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To the Editor.— The recent editorial on the Food and Drug Administration's (FDA) role in the drug approval process is appropriate. 1 In our opinion, the FDA has shown concern about infringement upon the practice of medicine. 2 Such may not be said for the Nuclear Regulatory Commission (NRC), in its interpretation of its statutory authority to regulate the radiation safety of radiopharmaceuticals in nuclear medicine. It has adopted the FDA package insert as dogma, particularly in respect to the route of injection of the radiopharmaceutical. 3 Nuclear Regulatory Commission inspectors have cited nuclear medicine physicians for license non-compliance when they have deviated from the package insert in their practice. The irony of this situation is that one regulatory agency (FDA) issues package insert "guidelines," which do not obligate the practicing physician, while another regulatory agency (NRC) adopts the "guidelines" as dogma in its regulation of nuclear medicine practice. A

To the Editor.— Marathon running is gaining increasing popularity. An understanding of the pathophysiology of exertion is important so that runners can be advised on how to minimize the medical hazards of their sport. We therefore read with great interest the report by Frizzell et al 1 describing severe acute hyponatremia in marathon runners. The authors attribute the hyponatremia detected in their patients to an excessive loss of sodium in sweat and to drinking hypotonic fluids. Undoubtedly these are important etiologic factors. The recent discovery of a putative natriuretic hormone, 2 atrial natriuretic peptide (ANP), is causing a major revision in the understanding of salt and water homeostasis. Increasing the circulating concentration of ANP has been shown to cause a salt-losing state in man. 3 There are to date no published data on the effects of exertion on circulating concentrations of ANP. We have therefore performed a pilot study to

THE MOST POTENT antihypertensive agents presently available are those which interfere with function of the sympathetic nervous system. Methyldopa (the levo isomer of alphamethyldopa), which is an effective decarboxylase inhibitor, diminishes the formation of catecholamines by inhibiting the conversion of dihydroxyphenylalanine (dopa) to dopamine. 1 Although it is not known whether the fall in blood pressure produced by this drug depends upon interference with sympathetic function, its antihypertensive effects are similar to those of other autonomic blocking agents. 2,3 It has been shown to be effective in the treatment of hypertension and reasonably free from side effects, and others have emphasized that it has a favorable effect on the recumbent blood pressure. 4-7 Since effective drugs of this type are presently available, the place of methyldopa in the treatment of hypertension will be determined by its ability to overcome the deficiencies in the other autonomic blocking agents, notably guanethidine sulfate.

Following the observation of split renal function studies by White in 1950, 1 later modified as a diagnostic test for renovascular hypertension by Howard et al in 1954, 2 it seemed possible that split renal function studies might be relied upon to provide a basis for the identification of patients with hypertension resulting from a diminished blood flow to one kidney. In 1957, Conner and associates 3 reported that in cases of unilateral renovascular disease the blood pressure improved after surgery only when the preoperative test had shown a diminished urine flow and sodium concentration on the involved side. A number of methods have subsequently been used to improve the performance or interpretation of split renal function tests, namely those of Rapoport in 1960, 4 Stamey in 1961, 5 and Birchall et al in 1962. 6 It is apparent from the number of tests which have been introduced as well as from published reports, 7-10 that no