AJP - Renal Physiology, Vol 253, Issue 2 269-F276, Copyright © 1987 by American Physiological Society
Dynamics of NAD in cortical nephron segments: effect of nicotinamide and of dietary phosphate intake
A. N. Yusufi, G. M. Kiebzak, E. Kusano, J. L. Werness, S. Homma and T. P. Dousa
NAD content and the rate of NAD hydrolysis were determined in proximal
convoluted tubules (PCT), proximal straight tubules (PST), and adjacent
cortical nephron segments microdissected from kidneys of
thyroparathyroidectomized (TPTX) rats. In the basal state, rats fed a
normal phosphate diet had an NAD content higher in PCT, PST, and in
cortical ascending limb (CAL) than in glomeruli. After intraperitoneal
injection of nicotinamide, the NAD content increased significantly in all
nephron segments except CAL; the greatest (delta + 277%) increase was found
in PCT, with less (delta + 82%) in PST. In experiments conducted on TPTX
rats stabilized on a low-phosphorus diet, NAD content increased in response
to a nicotinamide injection in PCT (delta + 197%), but did not change
significantly in PST. The catabolism of NAD was determined by generation of
[3H]adenosine, a major metabolite of [adenine-2,8-3H]NAD. The rate of
[3H]adenosine generation from [3H]NAD was significantly (P less than 0.001)
higher in PST than in PCT. We conclude that, in response to nicotinamide
administration in vivo, the NAD content increases more in PCT than in PST
and that this difference may be, at least partly, due to a lower rate of
NAD breakdown in PCT. In a state of dietary phosphate deprivation, NAD also
increases significantly in response to intraperitoneal nicotinamide in PCT,
but it does not increase significantly in PST. The nicotinamide-elicited
increase of NAD content in proximal tubules, mainly in PCT, may be related
to inhibition of Na+-gradient-dependent inorganic phosphate (Pi)
reabsorption across the brush-border membrane of proximal tubules and to
the phosphaturic effect of nicotinamide in rats fed normal-Pi diet.
