An Autoradiographic Study of the Renal Uptake and Metabolism of a Synthetic Adrenocorticotrophin

Abstract

The cellular and subcellular events in rat kidney following intravenous injection of the radioactively labelled adrenocorticotrophic hormone analogues, [³ H-Tyr²³] — Synacthen and [³ H-Tyr²³]—Synacthen (see preceding abstract), have been studied using microautoradiography and quantitative electron microscope autoradiography¹. The distribution of silver grains 3–7 min after injection is similar for both forms of the peptide and shows that after glomerular filtration most of the label is rapidly resorbed via endocytotic vesicles of the proximal convoluted tubule. After 22 min label from [³ H-Tyr²³]—Synacthen is twice as concentrated in the lysosomes as in endocytotic vesicles whereas, at 13 and 30 min after injection of [³ H-Tyr²] — Synacthen, label is three to four times more concentrated in lysosomes than in endocytotic vesicles. After 1h label from [³H-Tyr²³]—Synacthen is more randomly distributed as determined by the χ² test showing similar lysosomal nuclear and cytoplasmic concentrations.