Z. Z. To determine organ and development related differences in tissue norepinephrine concentration tNE in Dahl salt-sensitive S and Z. Z . -resistant R rats, we measured the tNE of 16 organs, including the heart left ventricle , kidney, cerebrum, brain stem, stomach, jejunum, ileum, colon, spleen, pancreas, liver, aorta, lung, bone, salivary gland, and muscle, at 1, 3, 5, 7, 9, 11 weeks old. Large differences were Z. found in tNE among the organs of both S and R rats, ranging from 4.0"1.1 ngrg tissue the bone of S rats to 1234.8"32.5 ngrg Z. tissue the salivary gland of R rats . tNE in R rats increased development-dependently in 12 of 16 organs, but did not significantly change in the other three organs, and decreased in the bone. On the other hand, the development-dependent increase in tNE was suppressed in S rats, and the tNE values of S rats were significantly lower than those of R rats in 14 of 16 organs. To eliminate the baroreflexive effects Z. on tNE, another group of 5-week-ol..