Potassium stimulation of aldosterone secretion in vivo is reversed by nisoldipine, a calcium transport antagonist.

The effects of a novel calcium transport antagonist, nisoldipine, on K-stimulated aldosterone secretion have been examined in vivo. Direct KCl infusion into the adrenal gland stimulated aldosterone secretion. Infusion of nisoldipine, concomitantly with KCl at two rates, abolished the stimulation of aldosterone independently of its effects on K transport. The results suggest that K stimulation of aldosterone secretion in vivo is at least in part mediated by alterations in transmembrane Ca flux.

Angiotensin-II induces changes in the cytosolic sodium concentration in bovine adrenal glomerulosa cells: involvement in the activation of aldosterone biosynthesis.

The homeostasis of cytosolic free calcium ([Ca2+]i) and intracellular free sodium ([Na+]i) are linked in many cell types. We, therefore, studied the effect on [Na+]i of two physiological stimulators of aldosterone synthesis that trigger the calcium messenger system, angiotensin-II (Ang II) and potassium ion (K+), in cultured bovine adrenal glomerulosa cells, using the intracellular fluorescent probe for sodium, sodium benzofuran isophthalate. Ang II induced a concentration-dependent and sustained increase in [Na+]i, from a resting value of 9.2 +/- 3.5 to a maximum of 48.5 +/- 5.5 mM (n = 14). This [Na+]i response was mediated by receptors of the AT1 subtype, because it was abolished by losartan (DuP 753). K+ (15 mM) induced a weaker [Na+]i response, from 5.9 +/- 2.6 to 16.8 +/- 2.5 mM (n = 9). In freshly prepared cells, basal [Na+]i was significantly higher (23.9 +/- 1.8 mM; n = 14; P < 0.01) than in cultured cells. Atrial natriuretic peptide, which is known to affect sodium transport in various cell types, did not alter the [Na+]i response elicited by Ang II. Ethylisopropylamiloride, an inhibitor of Na+/H+ exchange, and dichlorobenzamyl, an inhibitor of Na+/Ca2+ exchange, both inhibited in a concentration-dependent manner the Ang II- and K(+)-induced aldosterone response. Isoosmotic replacement of extracellular Na+ markedly reduced basal aldosterone synthesis. Under these conditions, the concentration-response curve for Ang II-induced aldosterone synthesis was shifted to the right, and its maximum was strikingly diminished. These results show that Ang II and, to a lesser extent, K+ induce significant changes in [Na+]i in bovine glomerulosa cells. These [Na+]i changes probably occur through the Na+/H+ and Na+/Ca2+ exchangers and are likely to play a role in activation of the steroidogenic cascade.

Cytosolic free calcium oscillates in single bovine adrenal glomerulosa cells in response to angiotensin II stimulation.

The characteristics of the change in cytosolic free Ca2+ concentration ([Ca2+]i) in response to agonist stimulation were studied in individual cells of the bovine adrenal zona glomerulosa. Following digestion and dispersion, the cells were loaded with the fluorescent Ca2+ indicator fura-2. The cells adhered to Concanavalin A-coated coverslips and were studied using dual excitation wavelength microfluorimetry. In this procedure individual cells under constant perfusion are visualized by microscopy and excited with light alternating rapidly between 340 and 380 nm. The ratio of fluorescence (F) emitted from the cell (F340/F380) correlates directly with [Ca2+]i. Continuous stimulation with angiotensin II (AII; 10 nmol/l) resulted in a brisk transient rise in [Ca2+]i within 8 s of application of the stimulus. In 50% of cells studied, this initial peak was followed by a series of oscillations in [Ca2+]i lasting up to 13 min, with an average period of 33.0 +/- 5.9 (S.E.M.) seconds. [Ca2+]i did not return to prestimulation levels and, subsequent to the oscillatory phase, the [Ca2+]i remained increased for several minutes. Upon removal of extracellular Ca2+ the oscillations ceased almost immediately although [Ca2+]i remained increased. However, in Ca2+-free medium, a single peak of [Ca2+]i still occurred in response to AII. Cells remained refractory to restimulation over a 15-min period. In contrast, stimulation with K+ (8 mmol/l) rapidly increased [Ca2+]i to a level similar to that induced by AII but without inducing oscillations. Moreover, the effect lasted only while K+ was present and was highly reproducible over multiple stimulations during a 15-min period. These results corroborate, at the single cell level, the known action of AII of causing release of intracellular Ca2+, but reveal a more complex mechanism of action on Ca2+ influx than previously recognized, possibly invoking a role for a putative second messenger-operated membrane Ca2+ channel.

Demonstration of an angiotensin II-induced negative feedback effect on aldosterone synthesis in isolated rat adrenal zona glomerulosa cells.

Although both angiotensin II (Ang II) and potassium ion (K+) induce marked elevations of cytosolic free calcium concentration, [Ca2+]c, in adrenal zona glomerulosa cells-an effect which is thought to trigger aldosterone synthesis-Ang II is also known to reduce the sustained [Ca2+]c rise induced by K+. We have examined whether this effect of Ang II on the calcium messenger system is reflected at the level of the final biological response, aldosterone synthesis. In superfused isolated rat glomerulosa cells, K+ (8 mM) induced a sustained, 60-fold increase in aldosterone production. In contrast, the maximal response to Ang II (10 nM) amounted to only 10 times the basal production. When added subsequent to K+ stimulation, Ang II provoked an immediate and dramatic drop in aldosterone synthesis, to levels obtained with Ang II alone. Under conditions of maximal K+ stimulation, this effect depended upon Ang II concentration, while the well-known synergistic effect was observed with submaximal concentrations of both agonists. The inhibitory effect of Ang II could be reproduced with dioctanoylglycerol, a selective activator of protein kinase C. By contrast, the aldosterone response to adrenocorticotropic hormone (ACTH) was not affected by Ang II. At submaximal concentrations of ACTH, the steroidogenic effect of Ang II was even additive to that of ACTH. Thus, we have shown that, under conditions of maximal stimulation, Ang II exerts a profound inhibition of steroidogenesis in K(+)-stimulated rat adrenal glomerulosa cells. This counter-regulatory mechanism may ensure adequate levels of aldosterone production in vivo.

No relationship between the size of the deletion and the level of developmental delay in cri-du-chat syndrome.

Molecular cytogenetic and developmental assessment was performed on 50 individuals with cri-du-chat syndrome. Fluorescent in situ hybridization analysis was used to confirm a terminal deletion karyotype and map more precisely the location of the deletion breakpoint. We identified terminal deletion breakpoints mapping from 5p15.2 to 5p13. Developmental assessment was performed using the Vineland Adaptive Behavior Scales test. Composite Vineland Scores ranged from 20-75. In general, the communication score was higher than the composite score. Comparison of the size of the deletion with the composite Vineland score, as well as the Vineland Communication score, demonstrated that there was no correlation between the size of the deletion and the level of developmental delay. These results demonstrate that patients with cri-du-chat syndrome show high variability in the level of developmental achievement.

Increased vasodilatory prostaglandin production in the diabetic rat retinal vasculature.

PURPOSE: This study was undertaken in order to investigate whether the production of vasodilatory prostaglandins is increased in the retinal vasculature of the diabetic rat. METHODS: Diabetes was induced in male Sprague-Dawley rats using streptozotocin. Diabetic rats were left uncontrolled for 3-4 weeks or were treated with insulin replacement throughout the period of diabetes. Control rats were age-matched. Retinal vessels extracted from retinae removed at sacrifice were incubated in a physiological salts solution. Prostaglandin E and prostaglandin I2 were measured in collected medium. RESULTS: The production of both prostaglandin E and prostaglandin I2 by blood vessels isolated from the retina was increased by approximately 40% in streptozotocin-diabetic rats, compared to controls, within 4 weeks of the onset of diabetes. This increase was reversed by treatment of streptozotocin-diabetic rats with insulin. The increase in prostaglandin production was not due to alteration in the maximal capacity of cyclooxygenase enzyme. CONCLUSIONS: Increased production of vasodilatory prostaglandins occurs in the rat retinal vasculature early in diabetes. Prostaglandins may contribute to altered retinal hemodynamics in early diabetic retinopathy.

Calcium antagonists and stimulus-secretion coupling of aldosterone.

Sheep whose left adrenal gland had been autotransplanted to a combined carotid artery-jugular vein skin loop in the neck were used to study the role of calcium in stimulus-secretion coupling for aldosterone biosynthesis. The calcium antagonists nisoldipine and verapamil were infused directly into the adrenal arterial blood supply during Na depletion or in Na replete sheep during concomitant adrenal arterial infusion of angiotensin II or KC1. The stimulation of aldosterone secretion following angiotensin II (1 nmol/l blood flow) or KC1 (delta [K] 1 mmol/l blood flow) was totally blocked by both verapamil (10(-4) mol/l blood flow) and nisoldipine (2.6 X 10(-6) mol/l blood flow). In contrast, neither antagonist had any significant effect on the established hypersecretion of aldosterone caused by 24 h Na depletion as a result of parotid salivary loss. The data suggest an important role for calcium in stimulus-secretion coupling during acute stimulation by K and angiotensin II, but not in the longer-term sodium depletion. The data further suggest that angiotensin may not be the sole sustaining stimulus to aldosterone in sodium depletion or its mechanism switches from a Ca-dependent to a Ca-independent mechanism with Na depletion.

Feasibility and validity of computerized ambulatory monitoring in stroke patients.

BACKGROUND: Computerized ambulatory monitoring provides real-time assessments of clinical outcomes in natural contexts, and it has been increasingly applied in recent years to investigate symptom expression in a wide range of disorders. The purpose of this study was to examine the feasibility and validity of this data collection strategy with adult stroke patients. METHODS: Forty-eight individuals (75% of the contacted sample) agreed to participate in the current study and were instructed to complete electronic interviews using a personal digital assistant 5 times per day over a 1-week period. RESULTS: More than 80% of programmed assessments were completed by the sample, and no evidence was found for fatigue effects. Expected patterns of associations were observed among daily life variables, and data collected through ambulatory monitoring were significantly correlated with standard clinic-based measures of similar constructs. CONCLUSION: Support was found for the feasibility and validity of computerized ambulatory monitoring with stroke patients. The application of these novel methods with stroke patients should provide complementary information that is inaccessible to standard hospital-based assessments and permit increased understanding of the significance of clinical results and test scores for daily life experience.

Norman MacAlister Gregg Lecture. The pathogenesis of diabetic retinopathy.

Diabetic retinopathy remains a major cause of loss of vision. The Diabetes Control and Complications Trial (DCCT) has implicated hyperglycaemia as a probable major direct causative factor in the pathogenesis of diabetic retinopathy. There are several plausible mechanisms by which high glucose concentrations could lead to the functional and later structural changes characterising diabetic retinopathy. These include increased activity of the aldose reductase pathway, increase de novo synthesis of diacylglycerol from glucose, causing protein kinase C activation, increased non-enzymatic glycation and increased oxidative damage. The demonstration of the potential roles of these pathways and the subsequent effects of growth factors in enhancing angiogenesis provide potential new approaches to the prevention and treatment of diabetic retinopathy.