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SUMMARY The extent ofneuroendocrine activation, its time course, and relation to left ventricular dysfunction and arrhythmias were investigated in 78 consecutive patients with suspected acute myocardial infarction. High concentrations of arginine vasopressin were found within six hours of symptoms, even in the absence of myocardial infarction (n = 18). Plasma catecholamine concentrations also were highest on admission, whereas renin and angiotensin II concentrations rose progressively over the first three days, not only in those with heart failure but also in patients with no clinical complications. Heart failure, ventricular tachycardia, and deaths were associated with extensive myocardial infarction, low left ventricular ejection fraction, and persistently high concentrations of catecholamines, renin, and angiotensin II up to 10 days after admission, whereas in uncomplicated cases concentrations had already returned to normal.The clinical presentation of acute myocardial infarction varies widely. Some patients have only mild constitutional upset, while others suffer intense vasoconstriction, arrhythmias, heart failure, or shock. In common with other major acute illnesses, myocardial infarction is accompanied by many metabQlic and hormonal changes which may be related to the severity ofillness and clinical outcome.' Although stimulation of neuroendocrine systems may be an appropriate response to acute myocardial injury, those hormones that promote vasoconstriction or tachycardia might also be harmful.Ofthe vasoconstrictor mechanisms, catecholamine release has been the most extensively studied.

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The new, long acting converting enzyme inhibitor enalapril was given to 26 patients with moderate to severe heart failure. In 23 cases the mean systolic blood pressure fell from 120 (SD 22) to 108 (25) mm Hg without adverse effects. Profound hypotension with severe bradycardia and sweating, however, occurred in three patients, most pronounced two to four hours after the first dose. The haemodynamic and biochemical changes in these patients were similar to those seen in patients with severe symptomatic hypotension after the first dose of the converting enzyme inhibitor captopril, except that with enalapril the changes occurred later and were longer lasting. Evidence of myocardial damage and reversible renal failure was seen in one patient, and acute reversible deterioration in renal function occurred in one other.In patients with heart failure converting enzyme inhibitors should be administered initially under strict medical supervision with appropriate facilities available for dealing with occasional profound hypotension. IntroductionEnalapril is the second orally active converting enzyme inhibitor to become available for use in hypertension and heart failure.

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