AJP - Renal Physiology, Vol 254, Issue 1 159-F163, Copyright © 1988 by American Physiological Society
A highly sensitive radioreceptor assay for atrial natriuretic peptide in rat plasma
B. J. Ballermann
Laboratory of Kidney and Electrolyte Physiology, Brigham and Women's Hospital, Boston, Massachusetts 02115.
To enable serial measurements of plasma atrial natriuretic peptide (ANP)
concentrations in the rat, a microradioreceptor assay (RRA) for this
hormone was developed. Glomerular microsomes bearing ANP receptors were
used to bind ANP. The smallest quantity of ANP detectable by this method
was 0.2 fmol/sample. By contrast, a radioimmunoassay for ANP was sensitive
to 2.4 fmol/sample. The intra- and interassay coefficients of variation for
the RRA were 4.1 and 11.6%, respectively. Recovery of 10, 20, 50, and 100
pM synthetic ANP added to unextracted rat plasma was essentially 100%.
Biologically inactive, synthetic amino- and carboxy-terminal ANP fragments
added to rat plasma were not detected. Plasma ANP was stable when measured
four consecutive times at 90-min intervals in 10 fasting rats. In a
separate group of rats, fasting plasma ANP levels averaged 34 +/- 3 and
rose to 57 +/- 5 pM in the postprandial state (P less than 0.001), whereas
levels in fasting time controls remained constant. It is concluded that the
RRA for ANP described here detects ANP in microliter quantities of
unextracted rat plasma. Thus serial measurements of ANP concentrations can
be undertaken in rats without inducing major changes in the volume status.
