Endocrine Abstracts

Proadrenomedullin N-terminal 20 peptide (PAMP) and adrenomedullin are hypotensive peptides that are cleaved from the proadrenomedullin peptide. Adrenomedullin can act via the complex calcitonin receptor like receptor (CRLR) and receptor activity modifying protein (RAMP) 2 or the putative receptor, CRLR/RAMP3 complex. CGRP (Calcitonin gene related peptide) binding is conferred by the CRLR/RAMP1 complex. This study was carried out to see how adrenomedullin and PAMP affected the mRNA expression of CRLR and the RAMPs in the human adrenocortical cell line, H295R.
H295R cells were treated for 24 hours with adrenomedullin 10^-7 or PAMP 10^-7. Interactions between these two peptides were then investigated by incubating one peptide for 24 hours and then the other for 4 hours. Cells were then harvested and mRNA was extracted. Expression was analysed by RT-PCR and Northern blot.
CRLR mRNA was detected in untreated cells and in cells treated with PAMP but was absent from cells treated with adrenomedullin. Four hour stimulation with PAMP reversed the effect of adrenomedullin. RAMP1 expression was detected in untreated and all cells that had been treated with PAMP. RAMP1 mRNA was not detected in adrenomedullin treated cells. Expression of RAMP2 and RAMP3 mRNA was detected in control and all treated cells.
In conclusion, adrenomedullin down-regulates both CRLR and RAMP1 mRNA expression in H295R cells. PAMP opposes this action. Thus, it appears that adrenomedullin down-regulates its own receptor and PAMP opposes this action. These data suggest that adrenomedullin binding may be regulated only by changes in CRLR expression. This is also the first study that shows opposing effects of adrenomedullin and PAMP.
Sponsored by the British Heart Foundation.