In previous studies we showed that in vitro uridine incorporation along the renal tubule is heterogeneous and that DOCA induces a stimulation of RNA synthesis in distal cortical and medullary structures. The present work examines by autoradiography of isolated tubules and renal tissue sections the cellular heterogeneity of the connecting (CNT) and cortical collecting (CCT) tubules after in vivo injection of [3H]uridine in normal and DOCA-treated rabbits. Data confirmed the profile of uridine incorporation along the tubule, which was found in in vitro experiments, and the DOCA-induced stimulation of RNA synthesis. In microdissected CNT and CCT of control kidneys, statistical analysis of the distribution of labeling revealed the presence of two distinct cell populations: one with low labeling (2-3 silver grains per nucleus) and one with high labeling (10-13), which represent 64 and 36%, respectively (CNT), and 74 and 26%, respectively (CCT), of the whole population. Histological data showed that the respective proportions of intercalated cells (29% in CNT; 21% in CCT) and connecting tubule cells (65%) or principal cells (79%) are close to those of the populations with high or low labeling. In addition, autoradiographs on renal sections directly demonstrated that the labeling of intercalated cells (19.3 silver grains/100 micron2 nuclear surface in CNT; 14.7 in CCT) was three times higher than that of connecting (6.6) or principal (5.8) cells. In isolated CNT and CCT, DOCA induced similar absolute increases in the labeling of the two populations. However, the relative increase was more than two times higher in the population with low labeling (+131% in CNT, +210% in CCT) than in the one with high labeling (+71% and +98%). We conclude that cell population of the collecting cortical tubule (CNT and CCT) is heterogeneous with regard to uridine incorporation, reflecting RNA synthesis.
Biosynthesis of growth hormone in the rat anterior pituitary gland. Stimulation of biosynthesis in vitro by insulin