Atrial natriuretic factor mRNA and binding sites in the adrenal gland

Interactions between ouabain, atrial natriuretic peptide, angiotensin-II and potassium: effects on rat zona glomerulosa aldosterone production

The effects of ouabain, atrial natriuretic peptide, angiotensin-II and potassium on aldosterone production by collagenase dispersed rat zona glomerulosa cells were studied. A-II and 10(-4) M ouabain-induced increases in aldosterone production was inhibited by 10(-9) M ANP at all potassium concentrations examined. 10(-4) M ouabain inhibited the A-II induced increase in aldosterone production at all potassium concentrations. The degree of this inhibition was smaller at higher potassium levels. Ouabain enhanced the inhibitory effect of ANP on A-II-induced aldosterone synthesis at all potassium concentrations. Interactions between A-II, ANP, ouabain and potassium may be of physiological significance in the regulation of aldosterone secretion.

Messenger RNAs encoding the natriuretic peptides and their receptors are expressed in the eye

The rates of secretion and removal of aqueous humour are major determinants of intraocular pressure (IOP). The natriuretic peptides, atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) are vasodilators with variable effects on electrolyte and water transport at sites such as the nephron. There is some evidence that they may also affect fluid balance in the eye. As a first step in understanding the function of these peptides in the eye, we have used the technique of cDNA amplification with the polymerase chain reaction to demonstrate the presence of mRNA transcripts encoding the three natriuretic peptide receptors (NPR-A, NPR-B and NPR-C) in the retina, choroid and ciliary process of the rat and rabbit eye. In addition we have observed a differential distribution of ANP, BNP and CNP mRNAs in ocular tissues suggesting that at least part of the natriuretic peptide immunoreactivity detected in the eye arises from local synthesis of peptide. Thus, the eye appears to be able to synthesize all the components of the natriuretic peptide system necessary to modulate IOP independently of changes in the plasma concentrations of these peptides.

Localization and coexistence of atrial natriuretic peptide (ANP) and neuropeptide Y (NPY) in vertebrate adrenal chromaffin cells immunoreactive to TH, DBH and PNMT

Antisera specific for mammalian atrial natriuretic peptide (ANP) and neuropeptide Y (NPY) were applied to examine, in immunofluorescence, the occurrence of cells immunoreactive to ANP and NPY in the adrenal organs of mammals, birds, reptiles, amphibians, and bony fish. Catecholamine-containing cells were identified using antisera against tyrosine-hydroxylase, dopamine-beta-hydroxylase, and phenylethanolamine-N-methyl-transferase. In all vertebrates studied, immunoreactivities to ANP and NPY occurred in adrenal chromaffin cells but were absent from the cortex or its homolog, the interrenal. The majority of immunoreactivities to ANP and NPY was confined to the adrenaline cells. In mammals, the number of ANP-immuno-reactive cells (60%-80% of the total cell population) exceeded that of the NPY-immunoreactive cells (35%-45%). In birds, reptiles, and Amphibia, the numbers of ANP-immunoreactive (35%-40%) and NPY-immunoreactive (30%-35%) cells were in a similar range. The bony fish showed a density of both ANP-immunoreactive (80%-90%) and NPY-immunoreactive (35%-40%) cells. In all species studied, immunoreactivities to ANP and NPY partially coexisted. Generally, 30%-55% of the ANP-immunoreactive cells also contained NPY-immunoreactivity. In rat, coexistence amounted to almost 100% and in quail to 95%. Except for the rat, three subpopulations of chromaffin cells seemed to occur: ANP-immunoreactive non-NPY-immunoreactive, ANP-immunoreactive+NPY-immunoreactive, and NPY-immunoreactive non-ANP-immunoreactive cells. Thus, adrenal ANP and NPY share a conservative history and coexist as early as at the level of bony fish. The endocrine actions of ANP and NPY derived from medullary cells on cortical cells as found in mammals might be based on an ancestoral paracrine system. In submammalians, ANP and NPY may not only act as endocrine hormones, but also influence steroid-producing interrenal cells in a paracrine manner, and act as modulators on chromaffin cells.

Differential regulation of natriuretic peptide receptor messenger RNAs during the development of cardiac hypertrophy in the rat

The heart expresses the three natriuretic peptide receptors (NPR), namely NPR-A, NPR-B, and NPR-C. We have examined the temporal relationship between the expression of mRNA transcripts for atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) and their receptors in the heart during the development of cardiac hypertrophy in the aortovenocaval fistula rat. Messenger RNAs were measured by cDNA amplification. Progressive cardiac hypertrophy was accompanied by increased ANP mRNA prevalence throughout the heart and increased BNP mRNA in the left atrium. The most striking observation was the gradual disappearance of NPR-C transcripts (the putative "clearance" receptor) in all chambers; this was in marked contrast to the increase in mRNA levels for NPR-A and NPR-B (the guanylyl cyclase-linked receptors). Our observations have important therapeutic implications if the transcript changes are mirrored at the receptor protein level because (a) the apparent down-regulation of NPR-C may enhance the local action of natriuretic peptides on the heart, and (b) the loss of NPR-C, particularly if it is widespread, may reduce the rate of elimination of the natriuretic peptides, restricting the therapeutic potential of specific NPR-C ligands designed to reduce peptide clearance.

A comparative study of the effect of atrial natriuretic peptide (ANP) on the secretory activity of rat adrenal cortex and angiotensin-II-responsive adrenocortical autotransplants

Rat adrenocortical autotransplants regenerated from capsular-tissue fragments implanted in the musculus gracilis displayed an in-vitro basal gluco- and mineralocorticoid secretion qualitatively similar to that of adrenal quarters from control rats. Moreover, like adrenal quarters, they responded to angiotensin-II (Ang-II, 10(-8) M) by raising their yield of 18-hydroxylated steroids (18-hydroxy-11-deoxycorticosterone, 18-hydroxycorticosterone and aldosterone). ANP (10(-8) M), one of the main negative modulators of the zona-glomerulosa (ZG) mineralocorticoid secretion, totally blocked the ANG-II stimulating effect on adrenal quarters, but not that on adrenocortical autotransplants. Autoradiography showed that, in contrast with ZG cells of control rats, ZG-like cells of transplants did not significantly bind 125I-ANP. The hypothesis is discussed that ZG-like cells of regenerated adrenocortical nodules lack specific receptors for ANP.