LOCALIZATION OF DIAZEPAM-BINDING INHIBITOR-RELATED PEPTIDES AND PERIPHERAL-TYPE BENZODIAZEPINE RECEPTORS IN THE FROG ADRENAL-GLAND

The adrenal gland of mammals contains high concentrations of periphera l-type benzodiazepine receptors (PBR) and diazepam-binding inhibitor ( DBI), a polypeptide which acts as an endogenous ligand for PBR. The ai m of the present study was to investigate the localization of DBI and PBR in the adrenal gland of the frog Rana ridibunda. Reverse transcrip tion followed by polymerase chain reaction with specific primers for t he frog DBI cDNA showed the presence of DBI mRNA in frog adrenal gland extracts. The cellular distribution of DBI and PER was investigated u sing an antiserum against the octadecaneuropeptide DBI [33-50] (ODN) a nd antibodies against the 18-kDa isoquinoline binding protein subunit of PBR (IBP), respectively. ODN-like immunoreactivity was found in chr omaffin cells and in Stilling's cells, but not in adrenocortical cells . IBP-like immunoreactivity was observed in chromaffin cells, in Still ing's cells and in a small proportion (11%) of steroid-secreting cells . The ODN- and IBP-immunoreactive materials were homogeneously distrib uted in the cytoplasm of chromaffin cells and concentrated at the peri phery of large cytoplasmic vesicles in Stilling's cells. The proportio n df ODN-positive Stilling's cells showed marked circannual variations with a maximum in July. Similarly, the proportion of IBP-positive Sti lling's cells was 17 times higher in July than in December. These resu lts indicate that, in the frog adrenal gland, DBI-related peptides and PER are simultaneously expressed in chromaffin cells and Stilling's c ells, suggesting that endogenous ligands for PER may play a physiologi cal role in the control of adrenal cell activity.