Potassium-induced relaxation of arteries in hypertension: modulation by extracellular calcium

Smooth muscle relaxation due to activation of Na+-K+-adenosinetriphosphatase (ATPase) (K+ relaxation) was studied in isolated tail arteries from stroke-prone spontaneously hypertensive (SHRSP) and Wistar-Kyoto (WKY) rats. Exposure to K+ (7 mM) relaxed a norepinephrine (1 microM) contraction induced in K+-free physiological salt solution (PSS) by 46 +/- 3% in WKY and by 81 +/- 3% in SHRSP. Incubation with monensin (10 microM) augmented the K+-relaxation in WKY to 61 +/- 5%. Incubation with amiloride (10 microM) or with low-Na+ (10 mM) PSS attenuated the K+ relaxation in SHRSP to 34 +/- 3 and 5 +/- 2%, respectively. Incubation with high-Ca2+ (6.6 mM) PSS attenuated the K+ relaxation in WKY to 25 +/- 3% but resulted in only a slight decrease in the relaxation in SHRSP (to 73 +/- 2%). We conclude 1) that a greater Na+ leakiness of the plasma membrane in SHRSP than in WKY while the Na+ pump is inactive in K+-free PSS can explain the greater relaxation observed when the Na+ pump is reactivated and 2) that the Na+ leakiness of the membrane is more attenuated by Ca2+ in the WKY than in the SHRSP. We hypothesize that this Ca2+ effect reflects a normally large amount of this ion that can be bound to and thereby stabilize the membrane of the WKY, decreasing its permeability to Na+. The membrane of the SHRSP is deficient in its Ca2+-binding sites. Hence the added Ca2+ does not further stabilize its membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelium-mediated spontaneous response in aortic rings of deoxycorticosterone acetate-hypertensive rats

Aortic rings isolated from normotensive Sprague-Dawley rats (CONT) exhibited spontaneous tone when the preparations were stretched. After administering deoxycorticosterone acetate (DOCA), the rats became hypertensive, and this spontaneous tone increased remarkably. The spontaneous tone was dependent on the extracellular calcium concentration. Incubation with the calcium entry blocker D-600 attenuated the spontaneous response to a greater degree in rings from DOCA rats than in rings from CONT rats. Nifedipine relaxed the already developed spontaneous tone. Removal of the endothelium greatly depressed spontaneous tone, but did not diminish the contraction caused by norepinephrine. On the basis of our findings, we conclude that 1) spontaneous tone depends on calcium influx, presumably through specific stretch-operated membrane channels, 2) these stretch-dependent channels are blocked by D-600 and nifedipine, 3) spontaneous tone is enhanced in DOCA hypertension, and 4) the endothelium appears to act as a receptor for stretch, mediating--at least in part--the spontaneous contractile response by releasing a constrictor agent.

Plasma membrane and its abnormalities in hypertension

The plasma membrane is composed of proteins embedded in a discontinuous fashion in a lipid bilayer. These proteins maintain the integrity of the membrane and play fundamental roles as ion transport channels and as receptors for agents that regulate cell function. The membrane is therefore an important regulator of vascular smooth muscle contraction. The plasma membrane in the hypertensive animal exhibits abnormal permeability for monovalent ions and defective calcium handling. This is reflected in fewer calcium-binding sites and, as a result, in deficient membrane stabilization. These defects have been identified in several cell types, including lymphocytes, red blood cells, adipocytes, and vascular smooth muscle cells. Evidence presented in the current review suggests that hypertension is associated with a generalized membrane defect. Abnormalities in ion transport in vascular smooth muscle cells are the most relevant to the pathogenesis of hypertension since they could be directly responsible for the rise in blood pressure. We hypothesize that the impaired stabilizing effect of calcium in vascular smooth muscle cells of hypertensive subjects renders the membrane more excitable and that this in turn leads to increased vascular reactivity and higher peripheral resistance. Peripheral vascular reactivity usually is increased in hypertension, suggesting increased responsiveness of the smooth muscle cells. Possible abnormalities of the several components of the contractile process of these cells have been investigated for the role they might play in this altered response. Abnormalities in the plasma membrane have been most clearly defined and are emphasized in this review.

A Report of Seven Long Survivors for Evidence of Prognostic Factors in Hairy Cell Leukemia

The clinical hematologic and pathologic findings of 30 patients with hairy cell leukemia observed between 1966 and 1979 were studied. Twelve patients had long-lasting course of the disease. Seven of them displayed a survival ≥ 120 months, whereas 18 patients died within 36 months of the diagnosis. Their clinical and laboratory characteristics (age of onset, sex, ESR, hemoglobin, WBC, neutrophils, monocytes, platelets, spleen and liver size) were analyzed to ascertain possible prognostic features. Multivariate discriminant analysis, performed both with a direct method and with a stepwise method (Wilks' method), provided a discriminant function able to correctly predict the prognosis of the disease in 83.3 % of the examined cases. Spleen size, neutrophil count, age of onset, ESR and liver size turned out to be the most important prognostic factors; in contrast, splenectomy did not significantly affect the prognosis in our cases.

The effect of substituted sydnonimines on coronary smooth muscle relaxation and cyclic guanosine monophosphate levels

In vitro experiments on precontracted canine coronary arteries were performed to study the direct relaxant effects of molsidomine (MOLS) and its active metabolite, SIN-1, and to determine if there is a relationship between effect and cGMP level elevations. The effects of MOLS and SIN-1 were compared with those of a classic vasodilator, nitroglycerin (NTG). At equimolar doses (10(-6)M) SIN-1 exerted greater relaxant effect than NTG (80 +/- 2% and 60 +/- 5%, respectively) in spite of the fact that it produced less of an increase in cyclic guanosine monophosphate (cGMP) levels. cGMP levels fell rapidly after they peaked, but relaxation was maintained. cGMP elevation preceded the induction of relaxation by NTG but not that induced by SIN-1. Relaxation occurred faster after NTG than after SIN-1. Since SIN-1 has a greater relaxant effect than NTG in spite of the fact that SIN-1 induces less of an increase in cGMP levels and the fact that the peak elevation does not precede the onset of relaxation, the causal nexus between GMP level elevation and relaxation effect after sydnonimines should be challenged.

Does acute L-DOPA increase active release of dopamine from dopaminergic neurons?

L-DOPA is believed to be decarboxylated by the residual striatal dopaminergic presynaptic terminals with formation of the putative neurotransmitter dopamine (DA) and with increased availability of DA at post-synaptic receptors. However there is no direct evidence that the DA formed is released into the synaptic cleft. We therefore investigated the biochemical modifications occurring in the dopaminergic system after acute administration of L-DOPA. After acute L-DOPA (100 mg/kg plus 25 mg/kg of benserazide p.o.) the levels of 3-methoxytyramine (3-MT), a metabolite reflecting release of the neurotransmitter DA, were significantly raised, following the same pattern as DA levels, indicating that DA release from DA nerve terminals is increased after L-DOPA administration. The increased DA release and 3-MT formation were not reduced by pretreatment with direct DA agonists such as apomorphine (5 mg/kg i.p.) or piribedil (120 mg/kg p.o.). Thus in this case DA release is not under the control of the compensatory mechanisms induced by post-synaptic receptor hyperstimulation.

Effects of angiographic contrast medium on isolated canine coronary arteries

In isolated canine coronary arteries previously contracted by high potassium concentration, angiographic contrast medium decreased active tension by 61 +/- 2%. The relaxant effect was dose dependent and was not prevented by beta-blockade with d-l-propranolol (10(-5) M). This effect was similar to that obtained with nitroglycerin (10(-6) M), and further relaxation was evident when this vasodilator was administered after exposure to the contrast medium. When arteries were precontracted by alpha-receptor stimulation with norepinephrine (10(-5) M) at normal potassium concentration, a maximal relaxation of 83 +/- 6% was elicited after exposure to contrast medium. The relaxant effect could not be reproduced by a similar increase in osmolarity brought about by addition of sucrose. When arterial strips were processed by radioimmunoassay for dosage of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) after the relaxing action of the contrast medium occurred, a decrease in cAMP from 2.61 +/- 0.86 to 0.63 +/- 0.1 pmol/mg protein (p less than 0.05) was observed, whereas no significant changes in cGMP were detected. These nucleotides do not appear to be involved in the relaxant effect of the dye in the same way as they are when relaxation is elicited by some other coronary vasodilators.