Coupling Osmotic Efficacy with Biocompatibility in Peritoneal Dialysis: A Stiff Challenge.

Peritoneal dialysis (PD) is a home-based efficacious modality for the replacement of renal function in end-stage kidney failure patients, but it is still under-prescribed. A major limitation is the durability of the dialytic technique. Continuous exposure of the peritoneum to bioincompatible conventional glucose-based solutions is thought to be the main cause of the long-term morpho-functional peritoneal changes that eventually result in ultrafiltration failure. Poor PD solution biocompatibility is primarily related to the high glucose content, which is not only detrimental to the peritoneal membrane but has many potential metabolic side effects. To improve the clinical outcome and prolong the survival of the treatment, PD-related bioincompatibility urgently needs to be overcome. However, combining dialytic and osmotic efficacy with a satisfactory biocompatible profile is proving to be quite difficult. New approaches targeting the composition of the PD solution include the replacement of glucose with other osmotic agents, and the addition of cytoprotective or osmo-metabolic compounds. Other strategies include the infusion of mesenchymal cells or the administration of orally active agents. In the present article, we review the current evidence on efforts to improve the biocompatible and functional performance of PD, focusing on studies performed in vivo (animal models of PD, human subjects on PD).

The risks associated with percutaneous native kidney biopsies: a prospective study.

BACKGROUND: The known risks and benefits of native kidney biopsies are mainly based on the findings of retrospective studies. The aim of this multicentre prospective study was to evaluate the safety of percutaneous renal biopsies and quantify biopsy-related complication rates in Italy. METHODS: The study examined the results of native kidney biopsies performed in 54 Italian nephrology centres between 2012 and 2020. The primary outcome was the rate of major complications 1 day after the procedure, or for longer if it was necessary to evaluate the evolution of a complication. Centre and patient risk predictors were analysed using multivariate logistic regression. RESULTS: Analysis of 5304 biopsies of patients with a median age of 53.2 years revealed 400 major complication events in 273 patients (5.1%): the most frequent was a ≥2 g/dL decrease in haemoglobin levels (2.2%), followed by macrohaematuria (1.2%), blood transfusion (1.1%), gross haematoma (0.9%), artero-venous fistula (0.7%), invasive intervention (0.5%), pain (0.5%), symptomatic hypotension (0.3%), a rapid increase in serum creatinine levels (0.1%) and death (0.02%). The risk factors for major complications were higher plasma creatinine levels [odds ratio (OR) 1.12 for each mg/dL increase, 95% confidence interval (95% CI) 1.08-1.17], liver disease (OR 2.27, 95% CI 1.21-4.25) and a higher number of needle passes (OR for each pass 1.22, 95% CI 1.07-1.39), whereas higher proteinuria levels (OR for each g/day increase 0.95, 95% CI 0.92-0.99) were protective. CONCLUSIONS: This is the first multicentre prospective study showing that percutaneous native kidney biopsies are associated with a 5% risk of a major post-biopsy complication. Predictors of increased risk include higher plasma creatinine levels, liver disease and a higher number of needle passes.

Biomarker-Development Proteomics in Kidney Transplantation: An Updated Review.

Kidney transplantation (KT) is the optimal therapeutic strategy for patients with end-stage renal disease. The key to post-transplantation management is careful surveillance of allograft function. Kidney injury may occur from several different causes that require different patient management approaches. However, routine clinical monitoring has several limitations and detects alterations only at a later stage of graft damage. Accurate new noninvasive biomarker molecules are clearly needed for continuous monitoring after KT in the hope that early diagnosis of allograft dysfunction will lead to an improvement in the clinical outcome. The advent of "omics sciences", and in particular of proteomic technologies, has revolutionized medical research. Proteomic technologies allow us to achieve the identification, quantification, and functional characterization of proteins/peptides in biological samples such as urine or blood through supervised or targeted analysis. Many studies have investigated proteomic techniques as potential molecular markers discriminating among or predicting allograft outcomes. Proteomic studies in KT have explored the whole transplant process: donor, organ procurement, preservation, and posttransplant surgery. The current article reviews the most recent findings on proteomic studies in the setting of renal transplantation in order to better understand the effective potential of this new diagnostic approach.

Fibrosis of Peritoneal Membrane as Target of New Therapies in Peritoneal Dialysis.

Peritoneal dialysis (PD) is an efficient renal replacement therapy for patients with end-stage renal disease. Even if it ensures an outcome equivalent to hemodialysis and a better quality of life, in the long-term, PD is associated with the development of peritoneal fibrosis and the consequents patient morbidity and PD technique failure. This unfavorable effect is mostly due to the bio-incompatibility of PD solution (mainly based on high glucose concentration). In the present review, we described the mechanisms and the signaling pathway that governs peritoneal fibrosis, epithelial to mesenchymal transition of mesothelial cells, and angiogenesis. Lastly, we summarize the present and future strategies for developing more biocompatible PD solutions.

Mild sodium reduction in peritoneal dialysis solution improves hypertension in end stage kidney disease: a case-report study.

INTRODUCTION: Blood Pressure (BP) control is largely unsatisfied in End Stage Kidney Disease (ESKD) principally due to sodium retention. Peritoneal Dialysis (PD) is the most common type of home dialysis, using a peritoneal membrane to remove sodium, though sodium removal remains challenging. METHODS: This is a case-study reporting two consecutive ESKD patients treated by a novel peritoneal PD solution with a mildly reduced sodium content (130 mmol/L) to treat hypertension. RESULTS: In the first case, a 78-year-old woman treated by Continuous Ambulatory PD (CAPD) with standard solution (three 4 h-dwells per day 1.36% glucose 132 mmol/L) showed resistant hypertension confirmed by ambulatory blood pressure monitoring (ABPM), reporting 24 h-BP: 152/81 mmHg, day-BP:151/83 mmHg and night-ABP: 153/75 mmHg, with inversion of the circadian systolic BP rhythm (1.01), despite use of three anti-hypertensives and a diuretic at adequate doses. No sign of hypervolemia was evident. We then switched from standard PD to low-sodium solution in all daily dwells. A six-months low-sodium CAPD enabled us to reduce diurnal (134/75 mmHg) and nocturnal BP (122/67 mmHg), restoring the circadian BP rhythm, with no change in ultrafiltration or residual diuresis. Diet and drug prescription were unmodified too. The second case was a 61-year-old woman in standard CAPD (three 5 h-dwells per day) suffering from hypertension confirmed by ABPM (mean 24 h-ABP: 139/84 mmHg; mean day-ABP:144/88 mmHg and mean night-ABP:124/70 mmHg). She was switched from 132-Na CAPD to 130-Na CAPD, not changing dialysis schedule. No fluid expansion was evident. During low-sodium CAPD, antihypertensive therapy (amlodipine 10 mg and Olmesartan 20 mg) has been reduced until complete suspension. After 6 months, we repeated ABPM showing a substantial reduction in mean 24 h-ABP (117/69 mmHg), mean diurnal ABP (119/75 mmHg) and mean nocturnal ABP (111/70 mmHg). Ultrafiltration and residual diuresis remained unmodified. No side effects were reported in either cases. CONCLUSIONS: This case-report study suggests that mild low-sodium CAPD might reduce BP in hypertensive ESKD patients.

How to Improve the Biocompatibility of Peritoneal Dialysis Solutions (without Jeopardizing the Patient's Health).

Peritoneal dialysis (PD) is an important, if underprescribed, modality for the treatment of patients with end-stage kidney disease. Among the barriers to its wider use are the deleterious effects of currently commercially available glucose-based PD solutions on the morphological integrity and function of the peritoneal membrane due to fibrosis. This is primarily driven by hyperglycaemia due to its effects, through multiple cytokine and transcription factor signalling-and their metabolic sequelae-on the synthesis of collagen and other extracellular membrane components. In this review, we outline these interactions and explore how novel PD solution formulations are aimed at utilizing this knowledge to minimise the complications associated with fibrosis, while maintaining adequate rates of ultrafiltration across the peritoneal membrane and preservation of patient urinary volumes. We discuss the development of a new generation of reduced-glucose PD solutions that employ a variety of osmotically active constituents and highlight the biochemical rationale underlying optimization of oxidative metabolism within the peritoneal membrane. They are aimed at achieving optimal clinical outcomes and improving the whole-body metabolic profile of patients, particularly those who are glucose-intolerant, insulin-resistant, or diabetic, and for whom daily exposure to high doses of glucose is contraindicated.

Predialysis and Dialysis Therapies Differently Affect Nitric Oxide Synthetic Pathway in Red Blood Cells from Uremic Patients: Focus on Peritoneal Dialysis.

Red blood cells (RBCs) have been found to synthesize and release both nitric oxide (NO) and cyclic guanosine monophosphate (cGMP), contributing to systemic NO bioavailability. These RBC functions resulted impaired in chronic kidney disease (CKD). This study aimed to evaluate whether predialysis (conservative therapy, CT) and dialysis (peritoneal dialysis, PD; hemodialysis, HD) therapies used during CKD progression may differently affect NO-synthetic pathway in RBCs. Our data demonstrated that compared to PD, although endothelial-NO-synthase activation was similarly increased, HD and CT were associated to cGMP RBCs accumulation, caused by reduced activity of cGMP membrane transporter (MRP4). In parallel, plasma cGMP levels were increased by both CT and HD and they significantly decreased after hemodialysis, suggesting that this might be caused by reduced cGMP renal clearance. As conceivable, compared to healthy subjects, plasma nitrite levels were significantly reduced by HD and CT but not in patients on PD. Additionally, the increased carotid intima-media thickness (IMT) values did not reach the significance exclusively in patients on PD. Therefore, our results show that PD might better preserve the synthetic NO-pathway in CKD-erythrocytes. Whether this translates into a reduced development of uremic vascular complications requires further investigation.

Nephrotoxicity Associated with Novel Anticancer Agents (Aflibercept, Dasatinib, Nivolumab): Case Series and Nephrological Considerations.

Cancer patients have an incidence of about 60% kidney disease development and are at elevated risk of acute renal damage. Kidney disease in these patients is frequently associated with nephrotoxicity from the ongoing oncological treatment. New anticancer therapeutic strategies, such as targeted therapies and immunotherapies, offer substantial benefits in the treatment of many neoplasms. However, their use is associated with significant nephrotoxicity, which qualitatively differs from that seen with traditional cytotoxic chemotherapy, while the underlying mechanisms are complex and still to be clearly defined. Nephrologists need to be knowledgeable about the array of such renal toxicities for effective collaboration with the oncologist in the prevention and management of kidney involvement. Renal adverse effects may range from asymptomatic proteinuria to renal failure, and their prompt identification and timely treatment is essential for optimal and safe care of the patient. In this article, after presenting clinical cases we discuss the differing renal toxicity of three novel anticancer agents (aflibercept, dasatinib, and nivolumab) and possible measures to counter it.

Proteomic Research in Peritoneal Dialysis.

Peritoneal dialysis (PD) is an established home care, cost-effective renal replacement therapy (RRT), which offers several advantages over the most used dialysis modality, hemodialysis. Despite its potential benefits, however, PD is an under-prescribed method of treating uremic patients. Infectious complications (primarily peritonitis) and bio-incompatibility of PD solutions are the main contributors to PD drop-out, due to their potential for altering the functional and anatomical integrity of the peritoneal membrane. To improve the clinical outcome of PD, there is a need for biomarkers to identify patients at risk of PD-related complications and to guide personalized interventions. Several recent studies have shown that proteomic investigation may be a powerful tool in the prediction, early diagnosis, prognostic assessment, and therapeutic monitoring of patients on PD. Indeed, analysis of the proteome present in PD effluent has uncovered several proteins involved in inflammation and pro-fibrotic insult, in encapsulating peritoneal sclerosis, or even in detecting early changes before any measurable modifications occur in the traditional clinical parameters used to evaluate PD efficacy. We here review the proteomic studies conducted thus far, addressing the potential use of such omics methodology in identifying potential new biomarkers of the peritoneal membrane welfare in relation to dialytic prescription and adequacy.

A Novel Formulation of Glucose-Sparing Peritoneal Dialysis Solutions with l-Carnitine Improves Biocompatibility on Human Mesothelial Cells.

The main reason why peritoneal dialysis (PD) still has limited use in the management of patients with end-stage renal disease (ESRD) lies in the fact that the currently used glucose-based PD solutions are not completely biocompatible and determine, over time, the degeneration of the peritoneal membrane (PM) and consequent loss of ultrafiltration (UF). Here we evaluated the biocompatibility of a novel formulation of dialytic solutions, in which a substantial amount of glucose is replaced by two osmometabolic agents, xylitol and l-carnitine. The effect of this novel formulation on cell viability, the integrity of the mesothelial barrier and secretion of pro-inflammatory cytokines was evaluated on human mesothelial cells grown on cell culture inserts and exposed to the PD solution only at the apical side, mimicking the condition of a PD dwell. The results were compared to those obtained after exposure to a panel of dialytic solutions commonly used in clinical practice. We report here compelling evidence that this novel formulation shows better performance in terms of higher cell viability, better preservation of the integrity of the mesothelial layer and reduced release of pro-inflammatory cytokines. This new formulation could represent a step forward towards obtaining PD solutions with high biocompatibility.

Recovery Time after Hemodialysis Is Inversely Associated with the Ultrafiltration Rate.

INTRODUCTION: The present study aimed to determine the variables that are associated with a longer dialysis recovery time (DRT) and to define the relationship that exists between DRT and the ultrafiltration rate (UFR) in prevalent chronic hemodialysis (CHD) patients. METHODS: We studied 210 prevalent CHD of 5 hemodialysis units in Central Italy. Patients were invited to answer to the question: "How long does it take you to recover from a dialysis session?" Answers to this question were subsequently converted into minutes. Demographic, clinical and laboratory parameters were recorded for each patient as well as the UFR (mL/kg/h), the dialysate sodium concentration and temperature. RESULTS: Median DRT was 180 min (60-420). Ninety five (45%) patients had a DRT ≥ the median value. Mean UFR was 9.2 ± 3.0 mL/kg/h. Patients with a lower DRT had a less prevalent disability in the instrumental activities daily living, had a higher UFR, and a lower dialysate temperature, as compared with subjects with higher DRT. According to the logistic regression model, UFR was associated with a DRT below the median (i.e., 180) in the unadjusted model (OR 1.12; 95% CI 1.02-1.23; p = 0.019), after adjusting for age and sex (OR 1.11; 95% CI 1.01-1.22; p = 0.025), and in the fully adjusted model (OR 1.11; 95% CI 1.04-1.22; p = 0.040). UFR increase was associated with increasing probability of DRT below the median (p for trend = 0.035). The highest tertile of DRT was associated with UFR below the mean value (i.e., 9.2 mL/kg/h) in multinomial logistic regression having the lowest DRT tertile as reference. DRT was significantly lower in patients with UFR > 13 mL/kg/h than in patients with UFR 10-13 or < 10 mL/kg/h. CONCLUSION: DRT is inversely associated with UFR in CHD patients. Whether a high UFR should be recommended to reduce the DRT needs to be elucidated through an adequate prospective randomized study.

Urinary Peptidomic Biomarkers in Kidney Diseases.

In order to effectively develop personalized medicine for kidney diseases we urgently need to develop highly accurate biomarkers for use in the clinic, since current biomarkers of kidney damage (changes in serum creatinine and/or urine albumin excretion) apply to a later stage of disease, lack accuracy, and are not connected with molecular pathophysiology. Analysis of urine peptide content (urinary peptidomics) has emerged as one of the most attractive areas in disease biomarker discovery. Urinary peptidome analysis allows the detection of short and long-term physiological or pathological changes occurring within the kidney. Urinary peptidomics has been applied extensively for several years now in renal patients, and may greatly improve kidney disease management by supporting earlier and more accurate detection, prognostic assessment, and prediction of response to treatment. It also promises better understanding of kidney disease pathophysiology, and has been proposed as a "liquid biopsy" to discriminate various types of renal disorders. Furthermore, proteins being the major drug targets, peptidome analysis may allow one to evaluate the effects of therapies at the protein signaling pathway level. We here review the most recent findings on urinary peptidomics in the setting of the most common kidney diseases.

Current Opinion on Usage of L-Carnitine in End-Stage Renal Disease Patients on Peritoneal Dialysis.

The advantages of peritoneal dialysis (PD) over hemodialysis (HD) are well-documented. Notwithstanding, only a small proportion of patients with end-stage renal disease (ESRD) are managed with PD. This may be related to the high glucose load that PD solutions in current use have on the patient. The effects of such excess glucose include the relatively early limitation of the ultrafiltration capacity of the peritoneal membrane, and the metabolic effects associated with hyperglycemia, e.g., decreased insulin sensitivity. This article describes the advantages that may be realized by the glucose-sparing effects of substituting part of the glucose load with other osmotically active metabolites, particularly L-carnitine. The latter is anticipated to have metabolic advantages of its own, especially as in PD patients, high plasma concentrations can be achieved in the absence of renal clearance. Besides its better biocompatibility, L-carnitine demonstrates anti-anemia action due to its effects on erythropoiesis, and positive effects on the longevity and deformability of erythrocytes. Observations from our trials on the use of carnitine-enriched PD solutions have demonstrated the effectiveness of L-carnitine as an efficient osmolyte in PD, and its favorable effect on the insulin sensitivity of the patients. The significance of these findings for future developments in the use of PD in the management of patients with ESRD is discussed.

Prevalence and associated variables of post-dialysis fatigue: Results of a prospective multicentre study.

AIM: The study aims to determine prevalence and severity of PDF and to define its associated variables. METHODS: In five haemodialysis units of northern-centre Italy, patients were regarded to suffer from PDF if they spontaneously offered this complaint when asked the open-ended question: Do you feel better or worse after dialysis? If worse, please specify in which way. A complaint of fatigue would be probed further with questions directed at its duration, frequency and intensity, allowing creation of a fatigue index of severity (one third of the sum of these three parameters, each rated from 1 to 5). Patients were stratified into three groups according the severity of PDF: 1) score = 0; 2) score = 1-3; 3) score > 3. RESULTS: We studied 271 patients: 164 had PDF and 107 did not. PDF patients had significantly longer time of recovery after dialysis (TIRD). TIRD was significantly associated with PDF duration, intensity, and frequency. Patients with PDF were older and had a lower ADL score. At multivariate analysis, PDF was significantly associated with TIRD. In a multivariate model that did not include TIRD, PDF was independently associated with age and ADL. Sixty patients had moderate PDF and 104 had severe PDF. In patients with severe PDF, age and dialytic age were higher, ADL and IADL scores were lower, TIRD was longer and the ultrafiltration rate was lower. At multivariate analysis, PDF severity was independently associated with TIRD. In the model without TIRD, PDF severity was associated with ADL only. CONCLUSION: Post-dialysis fatigue is frequent and associated with age and ADL. Dialytic variables seem unrelated to PDF.

Acetylcholine and acetylcarnitine transport in peritoneum: Role of the SLC22A4 (OCTN1) transporter.

A suitable experimental tool based on proteoliposomes for assaying Organic Cation Transporter Novel member 1 (OCTN1) of peritoneum was pointed out. OCTN1, recently acknowledged as acetylcholine transporter, was immunodetected in rat peritoneum. Transport was assayed following flux of radiolabelled TEA, acetylcholine or acetylcarnitine in proteoliposomes reconstituted with peritoneum extract. OCTN1 mediated, besides TEA, also acetylcholine and a slower acetylcarnitine transport. External sodium inhibited acetylcholine uptake but not its release from proteoliposomes. Differently, sodium did not affect acetylcarnitine uptake. These results suggested that physiologically, acetylcholine should be released while acetylcarnitine was taken up by peritoneum cells. Transport was impaired by OCTN1 inhibitors, butyrobetaine, spermine, and choline. Biotin was also found as acetylcholine transport inhibitor. Anti-OCTN1 antibody specifically inhibited acetylcholine transport confirming the involvement of OCTN1. The transporter was also immunodetected in human mesothelial primary cells. Extract from these cells was reconstituted in proteoliposomes. Transport features very similar to those found with rat peritoneum were observed. Validation of the proteoliposome model for peritoneal transport study was then achieved assaying transport in intact mesothelial cells. TEA, butyrobetaine and Na(+) inhibited acetylcholine transport in intact cells while efflux was Na(+) insensitive. Therefore transport features in intact cells overlapped those found in proteoliposomes.

New Treatment Approaches for the Anemia of CKD.

Normocytic normochromic anemia is a common complication in chronic kidney disease and is associated with many adverse clinical consequences. Erythropoiesis-stimulating agents (ESAs) and adjuvant iron therapy represent the primary treatment for anemia in chronic kidney disease. The introduction of ESAs into clinical practice was a success story, mediating an increase in hemoglobin concentrations without the risk for recurrent blood transfusions and improving quality of life substantially. However, recombinant ESAs are still expensive and require a parenteral route of administration. Moreover, concern has arisen following randomized clinical trials showing that higher hemoglobin targets and/or high ESA doses may cause significant harm. This, together with changes in ESA reimbursement policy in some countries, has resulted in a significant reduction in ESA prescribing and the hemoglobin level targeted during therapy. Several attempts are being made to develop new drugs with improved characteristics and/or easier manufacturing processes compared with currently available ESAs, including new treatment approaches that may indirectly improve erythropoiesis. We give an update on the new investigational strategies for increasing erythropoiesis, examining in depth their characteristics and possible advantages in the clinical setting and the caveats to be aware of at the present stage of development.

Nitric oxide synthetic pathway and cGMP levels are altered in red blood cells from end-stage renal disease patients.

Red blood cells (RBCs) enzymatically produce nitric oxide (NO) by a functional RBC-nitric oxide synthase (RBC-NOS). NO is a vascular key regulatory molecule. In RBCs its generation is complex and influenced by several factors, including insulin, acetylcholine, and calcium. NO availability is reduced in end-stage renal disease (ESRD) and associated with endothelial dysfunction. We previously demonstrated that, through increased phosphatidylserine membrane exposure, ESRD-RBCs augmented their adhesion to human cultured endothelium, in which NO bioavailability decreased. Since RBC-NOS-dependent NO production in ESRD is unknown, this study aimed to investigate RBC-NOS levels/activation, NO production/bioavailability in RBCs from healthy control subjects (C, N = 18) and ESRD patients (N = 27). Although RBC-NOS expression was lower in ESRD-RBCs, NO, cyclic guanosine monophosphate (cGMP), RBC-NOS Serine1177 phosphorylation level and eNOS/Calmodulin (CaM)/Heat Shock Protein-90 (HSP90) interaction levels were higher in ESRD-RBCs, indicating increased enzyme activation. Conversely, following RBCs stimulation with insulin or ionomycin, NO and cGMP levels were significantly lower in ESRD- than in C-RBCs, suggesting that uremia might reduce the RBC-NOS response to further stimuli. Additionally, the activity of multidrug-resistance-associated protein-4 (MRP4; cGMP-membrane transporter) was significantly lower in ESRD-RBCs, suggesting a possible compromised efflux of cGMP across the ESRD-RBCs membrane. This study for the first time showed highest basal RBC-NOS activation in ESRD-RBCs, possibly to reduce the negative impact of decreased NOS expression. It is further conceivable that high NO production only partially affects cell function of ESRD-RBCs maybe because in vivo they are unable to respond to physiologic stimuli, such as calcium and/or insulin.

A Moderate Carnitine Deficiency Exacerbates Isoproterenol-Induced Myocardial Injury in Rats.

PURPOSE: The myocardium is largely dependent upon oxidation of fatty acids for the production of ATP. Cardiac contractile abnormalities and failure have been reported after acute emotional stress and there is evidence that catecholamines are responsible for acute stress-induced heart injury. We hypothesized that carnitine deficiency increases the risk of stress-induced heart injury. METHODS: Carnitine deficiency was induced in Wistar rats by adding 20 mmol/L of sodium pivalate to drinking water (P). Controls (C) received equimolar sodium bicarbonate and a third group (P + Cn) received pivalate along with 40 mmol/L carnitine. After 15 days, 6 rats/group were used to evaluate function of isolated hearts under infusion of 0.1 µM isoproterenol and 20 rats/group were submitted to a single subcutaneous administration of 50 mg/kg isoproterenol. RESULTS: Isoproterenol infusion in C markedly increased the heart rate, left ventricular (LV) systolic pressure and coronary flow rate. In P rats, isoproterenol increased the heart rate and LV systolic pressure but these increases were not paralleled by a rise in the coronary flow rate and LV diastolic pressure progressively increased. Subcutaneous isoproterenol induced 15 % mortality rate in C and 50 % in P (p < 0.05). Hearts of surviving P rats examined 15 days later appeared clearly dilated, presented a marked impairment of LV function and a greater increase in tumor necrosis factor α (TNFα) levels. All these detrimental effects were negligible in P + Cn rats. CONCLUSIONS: Our study suggests that carnitine deficiency exposes the heart to a greater risk of injury when sympathetic nerve activity is greatly stimulated, for example during emotional, mental or physical stress.