Possible involvement of calcitonin gene-related peptide in seawater adaptation of flounder: Expression analysis of its receptor mRNA in the gill

To elucidate the physiological role of the calcitonin gene-related peptide (CGRP) in teleosts, the expressions of calcitonin gene-related peptide receptor (CGRPR) and CGRP mRNA were examined using the reverse transcription-polymerase chain reaction method in the gills of flounder during adaptation from seawater to freshwater. Another related receptor mRNA, which is estimated to be a calcitonin receptor (calcitonin receptor-like receptor; CTRLR), was also monitored in the gills. The expressions of CGRPR mRNA in the gills decreased after transferring flounder from seawater to dilute seawater and became undetectable in freshwater conditions. In contrast, CTRLR mRNA expression in the gills did not change during acclimation. Interestingly, CGRP mRNA was not detected in gills when flounder were transferred from seawater to dilute seawater or freshwater. Therefore, CGRP secreted from other tissue, such as the intestine, may act on the gills and play a role in the seawater adaptation of flounder.