Effects of routine heparin therapy on plasma aldosterone concentration

Can thromboembolism be the result, rather than the inciting cause, of acute vascular events such as stroke, pulmonary embolism, mesenteric ischemia, and venous thrombosis?: a maladaptation of the prehistoric trauma response

Thromboembolism is considered the inciting cause of many vascular disorders including acute coronary syndrome (ACS), ischemic stroke, pulmonary embolism (PE), deep vein thrombosis (DVT), and mesenteric ischemia. Adrenergia and inflammation are known to accompany these conditions, particularly among arterial thromboembolic disorders, but the teleologic basis of these associations remains poorly understood. We argue that thromboembolism may sometimes be the result, rather than the cause, of acute vascular events, and may be precipitated by underlying adrenergia. Thromboembolic events are most prone to occur during parts of the circadian, seasonal, lifespan, and reproductive cycles with sympathetic dominance, as well as during behavioral, exertional, physiologic, and iatrogenic activation of sympathetic stress. Molecular evidence suggests that adrenergia and inflammation can promote coagulation and lead to co-activation of the pathways. Acute vascular events that occur without angiographic evidence of occlusion suggest that some infarcts may be attributable to adrenergia alone. "Embolic" disorders may represent asynchronous systemic phenomena rather than clot migration. During acute thromboembolism, downstream tissue hypoxia can activate maladaptive self-propelling cycles of sympathetic bias, inflammation, and coagulation. The counterproductive co-activation of these pathways may reflect a maladaptive interlink forged during the primordial evolution of trauma physiology. Their rapid co-mobilization enables rapid control of hemorrhage, microbial defense, and perfusion maintenance during trauma, but the pathways may behave maladaptively in the setting of modern diseases where endothelial injury may be more often precipitated by smoking, diabetes, dyslipidemia, or hypertension. Sympathetic blockade is already employed in ACS, and beta-blockers are used as antihypertensives to prevent stroke. Our hypothesis suggests that the benefits of beta-blockers in stroke may be independent of antihypertensive effects, and that adrenergia may represent a target for managing all thromboembolic disorders, independent of anti-coagulative and thrombolytic therapies. Perhaps reducing adrenergia, rather than maintaining high cerebral perfusion pressure, may represent a counterintuitive strategy for treating stroke and for reducing reperfusion injury. Plausible mechanisms by which autonomic dysfunction may induce venous thrombosis are discussed, especially in those with baroreceptor dysfunction, immobilization, or dehydration. Unexplained hypercoagulability of cancer may also operate through tumor-induced adrenergia and inflammation.

Heparin-induced hyperkalemia after cardiac surgery

Surgeons are increasingly faced with patients suffering from complicated pathology in multiple organ systems, to which multiple therapeutic agents with complex adverse effects are often prescribed. We face a daily challenge in maintaining an up-to-date knowledge of these complications. Heparin is widely used in surgical practice, yet our awareness of its adverse effects, other than bleeding and thrombocytopenia, remains poor. We will present an example of heparin-induced hyperkalemia following administration for cardiopulmonary bypass and intraaortic balloon pump prophylaxis. This is a rare but serious complication of heparin therapy, not usually reported in the context of a cardiac surgical patient. We will also discuss the renal physiology leading to hyperkalemia and the options available for its management.

Heparin-induced hyperkalemia confirmed by drug rechallenge

Subcutaneous heparin is commonly used as a prophylaxis against deep venous thrombosis in a wide variety of hospitalized patients. As with most medications, heparin has a significant side effect profile; heparin-induced hyperkalemia is an unusual but well described side effect. To increase awareness of heparin-induced hyperkalemia and of those patients at greatest risk, we present two cases of documented hyperkalemia induced by heparin and reconfirmed by drug rechallenge.

Vascular remodeling and mineralocorticoids

Circulating mineralocorticoid hormones are so named because of their important homeostatic properties that regulate salt and water balance via their action on epithelial cells. A broader range of functions in nonclassic target cellular sites has been proposed for these steroids and includes their contribution to wound healing following injury. A chronic, inappropriate (relative to intravascular volume and dietary sodium intake) elevation of these circulating hormones evokes a wound healing response in the absence of tissue injury--a wound healing response gone awry. The adverse remodeling of vascularized tissues seen in association with chronic mineralocorticoid excess is the focus of this review.

Heparin-induced aldosterone suppression and hyperkalemia

PURPOSE

To review the effects of heparin and heparinoid compounds on aldosterone physiology and associated induction of hyperkalemia.

MATERIALS AND METHODS

A comprehensive literature search (of human and animal data) was carried out by computer and by using reference citations from primary sources.

RESULTS

Heparin and its congeners are predictable, potent inhibitors of aldosterone production. This inhibitory effect is specific for the zona glomerulosa; other corticosteroids are not affected. Aldosterone suppression occurs within a few days of initiation of therapy, is reversible, and is independent of either anticoagulant effect or route of administration. Decreases in aldosterone levels may occur with heparin dosages as low as 5,000 U BID. The most important, but probably not the only mechanism of aldosterone inhibition appears to involve reduction in both the number and affinity of the angiotensin-II receptors in the zona glomerulosa. Prolonged use of heparin causes marked reduction in the width of the adrenal zona glomerulosa.

CONCLUSIONS

Aldosterone suppression results in natriuresis and less predictably in decreased excretion of potassium. Greater than normal serum potassium levels occur in about 7% of patients, but marked hyperkalemia generally requires the presence of additional factors perturbing potassium balance (in particular, renal insufficiency, diabetes mellitus, or the use of certain medications). Heparin-induced increases in serum potassium need to be better anticipated by clinicians. Serum potassium levels should be monitored periodically in patients being given heparin for 3 or more days, and in patients at relatively high risk for hyperkalemia, the monitoring interval should probably be no greater than 4 days.

Chronic mineralocorticoid excess and cardiovascular remodeling

Chronic mineralocorticoid (MC) excess, whether due to elevated plasma aldosterone (ALDO) or deoxycorticosterone (DOC), is associated with a perivascular fibrosis of systemic and coronary arterioles. This remodeling of resistance vessels contributes to the appearance of hypertension. Chronic MC excess is also accompanied by cardiac myocyte necrosis, secondary to myocardial potassium depletion, and a subsequent reparative fibrosis that appears in the normotensive, nonhypertrophied right and hypertensive, hypertrophied left ventricles. Fibrosis contributes to the appearance of ventricular arrhythmias and dysfunction. Herein, clinical and experimental evidence linking chronic, inappropriate (relative to dietary sodium) elevations in circulating ALDO and DOC with these reactive and reparative forms of fibrous tissue formation in the heart and other tissues is presented.

Role of glucocorticoid in the development of glycyrrhizin-induced hypertension

Role of alterations of corticosterone metabolism in the expression of the mineralocorticoid activity of glycyrrhizin was explored in rats. While the mineralocorticoid actions of oral glycyrrhizin were not observed in bilaterally adrenalectomized rats and dexamethasone treated rats, the mineralocorticoid actions of glycyrrhizin were fully expressed in bilaterally adrenalectomized rats supplemented with physiological doses of corticosterone. Similar mineralocorticoid actions were observed in rats given glycyrrhizin, deoxycorticosterone and pharmacological doses of corticosterone. Although increases in mean blood pressure were suppressed only by concurrent administration of spironolactone to glycyrrhizin- and deoxycorticosterone-treated rats, increases in mean blood pressure were attenuated by both the glucocorticoid antagonist RU 38486 and spironolactone in pharmacological doses of corticosterone administered rats. Pressor responses to norepinephrine and angiotensin II infusions in rats given deoxycorticosterone and pharmacological doses of corticosterone were significantly higher than in glycyrrhizin-treated rats. These results confirmed the functional significance of 11-beta-hydroxysteroid dehydrogenase in expression of the mineralocorticoid activity of glycyrrhizin.