To the Editor.—
In their reply to our communication in the August 1980 Archives (116:863-864), Poh-Fitzpatrick and Mathews-Roth still insist that the studies of Piomelli et al1 were partly in vivo. To resolve this semantic discordance, we will present our concept of an in vivo biochemical experiment. We visualize (at least) the following two broad types of study: (1) Collect specimens from a live animal, make the animal undergo stress, and collect specimens at recorded intervals. The specimens are then analyzed for a metabolite of interest to determine the effect of the experimental stress on turnover of the metabolite. (2) Administer radiotracers to a live animal, collect specimens, and monitor the rise and fall of radioactivity in a metabolite of interest. This type of experiment was conducted by Scholnick et al2 and by Schwartz et al3 to monitor protoporphyrin (PP) turnover in patients with erythropoietic protoporphyria (EPP).
Johnson JA, Fusaro RM. Origin of Plasma Protoporphyrin in Patients With Erythropoietic Protoporphyria. Arch Dermatol. 1981;117(9):526. doi:10.1001/archderm.1981.01650090006007