To characterize natriuretic peptide receptor (NPr) gene expression in human tissues, we cloned portions of the cDNAs codifying for NPr with guanylyl cyclase activity (NPr-A and NPr-B) and without guanylyl cyclase activity (NPr-C). Total RNA was extracted from samples taken at surgery from normal human tissues. NPr-A and NPr-B cDNAs obtained from lung as well as NPr-C cDNA obtained from renal cortex were cloned, characterized, and used for comparative Northern analysis. NPr-A mRNA (approximately 4 kb) was most abundant in adipose tissue (8 patients) independently on the site of sampling, whereas it was approximately 2.5-fold and 5-fold less abundant, respectively, in kidney (either renal cortex or papilla from 3 patients) and adrenal (4 patients), known target tissues of natriuretic peptides. NPr-C mRNAs (approximately 7.7 and 6.8 kb) had a similar tissue distribution but the highest levels were found in renal tissue and only very low expression levels were found in adrenals (approximately 20-fold lower than renal cortex). The ratio of NPrA versus NPr-C mRNA levels were highest in adrenal and lowest in renal tissue. NPr-B mRNA (approximately 4 kb), which encodes the receptor for the C-type natriuretic peptide, had a different and wide tissue distribution, including expression in ileum and liver, with the highest levels in venous and prostatic tissue. These results indicate that, in humans, different patterns of NPr expression with different NPr-A/NPr-C mRNA level ratios, are present in known target tissues of natriuretic peptides. "Non-classic" target tissues, such as the adipose one, maximally expressed NPr-A and also NPr-C, suggesting that natriuretic peptides may have wider functional activities than those previously demonstrated.

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Type 1 angiotensin II (AII) receptors (AT1 receptors), besides stimulation of aldosterone secretion, seem to transduce the growth factor-like activity of AII on glomerulosa cells. Although a local renin-angiotensin system and AII synthesis have been found in human adrenals and aldosteronomas, it is unclear whether aldosteronomas express AT1 receptors. Utilizing polymerase chain reaction (PCR) and reverse transcription-PCR (RT-PCR) with primers complementary to both genomic and cDNA sequences of human AT1 receptor, we have amplified and cloned a 734 bp fragment of the AT1 coding region. This DNA, after cloning and sequencing, was used for Northern analysis. Total RNA was extracted from 5 non-tumorous adrenals and 5 aldosteronomas. AT1 mRNA (approximately 2.4 kb) was expressed in all the aldosteronomas tested. Densitometric analysis of AT1 signals, corrected by beta actin expression, when compared to non-tumorous adrenals, did not show significant differences. AT1 receptor density and affinity in cell membrane obtained from 9 non-tumorous adrenal cortex and 8 aldosteronomas were also studied. 125I-AII was used as ligand and Dup 753 as AT1 antagonist: AT1 receptor density and affinity were not significantly different in aldosteronomas vs non-tumorous adrenal cortex. In conclusion, the expression of AT1 gene and the formation of an apparently normal receptor suggest that AT1 receptor should have a role in aldosteronoma cell biology.

The local renin-angiotensin system may regulate adrenal cell growth and function. Angiotensinogen, renin, and angiotensin converting enzyme gene expression were studied in four normal adrenal glands (removed from patients with renal carcinomas) and five aldosterone-secreting adenomas. Northern blot analysis showed expression of angiotensinogen messenger RNA (mRNA) in normal adrenals at levels approximately 35 -fold lower than liver and sixfold lower than kidney. Similar angiotensinogen mRNA levels were present in two aldosteronomas, whereas a third had levels approximately 50% of those found in kidney. Renin mRNA was detectable in most normal adrenals and in three adenomas, one of which had relatively high renin mRNA levels. Angiotensin converting enzyme gene was expressed in adrenal tissue and in three adenomas. Portions from these normal adrenals and two of these aldosteronomas, as well as samples from two other adrenals and three aldosteronomas, were also studied in an in vitro supervision system coupled with active renin radioimmunometric assay, angiotensin II/HI, and aldosterone radioimmunoassay. Total amounts of active renin and angiotensin II/IH released from normal adrenals during 270 minutes of supervision were higher than the amounts released from aldosteronomas (312±35 versus 187+43 and 823±100 versus 436±55 pg/100 mg tissue, respectively; mean±SEM, p<0.05), whereas aldosterone release from the adenomatous tissue was approximately threefold higher (320±21 versus 115±18 ng/100 mg tissue; mean±SEM, p<0.01). Total amounts of active renin and angiotensin II/IH released by normal or adenomatous adrenal samples exceeded threefold to fourfold the amounts extracted from similar samples of the same surgical specimen. These findings provide evidence for a local renin-angiotensin system in human adrenals and in at least some aldosteronomas. (Hypertension 1992;19:702-707) KEY WORDS • angiotensinogen • renin • angiotensin II • adrenal glands • aldosterone • human studies • angiotensin converting enzyme T he renin-angiotensin system (RAS) has been considered as an endocrine system whose components are synthesized by different organs and interact in the circulation to generate the active peptide angiotensin II (Ang II), which then reaches target cells. In the past decade, several studies conducted on animals found evidence for a complete RAS within various tissues, suggesting that locally generated Ang II may act as an autocrine or paracrine mediator that might be independently regulated from circulating RAS.

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