Note:

Note:

by Kwok Fai (Simon) Leung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1990. / Bibliography: leaves 72-99. / ACKNOWLEDGEMENTS --- p.i / ABSTRACT --- p.ii / Chapter SECTION 1: --- Literature Review / Chapter 1.1 --- Historical perspectives of ANP --- p.1 / Chapter 1.2 --- Nature of ANP --- p.5 / Chapter 1.3 --- Release of ANP --- p.13 / Chapter 1.4 --- Biological effects of ANP --- p.17 / Chapter 1.5 --- Clinical implications --- p.24 / Chapter SECTION 2: --- Effect of ANP on Left Atrium / Chapter 2.1 --- Introduction --- p.29 / Chapter 2.2 --- Methods --- p.32 / Chapter 2.3 --- Results --- p.37 / Chapter 2.4 --- Discussion --- p.44 / Chapter SECTION 3: --- Effect of ANP on Mesenteric Artery / Chapter 3.1 --- Introduction --- p.47 / Chapter 3.2 --- Methods --- p.51 / Chapter 3.3 --- Results --- p.62 / Chapter 3.4 --- Discussion --- p.66 / Chapter SECTION 4: --- General Discussion --- p.67 / Chapter SECTION 5: --- References --- p.72

by Ngai Wing Keung Clement. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1992. / Includes bibliographical references (leaves 172-206). / Chapter 1. --- Acknowledgment --- p.iv / Chapter 2. --- Abstract --- p.v / Chapter 3. --- Lists of Tables and Figures --- p.vii / Chapter 4. --- General Introduction --- p.1 / Chapter 5. --- Review of Literature --- p.5 / Chapter 5.1. --- Historical Background of Natriuretic Peptides --- p.5 / Chapter 5.2. --- Secretion of Natriuretic Peptides --- p.8 / Chapter 5.3. --- Structure and Function Relationships --- p.12 / Chapter 5.4. --- Physiological Actions --- p.17 / Chapter 5.5. --- Natriuretic Peptide Receptors and Second Messengers --- p.22 / Chapter 5.6. --- Clinical Implications --- p.28 / Chapter 5.7. --- Review on Astrocytes --- p.31 / Chapter 6. --- General Materials and Methods --- p.43 / Chapter 6.1. --- Sources of Chemicals --- p.43 / Chapter 6.2. --- Culture of Mouse Astrocytes --- p.43 / Chapter 6.3. --- Culture of human astrocytoma cells --- p.57 / Chapter 6.4. --- Protein Determination --- p.57 / Chapter 6.5. --- Gamma Counting --- p.58 / Chapter 6.6. --- Beta Counting --- p.58 / Chapter 7. --- Receptor Identification and Characterization --- p.59 / Chapter 7.2 --- Materials and Methods --- p.60 / Chapter 7.3 --- Results --- p.66 / Chapter 7.4 --- Discussion --- p.81 / Chapter 8. --- Second Messenger Systems --- p.83 / Chapter 8.1 --- Introduction --- p.83 / Chapter 8.2 --- Materials and Methods --- p.85 / Chapter 8.3 --- Results --- p.97 / Chapter 8.4 --- Discussion --- p.109 / Chapter 9. --- Biological Actions of Natriuretic Peptides --- p.113 / Chapter 9.1. --- Potassium Transport --- p.113 / Chapter 9.1.1. --- Introduction --- p.113 / Chapter 9.1.2. --- Materials and Methods --- p.116 / Chapter 9.1.3. --- Results --- p.121 / Chapter 9.1.4. --- Discussion --- p.131 / Chapter 9.2 --- Taurine Release --- p.135 / Chapter 9.2.1. --- Introduction --- p.135 / Chapter 9.2.2. --- Materials and Methods --- p.137 / Chapter 9.2.3. --- Results --- p.139 / Chapter 9.2.4. --- Discussion --- p.143 / Chapter 9.3 --- Thymidine Incorporation --- p.144 / Chapter 9.3.1. --- Introduction --- p.144 / Chapter 9.3.2. --- Materials and Methods --- p.146 / Chapter 9.3.3. --- Results --- p.148 / Chapter 9.3.4. --- Discussion --- p.156 / Chapter 10. --- Interaction with Other Hormonal Systems --- p.160 / Chapter 10.1 --- Introduction --- p.160 / Chapter 10.2 --- Materials and Methods --- p.162 / Chapter 10.3 --- Result --- p.163 / Chapter 10.4 --- Discussion --- p.167 / Chapter 11. --- Conclusion --- p.169 / Chapter 12. --- References --- p.172 / Chapter 13. --- Appendix --- p.208

The recently discovered atrial natriuretic peptide (ANP) has potent diuretic, natriuretic and hypotensive effects, and is believed to be involved in the maintenance of sodium homeostasis in both normal and pathological conditions. The mammalian aging process is associated with a host of abnormalities that include, among others, a compromised ability to regulate sodium homeostasis. There are reports that demonstrate a positive correlation between plasma ANP levels and age in man; accordingly, the aim of this study was to examine whether age-related sodium imbalance is associated with disturbances in the homeostasis of ANP. Specifically, the intracellular storage, processing and secretion of ANP from the atrium was studied and associated with circulating ANP concentrations and ANP receptor binding kinetics. Studies were conducted with four groups of male Wistar rats designated as 1-, 3-, 10-, and 20-month-old. 24-hour renal clearances were conducted to assess age-related changes in renal functions. GFR and UNaV increased steadily from 1 to 10 months of age and decreased in the 20-month-old, while fractional excretion of water (FEH₂O) and sodium (FENa) declined initially (from 1 to 10 months) and then rose in the 20-month-old group. Circulating ANP levels in the rats was significantly correlated with the increase in age (N = 147, r = 0.59, p < 0.0005). Atria of the animals were isolated and superfused with a modified Langendorff apparatus. The spontaneous release of ANP increased from 1 to 3 months, and steadily decreased after 3 months. The results indicate that ANP secretion increases with maturation and thereafter declines with advancing age. ANP concentrations in the right and left atria were also quantified. The results revealed that atrial ANP content increased from 1 to 3 months and decreased progressively with age. There was a positive correlation between the rate of ANP release and atrial ANP content (N= 42, r=0.50, p<0.01), suggesting that the release of ANP from the right atrium was associated with the atrial content. The concurrence of a reduction in ANP secretion but with elevation in plasma ANP concentration in the aged (20-month-old) rats, suggests that there may be an impairment in renal clearance of ANP. It was established that the main molecular species present in the atrium was γ-ANP and that this was unaffected by age as assessed by reverse-phase high performance liquid chromatography (RP-HPLC) coupled with radioimmunoassay. The molecular forms of ANP secreted by the atrium consisted of predominantly α-ANP, with a smaller amounts of γ-ANP. γ-ANP constituted only 1% of the total secreted ANP in the 1-, 3-, or 10-month-old rats, but up to 8% was detected in 20-month-old rats. Although both α-ANP and γ-ANP were present in the circulation, the ratio of γ-ANP/α-ANP increased significantly with age. The concentration of γ-ANP in the plasma of the 20-month-old rats was two- to three-fold higher than in the two younger groups (1- and 3-month-old). These data imply that the post-transcriptional processing of prohormone γ-ANP to active α-ANP is altered with age. Radio-ligand binding experiments were carried out using glomerular ANP receptors to determine whether the age-related alterations in plasma ANP levels has an effect on the binding of ANP to its target tissues. Both the receptor density (Bmax) and the equilibrium dissociation constant (kd increased from 1 to 3 months but decreased from 3 to 20 months. Collectively, these results suggest that: 1) Aging affects atrial ANP content and consequently influences the release of ANP from the isolated atria. 2) The processing of prohormone γ-ANP to active α-ANP is modified with age. 3) Plasma levels of ANP increase with age, which may result in down-regulation of ANP receptor density and increased efficacy in receptor binding affinity. These may represent the compensatory responses. / Medicine, Faculty of / Medicine, Department of / Experimental Medicine, Division of / Graduate

Atrial natriuretic peptide (ANP) of atrial myocyte origin, has been shown to play a role in the diuresis, natriuresis, and antagonism of angiotensin and vasopressin. However, it is now apparent that in addition to the production of the peptide in the heart and in its role in fluid and electrolyte homeostasis, it is also produced in the central nervous system participating in the regulation of pituitary hormone secretion. Administration of ANP through both central and peripheral routes has been shown to inhibit secretion of luteinizing hormone (LH) in the gonadectomized rat model. A better understanding of the modulatory role of ANP on LH secretion and its possible mechanisms will add to our knowledge of the effects of neuropeptides on reproductive function. Brain natriuretic peptide (BNP) is a bioactive peptide of 26 amino acid residues recently identified in porcine brain. The peptide exerts potent diuretic-natriuretic and vasorelaxant effects, in a manner similar to that of ANP. BNP has a remarkable high sequence homology to ANP, especially in the 17 amino acid ring formed by an intramolecular disulfide linkage which is required for biological activity. The presence of BNP with ANP in the mammalian brain and remarkable resemblance in their molecular structures and physiological functions implies that BNP may also exert an inhibitory effect on LH secretion like ANP. This research focused on the effects of centrally administered ANP and BNP on pulsatile LH secretion and their possible mechanisms of action in ovariectomized rats. After third ventricle infusion of ANP or BNP, inhibition of mean plasma LH level, LH pulse amplitude and pulse frequency was observed. In searching for the possible mechanisms of inhibitory effect of ANP or BNP on pulsatile LH secretion, the effect of inhibiting the endogenous opiate system with naloxone on the action of centrally administered ANP or BNP was tested. Application of naloxone reversed the inhibitory effect of ANP and BNP on mean plasma LH level and LH pulse amplitude, but in terms of pulse frequency, naloxone treatment failed to reverse the inhibitory effect of ANP or BNP. In separate experiments, pretreatment with pimozide, a dopaminergic receptor blocker, prevented the inhibitory action of ANP and BNP on LH secretion. After infusion of ANP or BNP, there were no significant decrease in mean plasma LH level, pulse amplitude and pulse frequency in the pimozide-pretreated rats. In summary, the present study shows that both ANP and BNP inhibit pulsatile LH secretion, suggesting that the inhibitory effects on LH secretion once thought to be mediated by ANP alone may be regulated through a dual mechanism involving both ANP and BNP. Furthermore, the inhibitory mechanisms may involve the interactions of ANP and BNP with central opiate system and dopaminergic system on LH secretion. / Medicine, Faculty of / Obstetrics and Gynaecology, Department of / Graduate

Atrial natriuretic factor (ANF) is a cardiac hormone that helps maintain cardiovascular homeostasis. ANF secretion is linked to the constitutive, regulated and constitutive-like pathways. Presence of a monensin-sensitive pool that may follow constitutive-like secretion has previously been identified in an isolated atrial perfusion study. The intracellular ANF storage pools linked to each secretory pathway have not been identified. In this study, ANF storage and secretion was characterized in HL-1 atrial cardiomyocytes through the use of pharmacological agents, density gradient and RP- HPLC analysis. Treatment of HL-1 cells with monensin followed by cell fractionation was unsuccessful in identifying the monensin-sensitive pool. RP-HPLC analysis identified presence of low molecular weight ANF in low density gradient fractions that were defined by the presence of organelle markers of Golgi, early endosome, clathrin and corin. Since the monensin-sensitive pool was thought to be of a constitutive-like nature, targeting this pathway with pharmacological inhibitors of clathrin coat vesicle (CCV) formation and endosomal trafficking failed to prevent stimuli-independent secretion. Based on an inability to prevent ANF secretion by targeting the constitutive-like pathway and the presence of low molecular weight ANF in low density gradient fractions, stimuli- independent ANF secretion seems to be through a constitutive pathway.

Atrial natriuretic factor (ANF) is a cardiac hormone that helps maintain cardiovascular homeostasis. ANF secretion is linked to the constitutive, regulated and constitutive-like pathways. Presence of a monensin-sensitive pool that may follow constitutive-like secretion has previously been identified in an isolated atrial perfusion study. The intracellular ANF storage pools linked to each secretory pathway have not been identified. In this study, ANF storage and secretion was characterized in HL-1 atrial cardiomyocytes through the use of pharmacological agents, density gradient and RP- HPLC analysis. Treatment of HL-1 cells with monensin followed by cell fractionation was unsuccessful in identifying the monensin-sensitive pool. RP-HPLC analysis identified presence of low molecular weight ANF in low density gradient fractions that were defined by the presence of organelle markers of Golgi, early endosome, clathrin and corin. Since the monensin-sensitive pool was thought to be of a constitutive-like nature, targeting this pathway with pharmacological inhibitors of clathrin coat vesicle (CCV) formation and endosomal trafficking failed to prevent stimuli-independent secretion. Based on an inability to prevent ANF secretion by targeting the constitutive-like pathway and the presence of low molecular weight ANF in low density gradient fractions, stimuli- independent ANF secretion seems to be through a constitutive pathway.

Thesis (Ph.D.)--University of Alabama at Birmingham, 2009. / Title from PDF title page (viewed on Feb. 2, 2010). Includes bibliographical references.

Atrial natriuretic factor (ANF) is a cardiac hormone that helps maintain cardiovascular homeostasis. ANF secretion is linked to the constitutive, regulated and constitutive-like pathways. Presence of a monensin-sensitive pool that may follow constitutive-like secretion has previously been identified in an isolated atrial perfusion study. The intracellular ANF storage pools linked to each secretory pathway have not been identified. In this study, ANF storage and secretion was characterized in HL-1 atrial cardiomyocytes through the use of pharmacological agents, density gradient and RP- HPLC analysis. Treatment of HL-1 cells with monensin followed by cell fractionation was unsuccessful in identifying the monensin-sensitive pool. RP-HPLC analysis identified presence of low molecular weight ANF in low density gradient fractions that were defined by the presence of organelle markers of Golgi, early endosome, clathrin and corin. Since the monensin-sensitive pool was thought to be of a constitutive-like nature, targeting this pathway with pharmacological inhibitors of clathrin coat vesicle (CCV) formation and endosomal trafficking failed to prevent stimuli-independent secretion. Based on an inability to prevent ANF secretion by targeting the constitutive-like pathway and the presence of low molecular weight ANF in low density gradient fractions, stimuli- independent ANF secretion seems to be through a constitutive pathway.