Endogenous adrenomedullin system regulates the growth of rat adrenocortical cells cultured in vitro

The expression of adrenomedullin (AM) system (AM and its receptors), as mRNA and protein, has been detected in the mammalian adrenal zona glomerulosa (ZG) cells. Evidence has been also provided that exogenous AM is able to enhance in vivo and in vitro the proliferative activity of ZG cells. However, the possibility that endogenous AM system may act as a physiological ZG growth regulator has not yet been demonstrated. Hence, we investigated whether the prolonged (48-72 h) suppression of AM gene transcription by a specific antisense oligonucleotide or the long-lasting (24-96 h) blockade of AM receptors by the selective antagonist AM(22-52) are able to affect the growth of rat ZG cells cultured in vitro. Freshly dispersed cells were incubated for 3 h with an AM antisense or a scrambled oligonucleotide, then they were cultured for 48 or 72 h, and proAM mRNA expression and AM content was checked by reverse transcription-polymerase chain reaction and radioimmune assay, respectively. Other ZG cells were cultured in the presence of AM and/or AM(22-52). Growth assay showed that AM (10(-8) M) decreased and AM(22-52) (10(-6) M) increased the duplication time of cultured cells. AM (10(-8) M) raised proliferation index and decreased apoptotic index of cultured cells, and AM(22-52) reversed these effects. AM(22-52) (from 10(-7) to 10(-6) M) and pAM gene suppression by the antisense oligonucleotide significantly lowered proliferation index and increased apoptotic index of cultured cells, both these effects being abrogated by AM (10(-8) M). It is concluded that endogenous AM system plays a relevant role in the autocrine-paracrine regulation of cultured rat ZG-cell growth.