DISTRIBUTION OF THE PARATHYROID HORMONE-RELATED PEPTIDE AND ITS RECEPTOR IN THE SACCUS VASCULOSUS AND CHOROID-PLEXUS IN THE RED STINGRAY (DASYATIS-AKAJEI, ELASMOBRANCH)

1. The exact role of the parathyroid hormone-related peptide (PTHrP) i s not fully understood. We used immunohistochemistry to localize the P THrP and its receptor in the brain of the red stingray, particularly i n the saccus vasculosus (SV) and choroid plexus. 2. Immunoreactive PTH rP and its receptor were detected in the epithelial cells of the SV an d the choroid plexus. In addition, the neuronal perikarya in the nucle us of the SV located in the hypothalamus is positive for the PTHrP. 3. No PTHrP-containing neurons were detected in the choroid plexus. Extr acts of SV and choroid plexus showed positive reactions against the PT HrP and its receptor antibody in Western blot analysis. 4. High levels of immunoreactive PTHrP were detected in the plasma equivalent to tho se present in human humoral malignant hypercalcemia. In contrast, the immunoreactive PTHrP concentration in the cerebrospinal fluid was belo w detectable levels. 5. Our results suggest that the regulation of the PTHrP in the SV differs from that in the choroid plexus in the red st ingray.