AJP - Renal Physiology, Vol 244, Issue 6 628-F632, Copyright © 1983 by American Physiological Society
In vivo metabolism of tritiated LHRH by the whole kidney and individual tubules of rats
M. A. Stetler-Stevenson, G. Flouret, S. Nakamura, B. Gulczynski and F. A. Carone
[pyroglutamyl-3,4-3H]Luteinizing hormone-releasing hormone ([3H]LHRH) and
[14C]inulin were infused into individual nephrons in Inactin-anesthetized
rats and the amount of radioactive label and the identity of the
radioactively labeled material in urine were determined. The site of
infusion was identified by latex injection and microdissection. [3H]LHRH
was microinfused at 1.5 X 10(-5 M (concentration 10(6)-10(7) higher than in
plasma) and analysis of urinary metabolites was performed by
high-performance liquid chromatography. The urinary recovery of tritium
label was 81% when proximal tubules were infused and 94% when distal
tubules were infused. For proximal tubules 90% of the label recovered in
urine appeared as pGlu-His (metabolite 2), pGlu-His-Trp (metabolite 3), and
pGlu-His-Trp-Ser (metabolite 4), and 10% as LHRH. With distal tubules only
LHRH was detected in the urine. [3H]LHRH was presented to the renal artery
of the filtering rat kidney in vivo, and urine and renal venous blood were
analyzed for breakdown products. The urine contained metabolites 2, 3, and
4 and no LHRH, whereas venous blood contained mainly pGlu, metabolite 4,
and LHRH. When [3H]LHRH was perfused in vivo through the nonfiltering rat
kidney or rat lower limb, renal or femoral venous blood was found to
contain only LHRH. These studies suggest that [3H]LHRH undergoes glomerular
filtration and contact digestion by brush border enzymes of the proximal
tubule to produce metabolites 2, 3, and 4. These metabolites and possibly
LHRH are partially reabsorbed and undergo further intracellular degradation
to produce pGlu. Endothelial and interstitial cells in the kidney and leg
do not appreciably metabolize [3H]LHRH.
