Radioautographic localization of atrial natriuretic factor receptors in the rat testis

Regulation of steroidogenesis by atrial natriuretic peptide (ANP) in the rat testis: differential involvement of GC-A and C receptors

Previous studies have established a stimulatory effect of natriuretic peptides (NP) on testosterone production in mouse Leydig cells as intense as that of LH. Chronic administration of ANP in mice, on the other side, reduced testosterone levels. So, the understanding of the role of ANP on testicular steroidogenesis has been impaired by discrepant findings. The aim of the present study was to clarify the physiological role of ANP in the rat testis steroidogenesis using a model that preserves the interactions between testis cells and a medium devoid of any circulating factors that could interfere with testosterone production. First, ANP was immunolocalized in the interstitial compartment of the rat testis, mainly in Leydig cells. We also determined the presence of ANP and both GC-A (guanylyl cyclase A) and C receptors by real-time PCR in testis. Perfusion in vitro of testis with ANP (1 and 3x10(-7)M) stimulated testosterone production in a time- and dose-dependent manner. On the other side, testosterone secretion induced by LH was blunted by ANP. Similar effect was obtained using the specific C receptor ligand, cANF, indicating the involvement of C receptor in such response. In conclusion, ANP stimulated testosterone production in the rat testis perfused in vitro but decreased testosterone production LH-induced, effect that seems to involve C receptor. To this extent, our results suggest the existence of a local and complex peptidergic system in the rat testis, involving ANP and its receptors that could importantly modulate the androgen biosynthesis.

Atrial natriuretic peptide induces an acrosome reaction in giant panda spermatozoa and enhances their penetration of salt-stored porcine oocytes

Atrial natriuretic peptide (ANP) is a vasodilator peptide primarily produced in the heart. Locally synthesized ANP has been found in reproductive tissues of various mammals and humans, and plays an important role in rat oocyte maturation and human sperm function. The objective of the present study was to determine the effects of ANP on the function (acrosome reaction and zona penetration) of giant panda spermatozoa. In fresh and frozen-thawed spermatozoa that had been preincubated for 2.5h, treatment with ANP (for 60 min) significantly increased the proportion of acrosome-reacted spermatozoa; maximal response (an acrosome reaction in 18.3 and 21.8% of fresh and frozen-thawed spermatozoa, respectively) was detected at 1 nM ANP. Treatment with C-ANP-(4-23), an analogue of ANP and specific binder to natriuretic peptide receptors-C (NPRC), had no significant effect on the acrosome reaction. However, the cyclic guanosine 5'-monophosphate (cGMP)-dependent protein kinase (PKG) inhibitor KT5823 completely abolished the effect of ANP on acrosome reaction. The effects of ANP, caffeine and heparin on frozen-thawed sperm function were studied by insemination of porcine salt-stored oocytes in a modified Tris-buffered medium (mTBM). The presence of ANP, caffeine or heparin in the insemination medium resulted in a higher proportion (P < 0.05) of oocytes with spermatozoa in the zona and perivitelline space (PVS), and a higher average number of spermatozoa/oocyte (P < 0.05) in the zona and PVS. However, in the absence of ANP, caffeine and heparin, there were no oocytes with a spermatozoon in the PVS. There were no differences among ANP, caffeine or heparin treatments for the proportion of oocytes penetrated or average number of spermatozoa/oocyte in the zona and PVS. In conclusion, we inferred that ANP induced the acrosome reaction of preincubated giant panda spermatozoa by a PKG pathway. Furthermore, ANP enhanced the penetrability of porcine salt-stored oocytes by frozen-thawed giant panda spermatozoa.

Chronic administration of atrial natriuretic peptide reduces testosterone production of testes in mice

The purpose of the present study was to examine the effect of the long-term administration of human atrial natriuretic peptide (ANP) on testosterone production in male mice. Twenty-five mice received ANP (20 ng/hour/g body weight) for 7 days via mini-osmotic pump, and the other group (n = 25) received twice-daily intraperitoneal injections. After death, levels of follicle-stimulating hormone, luteinizing hormone (LH), and testosterone in plasma, pituitary gland, and testis were measured by radioimmunoassay. Five mice from each group were examined histologically. In the minipump group, pituitary and plasma levels were significantly higher than those in the control group (771.2 +/- 43.6 vs 644.8 +/- 24.9 ng/mg and 6.7 +/- 0.6 ng/mg vs 2.5 +/- 0.6 ng/mL, respectively). In the intraperitoneal group, plasma LH levels were significantly higher in the ANP-treated group than that in control mice (9.6 +/- 0.3 ng/mg vs 3.8 +/- 0.5 ng/mL), whereas pituitary levels did not differ significantly. In both studies, testicular and plasma testosterone levels were significantly lower than those in control mice (P <.02). Histological features of the testes in ANP-treated mice revealed structural disorganization and inhibition of spermatogenesis. We conclude that the chronic administration of ANP may result in reduced testosterone production due to testicular damage.

Localization of receptors for natriuretic peptide and endothelin in the duct of the epididymis of the freshwater turtle

The presence of receptor subtypes for natriuretic peptides (NPs) and endothelin (ET) in the epididymis of the freshwater turtle, Amyda japonica, was examined by quantitative in vitro autoradiography using iodinated mammalian-type atrial NP ((125)I-ANP((1-28))), phylogenically conserved C-type NP ((125)I-[Tyr(0)]-CNP((1-22))), and ET-1 ((125)I-ET-1) as radiolabeled ligands. To characterize NP receptor (NPR) subtypes, we also performed an activation of particulate guanylyl cyclase (GC) in membranes of the epididymis by NPs. Specific (125)I-ANP((1-28)) and (125)I-[Tyr(0)]-CNP((1-22)) bindings were localized in surrounding smooth muscle cell layer of the duct of the epididymis with an apparent dissociation constant (K(d)) of 0.84+/-0.15 and 1.74+/-0.39 nM and a maximal binding capacity (B(max)) of 0.47+/-0.11 and 0.08+/-0.01 fmol/mm(2), respectively. Bindings of (125)I-ANP((1-28)) and (125)I-[Tyr(0)]-CNP((1-22)) to these sites were also displaced by des[Gln(18),Ser(19),Gly(20), Leu(21),Gly(22)]ANF((4-23)), a specific ligand of the NP clearance receptor. Production of 3',5'-cyclic guanosine monophosphate by particulate GC in membranes of the epididymis was stimulated by ANP((1-28)), BNP((1-26)), and CNP((1-22)). Receptor subtypes for ET in the epididymis were characterized by competition with BQ 123 and BQ 788 as specific antagonists for ET receptors, type A (ET(A)) and type B (ET(B)) subtypes, respectively. Specific (125)I-ET-1 bindings were localized in the smooth muscle cell layer of the duct of the epididymis with K(d) and B(max) of 0.21+/-0.03 nM and 0.52+/-0.05 fmol/mm(2), respectively. These specific bindings were potently inhibited in a dose-dependent manner by BQ 123, whereas BQ 788 (10 microM) was not in competing for specific (125)I-ET-1 bindings in this structure. Therefore, these results indicate that specific NP and ET receptors are localized in surrounding smooth muscle cells of the duct of the epididymis of the freshwater turtle. It is also suggested that biological and clearance NPR-like subtypes coexist in these cells, and the predominant ET receptor subtype in this tissue is the ET(A)-like receptor. The localization of specific receptors for NPs and ET in the epididymis may be involved in the control of the transport of sperm in the freshwater turtle.

Characterization of the atrial natriuretic peptide system in the oviduct

The atrial natriuretic peptide (ANP) gene is expressed in several extraatrial tissues in which ANP may be involved in the regulation of autocrine or paracrine functions. In the ovary, the synthesis of ANP, its binding sites, and a physiological role were found. The ANP system in the oviduct, however, is yet to be defined. The purpose of the present study was to determine whether the ANP system is present in the oviduct and then to define its function. The serial dilution curves of oviductal extracts in rat and rabbit were parallel to the standard curve of ANP. Molecular profiles using reverse phase HPLC indicated that the prohormone and processed circulating peptide were the main forms present. The immunoreactive ANP content of the oviduct was 27.07 +/- 4.41 pg/mg tissue wet wt (1.19 +/- 0.19 ng/oviduct; n = 10; at metestrus) in rats and 1.21 +/- 0.12 pg/mg tissue wet wt (0.15 +/- 0.01 ng/oviduct; n 12) in rabbits. In adult 4-day cycling rats, the immunoreactive ANP contents in oviducts had a cyclic change characterized by the lowest level at proestrus (14.59 +/- 3.24 pg/mg; n = 12). A distinct and strong ANP immunoreactivity was found in the mucosal layer of rat oviduct, and ANP messenger RNA was also detected in the oviduct by reverse transcriptase-PCR. Specific high affinity binding sites for iodinated rat ANP ([125I]rANP) were observed in the mucosal layer of the oviduct in rats and rabbits. Specific [125I]rANP bindings localized in the mucosal layer of rabbit oviduct showed an apparent dissociation constant (Kd) of 18.69 +/- 5.55 nM and a maximal binding capacity of 14.85 +/- 6.19 fmol/mm2. These specific [125I]rANP bindings were not reversed by des-[Gln18,Ser19,Gly20,Leu21,Gly22]ANP-(4- 23) as a selective ligand of clearance receptor. Synthetic ANP inhibited both the frequency and amplitude of basal motility of rabbit oviduct in a dose-dependent manner. These results suggest that the oviduct has its own ANP system, and the system is involved in the regulation of oviductal motility.

Differential expression and autoradiographic localization of atrial natriuretic peptide receptor in spontaneously hypertensive and normotensive rat testes: diminution of testosterone in hypertension

Previous studies have shown that the diuretic hormone atrial natriuretic peptide (ANP) also regulates the steroidogenic responsiveness in isolated Leydig cells from mouse and rat testes. In the present study, we examined the distribution of specific receptors for ANP and C-type natriuretic peptide (CNP) in the testicular compartments of 12-week-old Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). We used an in vitro autoradiographic procedure on slide-mounted frozen testicular sections to localize the receptors of the natriuretic peptide hormone family using 125I-ANP and 125I-CNP as radioligands. A high level of specific 125I-ANP binding sites was localized largely in the Leydig cells of the interstitial compartment; other testicular cells were not significantly labeled. On the other hand, no significant difference was observed in 125I-CNP binding sites in the testicular cells of SHR and WKY. Semiquantitative analysis of the binding sites indicated that the density of 125I-ANP receptor binding in Leydig cells of WKY testis was ninefold higher than in those of SHR testis. A moderate level of 125I-ANP binding was also observed in seminiferous tubules, particularly in the spermatids of both SHR and WKY. 125I-ANP binding in WKY spermatids was approximately 2.5-fold higher than in SHR spermatids. Northern blot analysis showed that mRNA specific for guanylyl cyclase type A (Npra) was expressed at approximately twofold higher levels in WKY than in SHR testis. ANP (1 x 10(-8) mol/L) stimulated fourfold to fivefold increased levels of testosterone production in isolated Leydig cells from normotensive WKY compared with those from SHR. These findings support a new physiological role of ANP in Leydig cells, in which a functional relationship seems to exist between testicular ANP receptor expression and testosterone production and the state of hypertension in SHR.

Atrial natriuretic factor in mammalian testis: immunological detection in spermatozoa

Immunoreactive atrial natriuretic factor (ANF) was localized by immunochemistry and radioimmunoassay in mouse and rat testes. The analyses of acid extracts of testes by gel filtration and reverse phase high pressure liquid chromatography (HPLC) revealed the presence of a processed 31-residues peptide and the precursor form of 126-residues pro-ANF molecule corresponding to a molecular weights (Mr) of 3,300 and 18,000, respectively. The concentration of ANF in mice testis averaged 12 +/- 3 ng and in rat testis 8 +/- 2 ng per g of tissue. Specific immunochemical staining was localized in the spermatids and elongating spermatozoa of mammalian testis. The demonstration of immunoreactive ANF in testis and specific localization in spermatids reveals a new site at which ANF may be actively synthesized and regulate paracrine and/or autocrine function(s) during spermiogenesis, suggesting a broader spectrum of ANF action in addition to its known regulatory role in the control of blood pressure homeostasis.

Brain natriuretic peptide binding sites in rats: in vitro autoradiographic study

Brain natriuretic peptide (BNP) is a recently discovered family of natriuretic peptides highly homologous to atrial natriuretic factor (ANF). Quantitative in vitro autoradiography with a computerized microdensitometer demonstrated that the distribution of BNP binding sites is similar to the known distribution pattern of ANF binding sites in rat tissues. Analysis of saturation and competition curves disclosed that the maximal binding capacity for BNP-(Asp-81--Tyr-106) and ANF-(Ser-99--Tyr-126) is similar within the plexiform layer of the olfactory bulb, the choroid plexus, and the adrenal zona glomerulosa. Examination of the competition curves of BNP-(Asp-81--Tyr-106), ANF-(Ser-99--Tyr-126), and des-(Gln-116--Gly-120)ANF-(Asp-102--Cys-121)NH2 (C-ANF, a ligand highly specific for ANF-R2 receptors) for 125I-labeled BNP-(Asp-81--Tyr-106) and 125I-labeled ANF-(Ser-99--Tyr-126) binding revealed that ANF fully displaced 125I-BNP binding and, conversely, BNP completely displaced 125I-ANF binding in these tissues, whereas C-ANF partially displaced 125-BNP and 125-ANF binding. Angiotensin II, insulin, glucagon, and substance P had no influence on 125I-BNP binding in the above tissues. These results support the view that BNP and ANF share the same binding sites in rats.

Effects of acute and chronic treatments with atrial natriuretic factor (ANF) on the Leydig cells of the rat testis

Acute ANF bolus administration (40 micrograms.kg-1) did not affect secretory activity and morphology of rat Leydig cells. Prolonged (7-day) ANF infusion (20 micrograms.kg-1.h-1), on the contrary, elevated both basal and hCG-stimulated testosterone blood concentration, and caused a notable hypertrophy of rat Leydig cells. Leydig-cell hypertrophy was due to increases in the volume of all the organelles involved in cholesterol and testosterone synthesis (i.e. mitochondria, smooth endoplasmic reticulum and peroxisomes). These findings suggest that ANF, when chronically administered, is able to stimulate the growth and steroidogenic capacity of rat Leydig cells.