Atrial natriuretic peptide (ANP)-granules of auricular cardiocytes in dehydrated and rehydrated mice.

Atrial natriuretic peptide (ANP)-granules of auricular cardiocytes were examined by immunohistochemistry, transmission electron microscopy and ultrastructural morphometry in dehydrated and rehydrated mice. In addition, plasma ANP and tissue ANP mRNA levels were determined by radioimmunoassay and polymerase chain reaction, respectively. ANP immunoreactivity and the number of granules in the cardiocytes were increased with time in the dehydration group, while plasma ANP and tissue ANP mRNA levels were decreased on day 3 of dehydration. On day 3 of dehydration, the number of ANP-granules (153.2 +/- 8.3, mean +/- standard error) was significantly (p < 0.05) greater than in the control (125.8 +/- 6.7). IN the rehydration group, the immunoreactivity and number of ANP-granules were less than those in the group on day 3 of dehydration. The plasma ANP level during rehydration for 12 hr was slightly elevated in comparison with the group on day 3 of dehydration. The tissue ANP mRNA level after 12 hr of rehydration was lower than that on day 3 of dehydration. The diameter of ANP-granules was significantly (p < 0.01) smaller in all experimental groups than in the control. These findings suggest that synthesis and secretion of ANP are inhibited and ANP-granules are stored in auricular cardiocytes during dehydration.