A defect in platelet aggregation in Bartter's syndrome

Understanding the mechanisms of angiotensin II signaling involved in hypertension and its long-term sequelae: insights from Bartter's and Gitelman's syndromes, human models of endogenous angiotensin II signaling antagonism

Angiotensin II (Ang II) plays a key role in hypertension, renal and cardiovascular pathophysiology via intracellular pathways that involve the activation of a multiplicity of signaling mechanisms. Although experimental and genetic animal models have been developed and used to explore Ang II signaling's role in hypertension, a complete understanding of the processes mediating Ang II signaling in hypertension in humans remains elusive. One impediment is that these animal models do not exhibit all the traits of human hypertension, making it impossible to extrapolate from them to humans. To overcome this issue, we have used patients with Bartter's and Gitelman's syndromes, a human model of endogenously blunted and blocked Ang II signaling that presents a constellation of clinical findings which manifest themselves as the opposite of hypertension. This article reviews the aspects of the pathophysiology of human hypertension and its short and long term sequelae, and uses the results of our studies in Bartter's and Gitelman's syndromes along with those of others to gain better insight and understanding of the role of Ang II signaling in these processes.

SIRT1, heme oxygenase-1 and NO-mediated vasodilation in a human model of endogenous angiotensin II type 1 receptor antagonism: implications for hypertension

Reduced NO availability is associated with endothelial dysfunction, hypertension, insulin resistance and cardiovascular remodeling. SIRT1 upregulates eNOS activity and inhibits endothelial cell senescence, and reduced SIRT1 is related to oxidative stress and reduced NO-dependent dilation. Bartter's/Gitelman's syndromes (BS/GS) are rare diseases that feature a picture opposite to that of hypertension in that they present with normo/hypotension, reduced oxidative stress and a lack of cardiovascular remodeling, notwithstanding high levels of angiotensin II and other vasopressors, upregulation of NO system, and increased NO-dependent vasodilation (FMD), as well as increase in both endothelial progenitor cells and insulin sensitivity. To our knowledge, in BS/GS patients SIRT1 has never been evaluated. BS/GS patients' mononuclear cell SIRT1 (western blot), FMD (B-mode scan of the right brachial artery) and heme oxygenase (HO)-1 (sandwich immunoassay), a potent antioxidant protein, were compared with the levels in untreated stage 1 essential hypertensive patients (HPs) and in healthy subjects (C). SIRT1 (1.86 ± 0.29 vs. 1.18 ± 0.18 (HP) vs. 1.45 ± 0.18 (C) densitometric units, P<0.0001) and HO-1 protein (9.44 ± 3.09 vs. 3.70 ± 1.19 (HP) vs. 5.49 ± 1.04 (C) ng ml⁻¹, P<0.0001) levels were higher in BS/GS patients than in the other groups. FMD was also higher in BS/GS patients: 10.52 ± 2.22% vs. 5.99 ± 1 .68% (HP) vs. 7.99 ± 1.13% (C) (ANOVA: P<0.0001). A strong and significant correlation between SIRT1 and FMD was found only in BS/GS patients (r(2)=0.63, P=0.0026). Increased SIRT1 and its direct relationship with increased FMD in BS/GS patients, while strengthening the relationship among SIRT1, NO and vascular function in humans, point toward a role for reduced SIRT1 in the endothelial dysfunction of hypertension.

Vascular tone control in humans: Insights from studies in Bartter's/Gitelman's syndromes

Studies in patients with Bartter's and Gitelman's syndromes performed in the last 10 years have provided important insights into the mechanistic details of relevant pathways of angiotensin II signaling and vascular tone regulation, therefore making these syndromes a good human model to gain insight into the mechanisms responsible for maintaining/controlling vascular tone. Extensive studies of patients with Bartter's/Gitelman's syndromes have, in fact, shown biochemical abnormalities of angiotensin II short- and long-term cell signaling, which depict a mirror image of those found in hypertension. The information obtained from the study of this human model of altered vascular tone regulation show that it can be used to gather more general data and/or confirm mechanistic details of the cellular and biochemical events involved in the pathophysiology of vascular tone control and to shed light on the multiplicity of the angiotensin II signaling-related mechanisms responsible for the pathophysiology of hypertension and its long-term complication such as cardiovascular remodeling and atherogenesis.

Bartter's and Gitelman's syndromes: from gene to clinic

Bartter's and Gitelman's syndromes are characterized by hypokalemia, normal to low blood pressure and hypochloremic metabolic alkalosis. Recently, investigators have been able to demonstrate mutations of six genes encoding several renal tubular transporters and ion channels that can be held responsible for Bartter's and Gitelman's syndromes. Neonatal Bartter's syndrome is caused by mutations of NKCC2 or ROMK, classic Bartter's syndrome by mutations of ClC-Kb, Bartter's syndrome associated with sensorineural deafness is due to mutations of BSND, Gitelman's syndrome to mutations of NCCT and Bartter's syndrome associated with autosomal dominant hypocalcemia is linked to mutations of CASR. We review the pathophysiology of these syndromes in relation to their clinical presentation.

Inherited primary renal tubular hypokalemic alkalosis: a review of Gitelman and Bartter syndromes

Inherited hypokalemic metabolic alkalosis, or Bartter syndrome, comprises several closely related disorders of renal tubular electrolyte transport. Recent advances in the field of molecular genetics have demonstrated that there are four genetically distinct abnormalities, which result from mutations in renal electrolyte transporters and channels. Neonatal Bartter syndrome affects neonates and is characterized by polyhydramnios, premature delivery, severe electrolyte derangements, growth retardation, and hypercalciuria leading to nephrocalcinosis. It may be caused by a mutation in the gene encoding the Na-K-2Cl cotransporter (NKCC2) or the outwardly rectifying potassium channel (ROMK), a regulator of NKCC2. Classic Bartter syndrome is due to a mutation in the gene encoding the chloride channel (CLCNKB), also a regulator of NKCC2, and typically presents in infancy or early childhood with failure to thrive. Nephrocalcinosis is typically absent despite hypercalciuria. The hypocalciuric, hypomagnesemic variant of Bartter syndrome (Gitelman syndrome), presents in early adulthood with predominantly musculoskeletal symptoms and is due to mutations in the gene encoding the Na-Cl cotransporter (NCCT). Even though our understanding of these disorders has been greatly advanced by these discoveries, the pathophysiology remains to be completely defined. Genotype-phenotype correlations among the four disorders are quite variable and continue to be studied. A comprehensive review of Bartter and Gitelman syndromes will be provided here.

The pathophysiological and molecular basis of Bartter's and Gitelman's syndromes

Molecular defects affecting the transport of sodium, potassium and chloride in the nephron through the ROMK K+ channel, Na+/K+/2Cl- cotransporter, the Na+/Cl- cotransporter and chloride channel have been identified in patients with Bartter's and Gitelman's syndromes. Defects of the angiotensin II type I receptor and CFTR have also being described. These defects are simple (i.e., most are single amino acid substitutions) but affect key elements in tubular transport. The simplicity of the genetic defects may explain why the inheritance of these conditions remains unclear in most kindreds (i.e., not just recessive or dominant) and emphasises the crucial importance of the conformational structure of these channels. Application of this molecular information will allow the early genetic identification of patients with these syndromes and enable us to differentiate between the various disorders at a functional level. It may also identify a subgroup in which the heterozygous form may make patients potentially exquisitely sensitive to diuretics.

Bartter's syndrome: the unsolved puzzle

Bartter's syndrome is a congenital abnormality characterized by metabolic alkalosis [corrected], hyperreninemic hyperaldosteronism, and hypokalemia. Most patients present early in life with symptoms such as muscle weakness and polyuria, which may be attributed to potassium depletion. Despite the hyperaldosteronism, the patients tend to be normotensive, which is at least partially explained by vascular hyporesponsiveness to pressor hormones. Numerous studies have documented increased renal excretion of prostaglandins. Several different patterns of aberrant renal ion transport have been observed in patients with the syndrome, suggesting that it actually may represent a family of related but distinct tubular disorders. Therapeutic approaches to Bartter's syndrome include potassium supplementation, prostaglandin synthesis inhibitors (nonsteroidal anti-inflammatory agents), aldosterone antagonists, and converting enzyme inhibitors. During the first two decades following its initial description, Bartter's syndrome was the focus of widespread interest, based on the likelihood that its investigation might provide insight into the normal functioning of the renin-angiotensin-aldosterone and prostanoid hormone systems. During the past decade, however, little additional progress has been made in Bartter's syndrome, and its patho-physiology remains poorly understood.

The sensitivity of human blood platelets to the aggregating agent ADP during different dietary sodium intakes in healthy men

We have investigated the effect of varying sodium intake on the renin-angiotensin system, ADP-induced platelet aggregation in vitro, and blood 5-HT concentrations in 9 male volunteers. Systolic blood pressure was slightly reduced during a low sodium diet, whereas the diastolic pressure remained unchanged. Plasma renin activity and aldosterone concentration both fell significantly when sodium intake was increased; plasma angiotensin II concentration also fell, but not significantly. There was a significant fall in haematocrit after an increased sodium intake, but there was no change in the whole-blood platelet count after correcting for this. There were no significant changes in either total (i.e. PRP) or platelet 5-HT concentrations. The extent of platelet aggregation induced by 5 and 20 mumol.l-1 of ADP increased significantly when dietary sodium intake was increased. When compared with low or normal sodium intakes, lower concentrations of ADP were required to produce 50% of maximum aggregation after a high sodium intake. The 5-HT2 receptor antagonist ketanserin (1 mumol.l-1 in vitro) reduced the extent of aggregation induced by 5 mumol.l-1 ADP after the volunteers had taken a high sodium diet, whereas the angiotensin II receptor antagonist saralasin (1 nmol.l-1) increased the rate of aggregation after the low sodium diet. Thus, during a high sodium intake, human platelets become more sensitive to the aggregating agent ADP. It is possible that this effect is mediated via platelet 5-HT2 receptors, since ketanserin abolished the increase in salt-induced aggregation seen with 5 mumol.l-1 ADP.

Evidence that circulating 6keto prostaglandin E1 causes the platelet defect of Bartter's syndrome

Bartter's syndrome is associated with activation of prostaglandin metabolism. In the present study we provide several lines of evidence that a circulating metabolite of prostacyclin, 6ketoPGE1 is responsible for a defect in platelet function present in patients with Bartter's syndrome. In platelet aggregometry studies, plasma from patients contained platelet inhibitory activity which was fully neutralized by coincubation with antibody directed against 6ketoPGE1. Fractionation of lipophilic extracts of plasma by high pressure liquid chromatography yielded a platelet inhibitory fraction which comigrated with authentic 6ketoPGE1 and was neutralized by anti 6ketoPGE1 antibody. Lastly, direct measure of the plasma concentration of 6ketoPGE1 by specific radioimmunoassay indicates a 2-fold increase in patients with Bartter's syndrome (133 +/- 9.1 vs 60.7 +/- 12.3 picograms/ml; p less than 025). These studies provide firm evidence that the platelet dysfunction present in patients with Bartter's syndrome is attributable to an increase in the plasma concentration of 6ketoPGE1. In addition, these data provide further evidence in support of the centrality of activation of prostaglandin metabolism in the pathophysiology of Bartter's syndrome.

The renal concentrating defect associated with potassium depletion is independent of prostaglandin E2

Prostaglandin E2 (PGE2) impairs the hydrosmotic effect of vasopressin in toad bladder and mammalian kidney. Because some studies in animals have suggested that potassium depletion enhances renal PGE2 production, the present study examined whether the renal concentrating defect of potassium depletion in humans is mediated by PGE2. Five normal volunteers were studied before and after moderate potassium depletion achieved by 10 days of dietary potassium restriction and administration of a polystyrene sulfonate potassium exchange resin (Kayexalate). Maximal urinary osmolality (Umax) decreased from 1,094 +/- 58 (mean +/- SEM) to 820 +/- 26 mmol/kg (mOsm/kg) (P less than 0.01) following potassium depletion, but urinary PGE2 excretion did not change (496 +/- 145 and 435 +/- 186 ng/d, respectively). Indomethacin suppressed PGE2 excretion significantly, but failed to increase Umax in either the normal or the potassium-depleted state (1,094 +/- 34 and 825 +/- 56 mmol/kg, respectively). It is concluded that the renal concentrating defect produced by moderate potassium restriction in humans is not mediated by PGE2.

Role of prostaglandins and calcium in the effects of Entamoeba histolytica on colonic electrolyte transport

We have previously shown that Entamoeba histolytica lysates contain the neurohormones serotonin, neurotensin, immunoreactive substance P, and probably acetylcholine, and that amebic lysates inhibit sodium and chloride absorption and stimulate chloride secretion in the rat descending colon as measured by the Ussing chamber-voltage clamp technique. We now demonstrate that these transport effects have both calcium-dependent and calcium-independent components. In addition, arachidonic acid metabolites of the cyclooxygenase pathway are probably involved in the Entamoeba histolytica-induced changes in colonic transport that are not dependent on Ca++ entry. Prostaglandin E2 (10(-5) M), indomethacin (10(-6) M), piroxicam (5 x 10(-5) M), and mepacrine (10(-4) M) partially inhibited the amebic lysate effect on active transport in the rat descending colon. In addition, verapamil (10(-4) M) partially inhibited the effect of amebic lysates. The effect of verapamil was additive with that of indomethacin, totally blocking the effect of amebic lysate on short-circuit current. However, amebic lysates do not contain prostaglandin E2 as measured by sensitive radioimmunoassay. Amebic lysates stimulated prostaglandin E2 release from rat colonic mucosal strips. Amebic lysate significantly increased colonic cyclic adenosine monophosphate content. Piroxicam inhibited the lysate-induced increase in colonic cyclic adenosine monophosphate content. These results indicate that although amebic lysate does not contain prostaglandin E2, it caused arachidonic acid metabolites to be produced by the cyclooxygenase pathway, and these are probably involved in the Entamoeba histolytica-induced changes in colonic transport. Neurohormones in Entamoeba histolytica may act directly on colonic tissue to stimulate intestinal secretion, probably via a Ca+(+)-dependent mechanism that is blockable by verapamil, or indirectly via stimulation of prostaglandin E2 generation and release from the rat colon via a cyclic adenosine monophosphate-dependent mechanism. These effects appear separate. The cyclic adenosine monophosphate-dependent secretion is the predominant mechanism in this model of colonic amebic diarrhea.

Clinical syndromes associated with disorders of renal tubular chloride transport: excess and deficiency of a circulating factor?

Two contrasting patients are described, one with pseudo-Bartter's syndrome induced by frusemide abuse and the other a case of hyporeninaemic hypoaldosteronism. The clinical and biochemical features of these two conditions are the opposite of each other and, in the first patient, the effects of frusemide were antagonised by treatment with indomethacin while in the second frusemide itself corrected the syndrome. The decreased pressor sensitivity to infused angiotensin II seen in the patient with pseudo-Bartter's syndrome was corrected with indomethacin and the enhanced pressor sensitivity seen in hyporeninaemic hypoaldosteronism was reversed with frusemide. Frusemide, an agent which blocks chloride transport at the ascending limb of Henle's loop, was respectively thus the cause and the cure of these conditions. On the basis of this the suggestion is made that Bartter's syndrome and hyporeninaemic hypoaldosteronism represent respectively an excess and a deficiency of a circulating factor similar to frusemide capable of blocking renal tubular chloride transport.

Platelet aggregation in six families with Bartter's syndrome

Bartter's syndrome has so far been considered to be an autosomal recessive inherited disease, because of the occurrence of the syndrome in siblings. Both sexes are equally involved. Until now no family has been described in which parents as well as children suffered from the disease. It has recently been found that 'obligatory carriers', i.e. parents of affected children, showed the same pattern of platelet aggregation inhibition as their affected children. We investigated eight patients as well as their parents and siblings, and found that all persons included in the study showed impaired thrombocyte aggregation, especially after low salt intake. We conclude that the restriction of dietary sodium facilitates the measurement of the platelet abnormality.

Bradykinin-stimulated electrolyte secretion in rabbit and guinea pig intestine. Involvement of arachidonic acid metabolites

Bradykinin (BK) increases short-circuit current (Isc) when added to the serosal side of rabbit or guinea pig ileum or rabbit colon. Significant effects on Isc are seen at concentrations as low as 10(-10) M. Anion substitution experiments and unidirectional 36Cl flux measurements indicate that this effect of BK on Isc is due to Cl secretion. The effect of BK on Isc can be partially blocked (60-70% inhibition) by cyclooxygenase inhibitors (indomethacin and/or naproxen) and completely blocked by the phospholipase inhibitor, mepacrine. The combined cyclooxygenase/lipoxygenase inhibitors BW 755 and eicosa-5,8,11,14-tetraynoic acid (ETYA) also completely block the effect of BK on Isc but the slow-reacting substance of anaphylaxis (SRS-A) antagonist FPL 55712 has no effect. None of the above inhibitors diminish the effect on Isc of other exogenously added secretory stimuli such as vasoactive intestinal peptide (VIP), theophylline, or prostaglandin E2 (PGE2). Prior desensitization of rabbit ileum to PGE2 blocks the effect on Isc of BK but not those of VIP or theophylline. Conversely, prior desensitization of rabbit ileum to BK greatly reduces the effect of PGE2 on Isc. BK also stimulates the synthesis of PGE2 in rabbit ileal and colonic mucosa and this effect can be blocked by prior addition of either indomethacin or mepacrine. These effects of BK are similar to those of exogenously added arachidonic acid (AA). AA also stimulates Cl secretion and increases PGE2 synthesis and its effect on Isc can be inhibited by prior desensitization to PGE2 or by prior addition of indomethacin. The above results indicate that BK stimulates active Cl secretion in both small and large intestine and suggest that this effect is due to the intracellular release of AA. Although the prostaglandins appear to be the major products of AA metabolism contributing to the secretory response, lipoxygenase products may also play a role.

Inheritance of Bartter syndrome

The Bartter syndrome is regarded as an autosomal recessive trait because of sib occurrence, equal sex ratio, and normal parents. Recently, obligatory carriers were shown to have the same pattern of platelet aggregation inhibition as their affected children, possibly a reflection of altered prostaglandin action. We investigated eight patients, and their parents and sibs, and found that all persons included in the study had impaired thrombocyte aggregation. These aggregation studies support the hypothesis that the Bartter syndrome is an autosomal recessive trait.

Chloride secretion by canine tracheal epithelium: I. Role of intracellular c AMP levels

We measured the short-circuit current (Isc) across canine tracheal epithelium and the intracellular cAMP levels of the surface epithelial cells in the same tissues to assess the role of cAMP as a mediator of electrogenic Cl secretion. Secretogogues fall into three classes: (i) epinephrine, prostaglandin (PG) E1, and theophylline decrease both Isc and cellular cAMP levels; (ii) PGF2 alpha and calcium ionophore, A23187, increase Isc without affecting cell cAMP levels at the doses employed; and (iii) acetylcholine, histamine, and phenylephrine do not alter either Isc or cAMP levels. These findings indicate that: (i) increases in cAMP or Ca activity stimulate electrogenic Cl secretion by the columnar cells of the surface epithelium; (ii) cAMP mediates the effects of PGE1 and beta-adrenergic agonists; (iii) a strict correlation between cAMP levels and Cl secretion rate is not apparent from spontaneous variations in these parameters or from dose-response relations of Isc and cAMP to epinephrine concentration; and (iv) acetylcholine, histamine, and phenylephrine, agents that stimulate electrically-neutral NaCl secretion by submucosal glands, do not evoke cAMP-mediated responses by the surface epithelium. Addition of 10(-6) M indomethacin (or other prostaglandin synthesis inhibitors) to the mucosal solution decreases Isc and cellular cAMP levels and reduces the release of PGE2 into the bathing media by 80%. Indomethacin does not interfere with the subsequent secretory response to PGE1. This suggests that endogenous prostaglandin production underlies the spontaneous secretion of Cl across canine tracheal epithelium under basal conditions.

Chronologic aging alters the response to ultraviolet-induced inflammation in human skin

In order to determine the effect of age on the capacity of human skin to mount an inflammatory response, the sunburn reaction was studied quantitatively in 4 subjects aged 22-26 yr and 7 subjects aged 62-86 yr. Buttock skin of each subject was exposed to 3 time his minimal erythema dose, using the Hanovia mercury vapor lamp; 1 micrometer histologic sections and determinations of histamine and prostaglandin E2 (PGE2) from suction blister aspirates were used to monitor the reaction. Clinically, erythema and edema were less (p less than .05) in irradiated skin of the old subjects during the first 24 hr. Nonirradiated skin contained less histamine and PGE2 in old adults (p less than .05), approximately 50% of young adult levels. Histamine levels rose early in the reaction and returned to baseline by 24 hr; 4 hr peak values averaged 9.2 ng/ml in old vs. 18.3 ng/ml in young adults. PGE2 rose more slowly in blister aspirates from old adults (P less than .05), but reached comparable peaks, 6-9 pg/T.V., in both groups at 24 hr. Biopsies of control skin from old adult specimens contained fewer mast cells and venules (P less than .01). At 4 and 24 hr, old specimens revealed fewer sunburn cells and less striking alterations of perivenular mast cells and endothelial cells, but at 72 hr these changes were more prominent than in young adult specimens. The data suggest that with advancing age the sunburn reaction is quantitatively reduced and evolves more slowly following a standardize ultraviolet exposure.

Role of renal prostaglandins during antidiuresis and water diuresis in man

The relationship of renal prostaglandins to antidiuretic hormone action and water diuresis was examined in 13 normal subjects and 2 subjects with diabetes insipidus. Following overnight water deprivation, a oral water load caused a prompt and sustained rise in the rate of urinary PGE2 excretion from 7.7 +/- 1.2 to 81.6 +/- 26.4 ng/hr (P less than 0.0001) in 7 normal subjects. Because the simultaneous increase in urinary excretion of urea was only 17% of the rise in urinary PGE2, passive wash-out of renal PGE2 probably accounts for only a small fraction of the increment in PGE2 excretion. Administration of the antidiuretic hormone analogue DDAVP to 6 normal subjects during sustained water diuresis resulted in a decrease in PGE2 excretion and urine flow rate comparable to that of dehydrated subjects. Thus, PGE2 excretion varied directly with urine flow rate over a wide range of states of hydration in all 13 normal subjects. One patient with central diabetes insipidus and one with nephrogenic diabetes insipidus demonstrated a similar positive correlation of PGE2 excretion rate and urinary flow rate in states of hydration, dehydration, and after administration of DDAVP. In the patient with nephrogenic diabetes insipidus, this relationship of PGE2 excretion rate to urine flow rate was unaffedted by DDAVP over a broad range of urine flow rates. Inhibition of prostaglandin synthesis with indomethacin in 6 normal subjects resulted in a significant decline in free water clearance (7.7 +/- 1.0 to 4.7 +/- 0.9 ml/min. P less than 0.001) and an increase in the minimal UOsm (61 +/- 4 to 93 +/- 19 mOsm/kg. P less than 0.01) achieved during water diuresis without a change in creatinine or osmolar clearances. Furthermore, the tightly linked relationship of PGE2 excretion rate to urine flow rate was reduced in 5 of 6 subjects during indomethacin treatment. We conclude that urinary PGE2 excretion varies directly with urine flow rate and is not directly dependent on ADH activity or state of hydration in man. The rise in PGE2 excretion during water diuresis may enhance the excretion of free water since indomethacin treatment blunted free water clearance while suppressing the rise in PGE2 excretion.

Stimulation of renin release by 6-oxo-prostaglandin E1 and prostacyclin

1 Renin release induced by 6-oxo-prostaglandin E1 (6-oxo-PGE1) was compared to release in response to prostacyclin (PGI2) and 6-oxo-PGF1 alpha in slices of rabbit renal cortex. 2 Krebs-Ringer medium bathing slices of renal cortex was collected for renin assay after four successive 20 min intervals (periods I-IV). Renin release did not increase during periods I to IV in untreated slices. Agonists were added, only once, at the beginning of period III. Between periods III and IV, the incubation solution was aspirated and replaced with fresh medium. 3 PGI2 increased renin release during period III while 6-oxo-PGE1 stimulated release during periods III and IV. 6-oxo-PGE1 stimulated renin release (24%-74%) in concentrations ranging from 1-33 microM while PGI2 stimulated release at 10 microM (60%) but not at 5 microM. 6-oxo-PGF1 alpha, 10 microM, did not release renin during period III (period III, 9%), but caused a small rise in period IV (29%). 4 6-oxo-PGE1, unlike PGI2, was stable under the incubation conditions (pH 7.4, 37 degrees C) as indicated by recovery of undiminished platelet anti-aggregatory material after 20 min. 5 In the rabbit kidney, activity of 9-hydroxyprostaglandin dehydrogenase was greatest in the cortex and negligible in the papilla, corresponding to the zonal distribution of renin. 6 The prominent and sustained in vitro renin releasing effect of 6-oxo-PGE1, as well as the cortical localization of enzyme activity capable of generating this stable prostacyclin metabolite, suggest that formation of 6-oxo-PGE1 may contribute to PGI2-induced renin release and may explain the delayed stimulation caused by 6-oxo-PGF1 alpha.

The human sunburn reaction: histologic and biochemical studies

The ultraviolet-induced erythema reaction was investigated histologically and biochemically in four subjects, utilizing suction blister aspirates, analyzed for histamine and prostaglandin E2 (PGE2), and Epon-embedded 1-mu skin biopsy sections from control skin and from irradiated skin at intervals for 72 hours after exposure to a Hanovia lamp. Major histologic alterations in the epidermis included dyskeratotic and vacuolated keratinocytes (sunburn cells), and disappearance of Langerhans cells. In the dermis the major changes were vascular, involving both the superficial and deep venular plexuses. Endothelial cell enlargement was first apparent within 30 minutes of irradiation, peaked at 24 hours, and persisted throughout the 72-hour study period. Mast cell degranulation and associated perivenular edema were first apparent at 1 hour and striking at the onset of erythema, 3 to 4 hours postirradiation; edema was absent and mast cells were again normal in number and granule content at 24 hours. Histamine levels rose approximately fourfold above control values immediately after the onset of erythema and returned to baseline within 24 hours. PGE2 levels were statistically elevated even before the onset of erythema and reached approximately 150% of the control value at 24 hours. These data provide the first evidence that histamine may mediate the early phase of the human sunburn reaction and increase our understanding of its complex histologic and biochemical sequelae.

Hypokalemia, normal blood pressure, and hyperreninemia with hypoaldosteronism

The etiology of persistent hypokalemia and renal potassium loss was investigated in three children. Each had normal blood pressure but low plasma aldosterone values in relation to elevated plasma renin activity. None had a history of licorice abuse, laxative or diuretic use, persistent vomiting or diarrhea, pyelonephritis, or diabetes insipidus. Additional studies in one patient showed low prostaglandin E excretion and a normal platelet aggregation response to epinephrine and ADP. Although certain aspects of this condition resemble Bartter syndrome, the low concentrations of aldosterone and the absence of evidence for mineralocorticoid excess suggest a previously undescribed syndrome.

A study of induced hyponatremia in the prevention and treatment of sickle-cell crisis

Because the formation of sickle cells is dependent on the intracellular concentration of deoxyhemoglobin S, we investigated the possibility of altering or preventing sickle-cell crises by reducing serum sodium so as to cause red cells to swell. In three patients with sickle-cell anemia who had been disabled by recurrent painful crises, sustained dilutional hyponatremia was induced by 1-desamino-8-D-arginine vasopressin (DDAVP) in combination with a high fluid intake. Mean corpuscular hemoglobin concentration fell, and the degree of sickling at low partial oxygen pressure was reduced, as determined by morphologic criteria and by increased oxygen affinity of blood. Chronic hyponatremia (serum sodium, 120 to 125 mmol per liter) reduced the frequency of painful crises, whereas acutely induced hyponatremia abbreviated the duration of crises. These results, although preliminary, are encouraging enough to warrant further study of the safety and effectiveness of induced hyponatremia in the prevention and treatment of sickle-cell crises.