Digoxin-specific antibody fragments and a calcium antagonist for reversal of digoxin-induced mesenteric vasoconstriction

Signaling mechanisms that link salt retention to hypertension: endogenous ouabain, the Na(+) pump, the Na(+)/Ca(2+) exchanger and TRPC proteins

Salt retention as a result of chronic, excessive dietary salt intake, is widely accepted as one of the most common causes of hypertension. In a small minority of cases, enhanced Na(+) reabsorption by the kidney can be traced to specific genetic defects of salt transport, or pathological conditions of the kidney, adrenal cortex, or pituitary. Far more frequently, however, salt retention may be the result of minor renal injury or small genetic variation in renal salt transport mechanisms. How salt retention actually leads to the increase in peripheral vascular resistance (the hallmark of hypertension) and the elevation of blood pressure remains an enigma. Here we review the evidence that endogenous ouabain (an adrenocortical hormone), arterial smooth muscle α2 Na(+) pumps, type-1 Na/Ca exchangers, and receptor- and store-operated Ca(2+) channels play key roles in the pathway that links salt to hypertension. We discuss cardenolide structure-function relationships in an effort to understand why prolonged administration of ouabain, but not digoxin, induces hypertension, and why digoxin is actually anti-hypertensive. Finally, we summarize recent observations which indicate that ouabain upregulates arterial myocyte Ca(2+) signaling mechanisms that promote vasoconstriction, while simultaneously downregulating endothelial vasodilator mechanisms. In sum, the reports reviewed here provide novel insight into the molecular mechanisms by which salt retention leads to hypertension.

Treatment of digitalis intoxication with emphasis on the clinical use of digoxin immune Fab

Many studies and cases of digitalis intoxication have been reported since the time of William Withering's first publication in 1785. Recognition and management of digitalis toxicity is challenging. Before digoxin immune Fab was commercially available, treatment consisted of managing the signs and symptoms of toxicity until the digitalis was eliminated. Digoxin immune Fab offers a safe, effective, and specific method of quickly reversing digitalis toxicity. Factors that must be considered with the clinical use of this agent include the dosage calculation, administration technique, postdose monitoring, pharmacokinetics, mechanism of action, interference with commercially available digoxin assays, partial neutralizing dosing, rebound of free digoxin, and indications for use. For severe, life-threatening toxicity, digoxin immune Fab is the treatment of choice.

PY 108-068, a dihydropyridine derivative, and verapamil interact differently with the ouabain effects on the heart and the peripheral circulation

In previous experiments PY 108-068 (PY) has been found to have more potent calcium antagonistic effects on vascular smooth muscle than on myocardial tissue. We now investigated the effects of PY and verapamil (V) on the increases in myocardial contractile force (measured with a strain gauge) and regional vasoconstriction (measured with tracer microspheres) effected by an infusion of 40 micrograms/kg ouabain into anaesthetized cats. Ouabain significantly increased contractile force of the left ventricle and caused vasoconstriction in the heart, stomach, small intestine, pancreas, spleen and skin, but not in the kidneys, brain, adrenals and liver. PY (30 micrograms/kg i.v.) and V (0.3 mg/kg i.v.) antagonized the vasoconstrictor effects of the glycoside in all organs except the skin, i.e. also in organs, where the calcium antagonists normally do not cause vasodilatation. However, PY did not affect the increase in contractile force, whereas V attenuated both the cardiac and peripheral vascular effects of ouabain. The results demonstrate the preferential action of PY on peripheral blood vessels as opposed to left ventricular myocardial tissue. Heart rate was decreased by both PY and V but the PQ-interval was lengthened only by V suggesting that PY in contrast to V preferentially acts on the sinus node rather than A-V conduction. A combination of PY with a glycoside might be beneficial in the treatment of cardiac failure, since this calcium antagonist apparently does not antagonize the positive inotropic action of ouabain on the heart while reducing afterload and reversing the undesirable vasoconstriction induced by cardiac glycosides.