Developmental changes in the effect of atrial natriuretic peptide on tissue cyclic GMP content and particulate guanylate cyclase activity of aorta, kidney and lung of rats

Ontogeny of atrial natriuretic peptide and its receptor in the lung: effects on perinatal surfactant release

During the transition at birth to air breathing, regulation of surfactant release from alveolar type II (ATII) cells is critical. Atrial natriuretic peptide (ANP) stimulates natriuretic peptide receptor-A (NPR-A) and increases intracellular cGMP. We examined the changes in ANP and NPR-A in respiratory epithelium during the perinatal period using immunohistochemistry and studied the effect of ANP on surfactant release from ATII cells isolated from fetal and newborn lambs. NPR-A mRNA was detected in the fetal lung by Northern Blot and RT-PCR. At 100 d gestation (term 145 d), ANP staining was absent and NPR-A staining was weak in cuboidal epithelial cells. ANP and NPR-A staining was prominent in ATII cells at 136 d gestation and was undetectable postnatally. ANP stimulated (maximal effect at 10(-10)M) surfactant release from both late gestation fetal and neonatal ATII cells. Protein kinase G inhibition significantly blocked this release. We conclude that ANP stimulates surfactant release in isolated perinatal ATII cells by a cGMP-dependent mechanism. ANP and NPR-A expression in ATII cells is greatest in late gestation and declines sharply postnatally. We speculate that increased activity of the ANP/NPR-A pathway in late gestation may prime the surfactant system, preparing the lung for air breathing.

Human atrial natriuretic peptide prevents the increase in pulmonary artery pressure associated with aortic unclamping during abdominal aortic aneurysmectomy

OBJECTIVE

To assess the effect of human atrial natriuretic peptide (HANP) on the pulmonary and systemic circulations during infrarenal abdominal aortic aneurysmectomy.

DESIGN

A prospective, randomized study.

SETTING

A university hospital.

PARTICIPANTS

Forty-five patients undergoing infrarenal abdominal aortic aneurysmectomy.

INTERVENTIONS

Abdominal aortic aneurysmectomy patients were randomly assigned to 1 of 3 groups (n = 15 for each group). They were infused with normal saline solution (SA), 0.02 microg/kg/min of HANP (LH), or 0.05 microg/kg/min of HANP (HH), starting 5 minutes after clamping. Hemodynamic variables were measured before/after clamping and unclamping.

MEASUREMENTS AND MAIN RESULTS

Both mean pulmonary arterial pressure (MPAP) and the pulmonary vascular resistance index (PVRI) increased (v baseline) in the SA group. HANP attenuated the rises in MPAP and PVRI dose dependently (LH and HH groups v SA). Mean arterial pressure and systemic vascular resistance index were not significantly different among the 3 groups.

CONCLUSION

HANP, infused during aortic clamping and abdominal aortic aneurysmectomy, attenuates the rises in pulmonary artery pressure and vascular resistance without severe systemic hypotension. This may result from direct and/or indirect pulmonary vascular effects of HANP because no HANP-induced changes in endothelin-1, angiotensin-II, and thromboxane B(2) were detected.

Changes in ANP responsiveness of normal and hypertensive porcine intrapulmonary arteries during maturation

Pulmonary vascular resistance falls rapidly after birth, but endothelium-dependent relaxation is relatively poor during the perinatal period. Atrial natriuretic peptide (ANP) is a potent vasodilator; however, its role in the process of perinatal adaptation is uncertain. Porcine intrapulmonary conduit arteries (IPA) from fetal, newborn (< 5 min), 3-, 6-, and 17-d-old, and adult pigs, and from piglets made hypoxic from 0 to 3, 3 to 6, or 14 to 17 d, were isolated and mounted for isometric force recording. Rings were precontracted with prostaglandin-F2 alpha (PGF2 alpha, 10 microM) or KCl (40 mM). ANP was added cumulatively (10 pM to 100 nM). C-type natriuretic peptide (CNP) was added as a single concentration of 100 nM. Accumulation of cGMP under basal conditions and stimulated by ANP or CNP was measured by radioimmunoassay system. Frozen sections of lung tissue were incubated with 125I-labeled alpha-ANP, and binding site density was assessed on IPA with an image analysis system. ANP relaxed IPA in pigs at all ages, but the effect was significantly greater at 6 and 17 d of age. Hypoxia in animals from 14 to 17 d old impaired ANP-induced relaxation. CNP relaxed IPA poorly: < 12% at all ages. ANP increased cGMP accumulation in both normal and hypoxic animals. CNP did not increase cGMP generation in IPA from normal animals but did so in IPA from 3-d-old hypoxic animals. ANP-specific binding sites were demonstrated on the pulmonary artery smooth muscle cells, with greater binding in the young animals. The increased relaxant responses to ANP during adaptation may be important in maintaining low pulmonary vascular resistance. In contrast, CNP was largely ineffective in relaxing pulmonary arteries.

Pulmonary natriuretic peptide system during rat development

Maturational changes in the rat lung natriuretic peptide system were studied postnatally in 1-, 4-, and 22-day-old rats. Lung atrial natriuretic factor (ANF) content increased significantly from day 1 to day 4 (712+/-188 vs. 1905+/-520 pg/mg protein; p<0.01) but decreased to 532+/-41 pg/mg protein, on day 22. These changes paralleled ANF messenger RNA (mRNA) detected by reverse transcribed polymerase chain reaction (RT-PCR). Rat pulmonary development also was associated with quantitative and qualitative alterations in ANF receptors. Competitive-binding radioreceptor assays of lung membranes with 125I-ANF and increasing concentrations of unlabeled ANF revealed that the natriuretic peptide receptor-binding sites (Bmax) progressively increased with age from 112 +/-21 fmol/mg protein at day 1 to 211+/-16 (p<0.02) and 326+/-62 fmol/mg protein (p<0.04) in 4- and 22-day-old rats, respectively. Autoradiographic studies of 125I-tyr(0)CNP binding to lung sections revealed that the levels of the natriuretic peptide receptor B (NPR-B) were undetectable. On the other hand, binding of 125I-ANF increased with age, and the higher binding at 4 days was mainly due to increased density of the clearance receptor-C (NPR-C), and at 22 days due to increased natriuretic peptide receptor-A (NPR-A). The increase in natriuretic peptide binding was confirmed at the level of synthesis, where RT-PCR revealed that NPR-A mRNA significantly increased (p<0.01) in 22-day-old rats. In conclusion, these studies demonstrate that the rat pulmonary natriuretic peptide system is altered during development. The altered synthesis of lung natriuretic peptides and their receptors may play a role in the postnatal adaptation of pulmonary circulation.

Effect of age on the vasorelaxation elicited by cromakalim. Role of K+ channels and cyclic GMP

The objective of this study was to investigate whether age induces changes on vasodilator response induced by cromakalim, an ATP-sensitive K+ (K(ATP)) channel opener, as well as the underlying mechanism involved in this possible alteration. For this purpose, aortic segments from young (3-5 months) and old (3 years) rabbits were used, which were precontracted with noradrenaline (NA, 1 microM). The vasodilator response induced by cromakalim (0.01-100 microM) was reduced in intact segments from old rabbits, and endothelium removal reduced and did not modify this effect in young and old animals, respectively. In both groups of animals, glibenclamide (10 microM), a blocker of K(ATP) channels, significantly reduced the response elicited by cromakalim, which was not modified by the large conductance Ca2+-activated K+ channel blocker charybdotoxin (ChTX, 0.4 microM). Acetylcholine (ACh, 10 microM) and sodium nitroprusside (SNP, 100 microM) induced a lesser vasodilator effect in aortic segments from old compared with young rabbits. In segments precontracted with NA, 10 microM ACh or 100 microM SNP similarly increased cGMP levels in both groups of animals. However, basal cGMP level was reduced in segments from old rabbits. Incubation with 8-bromo-cGMP (100 microM) increased the response induced by cromakalim in both groups of animals, reaching similar maximum values in young and old rabbits. The response induced by cromakalim plus 8-bromo-cGMP was markedly decreased by glibenclamide and unmodified by ChTx in both types of animals. These results suggest that aging decreases the vasodilator response to cromakalim, mechanism in which appears to be involved the maintained low cGMP levels observed in old rabbits, and that this messenger modulates the degree of K(ATP) channel activation.

Developmental changes in lung cGMP phosphodiesterase-5 activity, protein, and message

During transitional circulation, the pulmonary vascular bed undergoes a rapid and profound reduction in both tone and vascular smooth-muscle (VSM) content. 3',5'-Guanylate cyclic monophosphate (cGMP) is a crucial mediator in the regulation of pulmonary vascular resistance (PVR) and VSM proliferation. Hydrolysis of cGMP is achieved predominately by cGMP-specific phosphodiesterases (PDEs). Among the cGMP-specific PDEs, PDE5 is quantitatively prevalent in lung tissue. We have investigated the levels of pulmonary PDE5 enzymatic activity, protein, and messenger RNA (mRNA) in ovine and mouse lung during perinatal development. We report that within 1 h following birth, PDE5 activity, protein, and mRNA levels decrease in both species, in a manner that correlates with known decreases in PVR in early transition. However, from 4 to 7 d following birth, a secondary increase in PDE5 activity, protein, and mRNA occurs in both ovine and mouse lung, suggesting a complex regulation of PVR and VSM proliferation in late perinatal development. Our data imply that PDE5 may be an important mediator in the regulation of PVR in normal and possibly in pathologic states, and may ultimately provide a basis for PDE5 inhibitors as a treatment for pulmonary hypertension.

Atrial natriuretic peptide accelerates proliferation of chick embryonic cardiomyocytes in vitro

The developing embryonic heart has been reported to contain significant levels of atrial natriuretic peptide (ANP). In this study, the role of ANP in cardiac development was evaluated using cultured cardiomyocytes isolated from chick embryos. We analyzed the effect of ANP on cell number, DNA synthesis, total RNA level, the expression of cell-cycle-specific and sarcomeric proteins, and levels of lactate dehydrogenase and creatine phosphokinase. ANP increased overall DNA synthesis (measured by BrdU incorporation, P < 0.01) and enhanced cell proliferation. Morphologically, the development of the cardiomyocyte network was distinctly enhanced in the ANP-treated cells. Cellular RNA content was elevated; likewise, myosin and tropomyosin biosynthesis was significantly greater in ANP-treated cells. In addition, expression of G1/S-specific protein increased, whereas G2/M-specific protein remained unchanged by ANP treatment. An antibody against ANP and a specific ANP receptor antagonist, HS-142-1, antagonized and/or attenuated the action of ANP on both cell proliferation and protein biosynthesis. These results indicate that ANP accelerates myocardial cell proliferation by enhancing entry into S phase and by increasing DNA synthesis during S phase specifically through receptor mediated pathway. The in vitro effects of ANP on myocardial cell proliferation, together with the elevated levels of ANP seen in vivo during normal heart formation, suggest a possible autocrine function of ANP in embryonic cardiac development.