Micropuncture Studies of Receptor-Mediated Endocytosis of Transferrin in the Rat Epididymis1

Abstract

The concentration of transferrin in fluids collected by micropuncture techniques from the rat testis and zones 1A, 2, 5A, and 6B of the rat ductus epididymidis was 44, 527, 113, and 49 ng/.mu.l, respectively. When changes in fluid volume were taken into account, it was found that transferrin was concentrated by the efferent ducts, whereas the amount of endogenous luminal transferrin declined from the caput to the cauda epididymidis. Using transferrin-gold as an electron dense marker, we showed that the decline in the concentration of transferrin along the epididymis could be attributed to its cumulative receptor-mediated endocytosis by the lining principal cells. No significant difference in the net receptor-mediated endocytosis of transferrin-gold was found between the proximal caput and corpus epididymidis in vitro.