The interplay of post-translational protein modifications in Arabidopsis leaves during photosynthesis induction

Diurnal dark to light transition causes profound physiological changes in plant metabolism. These changes require distinct modes of regulation as a unique feature of photosynthetic lifestyle. The activities of several key metabolic enzymes are regulated by light-dependent post-translational modifications (PTM) and have been studied at depth at the level of individual proteins. In contrast, a global picture of the light-dependent PTMome dynamics is lacking, leaving the response of a large proportion of cellular function undefined. Here, we investigated the light-dependent metabolome and proteome changes in Arabidopsis rosettes in a time resolved manner to dissect their kinetic interplay, focusing on phosphorylation, lysine acetylation, and cysteine-based redox switches. Of over 24 000 PTM sites that were detected, more than 1700 were changed during the transition from dark to light. While the first changes, as measured 5 min after onset of illumination, occurred mainly in the chloroplasts, PTM changes at proteins in other compartments coincided with the full activation of the Calvin-Benson cycle and the synthesis of sugars at later timepoints. Our data reveal connections between metabolism and PTM-based regulation throughout the cell. The comprehensive multiome profiling analysis provides unique insight into the extent by which photosynthesis reprograms global cell function and adds a powerful resource for the dissection of diverse cellular processes in the context of photosynthetic function.

Acetylation of conserved lysines fine-tunes mitochondrial malate dehydrogenase activity in land plants

Plants need to rapidly and flexibly adjust their metabolism to changes of their immediate environment. Since this necessity results from the sessile lifestyle of land plants, key mechanisms for orchestrating central metabolic acclimation are likely to have evolved early. Here, we explore the role of lysine acetylation as a post-translational modification to directly modulate metabolic function. We generated a lysine acetylome of the moss Physcomitrium patens and identified 638 lysine acetylation sites, mostly found in mitochondrial and plastidial proteins. A comparison with available angiosperm data pinpointed lysine acetylation as a conserved regulatory strategy in land plants. Focusing on mitochondrial central metabolism, we functionally analyzed acetylation of mitochondrial malate dehydrogenase (mMDH), which acts as a hub of plant metabolic flexibility. In P. patens mMDH1, we detected a single acetylated lysine located next to one of the four acetylation sites detected in Arabidopsis thaliana mMDH1. We assessed the kinetic behavior of recombinant A. thaliana and P. patens mMDH1 with site-specifically incorporated acetyl-lysines. Acetylation of A. thaliana mMDH1 at K169, K170, and K334 decreases its oxaloacetate reduction activity, while acetylation of P. patens mMDH1 at K172 increases this activity. We found modulation of the malate oxidation activity only in A. thaliana mMDH1, where acetylation of K334 strongly activated it. Comparative homology modeling of MDH proteins revealed that evolutionarily conserved lysines serve as hotspots of acetylation. Our combined analyses indicate lysine acetylation as a common strategy to fine-tune the activity of central metabolic enzymes with likely impact on plant acclimation capacity.

The functionality of plant mechanoproteins (forisomes) is dependent on the dual role of conserved cysteine residues

Forisomes are giant polyprotein complexes that undergo reversible conformational rearrangements from a spindle-like to a plug-like state in response to Ca²⁺ or changes in pH. They act as valves in the plant vasculature, and reproduce this function in vitro to regulate flow in microfluidic capillaries controlled by electro-titration. Heterologous expression in yeast or plants allows the large-scale production of tailor-made artificial forisomes for technical applications. Here we investigated the unexpected disintegration of artificial forisomes in response to Ca²⁺ following the deletion of the M1 motif in the MtSEO-F1 protein or the replacement of all four conserved cysteine residues therein. This phenomenon could be mimicked in wild-type forisomes under reducing conditions by adding a thiol alkylating agent. We propose a model in which reversible changes in forisome structure depend on cysteine residues with ambiguous redox states, allowing the formation of intermolecular disulfide bridges (confirmed by mass spectrometry) as well as noncovalent thiol interactions to connect forisome substructures in the dispersed state. This is facilitated by the projection of the M1 motif from the MtSEO-F1 protein as part of an extended loop. Our findings support the rational engineering of disintegrating forisomes to control the release of peptides or enzymes in microfluidic systems.

Mass Spectrometry-Based Quantitative Cysteine Redox Proteome Profiling of Isolated Mitochondria Using Differential iodoTMT Labeling

Mitochondria are central hubs of redox biochemistry in the cell. An important role of mitochondrial carbon metabolism is to oxidize respiratory substrates and to pass the electrons down the mitochondrial electron transport chain to reduce oxygen and to drive oxidative phosphorylation. During respiration, reactive oxygen species are produced as a side reaction, some of which in turn oxidize cysteine thiols in proteins. Hence, the redox status of cysteine-containing mitochondrial proteins has to be controlled by the mitochondrial glutathione and thioredoxin systems, which draw electrons from metabolically derived NADPH. The redox status of mitochondrial cysteines can undergo fast transitions depending on the metabolic status of the cell, as for instance at early seed germination. Here, we describe a state-of-the-art method to quantify redox state of protein cysteines in isolated Arabidopsis seedling mitochondria of controlled metabolic and respiratory state by MS²-based redox proteomics using the isobaric thiol labeling reagent Iodoacetyl Tandem Mass Tag™ (iodoTMT). The procedure is also applicable to isolated mitochondria of other plant and nonplant systems.

Two mitochondrial phosphatases, PP2c63 and Sal2, are required for posttranslational regulation of the TCA cycle in Arabidopsis

Protein phosphorylation is a well-established post-translational mechanism that regulates protein functions and metabolic pathways. It is known that several plant mitochondrial proteins are phosphorylated in a reversible manner. However, the identities of the protein kinases/phosphatases involved in this mechanism and their roles in the regulation of the tricarboxylic acid (TCA) cycle remain unclear. In this study, we isolated and characterized plants lacking two mitochondrially targeted phosphatases (Sal2 and PP2c63) along with pyruvate dehydrogenase kinase (PDK). Protein-protein interaction analysis, quantitative phosphoproteomics, and enzymatic analyses revealed that PDK specifically regulates pyruvate dehydrogenase complex (PDC), while PP2c63 nonspecifically regulates PDC. When recombinant PP2c63 and Sal2 proteins were added to mitochondria isolated from mutant plants, protein-protein interaction and enzymatic analyses showed that PP2c63 directly phosphorylates and modulates the activity of PDC, while Sal2 only indirectly affects TCA cycle enzymes. Characterization of steady-state metabolite levels and fluxes in the mutant lines further revealed that these phosphatases regulate flux through the TCA cycle, and that altered metabolism in the sal2 pp2c63 double mutant compromises plant growth. These results are discussed in the context of current models of the control of respiration in plants.

Single organelle function and organization as estimated from Arabidopsis mitochondrial proteomics

Mitochondria host vital cellular functions, including oxidative phosphorylation and co-factor biosynthesis, which are reflected in their proteome. At the cellular level plant mitochondria are organized into hundreds of discrete functional entities, which undergo dynamic fission and fusion. It is the individual organelle that operates in the living cell, yet biochemical and physiological assessments have exclusively focused on the characteristics of large populations of mitochondria. Here, we explore the protein composition of an individual average plant mitochondrion to deduce principles of functional and structural organisation. We perform proteomics on purified mitochondria from cultured heterotrophic Arabidopsis cells with intensity-based absolute quantification and scale the dataset to the single organelle based on criteria that are justified by experimental evidence and theoretical considerations. We estimate that a total of 1.4 million protein molecules make up a single Arabidopsis mitochondrion on average. Copy numbers of the individual proteins span five orders of magnitude, ranging from >40 000 for Voltage-Dependent Anion Channel 1 to sub-stoichiometric copy numbers, i.e. less than a single copy per single mitochondrion, for several pentatricopeptide repeat proteins that modify mitochondrial transcripts. For our analysis, we consider the physical and chemical constraints of the single organelle and discuss prominent features of mitochondrial architecture, protein biogenesis, oxidative phosphorylation, metabolism, antioxidant defence, genome maintenance, gene expression, and dynamics. While assessing the limitations of our considerations, we exemplify how our understanding of biochemical function and structural organization of plant mitochondria can be connected in order to obtain global and specific insights into how organelles work.

T-protein is present in large excess over the other proteins of the glycine cleavage system in leaves of Arabidopsis

T-protein is present in large excess over the other proteins of the glycine cleavage system in leaves of Arabidopsis and therefore, exerts little control over the photorespiratory pathway. T-protein is the aminomethyltransferase of the glycine cleavage multienzyme system (GCS), also known as the glycine decarboxylase complex, and essential for photorespiration and one-carbon metabolism. Here, we studied what effects varying levels of the GCS T-protein would have on GCS activity, the operation of the photorespiratory pathway, photosynthesis, and plant growth. To this end, we examined Arabidopsis thaliana T-protein overexpression lines with up to threefold higher amounts of leaf T-protein as well as one knockdown mutant with about 5% residual leaf T-protein and one knockout mutant. Overexpression did not alter photosynthetic CO₂ uptake and plant growth, and the knockout mutation was lethal even in the non-photorespiratory environment of air enriched to 1% CO₂. Unexpectedly in light of this very low T-protein content, however, the knockdown mutant was able to grow and propagate in normal air and displayed only some minor changes, such as a moderate glycine accumulation in combination with somewhat delayed growth. Neither overexpression nor the knockdown of T-protein altered the amounts of the other three GCS proteins, suggesting that the biosynthesis of the GCS proteins is not synchronized at this level. We also observed that the knockdown causes less T-protein mostly in leaf mesophyll cells, but not so much in the vasculature, and discuss this phenomenon in light of the dual involvement of the GCS and hence T-protein in plant metabolism. Collectively, this work shows that T-protein is present in large excess over the other proteins of the glycine cleavage system in leaves of Arabidopsis and therefore exerts little control over the photorespiratory pathway.

Beyond Histones: New Substrate Proteins of Lysine Deacetylases in Arabidopsis Nuclei

The reversible acetylation of lysine residues is catalyzed by the antagonistic action of lysine acetyltransferases and deacetylases, which can be considered as master regulators of their substrate proteins. Lysine deacetylases, historically referred to as histone deacetylases, have profound functions in regulating stress defenses and development in plants. Lysine acetylation of the N-terminal histone tails promotes gene transcription and decondensation of chromatin, rendering the DNA more accessible to the transcription machinery. In plants, the classical lysine deacetylases from the RPD3/HDA1-family have thus far mainly been studied in the context of their deacetylating activities on histones, and their versatility in molecular activities is still largely unexplored. Here we discuss the potential impact of lysine acetylation on the recently identified nuclear substrate proteins of lysine deacetylases from the Arabidopsis RPD3/HDA1-family. Among the deacetylase substrate proteins, many interesting candidates involved in nuclear protein import, transcriptional regulation, and chromatin remodeling have been identified. These candidate proteins represent key starting points for unraveling new molecular functions of the Arabidopsis lysine deacetylases. Site-directed engineering of lysine acetylation sites on these target proteins might even represent a new approach for optimizing plant growth under climate change conditions.

Radioimmunoassay of Endothelin in Human Plasma

A specific and sensitive radioimmunoassay (RIA) for determination of endothelin-1 (ET-1) in human plasma has been developed. Antibodies were raised in rabbits using synthetic ET-1 conjugated to thyroglobulin as immunogen. The antibodies obtained were used at a final dilution of 1:300,000 yielding maximum binding of 61.7 +/- 3.0% (mean +/- 1 SD, n = 20) of 125I-ET-1. The ID50 (inhibitory dose 50%) was 4.5 +/- 0.6 fmol/100 microliters (mean +/- 1 SD, n = 20). The sensitivity of the RIA was 0.33 fmol/100 microliters standard solution. No cross reactivity was observed with endothelin-3, big-endothelin-1, atrial natriuretic factor, angiotensin I or angiotensin II. The cross-reactivity with endothelin-2 was 100%. Endothelin was extracted from acidified plasma with Sep-pak C18 cartridges and recovery of ET-1 added to normal plasma was 70.9 +/- 10.3% (mean +/- 1 SD, n = 12). The concentration of ET-1 in plasma from normal subjects was 1.5 +/- 0.4 pmol/l (mean +/- 1 SD, n = 11) ranging from 1.0 to 2.2 pmol/1. Extracts of normal human plasma subjected to high performance liquid chromatography on a reverse phase C18 column showed one peak of immunoreactivity co-eluting with the standard for ET-1. From these data it is concluded that the immunoreactive material measured in normal plasma with the present RIA is identical to ET-1.

Converting enzyme inhibition in mild and moderate essential hypertension. I. Acute effects on blood pressure, the renin-angiotensin system and blood bradykinin after a single dose of captopril

The acute effects of 25 mg captopril on blood pressure, heart rate, components of the renin-angiotensin system and blood concentration of bradykinin were followed in a single-blind placebo study of untreated (group A, n = 15) and thiazide-treated (group B, n = 13) patients with mild or moderate essential hypertension. A drug-related fall in blood pressure was seen in both groups. The blood pressure reduction was more marked in group B than in group A. Heart rate remained unchanged. Plasma concentrations of angiotensin II decreased significantly with concurrent increases in plasma concentrations of renin and angiotensin I, indicating the in vivo inhibition of converting enzyme. Blood concentrations of bradykinin showed no systemic changes. The magnitude of blood pressure reduction was correlated both with the pretreatment levels and the concurrent decreases in plasma angiotensin II. Inhibition of angiotensin II formation can explain a large part of the acute hypotensive pharmacological action of captopril. Other vasoactive systems may be involved. The kallikrein-kinin system does not appear to participate as indicated by the unchanged concentrations of kinin in blood.

Simple screening procedure for the diagnosis of primary aldosteronism

A simple screening protocol for the diagnosis of primary aldosteronism was applied to 149 hypertensive patients. The diagnostic criterion for possible primary aldosteronism was the combination of supine plasma renin concentration less than 15 mIU/l (normal range 6-54) and plasma aldosterone concentration greater than 11 ng/100 ml (normal range 3-18). None of 63 persistently normokalaemic hypertensive patients fulfilled this criterion. Seventeen (20%) of 86 hypokalaemic patients showed hormonal values consistent with primary aldosteronism. The presence of an adrenal adenoma was verified in eight of these patients. Thus screening for primary aldosteronism can be restricted to hypokalaemic patients. The prevalence of primary aldosteronism in a hypertensive population was calculated to be less than 1%.

Localization of aldosterone-producing tumours in primary aldosteronism by adrenal and renal vein catheterization

Regional venous plasma aldosterone concentrations were determined and assessed against concurrent arterial levels in 16 patients with primary aldosteronism. The results obtained by sampling from the left adrenal vein or the left renal vein allowed correct side prediction of the presupposed adenoma in each patient. The problems caused by intermittent secretion of aldosterone by the tumour and the importance of correct positioning of the catheter are emphasized. Repeated sampling and continuing reference to systemic, arterial aldosterone levels proved valuable.

Converting enzyme inhibition in mild and moderate essential hypertension. II

In 24 patients with mild/moderate essential hypertension, we studied the effects of captopril with/without hydrochlorothiazide (Htz) on blood pressure, the renin-angiotensin system, blood bradykinin concentration (BBK), plasma volume, exchangeable sodium and glomerular filtration. Daily captopril doses of 75 and 150 mg were equally effective in reducing the blood pressure. Addition of Htz caused further blood pressure reductions. Nineteen patients attained a diastolic blood pressure less than or equal to 90 mmHg. Angiotensin converting enzyme inhibition with captopril led to a fall in plasma concentrations of angiotensin II (PAII) and renin substrate, and an increase in plasma concentrations of renin and angiotensin I. Patients starting with Htz had a higher PAII and subsequently a larger fall in blood pressure on captopril than untreated patients. BBK remained unchanged, indicating that the hypotensive action of captopril does not involve an accumulation of circulating kinin. Body fluid volumes and renal function were not affected by the various treatment regimens.

Generation and elimination of angiotensins I and II in the kidney, liver and lung

Inflow and outflow concentrations of angiotensins I (AI) and II (AII) from both kidneys, the liver and the lung were measured in 30 hypertensive patients, the majority having lateralization of the renin secretion. In the renin secreting kidney the data indicated a high generation rate of AI. In the contralateral kidney and splanchnic region both AI and AII were 'eliminated', and in the lungs the results confirmed previous evidence of converting enzyme activity.

A follow-up study of hypertensive patients after operative treatment of unilateral renovascular or renal disease

A study of 44 hypertensive patients with unilateral renovascular or renal parenchymal disease is presented. All patients underwent corrective surgery. Out of the 44 operated patients, five did not participate in the follow-up examination. The remaining 39 patients constitute the study population. The effects of surgery on the hypertensive state could be evaluated in 35 patients, whereas four died less than two months after the operation. Follow-up studies were carried out at 8-60 months after the operation. The average period of observation was 32 months; 24 patients were observed for more than two years. As a group, the patients had severe hypertension with extensive target organ damage and widespread atherosclerosis. A fairly rigorous selection process was applied, and an unsatisfactory response to medical management was considered a point of major importance. In the majority of cases, renovascular lesions were atherosclerotic, with only two cases of fibromuscular dysplasia. Unilateral nephrectomy was performed in 32 patients, whereas seven underwent reconstructive vascular surgery. Out of 35 patients, 22 (63%) were cured, 8 (23%) improved and 5 (14%) unaltered. A gratifying regression of hypertensive lesions in target organs was observed in patients who were cured or improved by surgery. The frequency and severity of postoperative complications were related to the presence of extrarenal vascular disease.

Multimodal assessment of dissociation in adolescents: inpatients and juvenile sex offenders

Two samples of adolescents were studied to assess the validity of several measures of dissociation. The first sample included 70 males from a residential treatment program for adolescent sex offenders (ASO). The second were 47 psychiatric inpatients. The measures included the DSM-IV field trial questionnaire for Dissociative Disorders of Childhood, Child Dissociative Checklist, Adolescent-Dissociative Experiences Schedule, Trauma Symptom Checklist for Children, and the Dissociation Research scale. Ten of the 70 adolescent sex offender subjects (14.3%) were identified as meeting DSM-IV criteria for a Dissociation-spectrum disorder diagnosis and two (4.2%) of the psychiatric patients. Between-groups analyses with the ASO revealed significant differences on the Child Dissociative Checklist and the Dissociation Research Scale. Cumulative trauma did not differ significantly between the dissociative and nondissociative groups of ASO, but physical abuse was related to a diagnosis of dissociation in this sample. The dissociation measures were highly intercorrelated for both groups, and suggest that they measure a similar construct.

Divergent cardiac response to exercise in essential hypertension vs. normotension and the effect of enalapril

The aims of this study were to examine (1) the cardiac response to exercise in essential hypertension and (2) the effect of long-term enalapril treatment on cardiac reserve. Ten normotensive control subjects and 15 patients with moderate, essential hypertension underwent radionuclide ventriculography during graded, supine exercise (0 W-50 W-100 W). The hypertensive patients were studied during monotherapy using hydrochlorothiazide and 3 and 12 months after supplementation with enalapril 10-40 mg o.d. During exercise, the control subjects demonstrated a 17% increase in left ventricular ejection fraction (LVEF) mediated by a 30% decrease in end-systolic volume, a small increase in stroke volume and a minor biphasic (increase-decrease) change in end-diastolic volume. In the hypertensive patients, both the end-diastolic and the end-systolic volume increased substantially with no increase in LVEF, although stroke volume increased by 33%. Long-term therapy with enalapril induced only a minor change towards a more normal pattern of cardiac response to exercise. The hypertensive patients increased their stroke volume during exercise by recruiting preload reserve instead of increasing contractility. Long-term treatment with enalapril had little, if any, effect on this abnormal cardiac response.

Nature of elevated blood pressure in normoalbuminuric type I diabetic patients. Essential hypertension?

This study was undertaken to characterize type I diabetic patients with essential hypertension with respect to kidney function, renal hormones, and endothelial function. After 4 weeks without antihypertensive treatment, a cross-sectional study was carried out in the following groups: group 1, 14 healthy controls; group 2, 13 nondiabetic patients with essential hypertension (blood pressure > or = 140/90 mm Hg); group 3, 11 type I diabetic patients with hypertension but urinary albumin excretion (UAE) persistently normal (UAE: 10 mg/24 h, range 3 to 18) both before, during, and after discontinuing antihypertensive treatment; group 4, 15 type I diabetic patients with clinical nephropathy (UAE: 611 mg/24 h, range 192 to 3837) and hypertension. Systolic and diastolic blood pressures were similar in the three hypertensive groups: 147/96 +/- 8/6, 150/94 +/- 11/9, and 152/92 +/- 12/6 mm Hg (groups 2, 3, and 4, respectively) but elevated compared with controls (114/74 +/- 9/9 mm Hg, P < .001). The diabetic patients with essential hypertension were hyperfiltering in contrast to patients with nephropathy (glomerular filtration rate 114 +/- 23 v 90 +/- 21 mL/min/173 m2, P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of onchocerciasis in selected river basins of four west African countries

Detailed epidemiological mapping of eight river basins was conducted in four West African countries as part of an effort to identify the communities at risk of onchocercal blindness to guide a programme of large scale ivermectin distribution, attempting control of eye disease. The results show a surprising variability of pattern in the geographical distribution of intensity of onchocerciasis infections in the communities of the river basins investigated. These patterns were at time very different from what was expected on the basis of the available entomological and demographic information. The technique of detailed mapping proved very useful in achieving an excellent coverage of the communities at risk of onchocercal blindness where, so far, satisfactory treatment coverage has been attained for four consecutive yearly treatments.

N-acetylcysteine inhibits angiotensin converting enzyme in vivo

Nitrate tolerance has been explained by 1) a direct loss of pharmacological effect due to reduced bioconversion and 2) an indirect effect due to activation of the renin/angiotensin system and counter-regulatory vasoconstriction. The sulfhydryl compound N-acetylcysteine (NAC) has been shown to attenuate and partly counteract tolerance to nitrates, and this effect has been attributed to a nitrate/sulfhydryl interaction and increased production of vasoactive intermediates. The effect of NAC on counter-regulatory mechanisms is, however, unknown. This study examined whether NAC modulates the function of the renin/angiotensin system in normal rats and in nitrate-tolerant healthy volunteers. Animal study: Conscious rats received NAC (5 mmol/kg/hr i.v., n = 8) or placebo (N-acetylserine, n = 8). Two hours of NAC infusion significantly reduced the pressor effect of angiotensin I (ANG I) by 39 +/- 14% (mean +/- SEM) and reduced angiotensin converting enzyme activity by 31% in plasma (N-acetylserine: 74 +/- 9 nmol/min/mg, NAC: 51 +/- 7) and 43% in kidney (N-acetylserine: 0.9 +/- 0.3, NAC: 0.5 +/- 0.1 nmol/min/mg protein) (P < .05). Clinical study: Isosorbide dinitrate (5 mg/hr) was infused into six male volunteers for 48 hr. NAC (2 g i.v. followed by 5 mg/kg/hr) was co-infused from 24 to 48 hr. Plasma angiotensin II (ANG II) increased during the first 24 hr of isosorbide dinitrate infusion and decreased from 28 +/- 4 to 14 +/- 2 ng/l after 2 hr of NAC infusion (P < .05). The results suggest that sulfhydryl supplementation modifies the function of the renin/angiotensin system in vivo, an effect probably mediated by inhibition of angiotensin converting enzyme activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial natriuretic peptide (ANP) decrease during normal pregnancy as related to hemodynamic changes and volume regulation

BACKGROUND

Volume regulation and hemodynamic functions change during pregnancy, leading to marked increases in blood volume and cardiac output, peripheral vasodilatation and reduced sensitivity to angiotensin. Atrial natriuretic peptide (ANP) is intimately involved in fluid and sodium homeostasis and exerts marked relaxant activity on vascular smooth muscle pre-contracted with angiotensin. This study was performed to clarify the role of ANP as a regulator of maternal physiology.

METHODS

40 normal primigravidae were examined five times during pregnancy plus 12 weeks after delivery. Each time were measured: ANP, aldosterone, renin, blood volume (carbon monoxide), cardiac output (Doppler), blood pressure and sodium excretion. Interdependence of the changes in ANP and in the other parameters was tested using Spearman's rank correlation test on the delta (delta)-values (the differences between investigations).

RESULTS

P-ANP in the 20th week was 11.4 (8.5-18.9) pmol.l-1 (median, 25 and 75 percentiles), the same as 12 weeks after delivery, 11.5 (9.6-15.2) pmol.l-1, and in a non-pregnant control group, 10.4 (9.0-12.5) pmol.l-1 (n = 20). All measurements of P-ANP during the 3rd trimester were lower than in the 20th week and 12 weeks after delivery, p < 0.0001 (Wilcoxon matched-pairs test). There was a negative correlation between changes in P-ANP and changes in: a) blood volume. R = 0.69, p < 0.0001, b) aldosterone, R = 0.58, p < 0.0001, c) renin, R = -0.54, p < 0.001, d) cardiac output, R = 0.61, p < 0.001. There was a positive correlation between changes in P-ANP and changes in: a) fractional excretion of sodium, R = 0.54, p < 0.0001, and b) total peripheral resistance. R = 0.52, p < 0.0001.

CONCLUSION

Decrease in p-ANP is one of the mechanisms whereby blood volume is increased and maintained during pregnancy. The competitive relationship between ANP and the renin aldosterone system in regulating sodium balance and fluid volume is preserved during pregnancy. The results substantiate the physiological importance of ANP as a regulator of blood volume. ANP does not function as a vasodilator during pregnancy.

Renal sites of action of physiological increases in plasma atrial natriuretic factor concentration in essential hypertension

OBJECTIVES

To investigate the renal, haemodynamic and neurohormonal responses to low-dose infusions of atrial natriuretic factor (ANF) in hypertensive humans.

DESIGN

Ten patients with mild-to-moderate essential hypertension received incremental infusions of 3 and 6 ng/kg per min ANF or vehicle alone whilst on a constant dietary sodium intake. A 90-min basal clearance period was followed by two 2-h infusion periods, with urine collection in the last 90 min of each period. In each of the three clearance periods, glomerular filtration rate (GFR), renal tubular function, and the activity of the renin-angiotensin and sympathetic nervous systems were determined.

METHODS

The renal sites of ANF action were established by simultaneous measurements of 51Cr-ethylenediaminetetraacetate lithium and sodium clearances. Plasma concentrations of neurohormones were measured by radioimmunoassays.

RESULTS

Plasma ANF concentrations increased by 1.6- and 2.5-fold during the lower and higher ANF infusion rates, respectively. Plasma cyclic guanosine monophosphate concentrations increased in parallel. ANF caused no changes in supine systolic and diastolic blood pressure or in heart rate. In contrast, haematocrit values increased progressively across the study. The renal effects of ANF administration were characterized by an unaltered GFR and significant increases in the renal clearances of lithium (a marker of end-proximal fluid delivery) and sodium when compared with vehicle infusions, whereas urine flow did not change. Estimated values of fractional proximal and distal tubular sodium reabsorption decreased significantly. Plasma concentration of active renin decreased during ANF infusions, but no significant changes in plasma levels of renin substrate, angiotensin I, angiotensin II or aldosterone were observed. A subtle activation of the sympathetic nervous system was indicated by a moderate increase in plasma noradrenaline during the ANF infusions.

CONCLUSIONS

These results indicate that even small increases in plasma ANF, as can be found during physiological conditions, induce natriuresis in patients with essential hypertension by enhancing fluid delivery from the proximal tubules, in addition to impairing distal fractional sodium reabsorption. With minor exceptions, the ANF infusions caused qualitatively and quantitatively similar renal, haemodynamic and endocrine effects in the hypertensive patients as in a previously studied group of normotensive subjects.

Effects of hyperglycaemia on kidney function, atrial natriuretic factor and plasma renin in patients with insulin-dependent diabetes mellitus

In normoalbuminuric patients with insulin-dependent diabetes mellitus, plasma atrial natriuretic factor (ANF), cyclic GMP and active renin and the renal clearances of [99Tcm]-diethylenetriaminepentaacetic acid (DTPA) lithium and sodium were studied on a hyperglycaemia day and a euglycaemia day. Baseline euglycaemia was achieved by an overnight variable insulin infusion, which during study days was fixed at the rate necessary to maintain euglycaemia in the morning. After a baseline euglycaemic clearance period of 90 min, measurements were repeated in a new 90-min period beginning 150 min later. On the hyperglycaemia day i.v. infusion of 20% glucose was started at the end of the euglycaemic baseline period, increasing blood glucose (5.3 +/- 1.3 vs 12.1 +/- 1.2 mmol l-1, p less than 0.01). On the euglycaemia day blood glucose declined (5.1 +/- 1.0 vs 4.2 +/- 1.0 mmol l-1, p less than 0.02). Glomerular filtration rate (GFR) was unchanged by acute hyperglycaemia (127 +/- 16 vs 129 +/- 24 ml min-1, NS), but nearly normalized during maintained euglycaemia on the euglycaemia day (124 +/- 17 vs 105 +/- 16 ml min-1, p less than 0.01). When comparing the hyperglycaemic study period with the similarly timed period on the euglycaemia day, GFR was elevated by hyperglycaemia (129 +/- 24 vs 105 +/- 16 ml min-1, p less than 0.01), while the renal clearances of lithium and sodium were similar. Consequently, the calculated absolute proximal reabsorption rate of sodium and water was elevated during hyperglycaemia. Hyperglycaemia reduced the slight decline in plasma concentrations of ANF and cyclic GMP observed on the euglycaemia day. Active renin, glucagon and plasma osmolality were unchanged. In conclusion, marked changes in glomerular filtration rate are induced by changes in blood glucose concentration, but the effect is delayed and thus not directly related to renal tubular transport of glucose. Hyperglycaemia does not affect renal clearances of lithium and sodium, while proximal tubular reabsorption is markedly stimulated. These changes are not related to changes in ANF, renin, glucagon or plasma osmolality.

Comparison of different standards used in radioimmunoassay for atrial natriuretic factor (ANF)

Six different standards for determination of atrial natriuretic factor (ANF) in human plasma samples have been compared using our radio-immunoassay for ANF: International standard 85/669, National Biological Standard Boards, UK; Bachem standard, Torrance, USA; Bachem standard, Bubendorf, Switzerland; Bissendorf standard, Wedemark, Germany; Peninsula standard, Belmont, USA; UCB-Bioproducts standard, Brussels, Belgium. Standard curves obtained with different preparations were in parallel but showed considerable quantitative differences. Standard curves referring to the Bissendorf standard and the International standard, respectively, were almost identical. The dose required for 50% of binding inhibition (ID50s) determined with the Peninsula, UCB and Swiss Bachem standards were higher and ID50 for the American Bachem standard was much lower than ID50 for the International standard. In consequence, estimates of the ANF content in human plasma samples with different standard preparations as the reference showed a considerable variability. With the international standard as the gold reference (plasma ANF concentration 100%) the apparent plasma ANF concentrations measured with the other reference preparations varied from 42% to 178%.

Efficacy of captopril in postponing nephropathy in normotensive insulin dependent diabetic patients with microalbuminuria

OBJECTIVE

To assess the effectiveness of angiotensin converting enzyme inhibition in preventing the development of diabetic nephropathy (albuminuria greater than 300 mg/24h).

DESIGN

Open randomised controlled study of four years' duration.

SETTING

Outpatient diabetic clinic in tertiary referral centre.

PATIENTS

44 normotensive (mean blood pressure 127/78 (SD 12/10) mm Hg) insulin dependent diabetic patients with persistent microalbuminuria (30-300 mg/24h).

INTERVENTIONS

The treatment group (n = 21) was initially given captopril (25 mg/24 h). The dose was increased to 100 mg/24 h during the first 16 months and thiazide was added after 30 months. The remaining 23 patients were left untreated.

MAIN OUTCOME MEASURES

Albuminuria, kidney function, development of diabetic nephropathy (albuminuria greater than 300 mg/24 h), and arterial blood pressure.

RESULTS

Clinical and laboratory variables were comparable at baseline. Urinary excretion of albumin was gradually reduced from 82 (66-106) to 57 (39-85) mg/24 h (geometric mean (95% confidence interval)) in the captopril treated group, whereas an increase from 105(77-153) to 166 (83-323) mg/24 h occurred in the control group (p less than 0.05). Seven of the untreated patients progressed to diabetic nephropathy, whereas none of the captopril treated patients developed clinical overt diabetic nephropathy (p less than 0.05). Systemic blood pressure, glomerular filtration rate, haemoglobin A1c concentration, and urinary excretion of sodium and urea remained practically unchanged in the two groups.

CONCLUSIONS

The findings suggest that angiotensin converting enzyme inhibition postpones the development of clinical overt diabetic nephropathy in normotensive insulin dependent diabetic patients with persistent microalbuminuria.

Effects of insulin on renal haemodynamics and sodium handling in normal subjects

Diabetic patients treated with insulin injected subcutaneously are characterized by peripheral hyperinsulinaemia and an increased mass of total body exchangeable sodium. We hypothesized that this may cause, at least in part, the glomerular hyperfiltration seen in the diabetic state. Six normal subjects were studied on 2 days in random order. Day A: Basal state for 40 min, hyperinsulinaemic euglycaemic clamp for 1 h (insulin infusion rate 2 mU kg-1 min-1 and 50% glucose infusion) and hyperinsulinaemic euglycaemic clamp combined with volume expansion (2 1 isotonic sodium chloride) for 2 h. Day B: as day A, but without insulin and glucose infusion. During combined volume expansion and hyperinsulinaemia an increase in glomerular filtration rate (GFR) (128 +/- 6 vs 117 +/- 8 ml min-1 1.73 m-2, p less than 0.01) and lithium clearance (CLi) (50 +/- 4 vs 33 +/- 5 ml min-1 1.73 m-2, p less than 0.01) was observed compared with basal conditions. GFR and CLi were unchanged during day B. Insulin infusion reduced renal sodium excretion. Absolute proximal tubular reabsorption was unchanged on both days. Insulin infusion without volume expansion caused a decrease of 24% in the fractional distal sodium excretion. Superimposed volume expansion and the concomitant increase in GFR and CLi was accompanied by a subsequent enhanced fractional distal sodium excretion of 27%. The changes in plasma concentrations of aldosterone, renin, angiotensin II, atrial natriuretic peptide and catecholamines did not explain the differences in GFR. An increase in GFR of 10%, comparable with that observed in diabetic patients, was induced by combined hyperinsulinaemia and volume expansion in euglycaemic normal subjects. The enhanced GFR is probably a compensatory response to the sodium retention induced by the action of insulin on the distal tubules.

Unchanged extraction of atrial natriuretic factor across the chronic ischemic human kidney

The extractions of atrial natriuretic factor (EANF) and the glomerular filtration marker 51Cr-ethylenediamine tetraacetic acid (EEDTA) were determined before and after intravenous injection of furosemide across each of the two kidneys during renal vein catheterization in hypertensive patients with unilateral or bilateral renovascular disease. Before administration of furosemide, EANF was approximately 55% across both the more and the less affected kidney while EEDTA was significantly decreased across the more affected kidney. Significant lateralization of renin secretion to the more affected kidney was found, demonstrating an enhanced ipsilateral formation of renin. Administration of furosemide caused a significant decrease in EEDTA across the less affected kidney while the ipsilateral EANF did not change. Furosemide caused no change in EEDTA or EANF across the more affected kidney. No significant correlations were found between EANF and EEDTA. These results demonstrate that the extraction of ANF is unchanged across the chronic ischemic human kidney. Furthermore, in the single kidney, changes in EEDTA, as induced by furosemide, are not related to changes in ipsilateral EANF. Since the relation between simultaneously determined single kidney extractions of ANF and 51Cr-EDTA reflects the relation between the single kidney clearance of ANF and the ipsilateral glomerular filtration rate, our data indicate a dissociation between changes in the single kidney glomerular filtration rate and the ipsilateral total renal clearance of ANF.

Renal and endocrine effects of physiological variations of atrial natriuretic factor in normal humans

The renal and endocrine effects of incremental infusions of 3 and 6 ng.kg-1.min-1 of exogenous atrial natriuretic factor (ANF)-(99-126) or placebo were investigated in 10 normal subjects. A 90-min basal period was followed by two 2-h infusion periods with urine collection in the last 90 min of each period. Plasma ANF concentration increased by 50 and 150%, respectively, from a basal value of 6.2 +/- 3.1 pmol/l. Plasma guanosine 3',5'-cyclic monophosphate concentration increased in parallel with ANF. Blood pressure and heart rate were unchanged, whereas hematocrit was stepwise increased. 51Cr-EDTA clearance (GFR) did not change, but ANF caused an increase in Li clearance (a measure of end-proximal fluid delivery), Na clearance, and urine flow compared with time-matched control values. These excretory effects of ANF were mainly due to prevention of the 20- to 50% decreases occurring in the placebo series. Calculated values of fractional proximal and distal tubular Na reabsorption decreased significantly. ANF caused a decrease in plasma concentrations of active renin and aldosterone, whereas renin substrate, angiotensin I, and angiotensin II concentrations were unaltered. A subtle increase in plasma concentrations of norepinephrine and epinephrine was observed during the ANF infusions. These data suggest that the natriuretic effect of ANF is caused by an increased fluid delivery from the proximal tubule in addition to a fall in fractional distal Na reabsorption.

Onchocerciasis distribution and severity in five West African countries

The Onchocerciasis Control Programme in West Africa recently extended its operation to Guinea, Guinea-Bissau, the western part of Mali, Senegal and Sierra Leone. To estimate the number of people infected and blinded by the disease and to determine its distribution and severity in the extension area, 215 villages were selected, using a stratified random sampling procedure, and surveyed. All the relevant entomological information available at the time was used in the sampling procedure and in the selection of 92 non-representative villages that were surveyed to confirm the findings. In addition, the populations of 608 villages were examined to map out in detail the distribution of onchocerciasis in the areas at a high risk of onchocercal blindness. The study estimated that 1,475,367 people were infected and 23,728 were blinded from onchocerciasis out of a rural population of 4,464,183. The northern and western part of the study area and the lower Niger basin presented a low or no risk of onchocercal blindness. The upper Niger basin, the south-central part of Sierra Leone, and three small foci in the Gambia, Bakoye, and lower Niger river basins were areas with a high risk of onchocercal blindness. The other parts of the study area presented a medium risk of onchocercal blindness. By detecting the communities at risk of onchocercal disease this study permits the selection of populations for disease control based on mass distribution of ivermectin, a microfilaricide.

Detailed epidemiological mapping of three onchocerciasis foci in West Africa

Detailed epidemiological mapping of three isolated foci of hyperendemic blinding onchocerciasis was undertaken in three West African countries as part of community trials of ivermectin, a new microfilaricide for the treatment of human onchocerciasis. The results show that the geographical distribution of the prevalence and intensity of onchocerciasis infection in the community can be very different from what was expected on the basis of demographic and entomological information. The technique of detailed epidemiological mapping is an important tool for the identification of target populations for large scale ivermectin treatment of onchocerciasis. It is being used extensively in the Onchocerciasis Control Programme in West Africa.

Enhanced fractional sodium reabsorption in the ischaemic kidney revisited with lithium as a probe

Extraction of lithium and 51Cr-EDTA across each of the two kidneys was determined during renal vein catheterization in 14 hypertensive patients with unilateral or bilateral renovascular disease before and after i.v. injection of furosemide. Before the administration of furosemide an increased fractional lithium reabsorption was demonstrated across the affected, or more affected kidney. This difference was abolished by furosemide. Using lithium as a probe for sodium, our data suggest an increased fractional tubular sodium reabsorption in the ischaemic human kidney probably located to the proximal tubules as well as to the loop of Henle. Determination of single-kidney fractional lithium reabsorption holds promise as a new research tool for future evaluation of functional abnormalities during divided renal function studies.

Does the decrease in heart rate prevent a detrimental decrease of the end-systolic volume during central hypovolemia in man?

Central hypovolemia occurring with epidural anesthesia was investigated by measurement of hemodynamic and endocrine variables in 10 patients. Responses fell into two categories. Four patients experienced a hypotensive bradycardic episode after seventeen +/- four minutes. In this group epidural anesthesia initially induced a tendency toward an increase in heart rate from 65 +/- 4 to 73 +/- 5 beats/min concomitantly with decreases in end-diastolic (172 +/- 22 to 138 +/- 16 mL), end-systolic (67 +/- 12 to 51 +/- 9 mL), and stroke (105 +/- 10 to 85 +/- 7 mL) volumes (radionuclide cardiography). A subsequent decrease in mean arterial pressure from 76 +/- 3 to 67 +/- 4 mmHg was associated with a decrease in venous return as reflected by the decrease in cardiac output from 6.1 +/- 0.4 to 4.7 +/- 0.7 L/min. In this situation when the venous return was critically reduced, the heart rate was 49 +/- 4 beats/min and no further reduction in end-diastolic and end-systolic volumes was observed. The observed endocrine changes were compatible with a response to central hypovolemia. In the other 6 patients the reaction to epidural anesthesia did not induce statistically significant changes in hemodynamic and endocrine variables. It is concluded (1) that the decrease in heart rate associated with central hypovolemia during epidural anesthesia seems to be elicited when the left ventricular end-systolic volume is decreased by about 25% and (2) that a further decrease in end-systolic volume during progressive central hypovolemia is avoided possibly as a direct consequence of the slowing of the heart.

Diurnal monitoring of blood pressure and the renin-angiotensin system in hypertensive patients on long-term angiotensin converting enzyme inhibition

The temporal blood pressure course and the diurnal profile of the renin-angiotensin system were examined in 13 patients with essential hypertension receiving hydrochlorothiazide and enalapril once daily. Blood samples were taken and blood pressure was measured before the habitual morning dose of hydrochlorothiazide and enalapril (at 8.00 a.m.) and at seven time points over the next 24 h. During the period of maximal effect of enalapril (from 11.00 a.m. to 2.00 p.m.), the increase in plasma renin concentration ranged from no change to an 800% increase. A negative correlation was observed between an increase in plasma renin and a decrease in immunoreactive plasma angiotensin II concentration (Spearman rank-order correlation coefficient = 0.83). Notably, the greatest changes in plasma renin and angiotensin II concentrations after enalapril were seen in those patients whose blood pressure fell most during the day. We conclude that hypertensive patients on long-term therapy with enalapril once daily vary widely in their between-dose biochemical response to the drug, and that there is a significant association between the responsiveness of the plasma renin-angiotensin system and the effect on 24 h blood pressure.

Solid-phase double-antibody radio-immunoassay for atrial natriuretic factor

A solid-phase radio-immunoassay for the determination of atrial natriuretic factor (ANF) in human plasma is described. Iodination of alpha hANF was carried out with the iodogen method. Purification of radio-iodinated alpha hANF was performed by chromatography on disposable columns of DEAE-Sephadex A-25. Studies of immunoreactivity and the elution pattern on HPLC showed perfect stability of the labelled compounds. The tracer was usable for 28 weeks after preparation, and the batch-to-batch variation in the quality of the tracer was satisfactory. Immunoreactive ANF was extracted from human plasma with Sep-Pak C18 cartridges. Recovery of alpha hANF added to whole blood was 85 +/- 12% (mean +/- SD, n = 12). The sensitivity of the radio-immunoassay was 1.6 pg/tube, equivalent to 1 pg/ml plasma when assaying the extract from 4 ml plasma. Mean plasma ANF values in normal subjects in the supine position was 23 +/- 12 pg/ml (mean +/- SD, n = 21).

Normal renal tubular response to changes of sodium intake in hypertensive man

In a comparative study the influence of changes in dietary sodium intake on blood pressure, renal function, extracellular fluid volume, the renin-angiotensin-aldosterone system and plasma concentrations of arginine vasopressin, atrial natriuretic factor and cyclic guanosine monophosphate (GMP) was investigated in 12 patients with essential hypertension and in 10 normotensive controls. The subjects were studied after 4 days on a low (50 mmol/day), medium (180 mmol/day) or high (380 mmol/day) sodium intake. Renal sodium handling was assessed by simultaneous measurements of 51Cr-ethylenediaminetetraacetic acid (EDTA), lithium and sodium clearances. Identical values for the extracellular fluid volume, glomerular filtration rate and proximal and distal tubular resorption rates of sodium and water were found in the hypertensive patients and the controls at all three levels of sodium intake. In both groups, raising the sodium intake from low to high significantly increased 51Cr-EDTA and lithium clearance (an indirect measure of end-proximal fluid delivery), with intermediate values for the medium-sodium diet. The estimated values of fractional proximal and distal sodium resorption decreased when sodium intake was raised; the absolute proximal sodium resorption rate did not change, whereas the absolute distal sodium resorption rate as well as the extracellular fluid volume and sodium clearance increased. Blood pressure and the heart rate were unaffected by sodium intake. In both hypertensives and controls, plasma concentrations of active renin, angiotensin II and aldosterone decreased with increasing sodium intake, arginine vasopressin did not change, and atrial natriuretic factor and cyclic GMP increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of musical processing in brain-damaged patients: implications for laterality of music

Reception and production aspects of musical ability were assessed in two studies of left cerebro-vascular accident (LCVA) and right cerebro-vascular accident (RCVA) patients and controls. Musical tasks included perception of rhythm and pitch variations in familiar and unfamiliar tunes; and production of a well-known song, three original melodies, and imitation of rhythm patterns. The only "laterality of music" effect to emerge in the first study was impaired ability in LVCA patients to correctly perceive rhythmic changes. In the second study LCVAs were poorer than the other two groups in the singing of novel melodies, and both lesioned groups were poorer than controls in singing a familiar tune and in tapping rhythms. Premorbid musical ability was significantly related to performance over all groups combined. The RCVA group showed an inconsistent pattern of performance. The LCVA group was consistently more impaired over all tasks but apart from the aforementioned effects this was nonsignificant. It is argued that laterality effects for music processing cannot be reliably established.

Captopril treatment in Bartter's syndrome

A 13-year-old girl presented with lassitude, polyuria and hypokalemia. Plasma renin concentration and urinary prostaglandin excretion were elevated, whereas plasma aldosterone concentration, urinary aldosterone excretion and blood pressure were normal. A diagnosis of Bartter's syndrome was made. The result of treatment with oral potassium was unsatisfactory. Treatment with acetylsalicylic acid had some effect, but an allergic reaction rendered withdrawal necessary. Treatment with the angiotensin converting enzyme inhibitor captopril and oral potassium led to clinical and biochemical improvement.