Stimulation of aortic tissue calcium uptake by an extract of spontaneously hypertensive rats erythrocytes possessing hypertensive properties

1986 ◽  
Vol 64 (12) ◽  
pp. 1515-1520 ◽  
Author(s):  
G. L. Wright ◽  
M. E. Rogerson ◽  
W. D. McCumbee
Keyword(s):  
Spontaneously Hypertensive Rats ◽  
Calcium Uptake ◽  
Vascular Tissue ◽  
Aortic Tissue ◽  
Hypertensive Rats ◽  
Spontaneously Hypertensive ◽  
High K ◽  
Tissue Sensitivity ◽  
Tissue Calcium

In earlier reports we have described the isolation of a fraction from the erythrocytes of spontaneously hypertensive rats that produced hypertension when administered to normotensive rats. In addition, it was found that the fraction stimulated the uptake of "lanthanum-resistant" calcium by aortic rings excised from normotensive rats. In these studies we have found that the fraction causes a greater increase in the in vitro uptake of calcium by aortic tissue than that produced by depolarization of the tissue with high K+ or the receptor-mediated influx of calcium induced with norepinephrine. The hypertensive fraction appeared to be more effective in promoting increased calcium uptake in rabbit than in rat aortic tissue, suggesting that significant differences in tissue sensitivity to the active compound(s) may exist between species. In addition, we obtained evidence indicating that the tissue sensitivity to the action of the hypertensive fraction was greater in aortae from spontaneously hypertensive rats than from those of normotensive animals. Attempts to block the action of the hypertensive fraction with verapamil, nifedipine, and sodium nitroprusside had no significant effect on the elevation in tissue calcium. It was found, however, that the action of the hypertensive fraction was temperature dependent with reduced activity at lower temperatures. The data suggest that a compound(s) is present in the erythrocytes of rats that may have a marked effect on vascular tissue metabolism of calcium.

An antihypertensive extract of erythrocytes: effects on 45Ca uptake and efflux

1986 ◽  
Vol 64 (4) ◽  
pp. 424-429
Author(s):  
G. L. Wright ◽  
G. O. Rankin ◽  
W. D. McCumbee
Keyword(s):  
Blood Pressure ◽  
Spontaneously Hypertensive Rats ◽  
Calcium Uptake ◽  
Slow Component ◽  
Present Report ◽  
Calcium Stores ◽  
Hypertensive Rats ◽  
Spontaneously Hypertensive ◽  
Washout Curves

The present report describes some aspects of the effects of a recently described antihypertensive extract of erythrocytes (AHF) on calcium uptake and efflux in rat aortae. AHF was found to be present in the erythrocytes of both spontaneously hypertensive rats and normotensive rats. Furthermore, AHF obtained from erythrocytes of SH rats was shown to be equally effective in suppressing lanthanum-resistant calcium uptake in aortae from hypertensive and normotensive rats. AHF treatment prior to incubation of aortae with 45Ca caused an apparent increase in the total 45Ca uptake. The analysis of calcium washout curves obtained for tissue in calcium-free or lanthanum-containing media indicated that AHF had no significant effect on the rate of calcium loss from the slow component of efflux, though this compartment tended to be reduced in size. This indicated that the increase in the 45Ca content of AHF-exposed aortae prior to rinsing was confined to the rapid component of efflux. The loss of calcium from the rapidly exchanging compartment was enhanced in either of the efflux media used. The results suggest that a principal action of AHF involves an increase in the lability and exchangeability of calcium stores. In addition to its effects in resting tissue, AHF abolished the increase in lanthanum-resistant calcium uptake induced in rat aortae by the addition of high K+ or norepinephrine to the incubation media. In a second part of the study, the effect of AHF on blood pressure and in vitro calcium uptake were compared with that of phosphatidylethanolamine (PEA), the probable identity of another endogenous antihypertensive (renin preinhibitor) compound earlier shown to share important functional similarities with AHF. The results reduce the likelihood that the two causal agents are identical. The AHF produced a significant (75 Torr, 1 Torr = 133.32 Pa) fall in the systolic blood pressure (SBP) of spontaneously hypertensive rats within 24 h following injection, whereas PEA had no effect on the SBP in this model. Both AHF and PEA reduced the resting in vitro uptake of "lanthanum-resistant" calcium in rat aortic segments. However, the AHF effect was significantly greater than PEA at each concentration studied.

The vascular sensitizing character of plasma from spontaneously hypertensive rats

1981 ◽  
Vol 59 (11) ◽  
pp. 1111-1116 ◽  
Author(s):  
Gary L. Wright
Keyword(s):  
Blood Pressure ◽  
Plasma Levels ◽  
Spontaneously Hypertensive Rats ◽  
Vascular Tissue ◽  
Sprague Dawley ◽  
Hypertensive Rats ◽  
Spontaneously Hypertensive ◽  
Tissue Sensitivity ◽  
Low Levels ◽  
Wistar Kyoto

Experiments were conducted to examine the effects of plasma from spontaneously hypertensive rats (systolic blood pressure (SBP) = 183 torr; 1 torr = 133.322 Pa) on the contractile properties of aortic strips from normotensive rats. While incubated in plasma from spontaneously hypertensive (SH) rats, the aortic strips of normotensive rats exhibited hyperresponsiveness to norepinephrine (NE) compared with those incubated in plasma obtained from Wistar–Kyoto (SBP = 128 torr) or Sprague–Dawley (SBP = 110 torr) rats. The washout of plasma and perfusion of the aortic strips with Krebs bicarbonate solution abolished the effect of SH plasma on the reactivity to NE but not potassium, suggesting a residual hypersensitivity. The comparison of these findings with results obtained for contractions of aortic strips in Krebs bicarbonate solution containing high and low levels of calcium indicated the effect of SH plasma on vascular tissue sensitivity was not directly related to an alteration in plasma levels of calcium.

Na+, K+ and water balance in young spontaneously hypertensive rats: relationship to blood pressure after high K+ treatment

1987 ◽  
Vol 72 (3) ◽  
pp. 321-327 ◽  
Author(s):  
A. Louise Sugden ◽  
Barbara L. Bean ◽  
James A. Straw
Keyword(s):  
Blood Pressure ◽  
Water Balance ◽  
Spontaneously Hypertensive Rats ◽  
Urine Volume ◽  
Extracellular Fluid ◽  
Maximum Level ◽  
Hypertensive Rats ◽  
Spontaneously Hypertensive ◽  
High K ◽  
Sufficient Magnitude

1. These studies were designed to investigate the effects of high dietary K+ on electrolyte and water balance in young spontaneously hypertensive rats (SHR) and to relate these effects to changes in blood pressure. 2. The high K+ diet reduced blood pressure by approximately 10 mmHg during the development of hypertension. Blood pressure, however, plateaued at the same maximum level as control by age 13 weeks. 3. Rats fed the high K+ diet showed a significant increase in water intake and urine volume throughout the treatment period but no change in plasma volume or extracellular fluid volume occurred. 4. A slight natriuresis was also observed in rats on the high K+ diet, but this was not of sufficient magnitude to decrease total body Na+. 5. These results confirm previous findings that K+ causes a diuresis and a natriuresis, but demonstrate that the diuretic action of K+ cannot explain its antihypertensive properties in young SHR.

High-potassium diet attenuates salt-induced acceleration of hypertension in SHR

1991 ◽  
Vol 260 (1) ◽  
pp. R21-R26 ◽  
Author(s):  
Y. Sato ◽  
K. Ando ◽  
E. Ogata ◽  
T. Fujita
Keyword(s):  
Blood Pressure ◽  
Renal Function ◽  
Spontaneously Hypertensive Rats ◽  
Hypertensive Rats ◽  
High Potassium ◽  
Spontaneously Hypertensive ◽  
Antihypertensive Action ◽  
High K ◽  
Wistar Kyoto ◽  
Renal Vascular

We studied the effects of K supplementation (8% KCl) for 4 wk on blood pressure (BP), Na space, and renal hemodynamics in 5-wk-old, spontaneously hypertensive rats (SHR) or age-matched Wistar-Kyoto rats (WKY) eating normal-NaCl (0.66%) or high-NaCl (8%) diet. In WKY, high-Na and/or high-K diets had no effects on BP. In SHR, Na load accelerated the development of hypertension, whereas K supplementation did not affect BP of normal-Na SHR but attenuated the increase in BP with Na load. Correspondingly, Na load in SHR significantly increased renal vascular resistance (RVR), and K supplementation attenuated the increased RVR of Na-loaded SHR. Moreover, Na space of SHR was increased compared with that of WKY, and although Na load did not affect Na space, K supplementation tended to decrease Na space in SHR. These results indicate that 9-wk-old SHR is relatively volume-expanded compared with age-matched WKY, and K supplementation could improve the lowered slope of the pressure-Na excretion relationship in SHR, resulting in maintenance of Na balance. Thus the data suggest that changes in RVR, which might be intimately related to renal function for Na excretion, contribute to both salt sensitivity of SHR and antihypertensive action of K supplementation in Na-loaded SHR.

Ca fluxes across duodenum and colon of spontaneously hypertensive rats: effect of 1,25(OH)2D3

1986 ◽  
Vol 251 (2) ◽  
pp. F278-F282 ◽  
Author(s):  
U. Gafter ◽  
S. Kathpalia ◽  
D. Zikos ◽  
K. Lau
Keyword(s):  
Calcium Transport ◽  
Spontaneously Hypertensive Rats ◽  
Calcium Absorption ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Calcium Flux ◽  
Hypertensive Rats ◽  
Spontaneously Hypertensive ◽  
Wistar Kyoto

Calcium absorption by spontaneously hypertensive rats (SHR) was variably reported to be different from normotensive Wistar-Kyoto (WKY) controls. Furthermore, blunted responsiveness to the intestinal effects of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] has also been postulated. To evaluate this hypothesis, calcium fluxes were measured by the Ussing technique across duodenum and descending colon with or without prior 1,25(OH)2D3 treatment. Duodenal mucosal-to-serosal calcium flux (Jm----s) (44.9 vs. 52.4 nmol X cm-2 X h-1), serosal-to-mucosal flux (Js----m) (25.6 vs. 28.4 nmol X cm-2 X h-1), and net flux (Jnet) were comparable. 1,25(OH)2D3 increased duodenal Jm----s in both SHR and WKY groups (95.2 and 86.8 nmol X cm-2 X h-1). Js----m was lower in SHR (26.1 vs. 35.6 nmol X cm-2 X h-1, P less than 0.01), although the tendency for a higher Jnet in SHR (68.6 vs. 51.2 nmoles X cm-2 X h-1) was statistically insignificant. Short-circuit current was higher in the colon of SHR, both before and after 1,25(OH)2D3, suggesting increased sodium transport. Basal colonic Jnet was virtually zero in both groups but comparably increased by 1,25(OH)2D3 because of stimulation in only Jm----s. Prevention of hypertension by hydralazine since the 4th wk of age did not alter the findings compared with the hypertensive SHR, suggesting calcium transport rates were unaffected by hypertension. These data indicate that in vitro, duodenal, and colonic active calcium transport by the SHR is similar to WKY. Their normal responses to 1,25(OH)2D3 do not support the hypothesis of intestinal resistance.

Myogenic tone in mesenteric arteries from spontaneously hypertensive rats

1996 ◽  
Vol 270 (1) ◽  
pp. H1-H6 ◽  
Author(s):  
A. S. Izzard ◽  
S. J. Bund ◽  
A. M. Heagerty
Keyword(s):  
Spontaneously Hypertensive Rats ◽  
Mesenteric Arteries ◽  
Myogenic Tone ◽  
Hypertensive Rats ◽  
Tension Development ◽  
Spontaneously Hypertensive ◽  
Wide Pressure Range ◽  
Wistar Kyoto ◽  
Wide Pressure

To investigate myogenic tone during the developmental and established phases of hypertension, segments of distal (6th order) mesenteric arteries from spontaneously hypertensive rats (SHR) at 5 and 20 wk were isolated and pressurized in vitro and compared with vessels from age-matched Wistar-Kyoto (WKY) control animals. At 5 wk, tone was significantly enhanced in the SHR. At 20 wk tone was no longer significantly increased over a wide pressure range, although arteries from the SHR were able to maintain diameter at all pressures studied, whereas vessels from the WKY exhibited forced distension at 180 and 200 mmHg. From the relative slope of the pressure-diameter relationship (myogenic index), no increase in peak myogenic responsiveness was observed in arteries from the SHR at either time point. Passive lumen diameters were significantly decreased in arteries from SHR at both time points. From the total and passive midwall circumference-tension relationships, total tension was observed at a reduced midwall circumference in the SHR, but increased absolute levels of total tension were not observed. The normalized midwall circumference-tension relationships in the two strains revealed increased total tension due to active tension development at a reduced normalized circumference at 5 wk in the SHR. At 20 wk the normalized midwall circumference-tension relationships in the two strains were identical. These results demonstrate that myogenic tone in mesenteric arteries is enhanced during the development of hypertension but not when it is established, except at high intraluminal pressures.

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