ABSORPTION OF 125I-LABELLED SHEEP GROWTH HORMONE IN SINGLE PROXIMAL TUBULES OF THE RAT KIDNEY

Abstract

SUMMARY: Techniques of kidney micropuncture and electron microscope autoradiography have been used to study the uptake of ¹²⁵I-labelled sheep growth hormone (GH) in rat renal proximal tubules. After microperfusion of a proximal tubule with ¹²⁵I-labelled GH, the transport of label by the tubular epithelium was studied autoradiographically at selected times up to 1 h. The sequential transfer of labelled material from tubule to microvilli, then to small and large apical vacuoles and finally to lysosomes followed the pattern of absorption that has been described for other proteins. Evidence of lysosomal degradation of the transported protein was obtained from studies in vitro; lysosomes isolated from the renal cortex rapidly converted ¹²⁵I-labelled GH to products of lower molecular weight. In addition to the absorptive pathway through the intracellular vacuolar apparatus it appeared that there was also an alternative pathway, less well defined, whereby GH could be absorbed without being degraded.