Effect of diabetes on fast response to norepinephrine in rat aorta.

The fast and slow components of the mechanical response to 1 microM norepinephrine (NE) were measured in aortic rings isolated from eight spontaneously diabetic rats, six streptozocin-induced diabetic (STZ-D) rats, six STZ-D rats treated with 2.5 U insulin/day during the 4 days before being killed, and six age- and sex-matched control rats. The total contraction to NE (i.e., the sum of fast and slow components) was similar in the four groups: spontaneously diabetic, 16.53 +/- 1.72 mN; STZ-D, 15.68 +/- 1.41 mN; insulin-treated, 16.17 +/- 2.05 mN; and control, 15.27 +/- 0.96 mN (NS). The fast component, measured graphically in a total contraction in 1.35 mM Ca, was greater in spontaneously diabetic (12.61 +/- 1.07 mN, P less than 0.05) and STZ-D (12.25 +/- 0.89 mN, P less than 0.05) rats compared with control (9.14 +/- 0.74 mN) or insulin-treated (8.58 +/- 1.23 mN) rats. The same increase of the fast component was detectable after 3 min of incubation in Ca-free medium + 2 mM EGTA (control 6.54 +/- 0.47 mN, spontaneously diabetic 9.07 +/- 0.76 mN, P less than 0.05; STZ-D 8.82 +/- 0.72 mN, P less than 0.05), and it was also abolished by insulin treatment (insulin-treated 6.29 +/- 0.36 mN). We conclude that the diabetic state increases the fast component of NE-induced contraction either in the absence or presence of Ca in the medium. This suggests that such an increase depends on a larger release of Ca from intracellular stores.

Blood pressure fall and increased relaxation of aortic smooth muscle in diabetic rats.

This study was designed to identify changes in endothelium-independent relaxation that could contribute to the depressed vascular reactivity and fall in blood pressure (BP) detected in rats after 5 weeks of streptozotocin (STZ)-induced (i.e. type 1) diabetes. Aortic rings were contracted by simultaneous activation of voltage-operated channels (KCl=80 mM) and alpha-adrenergic receptors (phenylephrine 1 microM) and then relaxed by simultaneous exposure to Ca2+-free PSS and 10 microM phentolamine. Additional relaxations were performed under conditions in which the plasma membrane Na-Ca exchanger (PMNaCa) or Ca-pump (PMCA), or the sarcoplasmic reticulum (SR) Ca-pump (SERCA) were blocked, to identify which mechanism(s) could modulate this process. The STZ-diabetic rats had a moderate but significant decrease of BP, and their aortic rings exhibited accelerated relaxation following a biexponential model, with a significantly decreased slow component. In control rats only the inhibition of the PMNaCa could slow down the fast component, while the slow component was insensitive to any blocking maneuver. In contrast, the diabetic animals' slow component was sensitive to the inhibition of both the PMNaCa and the SERCA. The SERCA-sensitive 45Ca2+ uptake by the SR was augmented in the aortas of STZ-treated animals. This hyperactivity of the SERCA, associated with augmented activity of the PMNaCa, at least partly induced by an increase of the plasma membrane Na+/K+-ATPase activity, could explain the decrease in BP and the accelerated aortic relaxation observed in the diabetic rats.

Dietary calcium and cell membrane abnormality in genetic hypertension.

Adult stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto (WKY) rats were maintained for 10 weeks on one of two diets: 1.0% calcium content and 2.5% calcium content. At the end of this time rats were anesthetized, and blood pressure was determined by means of aortic cannulation; then the rats were exsanguinated. Lymphocytes were isolated for determination of intracellular sodium and potassium concentrations, net sodium influx, net potassium efflux, and intracellular free calcium concentration. Serum ionized calcium was also measured. The increase in calcium content of their diet had no effect on intracellular sodium and potassium concentrations in lymphocytes from WKY rats and SHRSP. In lymphocytes from WKY rats, none of the parameters was affected by the change in dietary calcium intake. In contrast, in lymphocytes from SHRSP the increase in dietary calcium from 1.0 to 2.5% led to significant decreases in net potassium efflux (13.3 +/- 2.3 vs. 19.7 +/- 1.4 mmol/kg dry wt/hr, p less than 0.05, analysis of variance), intracellular free calcium concentration (114.5 +/- 10.2 vs. 166.2 +/- 11.2 nM, p less than 0.001), and systolic blood pressure (125.3 +/- 13.6 vs. 183.3 +/- 16.6 mm Hg, p less than 0.01). Serum ionized calcium increased in SHRSP (2.40 +/- 0.04 vs. 2.16 +/- 0.03, p less than 0.01) but not in WKY rats (2.34 +/- 0.05 vs. 2.31 +/- 0.05) fed the high calcium diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of several methodological procedures utilized to obtain in vitro vascular preparations on endothelial activity.

Several maneuvers usually employed to set up isolated vascular preparations could effect the endothelium-dependent relaxation (EDR). The effects of five such maneuvers were studied in rings of rat aorta: 1) Type of anesthesia, 2) Cold storage of the vessels, 3) Length of the stabilization period, 4) Repeated contractions during stabilization, and 5) Performance of washouts during stabilization. Repeated contractions with norepinephrine (NE) 0.1 microM after stabilization altered neither the contraction nor the EDR induced by acetylcholine (Ach) 1 microM. Pentobarbital anesthesia and cold storage of the preparations for 24 h significantly decreased the EDR without effecting the contractile response of the rings. The absence of washouts during stabilization increased the contractions to either NE 0.1 microM or KCl 80 mM by nearly 50%. This increase was prevented by endothelial disruption or, in the presence of intact endothelium, by repeated washouts or by incubation with Bosentan 22 microM. It is concluded that 1) Anesthesia of the animals and cold storage of the preparations can alter the EDR even in the absence of contractile changes in the smooth muscle, and 2) Accumulation of endothelin during the incubation period, even if not producing changes in the resting tension, can substantially alter the subsequent response to vasoactive interventions.

Insulin preincubation effects on rat vessel contractile responses: role of the endothelium.

The effect of contractions elicited with ET1 and AVP after preincubating rat aortic and tail artery rings with a hyperinsulinemic dose (3 nM) of insulin were studied. Insulin preincubation (120 min), in the presence of 0.1 mM L-NAME, depressed contraction of aortic rings to 0.01 microM ET1 (132 +/- 6 vs. 161 +/- 9 mg/mm2 in control, n = 25; p < 0.05) and to 1 microM AVP (84 +/- 7 vs. 110 +/- 9 mg/mm2 in control, n = 16; p < 0.05), but did not modify 45Ca influx to the cell. Insulin-induced relaxation was inhibited by indomethacin 10 microM, an antagonist of prostaglandin synthesis, and also by blockade of insulin receptors with 30 microM genistein. A short insulin preincubation (15 min) did not modify ET1 contractions. In rat tail artery, insulin preincubation (120 min) increased the force developed by ET1 (847 +/- 45 vs. 596 +/- 99 mgF/mgW in controls, n = 14) by stimulating TXA2 release and/or actions. In summary, the present results suggest that endothelial factors are involved in both the vasoconstrictor and vasodilator effects of insulin on rat vessels.

Insulin preincubation effects on rat vessel contractile responses: role of the sarcoplasmic reticulum.

In the present work, we studied the possible mechanisms involved in the insulin-induced acceleration of ET1 contractions. We observed a shortening of the half-life needed to achieve maximal developed force (t(1/2)) at 10(-7) M ET1 in rat aortic rings preincubated for 120 min with 3 nM insulin (control 380 +/- 15 s vs. 319 +/- 8 s with insulin, n = 28, p < 0.05). A tyrosine kinase linked receptor was involved in this effect because it was abolished by 30 microM genistein. Endothelium denudation and 10 microM indomethacin treatment did not effect this insulin effect, suggesting its independence of endothelial-derived factors. The effect was still present when the only source of Ca2+ was intracellular (t(1/2) values in the absence of external Ca2+: control 467 +/- 68 s vs. 213 +/- 28 s with insulin, n = 16, p < 0.05), but was blunted if the sarcoplasmic reticulum (SR) Ca2+ source was suppressed by exposure to 10 microM thapsigargin or 10 microM ryanodine. Preincubation with insulin did not potentiate either SR 45Ca2+ uptake or contractions evoked by caffeine-sensitive SR Ca2+ release. Since 30 microM cheleritrine abolished insulin-induced acceleration of ET1 contractions, we propose that the hormone might enhance a signal pathway related to PKC in order to produce a faster Ca2+ release from the SR.

Mechanical properties of human saphenous veins from normotensive and hypertensive patients.

BACKGROUND: Different reactivities of saphenous vein grafts in hypertensive and normotensive patients could lead to differences in the postoperative patency of the grafts. METHODS: In saphenous vein rings isolated from remnants of aorta-coronary grafts obtained from hypertensive and normotensive patients we studied the length-tension relationship; response to high levels of potassium, norepinephrine, and epinephrine; and relaxation in response to calcium deprivation. RESULTS: The rings from hypertensive patients were stiffer and developed more force (grams force/grams weight) than the rings from normotensive subjects to 80 mmol/L potassium (59+/-16 versus 25+/-5, p < 0.05) and to 1 micromol/L norepinephrine (61+/-8 versus 36+/-7, p < 0.05), but not to 10 micromol/L epinephrine (57+/-11 and 54+/-11; not significant). The rings from hypertensive patients relaxed more slowly than those of the normotensive subjects in a calcium-free medium (time to half-relaxation of 976+/-180 versus 548+/-81 seconds; p < 0.05). CONCLUSIONS: The saphenous vein from hypertensive patients is less distensible, slower to relax, and more reactive to at least two agonists. These differences could influence the graft's patency and the clinical outcome.

Short-term streptozotocin-induced diabetes induces blood pressure decrease associated with reduced aortic (45)Ca(2+) uptake and selective depression of the sustained noradrenergic contraction.

To test the hypothesis that diabetes can selectively affect the intracellular and extracellular components of the noradrenergic vascular response in rats, we studied changes in blood pressure, in vitro vascular contraction and (45) Ca(2+) uptake in experimental diabetes induced by injection of 60 mg/kg of streptozotocin (STZ). One week after induction of diabetes mean blood pressure decreased significantly from 106 +/- 3 mmHg to 89 +/- 2 mmHg. After incubation in Ca(2+) =1.6 mM, contraction of STZ aortic rings to 10(- 7) M of norepinephrine was preserved in its intracellular component (Control: 231 +/- 28, STZ: 274 +/- 22 mgForce/mgTissue, NS) but depressed in its extracellular component (Control: 277 +/- 24, STZ: 133 +/- 33 mgForce/mgTissue, P<0.05). Uptake of (45) Ca(2+) in the same rings was depressed in both components. Norepinephrine contractions due to extracellular Ca(2+) (prior depletion of norepinephrine-sensitive Ca(2+) stores) unexpectedly exhibited a initial component whose magnitude in control rings was similar to the response due to intracellular Ca(2+) (extra: 503 +/- 65 mg, intra: 411 +/- 30 mgForce/mgTissue), and was not depressed in STZ preparations (399 +/- 62 mgForce/mgTissue). The sustained contraction to norepinephrine in extracellular Ca(2+) was significantly reduced in STZ aortas (1163 +/- 92 vs. 528 +/- 95 mgForce/mgTissue). We conclude that: 1) Short-term streptozotocin-induced diabetes features reduced blood pressure along with deficient aortic (45) Ca uptake and contraction to norepinephrine, and 2) Only the sustained phase of the norepinephrine contraction, dependent on extracellular Ca(2+), was depressed in the diabetic rats and could possibly be associated with the observed fall in blood pressure.

Characteristics of the fast and slow components of the response to noradrenaline in rat aorta.

The fast and slow components of the response to noradrenaline in rat aorta were studied to assess their relative contribution to the total mechanical response. The fast component, the magnitude of which varied with the concentration of noradrenaline in a dose-dependent manner, was shown to be dependent on release of calcium from intracellular stores. In calcium-free medium with ethylene glycol bis-(beta-aminoethylether) N,N,N',N-tetra-acetic acid (EGTA) a noradrenaline challenge (1 microM) produced a transient increase in force which faded in about 10 mins. Addition of calcium at this point produces a slow component of similar amplitude to the total response to noradrenaline. Recycling of calcium through the intracellular store does not appear to play an important role under these experimental conditions, since the presence of noradrenaline in the bath prevented its refilling. It is concluded that extracellular calcium by itself (ie, the slow component) can account for the total contractile response to noradrenaline in rat aorta.

Effect of calcium antagonists on aortae isolated from normotensive and hypertensive rats: relaxation and calcium influx blockade.

Verapamil and diltiazem were equally potent (ie, similar EC50s) in relaxing potassium-contracted aortas of spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats. The mechanical EC50s produced approximately 50% calcium influx blockade, suggesting a causal link between relaxation and calcium influx blockade. Nitrendipine was about 250 times more potent in relaxing aortic smooth muscle in SHR than in WKY rats (EC50s in -log [M] were 14.10 +/- 0.30 and 11.70 +/- 0.54, respectively). This difference was not affected by endothelial denudation, and was present when nitrendipine was used by preincubation rather than during established potassium chloride contractions. In spite of the different relaxant potency of nitrendipine in SHR and WKY rats, both strains showed similar EC50s for calcium influx blockade for this compound (9.21 +/- 0.36 in SHR and 8.75 +/- 0.26 in WKY). The dissociation between aortic smooth muscle relaxation and calcium influx blockade after nitrendipine was more pronounced in the SHR strain. This suggests that mechanisms other than or in addition to calcium influx blockade play a role in the relaxation of potassium-contracted vascular smooth muscle with dihydropyridine compounds, but not with other calcium antagonists.

[Definition of hypertension based on a prevalence study of 1,423 young adults]. / Consideraciones sobre la definición de hipertensión arterial a partir de un estudio de prevalencia en 1423 jóvenes.

The prevalence of arterial hypertension (AH) was studied in 1423 individuals (702 males and 721 females) aged 21 years (Fig. 1, Table 1). Systolic (SBP) and diastolic (DBP) blood pressures and heart rate (HR) were measured three times on two different occasions separated by at least one week. Three different criteria were used to define AH (Table 3): 1) World Health Organization (WHO) [PAD > or = 95 mmHg in one casual determination]; Joint National Committee IV (JNC-4) [PAD > or = 90 mmHg on two different occasions]; and 3) Statistical [PAD > percentile 95 of the respective distribution]. BP was distributed normally in both males and females (Fig. 4). DBP decreased progressively along the six measurements (Fig. 2, Table 2), with the average of DBP determinations 4-6 being significantly lower than the average of determinations 1-3 (p < 0.05). SBP behaved in the same way (Fig. 2, Table 2), but in this case the 2nd and 3rd determinations within each occasion (2-3 and 5-6) were significantly lower than determinations 1 and 4, respectively (p < 0.05). As a result, the percentage of individuals of either sex with DBP > 90 mmHg was 14.7% based on the 1st determination (Fig. 5), but if the averages of determinations 1 to 3 or 1 to 6 were considered, these percentages decreased to 8.7% and 4% respectively (Fig. 5). With the WHO criterion (PAD > or = 160/95 mmHg based on the first determination) there were 3.3% of individuals with AH. With the statistical criterion the prevalence of AH was always 5%, but the actual value of percentile 95 was progressively lower as we took into account the 1st. determination, the average of 1-3 or the average of 1-6: 100, 95 and 90 mmHg in males and 90, 88 and 84 mmHg in females, respectively (Fig. 6). With the JNC-4 criterion there were 1.6% of individuals with AH (Fig. 5). These low figures were caused by the lack of repeatability of DBP readings in the second determination, since 79% of the individuals with DBP > or = 90 mmHg on the first occasion were normotensive on the second one, whereas more than 95% of those being initially normotensive remained in that category on the second visit (Fig. 7). The FC did not show important changes (Fig. 8), and the percentage of individuals with systolic AH was low (Table 4).(ABSTRACT TRUNCATED AT 250 WORDS)

[Structural and functional aspects of the human saphenous vein used as aorto-coronary graft in myocardial revascularization]. / Aspectos estructurales y funcionales de la vena safena humana utilizada como puente aorto-coronario en la cirugia de revascularización miocárdica.

The human saphenous vein (HSV) is currently used as a graft in coronary revascularization as well as in some other vascular beds, namely those of the inferior limbs. Since a significant proportion of HSV grafts develop stenosis, many studies have focused on the factors that could promote graft failure. This article reviews the results on structural and functional features that might be concurrent in the production of saphenous vein graft stenosis. The reactivity of HSV to several physiological agonists is analyzed, including those derived from the endothelium with contractile or relaxing properties, since these are relevant inducers of graft spasm and/or modifiers of the expression of graft factors involved in either tissue growth or thrombotic-atherosclerotic processes. Mechanisms that regulate vascular smooth muscle contractile state, in particular the activity of K+ channels of the plasma membrane, are described.

Sodium-calcium exchange in vascular smooth muscle of Wistar-Kyoto and stroke-prone spontaneously hypertensive rats.

The role of the sodium-calcium (Na-Ca) exchange in vascular smooth muscle contraction was examined in tail artery rings isolated from stroke-prone spontaneously hypertensive rats (SHRSP) and in normotensive Wistar-Kyoto rats (WKY). The rings were repeatedly stimulated with noradrenaline (1 microM) in physiological salt solution (Na = 130 mM), until two successive contractions were of the same magnitude. The rings were then placed in physiological salt solution with reduced sodium concentrations (65 mM or 0 mM, replaced isosmotically with sucrose), and the noradrenaline stimulations continued. In WKY rings, the reduction of sodium concentration produced an increase in the response to noradrenaline, which was significant in sodium-free physiological salt solution. In SHRSP rings, however, the same reductions in sodium concentration produced significantly less potentiation of the noradrenaline contraction, even in sodium-free physiological salt solution. We conclude that (1) in WKY, the reduced and reversed activity of the Na-Ca exchange produced by the reductions in sodium concentration makes more calcium available for contraction when the smooth muscle is stimulated with noradrenaline; and (2) the failure of sodium reductions to produce a normal potentiation of the response to noradrenaline in SHRSP indicates a depressed activity of the Na-Ca exchange in this tissue.

[Norepinephrine-sensitive calcium pools in tail arteries of normotensive and spontaneously hypertensive rats: effects of ryanodine and caffeine]. / Depósitos de calcio sensibles a la noradrenalina en arterias de la cola de ratas normotensas y espontáneamente hipertensas: efectos de la rianodina y cafeína.

The effects of Ryanodine (RY) and Caffeine (CF) on the norepinephrine (NE)-induced contraction were studied in tail artery rings from spontaneously hypertensive rats (SHR) and normotensive, Wistar Kyoto rats (WKY). The NE-sensitive intracellular store of calcium was completely depleted by NE (1 microM) in calcium-free physiological salt solution (Ca = 0-PSS), and accounted for approximately 40% of the total response to NE in regular PSS (Ca = 1.6 mM). However, only 60% of the NE-releasable store was utilized for the full contraction in PSS. Re-exposure to PSS completely replenished the NE-releasable store in 10 minutes. Over twice as much calcium appeared to be taken up by the SHR as by the WKY arteries in these conditions. RY prevented the refilling of the NE-sensitive calcium store in both SHR and WKY, without releasing calcium from the store and without affecting the influx of calcium through membrane pathways. CF also prevented the refilling of the NE-sensitive calcium store, but did release calcium from it. It can be concluded that: 1) Whereas the main action of RY on rat tail artery seems to be the inhibition of calcium uptake by the sarcoplasmic reticulum (SR), CF has several actions: a) inhibition of calcium uptake by the SR, b) release of calcium from the SR, and c) opening of calcium channels in the plasma membrane of the smooth muscle cell. 2) In SHR, but not in WKY, the loss of calcium from the membrane in Ca = 0-PSS renders it more permeable to calcium, permitting an enhanced calcium uptake during subsequent exposure to PSS.

Interaction between calcium and hydrogen ions in canine coronary arteries.

In vitro experiments were carried out to study the effects of "respiratory" and "metabolic" acid-base alterations on canine coronary arteries precontracted by high potassium. Alkalosis (pH 7.70 +/- 0.02) increased the coronary tone by 33 +/- 3% (P less than 0.05) and acidosis (pH 7.10 +/- 0.01) decreased it by 30 +/- 3% (P less than 0.05). The tension stabilized in approximately 15 mins and its variation was of similar extent whether changes in extracellular pH were produced by changes in PCO2 or in bicarbonate concentration. The contractile changes were not abolished neither by alpha or beta adrenergic blockade nor by endothelium denudation. The effect of pH could not be offset by altering extracellular potassium or calcium when the plateau of the relationship between contractility of the smooth muscle and concentration of these ions was reached. When tonus developed by the strips and [Ca2+]0 were plotted reciprocally, DTmax significantly increased in alkalosis and decreased in acidosis. No significant changes in Ca50 ([Ca2+]0 necessary to obtain 50% of maximal force) were detected. pH changes did not modify Ca2+ influx but a relaxation of similar extent induced by nifedipine produced a detectable decrease in Ca2+ influx. Ca2+ efflux was augmented in acidosis and depressed in alkalosis. Our data do not support the hypothesis of hydrogen ion changes inducing calcium influx alterations in a competitive fashion as the mechanism involved to contract or relax conduit coronary arteries. On the contrary, they suggest that acid-base variations alter the contractile activity of vascular smooth muscle by modulating Ca2+ efflux.

Decreased activity of the sodium-calcium exchanger in tail artery of stroke-prone spontaneously hypertensive rats.

The ability of the Na-Ca exchanger to modify vascular relaxation was studied in rings isolated from tail arteries of stroke-prone spontaneously hypertensive rats (SHRSP) and normotensive Wistar-Kyoto rats (WKY). The arteries were contracted with norepinephrine (NE) 1 microM and after stabilization they were transferred to a Ca-free physiological salt solution still in presence of NE. The time to 50% relaxation (T-50) in these conditions was significantly greater in SHRSP (78 +/- 7 s) than in WKY (50 +/- 7 s). When the calcium pump was stopped with vanadate (VAN), the Ca uptake by the sarcoplasmic reticulum with ryanodine (RY) and the Na-Ca exchanger with a Na-free PSS, the relaxation was slowed (T-50 increased to 198 +/- 16 s in SHRSP and to 162 +/- 14 s in WKY). Releasing the Na-Ca exchanger only (i.e. still with VAN and RY but with normal Na in the bath) the T-50 for relaxation in Ca-free PSS was, in WKY, nearly as fast as in control conditions (54 +/- 8 s). However, the Na-Ca exchanger in SHRSP was not so effective, and the T-50 for relaxation was slower than in control conditions (122 +/- 10 s). We conclude that the activity of the Na-Ca exchanger is depressed in tail arteries of SHRSP. This abnormality in resistance vessels, would contribute to the enhanced vascular tone present in hypertension.