AJP - Renal Physiology, Vol 246, Issue 1 59-F66, Copyright © 1984 by American Physiological Society
Renal gluconeogenesis: axial and internephron heterogeneity and the effect of parathyroid hormone
M. S. Wang and K. Kurokawa
To better understand the regulation of renal gluconeogenesis that occurs in
the proximal nephron, glucose production rates from various substrates were
determined in defined proximal tubule segments of the rat. Tubule segments
tested were the S1 and S2 segments of superficial (SF) nephrons, the S1
segments of juxtamedullary (JM) nephrons, and the S3 segments. Glucose
production (in decreasing order) was: from alpha-ketoglutarate, JM S1, SF
S1, SF S2; from pyruvate, SF S2, JM S1, and SF S1; from glutamine, SF S1,
JM S1; and from glutamate, SF S1 = JM S1. Little glucose was produced in
the S3 segments. Glucose production from glutamate was lower than that from
the other three substrates in JM S1, and glutamine was the best
gluconeogenic substrate in SF S1. The effects of parathyroid hormone (PTH),
a known stimulator of renal gluconeogenesis, and cAMP were examined using
alpha-ketoglutarate as the substrate. Both stimulated glucose production in
the S1 and S2 segments of the SF nephron. Although PTH stimulated adenylate
cyclase in the S1 segments of the SF and JM nephrons, it had no effect on
glucose production in the JM S1. Glucose production rose in the SF S1 and
JM S1 in response to increasing concentrations of hydrogen or calcium ions,
indicating that gluconeogenesis can be increased in these nephron segments.
Differences may therefore be present in the cellular responses to PTH
distal to cAMP formation in the nephron segments of the SF and JM nephrons.
These findings show the presence of both axial and internephron
heterogeneity of renal gluconeogenesis and suggest the difference in the
effects of PTH on the function of SF and JM nephrons.
