cyclic-gmp and marinobufagenin

Endogenous sodium pump inhibitors promote sodium excretion in normotensives and contribute to vasoconstriction in NaCl-sensitive hypertension. Marinobufagenin (MBG), an endogenous bufadienolide inhibitor of alpha-1 sodium pump, contributes to hypertension in Dahl salt-sensitive rats (DS). We hypothesized that in NaCl-loaded DS and normotensive Sprague-Dawley rats (S-D), MBG would elicit different patterns of sodium pump inhibition.. We compared systolic blood pressure (SBP), renal sodium excretion, activity of the sodium pump in aorta and renal medulla, and levels of MBG, atrial natriuretic peptide (ANP), and cyclic guanosine monophosphate (cGMP) in salt-loaded DS and S-D (20% NaCl, 2.5 ml/kg, intraperitoneally).. NaCl loading produced sustained elevations in renal MBG excretion in both DS (2.41 +/- 0.24 vs. 0.79 +/- 0.08 pmol/h/kg, P < 0.01) and S-D (1.97 +/- 0.37 vs. 0.60 +/- 0.07 pmol/h/kg, P < 0.01) vs. that at baseline (n = 10 for each group). In NaCl-loaded DS, SBP rose by 18 mm Hg (P < 0.01) and aortic sodium pump was inhibited by 22% (P < 0.05 vs. control), while in S-D, SBP and activity of aortic sodium pump did not change. NaCl-loaded S-D excreted twice as much sodium as DS; in S-D, renal sodium pump was inhibited by 24% vs. 14% inhibition in DS (P < 0.05). NaCl loading elicited increases in plasma ANP and in renal cGMP excretion in S-D but not in DS.. Our present observations demonstrate that in NaCl-loaded S-D and DS, a comparable MBG response is associated with preferential inhibition of the sodium pump in the kidney and in vascular smooth muscle, respectively, resulting in an adaptive natriuresis in S-D but sodium retention and pressor response in DS.

Topics: Animals; Bufanolides; Cardiac Glycosides; Cyclic GMP; Kidney; Male; Muscle, Smooth, Vascular; Ouabain; Rats; Rats, Inbred Dahl; Rats, Sprague-Dawley; Sodium; Sodium Chloride, Dietary; Sodium-Potassium-Exchanging ATPase

Cicletanine (CIC), an anti-hypertensive compound with direct vascular and natriuretic actions, is especially effective in salt-sensitive hypertension, in which dysregulation of the sodium pump plays an important pathogenic role, and digitalis-like cardiotonic steroids contribute to increased vascular tone. The purpose of the present study was to investigate whether, and by what mechanisms, cicletanine antagonizes the vasoconstrictor effects of cardiotonic steroids in isolated human arteries.. The effects of cicletanine on vascular tone were studied in isolated, endothelium-denuded rings of 2nd-3rd-order branches of human mesenteric arteries pre-contracted with bufodienolide marinobufagenin (MBG), an Na/K-ATPase inhibitor, or endothelin-1 (ET-1). Na/K-ATPase activity was measured in sarcolemmal membranes from the mesenteric artery. Activity of rat brain protein kinase C (PKC) was measured using the PepTag phosphorylation assay.. MBG and ET-1 both induced sustained vasoconstriction in human mesenteric artery rings, and cicletanine relaxed rings pre-contracted with either MBG (EC50 = 11 +/- 2 micromol/l) or ET-1 (EC50 = 6.4 +/- 1.1 micromol/l). Although 8-Br-cGMP (100 micromol/l) caused complete vasorelaxation of arterial rings pre-contracted with ET-1, it did not affect the MBG-induced vasoconstriction. An activator of PKC, phorbol diacetate (PDA) (50 nmol/l), attenuated CIC-induced vasorelaxation of mesenteric artery rings pre-contracted with MBG (EC50 > 100 micromol/l), but not rings pre-contracted with ET-1 (EC50 = 6.5 +/- 1.2 micromol/l). In mesenteric artery sarcolemma, 100 nmol/l MBG inhibited the Na/K-ATPase by 68 +/- 5% and cicletanine (100 micromol/l) attenuated this Na/K-ATPase inhibition by 85 +/- 6%. In the PepTag PKC assay, cicletanine produced a concentration-dependent inhibition of rat brain PKC activity (IC50 45 +/- 11 micromol/l). In the presence of 50 nmol/l PDA, 100 micromol/l cicletanine did not antagonize the Na/K-ATPase inhibition by MBG, and did not inhibit the PKC from rat brain.. Cicletanine antagonizes vasoconstriction induced by Na/K-ATPase inhibition via a PKC-dependent mechanism that does not involve inhibition of cyclic GMP phosphodiesterase (cGMP-PDE). This mechanism of action may be relevant to the greater potency of cicletanine in salt-sensitive hypertension in which plasma levels of endogenous digitalis-like cardiotonic steroids are elevated. Our findings also suggest that PKC is an important factor for cardiotonic steroid-Na/K-ATPase interactions on the vascular tone, and is therefore a potential target for therapeutic intervention in hypertension.

Topics: Animals; Antihypertensive Agents; Brain; Bufanolides; Cyclic GMP; Endothelin-1; Enzyme Inhibitors; Humans; In Vitro Techniques; Male; Mesenteric Arteries; Middle Aged; Protein Kinase C; Pyridines; Rats; Sodium-Potassium-Exchanging ATPase; Vasoconstriction