ADRENERGIC NERVOUS SYSTEM IN SODIUM METABOLISM: EFFECTS OF GUANETHIDINE AND SODIUM-RETAINING STEROIDS IN NORMAL MAN

GDMT for heart failure and the clinician's conundrum

Therapeutic advances in management of CHF have decreased mortality and have impacted progression in patients with mild to moderate heart failure. Aggressive campaigns by cardiology societies aimed at increasing implementation of these measures in routine practices have almost generalized the treatment of heart failure irrespective of individual variations of clinical status of patients and stages of heart failure. This explains why morbidity compression and quality of life improvement have not been realized fully particularly in patients with advanced disease. To examine whether GDMT for CHF is backed by unambiguous evidence of clinical efficacy for its global implementation in every patient at all stages of the syndrome. ACC/AHA, ESC Guidelines for CHF, and their updates were reviewed. Clinical trial cited in the guideline documents and other pertaining published literatures were analyzed.

Findings

Many of the recommended GDMT for CHF lack unequivocal evidence of clinical efficacy in patients with diverge etiology of heart failure and concomitant comorbid conditions Some of the recommendations which are useful in early stages, lack evidence of efficacy in more advanced stages of heart failure. Application of results of research trials in patients beyond their inclusion and exclusion criteria, appears mere extrapolation, Clinicians are faced with the conundrum of implementing the recommendations without indubitable evidence of their efficacy in every patient of their practice.

Conclusion

A reappraisal of Guidelines is needed to address outstanding questions pertaining to the efficacy of recommendations and plug the knowledge gaps without assumption and extrapolation of results of RCTs beyond their inclusion and exclusion criteria.

Long-term cardiovascular autonomic and clinical changes after immunoglobulin G immunoadsorption therapy in autoimmune autonomic ganglionopathy

: A 63-year-old male was diagnosed with autoimmune autonomic ganglionopathy based on the finding of plasma antibodies to the nicotinic acetylcholine receptor (nAChR) of autonomic ganglia. He complained of mouth and eye dryness, dysphagia, severe constipation, erectile dysfunction, urgency, frequent urination, habitual orthostatic syncope and presyncope. A remarkable symptomatic orthostatic hypotension without changes in heart rate was present. We here describe the 3-year time course of the changes in spectral indices of cardiovascular autonomic control LF/HF and LFSAP, dysautonomia symptoms intensity and anti-nAChR antibodies following repetitive selective immunoadsorptions. During the follow-up, the reduction of anti-nAChR antibodies produced by immunoadsorption was associated with a diminished orthostatic hypotension, a restored capability to increase LF/HF, LFSAP and norepinephrine in upright position, a decline in the intensity of autonomic symptoms and an improvement of life quality. Spectral parameters LF/HF and LFSAP may represent noninvasive, low-cost biomarkers suitable for autoimmune autonomic ganglionopathy patients' clinical follow-up.

Pharmacologic Management of Chronic Heart Failure: A Review

Standard drug therapy of systolic heart failure has been evaluated in large-scale randomized clinical trials and includes angiotensin-converting enzyme (ACE) inhibi tors, which should be used as first-line therapy, diuret ics for the management of extracellular fluid volume excess, and digoxin. In combination with ACE inhibitors and diuretics, with or without digoxin, some β-adrener gic receptor blockers attenuate disease progression and improve outcome in mild-to-moderate systolic heart failure. The pharmacologic management of chronic dia stolic heart failure is largely empirical and directed at reducing symptoms. Symptoms caused by increased ventricular filling pressures may be diminished by diuret ics and nitrovasodilators. Some calcium channel antago nists and most β-blockers prolong diastolic filling time by slowing heart rate, thereby improving the symptoms of diastolic heart failure.

Causes of inadequate response to antihypertensive drugs. Volume factors

Diuretic therapy, by producing a negative salt and water balance, eliminates the false tolerance to sympatholytic drugs that often occurs during long-term monotherapy. This tolerance results from salt and water retention produced by the drugs. Review of published results suggests a primacy for arterial pressure reduction in this fluid because suppressed renal sympathetic activity should facilitate salt and water excretion through lessened alpha-adrenergic influence on tubular reabsorption, and beta-adrenergic inhibition would diminish renin release thus promoting natriuresis. The return of hypertension that characterizes the false tolerances seems paradoxical because these drugs cause venodilation, which should provide ample storage of expanded blood volume without affecting cardiac output. However, animal studies have suggested that dilated veins have decreased compliance; if that is so, in humans it would mean that fluid retention would be accompanied by a redistribution of blood into the central circulation, with a rise in cardiac output.

Pathogenesis of sodium and water retention in edematous disorders

Edema is a collection of fluid within the body's interstitial space which occurs when there is an alteration of the Starling forces which control transfer of fluid from the vascular compartment to surrounding tissue spaces. Generalized edema results when altered Starling forces affect all capillary beds, such as occurs in cardiac failure, cirrhosis, and nephrotic syndrome. Common to these conditions is the development of increased total body sodium and water content. The kidneys play an essential role in the retention of this sodium and water. In this article we shall discuss the signals the kidneys receive for sodium and water retention in these edematous disorders (afferent mechanisms). We shall also examine the means by which the kidney responds to these signals and retains sodium and water (efferent mechanisms). As shall become apparent these edematous states may share many of the same afferent and efferent mechanisms for sodium and water retention.

Altered renal alpha 2-adrenergic receptor regulation in genetically hypertensive rats

Renal alpha 1 and alpha 2-adrenergic receptors were quantified in Dahl salt-sensitive and salt-resistant rats, in Okamoto-Aoki spontaneously hypertensive rats (SHR), in Wistar Kyoto "normotensive" (WKY), and in Charles River rats made hypertensive by the Grollman ligature technique and by DOC-NaCl administration after unilateral nephrectomy. The effect of high dietary NaCl on renal alpha receptors was studied in Dahl, SHR, and WKY rats. Renal alpha 1 and alpha 2 receptor densities were higher (p less than 0.05) in SHR and in Dahl salt-sensitive rats than in their normotensive controls. High dietary sodium increased renal alpha 2 receptors and blood pressure in SHR, WKY and Dahl salt-sensitive, but not in resistant Dahl rats. A study of time relationships revealed that the increase in renal alpha 2 receptors preceded most of the blood pressure elevation due to high dietary sodium. Renal alpha-adrenergic receptor densities of surgical (Grollman) and endocrine (DOC-NaCl) forms of rat hypertension were not different from normotensive controls. Thus, renal alpha 2 receptor density and increase thereof by dietary sodium may be: 1) a biochemical marker for genetic forms of hypertension in the rat, and 2) closely linked to the basic mechanism of high blood pressure.

Dietary sodium and renal alpha 2-adrenergic receptors in Dahl hypertensive rats

Dahl sodium-sensitive and resistant rats were fed low and high sodium diets. Renal plasma membrane alpha 2-adrenergic receptor concentrations were greater (p less than .05) in sensitive than in resistant rats while ingesting a low sodium diet. On a high sodium diet the alpha 2 receptor concentration increased (p less than .01) in sensitive but not in resistant rats. Since alpha 2 receptors are located in proximal tubules at sites where norepinephrine induces sodium reabsorption, we postulate that this genetically determined abnormal receptor regulation could lead to exaggerated sodium retention and possibly high blood pressure.

Diabetes mellitus and orthostatic hypotension resulting from ingestion of Vacor rat poison: endocrine and autonomic function studies

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The effect of high-sodium and low-sodium intakes on blood pressure and other related variables in human subjects with idiopathic hypertension

Nineteen patients with hypertension in whom all known causes of blood pressure elevation had been ruled out were classified as "salt-sensitive" or "nonsalt-sensitive" from the changes in blood pressure with changes in sodium intake from 9 meq to 249 meq/day. With the diet containing 249 meq sodium per day, there were no statistically significant differences in plasma sodium, potassium, chloride, aldosterone, cortisol or renin activity, or in urinary potassium, aldosterone or 17-hydroxycorticosteroids between the two groups. The "salt-sensitive" patients retained more sodium on the high-sodium diet than did the patients who were not sensitive to salt ("nonsalt-sensitive"); accordingly, sodium induced more weight gain in the salt-sensitive patients.

An assessment of the role of the sympathetic nervous system in experimental hypertension using normal and immunosympathectomized rats

1. The role of the sympathetic nervous system in experimental hypertension and associated changes in aortic sodium and potassium was studied using normal and immunosympathectomized Sprague-Dawley rats.2. A single injection of antiserum to nerve-growth factor to rats at birth produced less intensive destruction of the peripheral sympathetic system than did two injections (one daily for 2 days). The former are referred to as "partial" immunosympathectomized and the latter as "total" immunosympathectomized rats.3. Maintenance of rats on 1% sodium chloride after unilateral nephrectomy and implantation of 40 mg desoxycorticosterone acetate (DOCA) pellets resulted in sustained DOCA-NaCl hypertension in both normal and "partial" immunosympathectomized rats but not in "total" immunosympathectomized rats. Hypertension was associated with an increase in aortic sodium.4. Constriction of one renal artery with contralateral nephrectomy caused sustained hypertension and an increase in aortic sodium in normal and "partial" immunosympathectomized rats. Renal hypertension in "total" immunosympathectomized rats was not sustained.5. It is concluded that a certain minimum control of the cardiovascular system by the sympathetic system is essential for the production of experimental hypertension and associated electrolyte changes.

The role of renin in the exaggerated natriuresis of hypertension

Hypertensive patients were classified according to their plasma renin response when challenged by the potent diuretics, ethacrynic acid (50 mg IV), or furosemide (40 mg IV), into renin-unresponsive and renin-responsive groups. In the latter plasma renin activity rose by at least 0.5 ng of angiotensin/ml/hr after the diuretic. The response to volume expansion with 2 L of isotonic saline infused over 60 min was then studied. Peak rate of sodium excretion after saline loading was 994±186 µEq/min in the renin-unresponsive group and peak urine flow was 11.9 ± 2.1 ml/min. In the renin-responsive hypertensives peak sodium excretion was 448 ± 149 µEq/min and peak urine flow was 5.4 ± 1.5 ml/min. Both the sodium excretion and urine flow responses were significantly higher ( P < 0.05) in the renin-unresponsive group. The degree of saline-induced diuresis and natriuresis was not related to the preexisting level of aldosterone production. Plasma renin changed little in either group during saline infusion but tended to be higher at all times in the renin-responsive subjects. The enhanced capacity of the renin-unresponsive hypertensive subjects to excrete a salt load suggests either a functionally significant degree of extracellular fluid volume expansion or a direct role for renin in the natriuresis accompanying volume expansion.

Plasma volume expansion resulting from interference with adrenergic function in normal man

Guanethidine was administered to 10 normal subjects in order to examine the effects of reduced adrenergic function on plasma volume. An increase in the plasma volume was observed averaging 21.4% after 1 week, and 12.1% and 13.1% after 2 and 3 weeks of drug administration. A similar change in plasma volume resulted when alphaadrenergic blockade was produced with phenoxybenzamine. These changes occurred in the absence of sodium retention and were associated with attenuation of forearm venous sympathetic reflexes and a rise in forearm venous compliance. The increase in venous compliance which was observed was proportional to the changes in plasma volume in these subjects. Thus, the sympathetic nervous system through its control of venous resistance may provide a means whereby the blood volume can be regulated.

Natriuretic effect of angiotensin in dogs revealed after administration of reserpine and guanethidine

In untreated dogs anesthetized with morphine-chloralose, a small dose of angiotensin (0.0375 µg/kg per min) produced a large reduction in renal blood flow, a smaller reduction in glomerular filtration rate and an antinatriuresis. A graded change in the excretion of sodium in response to angiotensin occurred after the successive administration of reserpine and guanethidine. In reserpinetreated dogs, angiotensin did not produce an antinatriuresis, whereas in the same dogs after giving guanethidine, a natriuresis occurred in response to angiotensin (from a control of 60 to 189 µEq Na/min). The effects of angiotensin on blood pressure and glomerular filtration rate were similar in all dogs. The renal vasoconstrictor effect of angiotensin was decreased in 3 of 8 dogs after guanethidine. At the high dose of angiotensin (0.375 µg/kg per min), the natriuresis was larger (from a control of 75 to 353 µEq Na/min) and was unrelated to changes in glomerular filtration rate or renal blood flow. In reserpine- and guanethidine-treated dogs, angiotensin increased sodium excretion sufficiently during renal arterial constriction to produce a large reduction in renal blood flow and the filtered load of sodium. These results suggest that angiotensin has a renal tubular action that is uncovered by sympathetic blockade produced by reserpine and guanethidine.

Studies on the renal excretion of norepinephrine

Studies were carried out in anesthetized dogs to investigate the renal clearance of norepinephrine (NE) and to determine the origin of this amine in the urine. Infused radioactive NE was cleared from plasma at a rate averaging 63.8% of the glomerular filtration rate. NE was shown to be freely filterable, and evidence has been presented which suggests but does not prove that the amine is partially reabsorbed from the glomerular filtrate; metabolism of NE in the tubular fluid by catechol-o-methyl transferase has not been excluded. The clearance of this catecholamine was not affected by changes in urine pH or flow. Total chronic denervation of one kidney was shown to have no effect on the rate of excretion of endogenous NE. Therefore, the NE that is excreted in the urine would appear to be solely derived from the catecholamines in circulating blood.

The mechanism of suppression of proximal tubular reabsorption by saline infusions

The mechanism by which expansion of extracellular fluid volume with isotonic saline suppresses reabsorption in the proximal tubule was studied in rats by examining the relations among glomerular filtration rate (GFR), absolute and fractional reabsorption of filtrate, intrinsic reabsorptive capacity (rate of reabsorption per unit tubular volume), transit time, and tubular volume. Saline infusions reduced the per cent of the glomerular filtrate reabsorbed in the proximal tubule from 50% during antidiuresis to 25% during saline diuresis. The suppression of proximal reabsorption was the result of two factors: 1) a 30% reduction of intrinsic reabsorptive capacity, and 2) a 26% reduction of tubular volume per unit GFR.GFR invariably rose during saline diuresis. However, prevention of the rise in GFR by aortic clamping had no effect on either the inhibition of intrinsic reabsorptive capacity or the reduction in tubular volume per unit GFR produced by saline infusions. Expansion of extracellular fluid volume with isotonic saline, therefore, depressed intrinsic reabsorptive capacity and tubular volume per unit GFR by some mechanism completely independent of GFR. The effects of furosemide administration were contrasted with those of saline infusions. Furosemide inhibited intrinsic reabsorptive capacity by 40% but had no significant effect on proximal fractional reabsorption. The failure to suppress fractional reabsorption was the consequence of a disproportionate rise in tubular volume (relative to GFR) that was sufficient to completely overcome the inhibition of intrinsic reabsorptive capacity. Inhibition of intrinsic reabsorptive capacity alone, therefore, will not result in a net suppression of reabsorption of filtrate in the proximal tubule. We concluded that, although intrinsic reabsorptive capacity was inhibited during saline diuresis, the critical factor responsible for translating this inhibition into effective net suppression of proximal reabsorption was the observed reduction in tubular volume per unit GFR.

Abnormalities of renal function and circulatory reflexes in primary aldosteronism

The renal response to intravenous administration of isotonic saline solution and circulatory reflex reactivity was studied in nine patients with primary aldosteronism before and after surgical removal of an adrenal adenoma. In preoperative tests, infusion of saline was followed by abnormally rapid renal excretion of sodium and water, such as occurs in patients with autonomic insufficiency. Circulatory reflex function was also abnormal in all patients; the most severe impairment was shown by two patients with hypokalemia and weakness of long duration. Postoperatively, both renal and circulatory reflex responses returned to normal or near normal. In preoperative tests on three patients, potassium repletion effected a similar correction of both renal and circulatory reflex abnormalities. The cause of these abnormalities in patients with primary aldosteronism is not known. Potassium depletion may be a factor, although a general disturbance of autonomic cardiovascular function cannot be excluded.