Bruce A. Prins

Atrial and brain natriuretic peptides stimulate the production and secretion of C-type natriuretic peptide from bovine aortic endothelial cells.

C-type natriuretic peptide (CNP) is a member of the natriuretic peptide family which is produced in vascular endothelial cells and may play an important paracrine role in the vasaculature. We sought to determine the regulation of CNP production by other vasoactive peptides from cultured aortic endothelial cells. The vasoconstrictors endothelin-1 and angiotensin II had little effect on the basal secretion of CNP. In contrast, atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) strongly stimulated the secretion of CNP. BNP caused as much as a 400-fold enhancement above the basal accumulated secretion of CNP over 24 h at a concentration of 1 microM; this was 20 times greater than the stimulatory effect of ANP, BNP and ANP also significantly enhanced the production of new CNP protein (translation) and mRNA expressed in the BAEC. In contrast, C-ANP-4-23, a truncated form of ANP which selectively binds to the natriuretic peptide clearance receptor, did not stimulate CNP secretion. The enhanced production and secretion of CNP, caused by either ANP or BNP, was significantly prevented by LY 83583, an inhibitor of cGMP generation, and was also attenuated by KT 5823, an inhibitor of cGMP-dependent protein kinase. Our results indicate that ANP and BNP can stimulate CNP production through a guanylate cyclase receptor on endothelial cells. BNP is a much more potent stimulator of CNP secretion, compared to ANP. Our findings suggest that the vasodilatory, and anti-mitogenic effects of ANP and BNP in the vasculature could occur in part through CNP production and subsequent action if these interactions occur in vivo.

High density lipoproteins stimulate the production and secretion of endothelin-1 from cultured bovine aortic endothelial cells.

The concentration of HDL in the blood inversely correlates with the incidence of cardiovascular disease, probably related to the ability of these lipoproteins to efflux cholesterol from vascular cells. it is also possible that HDL affect the production or action of vasoactive peptides implicated in the development of vascular diseases. Therefore, we determined the effects of human HDL on the production and secretion of endothelin-1 (ET-1) from cultured bovine aortic endothelial cells. HDL produced a highly significant stimulation of endothelin secretion (maximum 240% of control), even at very low levels of lipoproteins (1 microgram/ml). HDL also stimulated the translation of ET-1 by twofold in the bovine aortic endothelial cells. In contrast, HDL had no significant effect on steady state mRNA levels, transcript degradation, or transcription. Stimulation of ET-1 secretion by HDL was dependent on protein kinase C activation. Purified apo A-I, the major apoprotein of HDL, increased ET-1 secretion and translation approximately 85% as potently as HDL. Our results indicate that low concentrations of human HDL strongly stimulate the production of ET-1, a powerful vasoconstrictor and mitogen for the vascular smooth muscle cell. We propose that HDL may participate in the regulation of vasomotor tone through this potentially important effect in the vasculature.

Helicobacter pylori Induces Apoptosis in Human Epithelial Gastric Cells by Stress Activated Protein Kinase Pathway

The pathway by which Helicobacter pylori induces apoptosis in gastric epithelial cells is not known. The aim of this study was to determine whether H. pylori‐induced apoptosis is associated with SAPK/JNK activity in human gastric cancer KATO III cells.

Na-K-ATPase inhibitor dissociated from hypertension-associated plasma protein

It has been demonstrated that human plasma contains a low molecular weight sodium-potassium-stimulated adenosine triphosphatase (Na-K-ATPase) inhibitor, which can be dissociated from a circulating protein with a molecular weight of approximately 12,000 daltons. The dissociated factor was found to have a molecular weight <500 daltons, and shared many characteristics with ouabain. Similar to ouabain, this factor was found to be a potent inhibitor of both the Na-K-ATPase and potassium-stimulated para-nitrophenyl phosphatase (K-pNPPase) enzyme systems, and to bind to both high- and low-affinity binding sites on Na-K-ATPase, but unlike ouabain did not cross-react with digoxin antibody. The factor was further separated by HPLC and electrochemical detection into two active compounds (p-NKAI-1 and p-NKAI-2). P-NKAI-1 was demonstrated on mass spectroscopy to have a molecular weight of 408 daltons. In a vasoconstrictor assay employing rabbit femoral artery segments, this compound was a direct vasoconstrictor and potentiated the vasoconstriction produced by norepinephrine. It behaved similarly to ouabain in counteracting the relaxing effect on rabbit femoral artery of increasing potassium concentrations in the tissue bath.

Natriuretic peptides and hypertension

Natriuretic peptides are produced in the brain, heart and vasculature, and cause vasodilation, sodium excretion, and diuresis. Recent advances indicate that they play important roles in blood-pressure homeostasis, both in normal and in pathophysiological conditions. Although therapeutic interventions which elevate plasma natriuretic peptide levels do not have great antihypertensive efficacy, animal studies suggest that they may be useful in combination treatment strategies.

Comparison of Low-molecular-weight Plasma and Urine Na-k-atpase Inhibitors/hypertensive Factors

Two highly purified low-molecular-weight (< 500 Da) Na-K-ATPase inhibitors, one originating from human plasma and the second from human urine, which both eluted in the identical locus from a C18 reversed-phase high-pressure liquid chromatography (HPLC) column, were compared with respect to (a) K effect on Na-K-ATPase inhibition; (b) displacement of [3H]ouabain from binding sites on purified hog brain Na-K-ATPase; (c) cross-reactivity with digoxin antibodies; and (d) vasoconstrictor effects in isolated rabbit femoral arteries. Inhibition of Na-K-ATPase by the plasma factor correlated inversely with K concentration, whereas inhibition by the urine factor correlated directly with K concentration. In the absence of K, the plasma factor displaced [3H]ouabain from both high- and low-affinity binding sites, whereas the urine factor displaced [3H]ouabain only from the low-affinity binding site. Neither factor possessed digoxin-like immunoreactivity. Both factors acted as direct vasoconstrictors, and potentiated the vasoconstrictor action of norepinephrine. The degree of vasoconstriction caused by the plasma factor diminished progressively with added K, indicating that the vasoconstrictor effect of this factor was mediated by the Na-K-ATPase pump. Thus, although both the plasma and urine Na-K-ATPase inhibitors are vasoconstrictors, their mechanisms of action are different.

Characterization of a Low Molecular Weight Na-K-ATPase Inhibitor of Urinary Origin

It has been demonstrated that expansion of extracellular fluid volume induces the release of a low-molecular-weight natriuretic and sodium-potassium-activated adenosine triphosphatase inhibiting hormone (NKAI). In this study, we used a highly purified hormone extracted from pooled hypertensive urines (u-NKAI). Like ouabain, this compound was found to be a potent inhibitor of the sodium-potassium-activated adenosine-triphosphatase and potassium-stimulated paranitrophenyl phosphatase enzyme systems as well as a vasoconstrictor in vitro. In contrast to ouabain, which is a competitive inhibitor of both enzyme systems with respect to potassium, u-NKAI is noncompetitive. Furthermore, u-NKAI differs from ouabain by its lack of cross-reactivity with digoxin antibodies. In addition, whereas ouabain binds to both high-affinity and low-affinity binding sites on the sodium-potassium-activated adenosine-triphosphatase enzyme in the absence of potassium, u-NKAI binds only to the low-affinity binding sites. This study demonstrates that the highly purified u-NKAI, although ouabain-like in certain respects, is not an “endogenous ouabain.”