Nociceptin/orphanin FQ increases ANP secretion in neonatal cardiac myocytes

Nociceptin (N/OFQ) is a novel heptadecapeptide with an amino acid sequence similar to that of endogenous opioid peptide dynorphin A. Dynorphin have been reported to increase the secretion of atrial natriuretic peptide (ANP) via selective activation of kappa-opioid receptor in cultured atrial cardiocytes. The present study was designed to investigate the direct effect of N/OFQ on the ANP secretion in cultured neonatal rat cardiac myocytes via N/OFQ receptor (NOP) activation. The secretion of ANP from cultured neonatal cardiac myocytes was increased in terms of incubation time. N/OFQ, at a dose of 0.3, 1, 3, and 10 microM, caused increases in ANP secretion in a dose-dependent manner. The N/OFQ-induced ANP secretion was completely antagonized by antagonists of NOP, 1 microM each of [Phe1 (CH2-NH) Gly2] nociceptin (1-13)-NH2 ([FG]N/OFQ(1-13)NH2) or naloxone benzoylhydrazone. In contrast, naloxone (1 microM), the non-selective opioid receptor antagonist, did not alter ANP response to N/OFQ. N/OFQ at 3 microM inhibited basal and forskolin-stimulated cAMP production, which was partially antagonized with the pretreatment of [FG]N/OFQ(1-13)NH2. An increase in ANP secretion by N/OFQ was also partially blocked by the pretreatment of forskolin. Homologous competition studies in neonatal cardiomyocyte membranes revealed the presence of two distinct sites. The high affinity site (10.9 +/- 1.6 nM) was far less abundant than the low affinity site. Therefore, these results suggest that N/OFQ causes an increase in ANP secretion in cultured neonatal cardiac myocytes by decreasing cAMP through its binding sites.

Accentuation of ANP secretion to endothelin-1 in hypertrophied atria

To investigate modulation of ANP secretion by atrial hypertrophy, the secretion of ANP in response to stretch and endothelin-1 was studied using isolated perfused quiescent atria from rats treated with monocrotaline (MCT). Male Sprague-Dawley rats were given a single subcutaneous injection of 50 mg/kg MCT or saline and were sacrificed at 6 weeks. Rats with right heart hypertrophy showed an increase in ANP mRNA and decrease in tissue concentration of ANP in hypertrophied atria and a marked increase in plasma concentration of ANP. In isolated perfused hypertrophied right atria from MCT rats, changes in atrial volume induced by increased atrial pressure caused proportional increases in mechanically stimulated extracellular fluid (ECF) translocation and stretch-activated ANP secretion. Changes in atrial volume and mechanically stimulated ECF translocation in hypertrophied right atria were not different from those in control right atria. The stretch-activated ANP secretion was suppressed without significant difference in basal ANP secretion, as compared to control right atria. Therefore, the stretch-activated ANP secretion from hypertrophied right atria into the atrial lumen in relation to the ECF translocation (ANP concentration in the interstitium) was lower than that from control atria. A positive correlation between the stretch-activated ANP secretion in relation to the ECF translocation and tissue ANP content was found in control atria but not in hypertrophied atria. Endothelin-1 caused increases in stretch-activated ANP secretion in a dose-dependent manner, which were accentuated in hypertrophied right atria. Therefore, we suggest that atrial hypertrophy causes an attenuated response to stretch and accentuated response to endothelin-1 of ANP secretion.

C-type natriuretic peptide system in rabbit oviduct

C-type natriuretic peptide (CNP), a third member of the natriuretic peptide family, is known to be distributed mainly in brain and vascular endothelium and is considered to act as a local regulator in many tissues. The purpose of this study was to determine the presence of CNP system and its biological function in rabbit oviduct. The serial dilution curve of tissue extracts was parallel to the standard curve of CNP((1-22)) and a major peak of molecular profile of tissue extracts by HPLC was CNP((1-53)). mRNA of CNP which was the same size as positive control was also detected by Southern blot analysis. CNP increased the production of 3',5'-cyclic guanosine monophosphate (cGMP) in the purified membrane of oviduct, which was more in membranes derived from the isthmic portion than in the ampullar portion. The presence of mRNAs of natriuretic peptide receptor-A (NPR-A) and NPR-B was demonstrated by RT-PCR. Synthetic CNP((1-22)) inhibited both frequency and amplitude of basal motility of oviduct in a dose-dependent manner. The inhibitory effect of CNP on the basal motility was more potent in the isthmic portion than in the ampullar portion. These results demonstrate the presence of CNP system in the oviduct and regional differences in motility inhibition by CNP between isthmic and ampullar portions. Therefore, these findings suggest the possible existence of a CNP system that may exert a local regulator of basal motility, either alone or in concert with other hormones.

Distinct roles for L- and T-type Ca(2+) channels in regulation of atrial ANP release

Atrial secretion of atrial natriuretic peptide (ANP) has been shown to be regulated by atrial workload. Although modulating factors for the secretion of ANP have been reported, the role for intracellular Ca(2+) on the secretion of ANP has been controversial. The purpose of the present study was to define roles for L- and T-type Ca(2+) channels in the regulation of ANP secretion in perfused beating rabbit atria. BAY K 8644 (BAY K) increased atrial stroke volume and pulse pressure. BAY K suppressed ANP secretion and ANP concentration in terms of extracellular fluid (ECF) translocation concomitantly with an increase in atrial dynamics. BAY K shifted the relationship between ANP secretion and ECF translocation downward and rightward. These results indicate that BAY K inhibits myocytic release of ANP. In the continuous presence of BAY K, diltiazem reversed the effects of BAY K. Diltiazem alone increased ANP secretion and ANP concentration along with a decrease in atrial dynamics. Diltiazem shifted relationships between ANP secretion and atrial stroke volume or ECF translocation leftward. The T-type Ca(2+) channel inhibitor mibefradil decreased atrial dynamics. Mibefradil inhibited ANP secretion and ANP concentration in contrast with the L-type Ca(2+) channel inhibitor. These results suggest that activation of L- and T-type Ca(2+) channels elicits opposite effects on atrial myocytic release of ANP.

Coexistence of C-type natriuretic peptide and atrial natriuretic peptide systems in the bovine cornea

PURPOSE

To determine whether the cornea synthesizes natriuretic peptides and contains their receptors.

METHODS

The synthesis of the natriuretic peptides, C-type natriuretic peptide (CNP) and atrial natriuretic peptide (ANP), in the bovine cornea was determined by high-performance liquid chromatography (HPLC) with radioimmunoassay and Southern blot analysis. The presence of natriuretic peptide receptor (NPR)-A and -B and their localizations were measured by reverse transcription-polymerase chain reaction (RT-PCR), in vitro autoradiography, and the activation of particulate guanylyl cyclase by natriuretic peptides in the corneal membrane.

RESULTS

The serial dilution curves of corneal extracts were parallel to the standard curves of CNP and ANP. With reversed-phase HPLC, a major immunoreactive peak of CNP or ANP was observed at the elution time corresponding with synthetic CNP(1-53) or atriopeptin III (APIII), respectively. The presence of mRNAs of CNP and ANP was also detected in the cornea by RT-PCR and/or Southern blot analysis. Production of 3',5'-cyclic guanosine monophosphate (cGMP) by the activation of particulate guanylyl cyclase in the corneal membrane was stimulated by ANP, BNP, and CNP. More cGMP was produced by CNP than by the other natriuretic peptides. Specific 125I-[Tyr0]-CNP(1-22) binding sites were localized in the endothelial cell layer of cornea. The apparent dissociation constant (Kd) value of the cornea was 3.06 +/- 0.73 nM and the maximum binding capacity was 3.40 +/- 0.63 femtomoles/mm2. Both NPR-A and NPR-B mRNAs were detected by RT-PCR.

CONCLUSIONS

The cornea synthesizes CNP and ANP and contains their receptors. These results suggest that the CNP and ANP systems coexist in the bovine cornea.

Mouse connexin37: gene structure and promoter analysis

Connexin37 (Cx37) is a subunit gap junction protein which exhibits limited expression in only a few cell types, predominantly in endothelial cells and in the lung. To begin to analyze Cx37 expression, we isolated a 1.6 kb mouse Cx37 cDNA from a mouse lung cDNA library and isolated corresponding mouse genomic clones from a bacterial artificial chromosome library. Sequencing and comparison of these clones showed that the Cx37 gene contained a short first exon, an 1.0 kb single intron and a second exon containing the complete coding region and 3'-untranslated region (UTR). The 5'-UTR of the mouse cDNA showed 70% identity to that of human Cx37. Primer extension experiments performed using mouse lung RNA gave two bands of sizes consistent with the transcription start site predicted from the cDNA. Sequence analysis showed that the regions flanking exon I contained a consensus 'TATA box' 43 bp 5' from the transcription start site preceded by several putative transcription factor binding sites and a 282 bp truncated L1Md interspersed element. Luciferase reporter gene transfections suggested that an area of 268 bp 5' from the first exon acted as a basal promoter for Cx37 and that there was a strong negative regulatory element in the intron.

Modulation of intercellular communication by differential regulation and heteromeric mixing of co-expressed connexins

Intercellular communication may be regulated by the differential expression of subunit gap junction proteins (connexins) which form channels with differing gating and permeability properties. Endothelial cells express three different connexins (connexin37, connexin40, and connexin43) in vivo. To study the differential regulation of expression and synthesis of connexin37 and connexin43, we used cultured bovine aortic endothelial cells which contain these two connexins in vitro. RNA blots demonstrated discordant expression of these two connexins during growth to confluency. RNA blots and immunoblots showed that levels of these connexins were modulated by treatment of cultures with transforming growth factor-ss1. To examine the potential ability of these connexins to form heteromeric channels (containing different connexins within the same hemi-channel), we stably transfected connexin43-containing normal rat kidney (NRK) cells with connexin37 or connexin40. In the transfected cells, both connexin proteins were abundantly produced and localized in identical distributions as detected by immunofluorescence. Double whole-cell patch-clamp studies showed that co-expressing cells exhibited unitary channel conductances and gating characteristics that could not be explained by hemi-channels formed of either connexin alone. These observations suggest that these connexins can readily mix with connexin43 to form heteromeric channels and that the intercellular communication between cells is determined not only by the properties of individual connexins, but also by the interactions of those connexins to form heteromeric channels with novel properties. Furthermore, modulation of levels of the co-expressed connexins during cell proliferation or by cytokines may alter the relative abundance of different heteromeric combinations.

Functional expression and biochemical characterization of an epitope-tagged connexin37

To study the gap junction protein connexin37 (Cx37), we stably transfected cell lines with constructs of human Cx37 containing the epitope tag FLAG (DYKDDDDK). A Cx37 construct containing the FLAG moiety at the carboxyl terminus (Cx37F) was expressed in BWEM cells, and did not substantially alter the levels of endogenous Cx43 in these cells. Immunostaining showed that Cx37F colocalized with Cx43 at cell-cell contacts. Pulse-chase metabolic labeling and immunoprecipitation with anti-FLAG antibodies indicated that Cx37F was synthesized as a protein that ran at 35.9 +/- 0.9 kDa on reducing SDS-PAGE but chased into a slower migrating band at 38.0 +/- 1.0 kDa. This shift in mobility was due to phosphorylation on serine residues, based on [(32)P]-metabolic labeling, immunoprecipitation, and phosphoamino acid analyses. The transition to the phosphoCx37F correlated with a loss of solubility in 1% Triton X-100. Based on the [(35)S]-methionine pulse-chase experiments, the half-life of the labeled Cx37F was approximately 3 h, which is within the range reported for other connexins. Analysis of dye injection experiments indicated that dye transfer was reduced in Cx37-transfected cells in comparison to parental BWEM cells, suggesting that formation of heteromeric Cx37-Cx43 channels reduced the molecular permeability of communication between these cells. Moreover, the similarities of previously demonstrated kinetic details and modification of Cx43 to our new data regarding Cx37 provide evidence for a commonality in processing and assembly steps of these two connexins.

Mouse connexin40: gene structure and promoter analysis

A family of related connexin genes encodes the subunit gap junction proteins that form intercellular channels in different tissues. Connexin40 (Cx40) is one of these proteins, and it exhibits limited expression only in a few cells of the cardiovascular system. To begin to analyze Cx40 expression, we isolated a 3.3-kb rat Cx40 cDNA by hybridization screening of a bacteriophage library prepared from BWEM cells and isolated corresponding mouse genomic clones from a bacterial artificial chromosome library. Restriction mapping, sequencing, and comparison to the rat cDNA showed that the mouse Cx40 gene contained a short first exon, an 11.4-kb intron, and a second exon containing the complete coding region and 3'-UTR. Exon I contained only 1 base that differed between rat and mouse. Primer extension experiments yielded a single band and confirmed the position of the transcriptional start site. We obtained 1.2 kb of sequence 5' of the transcriptional start site and 400 bp 3' of exon I. Exon I was closely preceded by a consensus TATA box. The flanking sequences contained a number of potential transcription factor binding sites (including AP-1, AP-2, SP1, TRE, and p53). To identify transcriptional regulatory elements in the Cx40 promoter region, a series of DNA deletion fragments flanking exon I was prepared, subcloned adjacent to a luciferase reporter gene, and used for transient transfections of BWEM, SHM, and N2A cells. The resulting luciferase activity determinations suggested that an area of 300 bp 5' of the transcription start site acted as a basal promoter for Cx40 and that there was a strong negative regulatory element in the region from +100 to +297.

Evidence for heteromeric gap junction channels formed from rat connexin43 and human connexin37

Homomeric gap junction channels are composed solely of one connexin type, whereas heterotypic forms contain two homomeric hemichannels but the six identical connexins of each are different from each other. A heteromeric gap junction channel is one that contains different connexins within either or both hemichannels. The existence of heteromeric forms has been suggested, and many cell types are known to coexpress connexins. To determine if coexpressed connexins would form heteromers, we cotransfected rat connexin43 (rCx43) and human connexin37 (hCx37) into a cell line normally devoid of any connexin expression and used dual whole cell patch clamp to compare the observed gap junction channel activity with that seen in cells transfected only with rCx43 or hCx37. We also cocultured cells transfected with hCx37 or rCx43, in which one population was tagged with a fluorescent marker to monitor heterotypic channel activity. The cotransfected cells possessed channel types unlike the homotypic forms of rCx43 or hCx37 or the heterotypic forms. In addition, the noninstantaneous transjunctional conductance-transjunctional voltage (Gj/Vj) relationship for cotransfected cell pairs showed a large range of variability that was unlike that of the homotypic or heterotypic form. The heterotypic cell pairs displayed asymmetric voltage dependence. The results from the heteromeric cell pairs are inconsistent with summed behavior of two independent homotypic populations or mixed populations of homotypic and heterotypic channels types. The Gj/Vj data imply that the connexin-to-connexin interactions are significantly altered in cotransfected cell pairs relative to the homotypic and heterotypic forms. Heteromeric channels are a population of channels whose characteristics could well impact differently from their homotypic counterparts with regard to multicellular coordinated responses.

Mechanical basis of ANP secretion in beating atria: atrial stroke volume and ECF translocation

To investigate the mechanism by which an increase in pacing frequency or distension increases the secretion of atrial natriuretic peptide (ANP), the changes in atrial volume during contraction (atrial stroke volume), transmural transport of the extracellular fluid (ECF), and ANP secretion were quantified in the beating perfused rabbit atria. The atrium was stimulated by transmural field stimulation or by atrial distension induced by an increase in intraatrial pressure. Atrial stretch and incremental increases in pacing frequency up to 2 Hz activated the secretion of ANP coincident with an increase in atrial stroke volume and the transendocardial translocation of the ECF. These results showed positive relationships between changes in the secretion of ANP and the atrial stroke volume or the translocation of the ECF. The translocation of the ECF was also positively correlated with the change in atrial stroke volume. The accentuated secretion of ANP and translocation of the ECF waned at higher stimulating rates to show a peak value. Even under this condition, the secretion of ANP was a function of the translocation of the ECF. These data suggest that the increases in atrial stroke volume and translocation of ECF are fundamental factors in the ANP stimulation in response to atrial stretch and increases in atrial rate.

Effect of extracellular calcium depletion on the two-step ANP secretion in perfused rabbit atria

Employing isolated perfused rabbit atrial model we have found that stretch-activated atrial natriuretic peptide (ANP) secretion takes place in two steps: release of ANP from myocytes into surrounding intercellular space, and then translocation of the released ANP into atrial lumen along with the extracellular fluid (ECF) translocated upon releasing the stretch. Ca2+, one of the most important factors regulating secretory processes, has been reported by many workers to have influence on the ANP secretion, but at large variance. In the present study, therefore, we undertook to clarify the influence of Ca2+ depletion on ANP secretion and further to define which of the two steps is affected by Ca2+ removal. Extracellular Ca2+ depletion resulted in increased basal secretion and in accentuated secretion of immunoreactive (ir) ANP in response to mechanical stimuli. The translocation of ECF increased in response to atrial stretch-and-release, but it was not affected by Ca2+ depletion. The irANP concentration in the extracellular space calculated as the amount of irANP secreted in relation to the ECF translocated significantly increased when extracellular Ca2+ was depleted. These results indicate that extracellular Ca2+ depletion accentuates the stretch-induced ANP secretion through the augmentation of ANP release into the interstitium without changes in the ECF translocation.

Atrial natriuretic peptide immunoreactivity in the eggs of the silkworm Bombyx mori

Synthesis and secretion of atrial natriuretic peptides (ANPs) are not confined to the atrium, but are also present in other tissues. Recently, we have found synthesis of ANP in the eggs of several vertebrate animals. The present study was undertaken to determine whether immunoreactive ANP (irANP) is present in the egg of an invertebrate, the silkworm (Bombyx mori L.). The serial dilution curve of egg extracts of silkworm was parallel to the standard curve of atriopeptin III. Analysis of ANP immunoreactivity by gel filtration chromatography and reverse-phase HPLC showed that the major immunoreactivity corresponded to rat proANP. The semipurified irANP of egg extracts produced a dose-dependent relaxation on rat aortic strips, which was blocked by preincubation with anti-ANP antiserum. Therefore, we suggest that ANP is synthesized in the silkworm egg.

Identification of immunoreactive atrial natriuretic peptide in the gallbladder and bile juice of rabbit, pig and human

The presence of immunoreactive atrial natriuretic peptide (irANP) in rabbit, pig and human gallbladders was investigated using radioimmunoassay and immunohistochemistry. Serial dilution curves of gallbladder tissue and bile juice extracts were paralleled to the standard curve of atriopeptin III. Gel filtration profiles of gallbladder tissue extracts showed a major peak corresponding to rat pro-ANP. The amounts of irANP in rabbit, pig and human gallbladders were 30.0 +/- 12.3 pg/mg (n = 7), 7.0 +/- 2.0 fg/mg (n = 7) and 17.7 +/- 2.0 fg/mg wet tissue (n = 8), respectively. Bile juice was also shown to contain irANP but with small molecular mass. The amounts of irANP in the rabbit, pig and human bile juice were 25.0 +/- 2.0 (n = 7) and 0.50 +/- 0.02 (n = 7), and 1.3 +/- 0.1 pg/ml (n = 8), respectively. The immunohistochemical staining of the rabbit gallbladder tissue revealed the presence of irANP in the luminal epithelium and smooth muscle layer. The amount of irANP was higher in the luminal epithelium than in the rest of the gallbladder tissue from rabbits (0.30 +/- 0.06 vs. 0.01 +/- 0.01 pg/microgram protein, P < 0.01). These findings suggest that ANP may be synthesized and stored in the gallbladder, and may have a role in the regulation of fluid balance and cystic motility.

Effects of positive acceleration on atrial natriuretic peptide in humans

To study the effects of positive acceleration on the plasma atrial natriuretic peptide (ANP) and renin concentration (PRC), students of the Korean Air Force Academy and pilots were exposed to +6 Gz for 30 s in a human centrifuge without anti-G suits. An acceleration to +6 Gz caused a significant increase (p < 0.01) in the heart rate of both the student and pilot groups. We performed blood collection within 2 min after terminating centrifugation. Systolic blood pressure was increased significantly (p < 0.01), and heart rates were elevated and did not return to control levels by 2 min after centrifugation. Plasma ANP decreased significantly in both groups (p < 0.05). The difference in the percentage of ANP decrement was not significant between student and pilot groups. PRC increased significantly (p < 0.05) in both groups. This study demonstrated that high +Gz exposure in man caused a significant reduction of plasma ANP concentration, although PRC, heart rate, and blood pressure increase.

Extracellular fluid translocation in perfused rabbit atria: implication in control of atrial natriuretic peptide secretion

1. Transmural transport of 22Na+, 51Cr-EDTA, [3H]inulin and [14C]Dextran (57 kDa) was measured in perfused rabbit atria. The radiolabelled extracellular space (ECS) markers and [14C]Dextran were introduced into the pericardial space or atrial lumen. Atrial volume changes were induced by steps up and down in atrial pressure. 2. Basal rates of transmural transport of radiolabelled ECS markers across the atrial wall were relatively stable up to 70 min. Atrial stretch and release resulted in a rapid but transient, and reversible increase in the ECS fluid (ECF) translocation. The increased translocation of the ECF into the atrial lumen occurred within 15 s of the reduction of atrial distension and returned to the baseline level within 60 s. 3. Transmural transport of [3H]inulin across the atrial wall was bidirectional. 4. The clearance of radiolabelled ECS markers was molecular-size dependent. The transmural clearance of [3H]inulin was dependent on the distension-reduction volume changes induced by atrial stretch and release. Little transport of [14C]Dextran across the atrial wall was observed. 5. The ECF translocation across the atrial wall was not influenced by changes in external Ca2+ but was suppressed by low temperature. 6. Dynamic changes in the ECS of the atrium were observed in response to atrial distension and reduction. The ECS of the atrium increased on distension and decreased on reduction of atrial distension. 7. Reduction in atrial distension resulted in an increase in the secretion of immunoreactive atrial natriuretic peptide (ANP) which coincided with an increase in the translocation of the ECF. The secretion of immunoreactive ANP was a function of the translocation of the ECF. 8. It is suggested that atrial stretch and release may play a role in driving fluid flow within the interstitium and fluid translocation out of the interstitium. This fluid movement presumably leads to convective transport of released ANP into the atrial lumen.

Immunoreactive atrial natriuretic peptides in the oocyte

1. The presence and partial characterization of immunoreactive ANP (irANP) in eggs were investigated using high performance liquid chromatography (HPLC), immunohistochemistry and Northern-blot hybridization in mammalian and nonmammalian vertebrates. 2. Serial dilution curves of egg extracts from frogs and freshwater teleostean fishes (silver crusian carp and loach) were parallel to the standard curve of atriopeptin III. Rat oocytes also contained irANP (25-30 pg/egg). 3. The HPLC profile of irANP showed two main peaks corresponding to low and high molecular weight of irANP. 4. ANP mRNA was detected in the fish eggs. With immunohistochemical analysis of the rat ovarian follicles, this ANP-like material was localized mainly at the oocytes. 5. We, therefore, suggest that the vertebrate oocytes synthesize ANP and that the presence of ANP in the oocytes may be linked with the cell differentiation.

Single injection of pentobarbital induces long-lasting effects on ANP synthesis and gene expression in the rat atria

To define the long-term effects of pentobarbital sodium on the plasma and atrial atrial natriuretic peptide (ANP) system, experiments were performed in female Sprague-Dawley rats. The plasma levels of immunoreactive (ir) ANP showed chronic as well as acute response to pentobarbital sodium administration. A single dose (30 mg/kg, i.p.) of pentobarbital sodium resulted in a suppression in the plasma levels of irANP up to 1 week of administration. The suppressive effect on plasma irANP concentrations was dose-dependent. Right but not left atrial contents of irANP increased by an administration of pentobarbital sodium up to 4 weeks. ANP mRNA contents of the atrial exposed to pentobarbital sodium began to increase after 2 days, reached to the peak after 2 weeks, and began to return to control values after 6 weeks. Surgical stress accentuated these patterns of plasma and atrial ANP responses to pentobarbital sodium treatment. The present data, therefore, suggest that even a single anesthetic dose of pentobarbital could elicit long-lasting profound changes in ANP system, i.e., changes in gene expression, synthesis and the secretion of ANP.

Presence and release of immunoreactive atrial natriuretic peptide in granulosa cells of the pig ovarian follicle

Atrial natriuretic peptide (ANP) has been reported to be locally synthesized in the ovary although its physiological roles are still unknown. To define the origin of ovarian ANP, we demonstrated the presence and release of immunoreactive (ir) ANP in pig granulosa cells and characterized its biochemical properties. Serial dilution curves made with the extracts of pig granulosa cells, their perfusates and follicular fluid were paralleled to the standard curve of ANP. The amount of irANP in the granulosa cell was 2 fg/cell. The total amount of irANP in granulosa cells significantly correlated with the levels of irANP in follicular fluid. Additionally, the total content of irANP in the follicle negatively correlated with the follicular size. On reverse phase HPLC, the major form of irANP in granulosa cells and follicular fluid was high molecular weight but that in perfusate was low molecular weight. In Northern blot analysis, ANP mRNA was detected in the pig granulosa cells. Immunohistochemistry showed ANP prohormone location in granulosa cells of rat ovary. These data strongly suggest that the granulosa cells synthesize and secrete ANP.

Right atrial predominance of atrial natriuretic peptide secretion in isolated perfused rat atria

In order to investigate the regulatory mechanism for the atrial release of atrial natriuretic peptide (ANP), a perfused rabbit atrial model was devised. In the present experiments, the effect of a reduction in atrial distension on the immunoreactive ANP (irANP) secretion was investigated and compared in the perfused right and left atria of rats. Elevations in right and left atrial pressure resulted in proportional increases in the volume of atrial distension-reduction which was larger in the right than in the left atria. The basal rate of irANP secretion was higher in the right than in the left atria. Increases in the volume of atrial distension-reduction resulted in proportional increases in irANP secretion in both atria. Increment in irANP secretion in response to a reduction in atrial distension was significantly higher in the right than in the left atria. Higher rate of irANP secretion in response to unit volume change was observed in the right atria. Increases in the volume of atrial distension-reduction resulted in accentuated irANP responses in the right atrium. IrANP content was significantly higher in the right than in the left atria. The results suggest that the right atrium is a predominant site in ANP secretion in rats.

Ovarian atrial natriuretic peptide during the rat estrous cycle

The changes in ovarian levels of immunoreactive atrial natriuretic peptide (irANP) and arginine vasopressin (irAVP) were observed during the estrous cycle of rat. We also demonstrated the synthesis of ovarian ANP. In adult 4-day cycling rats, ovarian level of irANP was found to be the highest on proestrus and was to be the lowest on diestrus. Ovarian irANP level inversely correlated with ovarian level of irAVP. On reverse-phase HPLC, two distinct peaks of ovarian irANP, high and low molecular weight forms, existed in the each stage of the estrous cycle. However, no significant changes in plasma and atrial concentrations of ANP were observed during the cycle. The rat ovary contained mRNA coding for ANP. These data showing the synchronized cyclic change of ovarian irANP and irAVP with the estrous cycle suggest that the ovary locally synthesizes ANP and ovarian ANP may play regulatory roles on the follicular fluid dynamics.

Atrial pressure, distension, and pacing frequency in ANP secretion in isolated perfused rabbit atria

It has been suggested in this laboratory that the principal stimulus for the secretion of atrial natriuretic peptide (ANP) is the reduction of atrial distension and that the secretion of ANP is dependent on both atrial reduction volume and reduction frequency. To investigate the relationship among the changes in atrial pressure, distension, pacing frequency, and ANP secretion, we performed a series of experiments in the isolated perfused rabbit atria. Increase in atrial pressure without changes in transmural pressure and thus without volume changes did not raise immunoreactive ANP (irANP) secretion. Atrial distension without changes in intracavitary atrial pressure increased irANP secretion with the reduction. Electrical stimulation with atrial distension resulted in an increase in irANP secretion in proportion to pacing frequency. Incremental response of irANP secretion to electrical stimulation was accentuated by increasing atrial distension. Neither atrial pacing without distension nor distension without pacing raised irANP secretion. These results suggest that the direct and principal stimulus for irANP secretion in response to atrial pacing and distension is the length shortening of atrial myocytes and that the incremental response of irANP secretion to increasing pacing frequency is the result of an increase in frequency of the length shortening of atrial myocytes.

Sequential mechanism of atrial natriuretic peptide secretion in isolated perfused rabbit atria

It is well known that the secretion of atrial natriuretic peptide (ANP) is dependent on the atrial stretch. It has been claimed in this laboratory that the secretion of ANP occurs with a reduction in atrial distension. It was shown in the present experiment that the secretion of immunoreactive (ir) ANP occurs coincidently with a translocation of extracellular space marker (3-H)-inulin in the isolated perfused rabbit atria. Translocation of extracellular space fluid was observed with a reduction in atrial distension. The secretion of irANP into the atrial lumen occurs less than 15 sec of the reduction in atrial distension. It is therefore suggested that the incremental response of irANP secretion to the reduction in atrial distension is a sequential mechanism of ANP secretion, in which first is the release of ANP from the atrial myocytes into the extracellular space and then second is the translocation of ANP with extracellular space fluid into the atrial lumen with a reduction in atrial distension.

Presence of immunoreactive atrial natriuretic peptides in pericardial fluid of human subjects with congenital heart diseases

The epicardial release of immunoreactive atrial natriuretic peptides (ir-ANPs) in inside-out perfused rabbit atria has been reported. In order to determine the presence of ir-ANPs in pericardial fluid and to evaluate their biochemical characteristics, we measured the concentration of ir-ANPs in pericardial fluid obtained from the patients with congenital heart diseases during open heart surgery. Serial dilution curves made with the extrats of pericardial fluid using Sep-Pak C18 cartridges were parallel with standard curve. The concentration of ir-ANPs in pericardial fluid was significantly lower than the corresponding plasma concentration. On gel permeation and reverse-phase high performance liquid chromatography, the ir-ANPs in pericardial fluid, plasma and atrial appendage showed both high and low molecular weights. The major peak of ir-ANPs in plasma was observed at the corresponding fraction to the alpha-human ANP and considerable amount of high molecular weight form of ir-ANPs was observed in pericardial fluid. However, the major peak of ir-ANPs in atrial appendage was observed at the corresponding fraction to the rat pro-ANP. The data suggest that ir-ANPs exist both high and low molecular weight forms in pericardial fluid.

Reduction volume dependence of immunoreactive atrial natriuretic peptide secretion in isolated perfused rabbit atria

A new technique to permit gradual changes in atrial distension has been developed in an isolated perfused rabbit atrium preparation. Graded volume reduction in the atrium was induced by changing the elevation of the outflow catheter tip. Pressure reduction from 6 cm H2O atrial distension resulted in a decrease in atrial distension volume. Atrial distension by 6 cmH2O did not change the release of immunoreactive atrial natriuretic peptide (irANP). The graded reduction in atrial distension from 0.11 +/- 0.03 (1.5 cm H2O) to 1.36 +/- 0.19 microliters/mg wet weight (6.0 cm H2O) resulted in 1.7 (6.76 +/- 2.05 versus 3.83 +/- 1.18 pg/mg per min, n = 9, P less than 0.025) to 40.1-fold (77.66 +/- 17.82 versus 3.0 +/- 1.14 pg/mg per min, n = 11, P less than 0.025) increases in irANP release. IrANP release in response to the reduction of atrial distension was volume dependent. The relation of percentage increase in irANP release with the percentage reduction of atrial distension was exponential. The data suggest that the atrial muscle shortening, but not stretch per se, may be a potent direct stimulus for the regulation of irANP secretion.

Phylogenetic study on the immunoreactive atrial natriuretic peptide in the heart

Using two antisera against atriopeptin III (AP III) which had different characteristics in cross-reactivities with atrial natriuretic peptide (ANP) analogs, we have measured an immunoreactive ANP (ir-ANP) in the heart extracts of several species. ir-ANP in atrial extracts showed both high and low molecular weights. Serial dilutions of atrial extracts from chickens, turtles, frogs, and fish yielded competition curves which were parallel to the standard curve of AP III with antiserum No. 4. In comparison with two serial dilution curves of atrial extracts made using two antisera, No. 4 and No. 9, we suggest that the amino acid at position 12 of ir-ANP in the atrial extracts of chicken, turtle, frog, and fish is not isoleucine but is some other amino acid.

Presence of immunoreactive atrial natriuretic peptide in follicular fluid, ovary and ovarian perfusates

Immunoreactive atrial natriuretic peptide (ir-ANP) was measured in the follicular fluid of pig ovarian follicle, and rabbit ovarian homogenates and perfusates using a specific radioimmunoassay (RIA). Serial dilution curves made with the extracts of follicular fluid, ovarian homogenates and perfusates using SepPak C18 cartridges were parallel with the RIA standard curve. On gel filtration chromatography and reverse phase HPLC, all extracted materials showed high and low molecular weight forms of ir-ANP. The amount of ir-ANP in rabbit ovary was 40.70 +/- 0.39 pg/mg and that in follicular fluid of pig ovarian follicle was 18.88 +/- 2.49 pg/ml.

Plasma concentration of atrial natriuretic peptide in different phases of Korean hemorrhagic fever

Korean hemorrhagic fever (KHF) is an epidemic viral disease characterized by high fever, hemorrhagic tendency and renal failure, and by hemorrhages of right atrium and renal medulla as well as necrosis of anterior hypophysis. Plasma immunoreactive atrial natriuretic peptide (irANP) levels of 15 patients in the oliguric phase was 94.8 +/- 8.4 pg/ml (mean +/- SEM), 80% higher than of the normal control group (53.0 +/- 4.7 pg/ml; n = 28). In the diuretic phase it declined to 63.7 +/- 5.3 pg/ml (n = 26). Plasma renin activity (PRA) in the oliguric phase was 19.0 +/- 1.3 ng AI/ml/h, and in the diuretic phase 5.3 +/- 0.9 ng AI/ml/h, significantly higher than the control value (2.5 +/- 0.1 ng AI/ml/h). Elevations of irANP and PRA were not correlated in each group. Also systemic blood pressure as well as heart beats were significantly increased in the oliguric phase. These findings suggest that the increased irANP may have resulted from increased circulatory volume and that the ANP secretory process may not be affected by the disease.

Characteristics of distension-induced release of immunoreactive atrial natriuretic peptide in isolated perfused rabbit atria

Atrial pressure- or distension-induced release of atrial natriuretic peptide (ANP) has been considered as an important regulatory mechanism of ANP release in cardiac atria. A new technique to permit graded continuous atrial distension has been developed in an isolated perfused single rabbit atrium. Graded atrial distension was induced by changing the elevation of the outflow catheter tip. Intra-atrial volume expansion resulted in an increase in immunoreactive ANP release. The graded increase in atrial distension from 43.9 +/- 10.2 to 207.7 +/- 29.1 microliter resulted in 6.2-27.1-fold increases in volume-dependent immunoreactive ANP release. A rise in immunoreactive ANP release induced by increasing atrial distension did not occur in the state of atrial distension but occurred only after return to the reduced distension. However, in the case of atrial distension with pacing, an increase in immunoreactive ANP release was observed during atrial distension with pacing and after return to the basal level. The present study shows that the new technique is applicable to the study of the 'stretch-secretion coupling' mechanism of ANP release in vitro, and that the more important factor involved in the release of immunoreactive ANP induced by atrial distension may be the atrial reduction to basal level after distension rather than the stretch itself.

Epicardial release of immunoreactive atrial natriuretic peptides in inside-out perfused rabbit atria

An easy and convenient isolated atrial perfusion technique was developed. The effect of stretch of the atrial subpericardial myocytes was investigated in the inside-out perfused rabbit atria. Graded distension of the inverted atria was induced by changing the elevation of the atrial catheter tip. Intra-luminal volume expansion resulted in an increase in release of immunoreactive atrial natriuretic peptides (irANPs). The response was volume, or pressure dependent. Distension-induced release of irANPs occurred at the reduction of the distension. IrANPs in epicardial perfusate showed both high and low molecular weights. The major peak of irANP was observed at the corresponding fraction to the rat ANP-(1-28) in the Sephadex G-50 gel chromatography. The data suggest that the epicardial release of irANP is stretch-induced response and that the release may be involved in the regulation of cardiac function.

Renal and renin effects of sodium thiopental in rabbits

Unilateral renal arterial infusion of sodium thiopental on renal function and renin secretion were investigated in unanesthetized rabbits. Sodium thiopental infusion in doses of less than 0.3 mg/kg/min into unilateral renal artery caused dose-dependent increases in urine flow, urinary excretion of electrolytes, fractional excretion of sodium and free water clearance with no changes in systemic blood pressure and clearance of p-aminohippuric acid (renal blood flow). An anesthetic dose of sodium thiopental administered intravenously caused decreases in systemic blood pressure, renal hemodynamics, urine flow and free water clearance during the early period of anesthesia followed by increases in urinary excretion of sodium and fractional excretion of sodium. Unilateral renal arterial infusion of sodium thiopental decreased the renin secretion rate and plasma norepinephrine concentration in renal vein, whereas an anesthetic dose of sodium thiopental administered intravenously increased the renin secretion rate. These observations suggest that the diuretic, natriuretic and renin suppressive effects of sodium thiopental may be due to an inhibition of intrarenal sympathetic nervous system or due to a direct tubular action.

Characterization of angiotensin I-converting enzyme activity in the freshwater turtle, Amyda japonica

1. Angiotensin I-Converting Enzyme (ACE) activity has been characterized in the freshwater turtle, Amyda japonica. 2. Peak activity of ACE in plasma from the freshwater turtle was shown at pH 9.0, which was more alkaline compared to that of mammals. 3. Chloride requirements for the optimal ACE activity were different from species. 4. ACE inhibitors, EDTA, teprotide (SQ 20,881), Captopril (SQ 14,225) showed dose-dependent inhibitions of ACE activity in plasma from the freshwater turtle as well as mammals. 5. ACE activity was found in several different tissues with a different activity showing the highest activity in kidney homogenate from the freshwater turtle, Amyda japonica.

Unilateral renal arterial infusion and renal vein catheterization in rabbits. Study of renal function and renin release

This study evaluates the direct effects of verapamil and furosemide infused into the unilateral renal artery on renal function and the renin secretion rate in renal vein-catheterized rabbits. Catheterization did not alter the renal function parameters of the kidney. Verapamil and furosemide increased renal blood flow, urine flow, and urinary sodium, potassium and chloride excretions confined to the infused kidney. Verapamil increased the glomerular filtration rate and free water clearance. The renin secretion rate was increased by furosemide but not by verapamil. The present study shows that the technique is applicable to renal function studies in which unilateral renal arterial infusion of the agents studied is required. The contralateral kidney can be a reliable control for the infused kidney. It also provides a useful technique for the study of renin release in rabbits.