The ,B-adrenergic blocker, practolol, proved to be an effective antihypertensive agent in a single-blind crossover trial, involving I7 patients with essential hypertension of mild to moderate severity. After a 2-month placebo period, dosage was begun at IOO mg twice a day, and titrated against blood pressure response up to a maximum dose of 400 mg twice a day, leading to an average reduction in blood pressure of 20/18 mmHg, and satisfactory control in I4 of I6 patients (one defaulter). The clinical and physiological data were analysedfor prediction of response to practolol. The urinary noradrenaline response to head-up tilt, an index of the responsiveness of the sympathetic nervous system, correlated significantly with subsequent blood pressure reduction with practolol IOO mg twice a day (r=0-62, P< O.OI). In 8 patients, responsiveness to tilt was retested after control of blood pressure: changes in diastolic blood pressure and pulse rate while on practolol were both significantly less than pretreatment responses. The urinary noradrenaline response was also reduced (+o -o 5,tg/hr vs. pretreatment mean of + i *64,tg/hr; P< o oI), a finding not explicable in terms of known receptor-blocking properties of the drug. It is suggested that the antihypertensive action of /3-adrenergic blockers may be related to a reduction in the reflex activity of the sympathetic nervous system. Plasma renin activity, which was normal in the recumbent state, rose with tilting. The response with tilt was significantly reduced with practolol, though plasma renin activity during recumbency was only marginally lowered by the drug.Although fl-adrenergic blocking drugs are finding increasing application in the treatment of hypertension, the mechanism by which they lower blood pressure remains uncertain. The antihypertensive effect has been attributed to a reduction in cardiac output (Frohlich et al., I968) but a satisfactory reduction in blood pressure with oral medication has been stated to occur after a latent period of several weeks (Prichard and Gillam, I969), whereas the effect on cardiac output is rapid. An unexplained phenomenon is the extreme range of sensitivity to the blood pressure-lowering effects of ,B-blockers shown by essential hypertensives, dose requirements of propranolol varying between perhaps o-i and 3 g daily (Zacharias, I97I; Prichard, 1970).Essential hypertensives exhibit a broad range of sympathetic nervous system responsiveness when subjected to postural stresses, extending from underactivity in patients responding to tilting with pos-

With fhe technical assistance of A. J. Broad• After a fatty meal, plasma lipemia, as measured by increase in optical density in a colorimeter, is significantly greater throughout the period of absorption in patients with ischemic heart disease than in control subjects.1 ' " The extent of the lipemia depends on contemporary processes of absorption and fat clearance. The rate of absorption depends on such factors as gastric emptying and the form and quantity of the ingested fat; the total amount of fat absorbed is not likely to be greater in subjects with ischemic heart disease, since normal subjects absorb at least 95 per cent of ingested fat.The variable effect of absorption can be excluded by intravenous infusions of fat. The mean rates of removal of artificially emulsified cottonseed oil (Lipomul), when administered intravenously, were found to be similar in patients with ischemic heart disease and in matched controls.3 ' 4 However, such emulsions are initially removed by the reticuloendothelial system, and in this way their metabolism differs significantly from that of chylomicrons.A similar study of the removal of intravenously administered human chylomicrons would be preferable and will be presented in this paper. However, several factors which

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