in body weight that could be directly correlated with the increase in prolactin levels. Adult pituitary grafting resulted in an increased body weight in females with no effects being detected in males. In 30 day-old grafted male and female rats, marked body weight increases were seen, over the whole studied period, together with an increase in nose-tail length (1 cm in female and 1.5 cm in males longer than the control animals). All these changes do not seem not be related to GH modifications in pituitary grafted rats, since GH changes were very slight with a final tendency to lower values in female rats but not in males. All these data could suggest that prolactin might exert a direct effect on growth both in male and female rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Possible role of endogenous morphine and codeine on growth regulation of lung tissue

The literature indicates that morphine can inhibit the growth of both small cell and non small cell lung cancer cell lines and that nicotine can reverse this inhibition. In this report we present data showing that mammalian lung tissue contain the opiate alkaloids morphine and codeine and that these alkaloids are also to be found in normal lung cell lines. However, analysis of both small cell and non small cell lung cancer cells indicate that they do not contain these opiate alkaloids endogenously. If morphine exerts an inhibitory effect on proliferation of these cells it is interesting that the lung cancer cell lines lack the opiate alkaloids endogenously. Our studies also present data indicating that the circulating levels of morphine and codeine are elevated in smokers as compared to non smokers which we hypothesize to reflect the invocation of a compensatory mechanism.     

Exercise prescription for patients with a Fontan circulation: current evidence and future directions

It is well documented that children with a Fontan circulation have a reduced exercise capacity. One of the modalities to improve exercise capacity might be exercise training. We performed a systematic literature review on the effects of exercise training in patients with a Fontan circulation. Six published studies were included that reported on the effects of exercise training in 40 patients. All studies had a small sample size and/or did not include a control group. Based on the six published studies we can conclude that children who have undergone a Fontan operation and who are in a stable haemodynamic condition can safely participate in an exercise training programme and that exercise training results in an improved exercise capacity. However, more research is needed to establish the optimal exercise mode, dose-response relation, and the effects of exercise training on cardiac function, peripheral muscle function, physical activity, and health-related quality of life. (Neth Heart J 2007; 15:142-7.) Based on the six published studies we can conclude that children who have undergone a Fontan operation and who are in a stable haemodynamic condition can safely participate in an exercise training programme and that exercise training results in an improved exercise capacity. However, more research is needed to establish the optimal exercise mode, dose-response relation, and the effects of exercise training on cardiac function, peripheral muscle function, physical activity, and health-related quality of life. (Neth Heart J 2007; 15:142-7.)     

Possible role of prostaglandins in the regulation of mouse myoblasts

A differentiation-defective mouse myoblast subclone (DD-1), cells of which do not fuse into myotubes nor synthesize muscle-specific proteins, was employed to help define the role of eicosanoids in mouse myoblast differentiation. We observed by hplc, tlc, and radioimmunoassay that the DD-1 cells release strikingly higher levels of cyclooxygenase pathway products prostaglandin E2 and F2 alpha into the culture medium than the parental non-differentiation-defective cells (DZ). In contrast, the levels of 15-hydroxyeicosatetraenoic acid (15-HETE), a lipoxygenase product, and a putatively identified second lipoxygenase product (LLP) did not differ greatly in the two cell types. The DD-1 cells also have strikingly higher levels of cyclooxygenase activity than the parental cells as determined by intact and broken cell assays. Additional fusion-defective clones were isolated on the basis of their flattened appearance and ability to grow in "mitogen-poor" medium and these cells also released strikingly higher levels of prostaglandins E2 and F2 alpha into the growth medium. The "turn on" of the cyclooxygenase pathway in the DD-1 cells and other fusion-defective cells is consistent with the hypothesis that the products of this pathway contribute to the inability of myoblasts to fuse with one another. This hypothesis is supported by the observation that there is a dose-dependent decrease in fusion of DZ cells when PGE2 is added to commitment medium.     

Novel regulation of adrenomedullin receptor by PDGF: role of receptor activity modifying protein-3

Receptor activity modifying protein-3(RAMP-3) has been shown to complex with the calcitonin receptor-likereceptor, establishing a functional receptor for adrenomedullin (AM).AM exhibits potent antiproliferative and antimigratory effects on ratmesangial cells (RMCs). In this study we investigated the effect ofplatelet-derived growth factor (PDGF) on RAMP-3 expression in RMCs. Weshow here that PDGF-BB stimulates RAMP-3 mRNA expression in aconcentration-dependent manner. Pretreatment with actinomycin-D and-amanitin demonstrates that this effect is independent of new RNAsynthesis. Furthermore, PDGF increased the half-life of RAMP-3 mRNAfrom 66.5 to 331.6 min. Using selective inhibitors, our results alsoindicate that the increase in RAMP-3 mRNA is mitogen-activated proteinkinase (MAPK) kinase (MEK)/MAPK and p38 MAPK dependent. PDGF alsocaused a corresponding elevation in membrane-associated RAMP-3 protein. Associated with this increase, PDGF pretreatment led to a significantly higher AM-mediated adenylate cyclase activity, suggesting a functional consequence for the PDGF-induced increase in RAMP-3 expression. Takentogether, these data identify PDGF-dependent regulation of RAMP-3expression as a possible mechanism for modulating the responsiveness ofthe mesangial cell to AM.

     

Possible regulation of the growth of thyroid tissue by plasma iodide

Rats on iodine deficient diet for 6 months received propylthiouracil (PTU) (0.15%) during the last 2 months. At the end of this treatment, PTU was withdrawn and the rats were iodine refed. 48 hrs. before the iodine refeeding all rats were injected with 3H thymidine. The results showed that some prelabelled cells in the hyperplastic goitre preferentially disappeared during its involution and therefore are more sensitive to iodine.     

Structure-activity relationships of adrenomedullin in the circulation and adrenal gland

Adrenomedullin (ADM) is a recently discovered vasoactive peptide that has potent vasodilator activity in the pulmonary and peripheral vascular beds and has significant effects on endocrine function. ADM is a member of the CGRP/amylin superfamily of peptides based largely on the presence of the six-membered ring structure and C-terminal amidation that is highly conserved in this family. Proadrenomedullin is a 185 amino acid precursor with enzymatic cleavage sites for both ADM and a unique 20 amino acid peptide named proadrenomedullin N-terminal 20 peptide (PAMP). ADM and PAMP are found in a variety of organ systems, and plasma levels of the peptides are increased in pathophysiologic conditions. Both peptides have hypotensive and vasodilator activity in the pulmonary and regional vascular beds and have significant effects on the endocrine system, including the adrenal gland. ADM (15-52), which retains the six-membered ring structure, maintains the vasodilator activity of ADM, suggesting that the 14 amino acid N-terminal extension is not necessary for the full agonist activity. However, analogs, such as ADM-(22-52) and ADM-(40-52), which do not contain the six-member ring structure, lack agonist activity. Unlike the full-sequence peptide, hADM-(15-22) and ADM-(16-21), which contain the ring structure, increase systemic arterial pressure in the rat but not in the cat. The present review discusses the structure-activity relationship for the actions of ADM and related peptides and discusses the mechanisms which mediate responses to these widely distributed peptides.     

The role of the leukocytes in the blood-vasal regulation of the blood circulation

The ability of N-formyl-methionyl-leucyl-phenylalanine-activated leukocytes to influence platelets and vessels was studied. It is shown, that of activation of leukocytes causes a vasoconstriction. The de-endothelialization of the vessels increased this effect. In addition, activated leukocytes increased the platelet aggregation. It was concluded, that activation of leukocytes can trigger thrombogenesis, angiospasm, microembolic syndrome and other disturbances of blood circulation.     

Recovery of atrial transport function after a maze procedure for atrial fibrillation in conversion of a failing Fontan circulation

Surgical ablation for atrial arrhythmias at conversion of atriopulmonary or ventriculopulmonary Fontan to a total cavopulmonary connection is feasible with recovery of both sinus rhythm and atrial transport function. Recovery of the patient’s physical condition may take up to a year. (Neth Heart J 2008;16:170-2.)     

The role of the mature part of secretory proteins in translocation across the plasma membrane and in regulation of their synthesis in Escherichia coli

Presently available data are reviewed which concern the role of the mature parts of secretory precursor proteins in translocation across the plasma membrane of Escherichia coli. The following conclusions can be drawn; i) signals, acting in a positive fashion and required for translocation do not appear to exist in the mature polypeptides; ii) a number of features have been identified which either affect the efficiency of translocation or cause export incompatibility. These are: alpha) protein folding prior to translocation; beta) restrictions regarding the structure of N-terminus; gamma) presence of lipophilic anchors; delta) too low a size of the precursor. Efficiency of translocation is also enhanced by binding of chaperonins (SecB, trigger factor, GroEL) to precursors. Binding sites for chaperonins appear to exist within the mature parts of the precursors but the nature of these sites has remained rather mysterious. Mutant periplasmic proteins with a block in release from the plasma membrane have been described, the mechanism of this block is not known. The mature parts of secretory proteins can also be involved in the regulation of their synthesis. It appears that exported proteins are already recognized as such before they are channelled into the export pathway and that their synthesis can be feed-back inhibited at the translational level.     

Up-regulated synthesis of mature-type adrenomedullin in coronary circulation immediately after reperfusion in patients with anterior acute myocardial infarction

OBJECTIVE: Levels of adrenomedullin (AM), a potent vasodilatory peptide, have been shown to increase in the early stage of acute myocardial infarction (AMI). The purpose of this study was to determine whether coronary sinus-aortic step-up of mature forms of AM is accelerated in patients with AMI after reperfusion. METHODS: The subjects were 29 consecutive patients with a first episode of anterior AMI and 10 normal controls. All patients with AMI underwent balloon reperfusion therapy within 24 h after symptom onset. Plasma levels of two molecular forms of AM (an active, mature form [AM-m] and an intermediate, inactive glycine-extended form [AM-Gly]) in the aorta and coronary sinus (CS) were measured by specific immunoradiometric assay after reperfusion. RESULTS: Plasma levels of AM-m and AM-Gly in the aorta and CS were higher in AMI patients than in controls. CS-aortic step-up of AM-m, which is an index of myocardial production of AM-m, was significantly greater in AMI patients than in controls (1.7 +/- 1.4 vs. 0.4 +/- 0.3 pmol/L, P < 0.01). However, there was no significant difference in CS-aortic step-up of AM-Gly (P = 0.30). AMI patients with left ventricular dysfunction (n = 10) had a significantly higher CS-aortic AM-m step-up than AMI patients without left ventricular dysfunction (n = 19). AM-m in the aorta and CS negatively correlated with the left ventricular ejection fraction (r = -0.50, r = -0.48, P < 0.01). CONCLUSIONS: Myocardial synthesis of AM-m is accelerated in patients with reperfused AMI, especially in patients with critical left ventricular dysfunction. Increased myocardial synthesis of active AM may protect against cardiac dysfunction, myocardial remodeling, or both after the onset of AMI.