Atrial natriuretic factor receptor subtypes in the rat central nervous system

Atrial natriuretic peptide negatively regulates follicle-stimulating hormone-induced porcine oocyte maturation and cumulus expansion via cGMP-dependent protein kinase pathway

This study examined the effect of atrial natriuretic peptide (ANP) on porcine cumulus-enclosed oocyte (CEO) maturation and cumulus expansion. ANP negatively regulated follicle-stimulating hormone (FSH)-stimulated germinal vesicle breakdown (GVBD; 90.1, 81.2 and 68.2% for FSH, FSH+10nM ANP and FSH+1 microM ANP, respectively), first polar body emission (PB1; 86.1, 75.3 and 53.3% for FSH, FSH+1 nM ANP and FSH+1 microM ANP, respectively) and cumulus expansion (CEI; 3.47, 3.16 and 2.43 for FSH, FSH+1 nM ANP and FSH+1 microM ANP, respectively) in a dose-dependent manner when CEOs were cultured in the maturation medium containing porcine follicular fluid (pFF). This negative effect showed a time-dependent manner after preincubation with 100 nM ANP for 5h (78.4% PB1), 10h (81.7% GVBD and 74.1% PB1), 20 h (78.5% GVBD and 68.9% PB1), and 44 h (75.3% GVBD and 60.5% PB1), respectively. ANP also significantly inhibited FSH-induced porcine oocyte GVBD (47.6% versus 83.8%) and PB1 emission (22.4% versus 45.2%) when CEOs were cultured in pFF-free maturation medium. cGMP analog 8-Br-cGMP (10 microM to 1mM) mimicked the effects of ANP on GVBD, PB1, and CEI. The negative effect of ANP was completely reversed by KT5823 (a specific inhibitor of cGMP-dependent protein kinase), while C-ANP-(4-23) (an analogue of ANP and specific binder for natriuretic peptide receptors-C) was ineffective in oocyte maturation. Neither ANP nor C-ANP-(4-23) had an effect on spontaneous porcine oocyte maturation and cumulus expansion. These results suggested that ANP negatively regulates FSH-activated porcine oocyte meiotic resumption, meiotic maturation and cumulus expansion. The function of ANP on porcine oocyte maturation is via the cGMP dependent protein kinase (PKG) pathway.

Differences between natriuretic peptide receptors in the olfactory bulb and hypothalamus from spontaneously hypertensive and normotensive rat brain

Natriuretic peptide receptor-A (NPR-A) functional characteristics in the hypothalamus and olfactory bulb (OB) have been investigated in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). Autoradiographic studies demonstrate a decreased number of atrial natriuretic peptide (ANP) binding sites in the olfactory bulb and hypothalamus in SHR compared to WKY rats. We found that NPR-A showed a lower maximal binding capacity (B(max)) and higher affinity in SHR than in WKY rats both in the olfactory bulb and hypothalamus. However, despite the lower B(max) in SHR, both ANP(1-28) and ANP(5-25) stimulated similar or greater cGMP production than in WKY rats. These differences were found even before the development of hypertension. NPR-A in the olfactory bulb and hypothalamus from 3-week-old SHR showed a lower B(max) and K(d) and a higher cGMP production rate than in WKY rats, suggesting that these characteristics are intrinsic of NPR-A in SHR, instead of being a result of hypertension itself. The present study provides evidences for altered NPR-A receptor properties and function in the olfactory bulb and hypothalamus from SHR, which might be involved in the pathogenesis of hypertension.

Type B and type C natriuretic peptide receptors modulate intraocular pressure in the rabbit eye

We investigated (1) the in vivo functional significance of the type B (ANP(B)) and type C (ANP(C)) natriuretic peptide receptors in the rabbit eye by evaluating the effect of intracameral administration of C-type natriuretic peptide (CNP) and C-ANP-(4-23) on intraocular pressure, and (2) the action of CNP on guanylate cyclase activity in the rabbit ciliary process membranes. Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) were also studied for comparison. We demonstrated that the natriuretic peptides decrease intraocular pressure and stimulate guanylate cyclase activity, CNP being the most potent. The duration of the effect of C-ANP-(4-23) on intraocular pressure reduction was almost 9-fold that of the BNP and 20-fold that of ANP and CNP effect. This ligand increased threefold the immunoreactive natriuretic peptides levels in aqueous humour. Our data demonstrate the presence of functional ANP(A) and ANP(B) receptors in the rabbit eye and that the ANP(C) receptor modulates the concentration of the natriuretic peptides in the aqueous humour.

Higher proportions of type C than of types A and B natriuretic peptide receptors exist in the rat ciliary body

We investigate the interaction of atrial natriuretic peptide (ANP) brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) with their receptors (NPRA, NPRB and NPRC), as well as the proportion and localization of those receptors in the rat ciliary body. Binding assays and affinity cross-linking experiments demonstrated the presence of the NPRC receptor type. However, the three natriuretic peptides stimulate the guanylate cyclase activity in the ciliary body membranes suggesting the presence of the NPRA and NPRB receptor type. Microautoradiographic data show that the NPRs are localized in the whole ciliary body. Our results indicated that NPRC is the most prominent receptor type in this tissue.

Receptors for atrial natriuretic peptide in adrenal chromaffin cells

Receptors for atrial natriuretic peptide (ANP) in isolated bovine adrenal chromaffin cells were characterized. 125 I-ANP specifically bound to the cells with a Kd of 103 pM and a Bmax of 5.6 fmol/10(6) cells (16.5 fmol/mg of cell protein). C-ANF, a highly selective ligand for ANP-C receptors of natriuretic peptides, did not compete for 125 I-ANP binding at concentrations up to 10nM. Chemical cross-linking of 125I-ANP to the cells showed a single molecular size of the 120 kDa binding site on SDS gel electrophoresis under reducing conditions. CNP, a specific peptide for the ANP-B receptor, was much less potent than ANP in inhibiting 125 I-ANP binding and in displacing 125 I-ANP from the 120 kDa band. These results suggest that ANP specifically binds to the ANP-A receptor of 120 kDa and that there is no ANP-C receptor in bovine adrenal chromaffin cells.

Atrial natriuretic factor inhibits noradrenaline release in the presence of angiotensin II and III in the rat hypothalamus

1. Atrial natriuretic factor effects on neuronal noradrenaline release evoked by angiotensin II or III and high potassium solution plus angiotensin II and III in the rat hypothalamus were studied. 2. Atrial natriuretic factor (10 nM) did not modify spontaneous noradrenaline release. On the other hand, the atrial factor diminished the increase of noradrenaline release induced by both angiotensin II (1 microM) or angiotensin III (1 microM). 3. Ten nanomolar ANF reduced the amine output induced by 100 nM KCl. Both angiotensins enhanced the 3H-noradrenaline secretion stimulated by high potassium solutions. When atrial natriuretic factor was added to the medium containing the depolarizing KCl solution plus angiotensin II or III (1 microM), the diminishing effects were greater than when the atrial factor was added to the depolarizing solution alone. 4. Our results suggest that atrial natriuretic factor effects on noradrenaline release, evoked by angiotensin II, III and KCl, may be involved in the regulation of the central catecholamine pathways and sympathetic activity.

Localization and characteristics of atrial natriuretic peptide receptors in prenatal and postnatal rat brain

We studied the expression of atrial natriuretic peptide (ANP) receptor subtypes during development in the rat forebrain, using quantitative autoradiography. Highest ANP binding was observed in the cortical neuroepithelium at embryonic day 17. Lower ANP binding was found in cingulate and frontal cortices at postnatal day 10, but none was detectable at 8 weeks of age. In the neuroepithelium of the embryonic rat, binding was displaced with a potency of rat ANP-(1-28) (rANP) > porcine type-C natriuretic peptide (pCNP-22) = rat ANP fragment C-ANP-(4-23) (rC-ANP-(4-23)) = rat brain natriuretic peptide (rBNP-32), different from that of any of the well-characterized (ANPA, ANPB, and ANPC) natriuretic peptide receptors. The present results support the hypothesis of a role for ANP during brain maturation and indicate that the ANP receptors highly expressed in the embryonic neuroepithelium may belong to a new ANP receptor subtype not yet characterized.

Central action of C-type natriuretic peptide on vasopressin secretion in conscious rats

The effect of intracerebroventricular injection of C-type natriuretic peptide (CNP) on arginine vasopressin (AVP) secretion was studied in conscious rats, and was compared to that of atrial natriuretic peptide (ANP). The AVP secretion induced by central injection of 0.1 nmol angiotensin II was significantly suppressed by the pretreatment with 1 nmol CNP. ANP at a dose of 0.1 nmol elicited almost equivalent suppressive action to 1 nmol CNP. Considering that CNP is a specific ligand for ANP-B receptor, while ANP is that for ANP-A receptor, the result demonstrates that CNP possesses the similar central action to ANP, and suggests that the distribution of ANP-A and ANP-B receptors and/or their affinity towards each natriuretic peptide are different in the central nervous system.

Effect of angiotensin II and atrial natriuretic factor on neurons in the subfornical organ of ducks and rats in vitro

Atrial natriuretic factor (ANF) antagonizes many angiotensin II (ANGII)-induced effects on osmoregulatory relevant parameters in vivo. In this study ANF analogues decreased the spontaneous and the ANGII-induced electrical activity of subfornical organ (SFO) neurons in rats, but had no effect on ANGII sensitive or insensitive SFO neurons in ducks. These results suggest a more distinct functional separation for the responsiveness to ANGII and ANF in birds compared to mammals.

Autoradiographic visualization of the natriuretic peptide receptor-B in rat tissues

Natriuretic peptide receptor-B (NPRB) was visualized in rat tissues by in vitro autoradiography, using its putative physiological agonist C-type natriuretic peptide (CNP). In initial studies, we determined that atrial natriuretic peptide (ANP) is not a suitable ligand for labeling the NPRB: in tissues reported to contain NPRB transcripts, CNP did not inhibit [125I]ANP binding except to NPRC sites. Therefore, to visualize the NPRB we used 125I[Tyr(o)]-CNP as a radioligand with an excess of NPRC-blocking peptide: C-ANP. With this approach we detected the highest number of NPRB-like sites in the pars intermedia of the pituitary gland. A large number of these sites were present in pituitary neural and anterior lobes, area postrema, adrenal medulla and cortex. A moderate NPRB population was observed in the subfornical organ, plexiform layer of the olfactory bulb and kidney. Low concentrations of NPRB were noted in the cerebellum and cerebrum but not in the choroid plexus and pia-arachnoid. Saturation experiments performed on cerebellum sections revealed a very low concentration (Bmax 4.8 fmol/mg protein) of high affinity (Kd 1.2 nM) NPRB-like sites. This study is the first demonstration of 125I[Tyr(o)]-CNP binding sites with characteristics of the NPRB in intact tissues.

C-type natriuretic peptide-22 differentiates between natriuretic peptide receptors in rat choroid plexus and subfornical organ

Atrial natriuretic peptide (ANP) receptors in the rat choroid plexus and subfornical organ were characterized with C-type natriuretic peptide-22 (CNP-22) and 125I-Tyr0-CNP-22. The receptor autoradiographic method we used revealed that 125I-Tyr0-CNP-22 specifically bound to the choroid plexus, but only slightly to the subfornical organ, areas densely labeled with 125I-alpha-rat ANP (125I-rANP). CNP-22 significantly inhibited 125I-rANP binding to the choroid plexus; however, the peptide did not affect 125I-rANP binding to the subfornical organ. Thus, the characteristics of ANP receptors in the rat choroid plexus and subfornical organ are probably different.