Localization of the Neuropeptide Arginine Vasotocin and Its Receptor in the Osmoregulatory Organs of Black Porgy, : Gills, Kidneys, and Intestines.

The neurohypophysial hormone arginine vasotocin () and its receptor () regulates ions in the osmoregulatory organs of euryhaline black porgy (). The localization of and transcripts in the osmoregulatory organs has yet to be demonstrated. Thus, in the present study, we performed an in situ hybridization analysis to determine the localization of and in the gills, kidneys, and intestines of the black porgy. The and transcripts were identified in the filament and lamellae region of the gills in the black porgy. However, the basal membrane of the filament contained more and transcripts. Fluorescence double tagging analysis revealed that and mRNAs were partially co-localized with α-Nka-ir cells in the gill filament. The proximal tubules, distal tubules, and collecting duct of the kidney all had positive hybridization signals for the and transcripts. Unlike the α-Nka immunoreactive cells, the and transcripts were found on the basolateral surface of the distal convoluted tubule and in the entire cells of the proximal convoluted tubules of the black porgy kidney. In the intestine, the and transcripts were found in the basolateral membrane of the enterocytes. Collectively, this study provides a summary of evidence suggesting that the neuropeptides and with α-Nka-ir cells may have functions in the gills, kidneys, and intestines via ionocytes.