Erythrocytosis in spontaneously hypertensive rats

Static magnetic field on behavior, hematological parameters and organ damage in spontaneously hypertensive rats

Previous studies showed contradictory results of static magnetic field (SMF) influence on behavior, hematological parameters and organ damage. The aim of this study was to investigate influence of subchronic continuous exposure to upward and downward oriented SMF of moderate intensity on behavior, hematological characteristics, heart and kidney tissue of spontaneously hypertensive rats. SH rats exposed to downward oriented SMF demonstrated lack of anxious-like behavior. SMF of either orientation caused decrease in the number of platelets in peripheral blood, granulocytes in the spleen and bone marrow and increase in the number of erythrocytes in the spleen, in both exposed groups. We also demonstrated that spontaneously hypertensive rats exposed to upward oriented SMF exhibited decreased lymphocytes count in blood, decreased bone marrow erythrocytes count and rats exposed to downward oriented SMF had increased lymphocytes count in bone marrow. The results showed adverse effect of differently oriented SMF on hematological parameters of spontaneously hypertensive rats. Also, exposure to different oriented SMF didn't affect their heart and kidney morphological characteristics.

Endobiogeny: a global approach to systems biology (part 2 of 2)

ENDOBIOGENY AND THE BIOLOGY OF FUNCTIONS ARE BASED ON FOUR SCIENTIFIC CONCEPTS THAT ARE KNOWN AND GENERALLY ACCEPTED: (1) human physiology is complex and multifactorial and exhibits the properties of a system; (2) the endocrine system manages metabolism, which is the basis of the continuity of life; (3) the metabolic activity managed by the endocrine system results in the output of biomarkers that reflect the functional achievement of specific aspects of metabolism; and (4) when biomarkers are related to each other in ratios, it contextualizes one type of function relative to another to which is it linked anatomically, sequentially, chronologically, biochemically, etc.

Age-dependent salt hypertension in Dahl rats: fifty years of research

Fifty years ago, Lewis K. Dahl has presented a new model of salt hypertension - salt-sensitive and salt-resistant Dahl rats. Twenty years later, John P. Rapp has published the first and so far the only comprehensive review on this rat model covering numerous aspects of pathophysiology and genetics of salt hypertension. When we summarized 25 years of our own research on Dahl/Rapp rats, we have realized the need to outline principal abnormalities of this model, to show their interactions at different levels of the organism and to highlight the ontogenetic aspects of salt hypertension development. Our attention was focused on some cellular aspects (cell membrane function, ion transport, cell calcium handling), intra- and extrarenal factors affecting renal function and/or renal injury, local and systemic effects of renin-angiotensin-aldosterone system, endothelial and smooth muscle changes responsible for abnormal vascular contraction or relaxation, altered balance between various vasoconstrictor and vasodilator systems in blood pressure maintenance as well as on the central nervous and peripheral mechanisms involved in the regulation of circulatory homeostasis. We also searched for the age-dependent impact of environmental and pharmacological interventions, which modify the development of high blood pressure and/or organ damage, if they influence the salt-sensitive organism in particular critical periods of development (developmental windows). Thus, severe self-sustaining salt hypertension in young Dahl rats is characterized by pronounced dysbalance between augmented sympathetic hyperactivity and relative nitric oxide deficiency, attenuated baroreflex as well as by a major increase of residual blood pressure indicating profound remodeling of resistance vessels. Salt hypertension development in young but not in adult Dahl rats can be attenuated by preventive increase of potassium or calcium intake. On the contrary, moderate salt hypertension in adult Dahl rats is attenuated by superoxide scavenging or endothelin-A receptor blockade which do not affect salt hypertension development in young animals.

Adenosine deaminase-adenosine pathway in hemolysis-associated pulmonary hypertension

Hemolysis-associated pulmonary hypertension (HA-PH) is a serious clinical complication of various hemolytic disorders, and pulmonary hypertension (PH) is considered the greatest risk factor for death in patients with a hemolytic disorder. It is now well established that hemolysis causes the release of soluble hemoglobin and arginase from injured erythrocytes into plasma. This leads to nitric oxide (NO) deficiency, oxidative stress and a state of endothelial dysfunction that is associated with clinical development of PH. We challenge this concept and propose that in addition to the NO-arginase pathway, the adenosine deaminase-adenosine pathway plays a significant role in HA-PH and that modulation of this pathway may offer protective/therapeutic effects in HA-PH. Our preliminary data suggest that in HA-PH adenosine deaminase (ADA) is released from injured erythrocytes into plasma and that metabolic conversion of adenosine (ADO) to inosine by ADA reduces extracellular ADO levels. Adenosine, mainly via activation of adenosine A(2A) receptors, mediates a number of biological responses that may reduce hemolysis-induced vasculopathy and the risk of PH. Hypoxia is the strongest stimulus for ADO synthesis, and this increased ADO production counteracts some of the tissue/vascular injury caused by hypoxia itself. Unfortunately, under hypoxic conditions (anemia, vasoconstriction, and vaso-occlusion) in HA-PH, this "ADO negative-feed back" is abolished and the vascular protective effects of ADO are severely diminished by ADA released from injured erythrocytes. We hypothesize that in hemolytic anemia the repetitive release of ADA increases the risk for vaso-occlusive events and PH. We also propose that increase in extracellular ADO levels or activation of adenosine A(2A) receptors attenuates HA-PH, and we suggest further preclinical and clinical investigation of ADA inhibitors and ADO agonists in HA-PH.

Relationships between membrane lipids and ion transport in red blood cells of Dahl rats

Distinct changes of membrane lipid content could contribute to the abnormalities of ion transport that take part in the development of salt hypertension in Dahl rats. The relationships between lipid content and particular ion transport systems were studied in red blood cells (RBC) of Dahl rats kept on low- and high-salt diets for 5 weeks since weaning. Dahl salt-sensitive (SS/Jr) rats on high-salt diet had increased blood pressure, levels of plasma triacylglycerols and total plasma cholesterol compared to salt-resistant (SR/Jr) rats. Furthermore, RBC of SS/Jr rats differed from SR/Jr ones by increased content of total membrane phospholipids, but membrane cholesterol was not changed significantly. SS/Jr rats had higher RBC intracellular Na+ (Na(i)+) content and enhanced bumetanide-sensitive Rb+ uptake. RBC membrane content of cholesterol and phospholipids correlated positively with RBC Na(i)+ content, with the activity of Na+-K+ pump and Na+-K+-2Cl- cotransport and also with Rb+ leak. The content of phosphatidylserines plus phosphatidylinositols was positively associated with RBC Na(i)+ content, with the activity of Na+-K+ pump and Na+-K+-2Cl- cotransport and with Rb+ leak. The content of sphingomyelins was positively related to Na+-K+-2Cl- cotransport activity and negatively to ouabain-sensitive Rb+-K+ exchange. We can conclude that observed relationships between ion transport and the membrane content of cholesterol and/or sphingomyelins, which are known to regulate membrane fluidity, might participate in the pathogenesis of salt hypertension in Dahl rats.

Nephron pO2 and renal oxygen usage in the hypertensive rat kidney

BACKGROUND

The kidney has a high rate of oxygen usage (QO2) that is closely dependent on tubular Na+ transport (TNa). However, little is known concerning the regulation of the cortical partial pressure of oxygen (pO2).

METHODS

First, the pO2 was measured in the outer cortical proximal (PT) and distal tubules (DT), efferent arterioles (EA), and superficial (SC) and deep cortical (DC) tissues in normotensive Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHRs) using an ultramicrocoaxial O2 electrode. We next assessed the determinants of QO2 and tubular reabsorption of sodium (TNa) for whether they could account for any differences in renal cortical pO2 in SHRs.

RESULTS

The pO2 in the EA was reduced 40 to 50% compared with arterial values but was similar in the two strains (WKY rats 45 +/- 2 vs. SHRs 41 +/- 1 mm Hg, P = NS). The pO2 value in the PT, DT, and SC did not differ within strains. All were significantly (P < 0. 001) lower in SHRs (for example, pO2 in PT of WKY rats 39 +/- 1 vs. SHRs, 30 +/- 1 mm Hg). The pO2 in the renal vein was above that at any site in the EA or the cortex, implying a precapillary shunting of O2 from the artery to vein. SHRs had reduced renal blood flow (RBF) leading to a reduced (P < 0.05) rate of O2 delivery (WKY rats 42 +/- 6 vs. SHRs 30 +/- 1 micromol. min-1. g-1) and a reduced glomerular filtration rate, leading to a lower (P < 0.001), TNa (WKYs 115 +/- 9 vs. SHRs 66 +/-8 micromol. min-1. g-1). However, despite the 43% reduction in TNa, the renal O2 usage was not significantly different between strains (WKY rats 7.6 +/- 0.8 vs. SHRs 9.0 +/- 1.0 micromol. min-1. g-1). Therefore, the SHRs had a sharp reduction (P < 0.001) in the O2 efficiency for Na+ reabsorption (TNa/QO2; WKY rats 15.1 +/- 1.6 vs. SHRs 7.3 +/-1.0 micromol-1).

CONCLUSIONS

A precapillary O2 shunt reduces the pO2 of cortical nephrons. The pO2 is reduced further in SHRs because of less efficient O2 usage for Na+ transport.

Perinatal growth disturbance in the spontaneously hypertensive rat

Disproportionate fetal and placental growth are associated with the development of hypertension in the rat and human. Here we report differences in fetal, neonatal, and placental growth, and in metabolism and endocrinology, between the spontaneously hypertensive rat (SHR), a genetic model for human essential hypertension, and the control Wistar-Kyoto (WKY) strain. Gestation in SHR (23 d) was longer than in WKY by 20 h. Body weights were lower in the SHR from fetal d 16 to 20 and on postnatal d 15. However, on fetal d 22 and postnatal d 1, there was no significant difference in body weight between SHR and WKY. SHR placentas were larger than those of WKY at d 20, and by term there was a difference of 30% (p < 0.01). Other indices of disproportionate growth were hypertrophy of the fetal heart and kidney and decreased ponderal index in the SHR neonate. Blood glucose in SHR fetuses was lower than in WKY fetuses (p < 0.05), whereas blood lactate was higher (p < 0.05) and fetal hematocrit was reduced (p < 0.001). These findings suggest undernutrition and placental insufficiency may occur in SHR fetuses. Plasma IGF-II was increased on the last day of gestation in both strains, whereas IGF-I was unaltered. Fetal liver IGFBP-2 mRNA and plasma IGFBP-2 levels were reduced in SHR on fetal d 20 and 22 (p < 0.01). Differences in growth and endocrine and metabolic parameters suggest abnormal perinatal physiology in the SHR, which may influence the later development of hypertension.

Mapping genes controlling hematocrit in the spontaneously hypertensive rat

The genes that determine the baseline hematocrit level in humans and experimental animals are unknown. The spontaneously hypertensive rat (SHR), the most widely used animal model of human essential hypertension, exhibits an increased hematocrit when compared with the normotensive Brown Norway (BN-Lx) strain (0.54 +/- 0.02 vs. 0.44 +/- 0.02, p < 0.01). Distribution of hematocrit values among recombinant inbred (RI) strains derived from SHR and BN-Lx progenitors was continuous, which suggests a polygenic mode of inheritance. The narrow heritability of the hematocrit was estimated to be 0.32. The Eno2 marker on Chromosome (Chr) 4 showed the strongest association (p < 0.0001) with the observed variability of hematocrit among RI strains. The erythropoietin (Epo) gene, originally reported to be syntenic with Eno2, has been mapped to Chr 12, thus excluding it as a potential candidate gene for the increased hematocrit in the SHR. The current linkage data extend homologies between rat, mouse, and human chromosomes.

Hematocrit, blood pressure, and hypertension. The Gubbio Population Study

Baseline data from the Gubbio Population Study in north central Italy were used to investigate the relation of hematocrit to blood pressure and hypertension among 2,809 men and women aged 25-74 years. Independent of gender, age, and other confounders, the hypertensive group had a higher hematocrit than the nonhypertensive group (p less than 0.001). In comparison with the untreated hypertensive group, the hypertensive group being treated with diuretics or with other drugs only had similar mean hematocrit levels despite significantly lower blood pressures. Hematocrit was positively correlated with systolic pressure (r = 0.085, p less than 0.01 and r = 0.264, p less than 0.001 for men and women, respectively) and diastolic pressure (r = 0.214, p less than 0.001 and r = 0.266, p less than 0.001). In both sexes, whether or not the treated hypertensive group was included, age-adjusted prevalence of hypertension and average blood pressure were higher for persons in higher quintiles of hematocrit (p less than 0.001). The association of hematocrit with blood pressure and hypertension was significant and independent of several confounders. The regression coefficient of blood pressure on hematocrit ranged between 0.410 and 0.620 mm Hg per unit of hematocrit for systolic pressure and between 0.371 and 0.581 for diastolic pressure, depending on gender and whether the treated hypertensive group was included in multiple regression analysis. Based on exponentiation of the multiple logistic coefficient, prevalence of hypertension was at least two times greater for persons whose hematocrit levels were higher by 10 units.

Enhanced renal response to intracerebroventricular angiotensins II and III in spontaneously hypertensive rats

The acute effects of intracerebroventricular (i.c.v.) administration of angiotensin III (ANG III) on blood pressure (BP) and renal function were investigated in spontaneously hypertensive rats (SHR, n = 31) and Wistar-Kyoto (WKY) normotensive rats (n = 6). ANG II was also administered to the same rats for comparison of its renal effect. BP and renal clearance responses were measured before and during ANG injections. The results showed that i.c.v. injections of 1, 5 and 50 pmol of ANG III did not significantly alter BP in SHR, but a high dose of ANG III (50 pmol) caused a vasopressor effect (7 +/- 4 mmHg) in WKY rats. There were significant increases in renal plasma flow (RPF), glomerular filtration rate (GFR), urine flow, absolute and fractional excretions of sodium and potassium, osmolar clearance and free water reabsorption rate following i.c.v. administration of ANG III in both SHR and WKY rats. However, the enhancement in renal responsiveness to ANG III was greater in SHR than in the WKY group. At 5 pmol of ANG III, the peak increases in GFR (96 +/- 23%), diuresis (316 +/- 102%) and natriuresis (712 +/- 281%) in SHR were significantly greater than those in WKY rats (40 +/- 13%, 152 +/- 89%, 229 +/- 130%, resp.). The renal effect of central ANG III was blocked by i.c.v. ANG III antagonist, [Ile7]-ANG III, but was enhanced by bestatin, an ANG III metabolic enzyme inhibitor. I.c.v. administration of ANG II at 50 pmol increased BP in both SHR and WKY rats (14 +/- 3 and 10 +/- 3 mmHg, resp.). Greater diuretic and natriuretic responses to ANG II were also noted in SHR than in WKY rats. These results indicate that central ANG III is as active as ANG II in modulating renal function. Furthermore, the enhanced renal response to i.c.v. ANGs II and III in SHR suggests a hyperactive central RAS implicated in BP and body fluid regulation in this genetic hypertensive strain.

Inverse changes in erythroid cell volume and number regulate the hematocrit in newborn genetically hypertensive rats

Erythrocytosis and microcytosis have been described in strains of genetically hypertensive rats and in essentially hypertensive humans. Published discussion of these phenomena has centered around their relationship to observed alterations in ionic transport and the pathogenesis of hypertension. In presenting data for another strain of spontaneously hypertensive rats in which these findings are exhibited, we note that erythroid cell size decreases concurrently with the increase in cell numbers so that the hematocrit and the mean corpuscular hemoglobin concentration remain constant. Data from the literature support the hypothesis that erythroid cell size is inversely proportional to cell count in a large number of species. Erythrocytosis, as it develops in the neonatal rat, is a consequence of the marked immaturity of this species at birth. Erythrocytosis in the spontaneously hypertensive rat is not due to a difference in the affinity of its hemoglobin for oxygen or to significant tissue anorexia. Microcytosis in the spontaneously hypertensive rat is the consequence of a continuation of the linear volume decrease with age of its erythroid cells seen in the normotensive animals and may be accounted for by the production of smaller cells with concomitant regulation of individual cell volume.

Transitions in CD45 isoform expression indicate continuous differentiation of a monoclonal CD5+ CD11b+ B lineage in Waldenstrom's macroglobulinemia

Waldenstrom's macroglobulinemia (WM) has been hypothesized to be a pleomorphic B-cell malignancy with persistent maturation towards plasma cells in all lymphoid tissue. This proposal is based on detection of a heterogeneous density of monoclonal Ig on peripheral blood B-cells in patients with WM. We now present data derived from 2- and 3-color immunofluorescence and flow cytometric analysis that strongly supports this hypothesis. Abnormally high numbers of B lineage cells, defined by expression of CD19, CD20, and CD24, were found among peripheral blood mononuclear cells (PBMC). These B-cells are monoclonal as defined by light chain expression and by the existence of rearranged Ig genes (Southern blot analysis), although they exhibit heterogeneity in the density of surface light chain. Unlike normal PBMC B-cells, the monoclonal B-cells bear CD5 and CD10 (CALLA), express adhesion and adhesion-related molecules (CD11b, CD9), and appear to be actively differentiating during the course of the disease, based on the pattern of CD45 isoform expression. At any given point in time, the population of monoclonal B-cells is heterogeneous in differentiation stage based on transitions in the expression of CD45 isoforms from expression of CD45RA, the high molecular mass isoforms of CD45, to the low molecular mass isoform CD45R0 which appears only on very late stage B-cells and early plasma cells. For one patient, analysis of CD45 isoform expression over 2 years showed that the monoclonal B-cell population as a whole progressed towards terminal differentiation as defined by loss of CD45RA and acquisition of CD45R0. This indicates a continuously differentiating lineage of an unusual B-cell phenotype, and/or malignant transformation of a distinct lineage of B-cells in WM.

Megakaryocytopoiesis in spontaneously hypertensive rats (SHR)

Bone marrow megakaryocytes and their progenitors were studied in SHR in order to obtain more information about megakaryocytopoiesis in hypertension since it is known that various anomalies of platelet function occur in hypertension. Megakaryocytopoiesis under steady state conditions and following stimulated erythropoiesis and thrombocytopenia was not found to be significantly different in SHR from that in normotensive Wistar controls.

Effect of protein kinase C activation on cytoskeleton and cation transport in human erythrocytes. Reproduction of some membrane abnormalities revealed in essential hypertension

Certain manifestations of alterations of membrane cytoskeleton, protein kinase C activity, and ion transport were revealed in erythrocytes of patients with essential hypertension: 1) the average volume of erythrocytes is reduced by 4%; 2) about 7% of the total number of erythrocytes is represented by cup-shaped forms compared with 1.5 to 3.0% in the control group; 3) basal phosphorylation of Band 4.9 protein is increased 1.6-fold to 1.8-fold; 4) activity of protein kinase C is increased by 60 to 70%; 5) the rate of proton electrochemical gradient (delta mu H+)-induced Na+-H+ exchange is increased twofold. Treatment of erythrocytes of healthy donors with protein kinase C activator (12-O-tetradecanoylphorbol-13-acetate) leads to similar but more marked changes in cell shape (17% of cup-shaped forms), volume reduction (by 7%), an increase of Band 4.9 protein phosphorylation (threefold), and an increase in the rate of Na+-H+ exchange (fourfold). Protein kinase activation does not modify Na+-Li+ exchange and slightly increases (by 20-50%) Na+-K+ pump activity, Na+-K+ cotransport, and the rate of 45Ca influx. It may be assumed that the increase of protein kinase C activity is one of the most probable molecular mechanisms conditioning abnormalities of the membrane skeleton and Na+-H+ exchange in primary hypertension.

Increased rigidity of red blood cell membrane in young spontaneously hypertensive rats

The micropipette test was used to study the effects of age on the elasticity of red blood cell (RBC) membrane in spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar-Kyoto rats (WKY), ranging from 3 to 23 weeks of age. The development of hypertension in the SHR started at 3 weeks and was fully established at 7 to 8 weeks. In the developmental phase of hypertension (3-5 weeks), the SHR showed a significant increase in RBC membrane elastic modulus (i.e., a decrease in RBC membrane deformability) when compared with the age-matched normotensive control rats (WKY). After the establishment of hypertension (7-8 weeks), however, the deformability of the RBC membrane of SHR improved and became comparable to that of the WKY. These results indicate that abnormal erythrocyte membrane elasticity is an early event in SHR and that adaptive recovery occurs when hypertension is fully developed.

Similarities of essential and spontaneous hypertension. Volume and number of blood cells

Spontaneously hypertensive rats have long been used as an animal counterpart of human essential hypertension. The validation of this strain as a model rests mainly on the "clinical" similarity of the two syndromes, but it has scarcely been founded on numerical comparison of measurable parameters. We investigated three hematological indexes previously recognized to be altered in spontaneously hypertensive rats: the single-cell volume of erythrocytes, the single-cell volume of platelets, and the erythrocyte number. Erythrocyte volume was lower by 7%, platelet volume was higher by 12%, and erythrocyte count was higher by 22% in spontaneously hypertensive rats in comparison with Wistar-Kyoto controls. More unexpectedly, it was found that erythrocyte volume is lower by 2%, platelet volume is higher by 3%, and erythrocyte number is higher by 6% in essential hypertensive subjects when compared with normotensive healthy subjects. These results, combined with previously reported blood cell alterations in subjects and rats, reinforce the evidence of a biological similarity between essential and spontaneous hypertension.

Lymphocyte abnormalities in three types of hypertension in the rat

Lymphocyte number and weight and their sodium and potassium contents and net passive fluxes were measured in spontaneously hypertensive stroke-prone rats, deoxycorticosterone acetate-treated rats, and two-kidney, one clip renal hypertensive rats. Wistar-Kyoto rats were used as controls for the spontaneously hypertensive stroke-prone rats, and normal intact Sprague-Dawley rats were used as controls for the others. Blood lymphocyte count was higher and lymphocyte weight was lower in the hypertensive rats. Intralymphocytic sodium content (millimoles per kilogram of dry weight) was elevated in the three forms of hypertension as compared with control values (spontaneously hypertensive stroke-prone rats, 43.0 +/- 1.7 vs Wistar-Kyoto rats, 37.3 +/- 1.3; deoxycorticosterone acetate-treated rats, 44.4 +/- 3.1 vs Sprague-Dawley rats, 36.1 +/- 1.7; one-kidney, one clip rats, 50.5 +/- 3.7 vs Sprague-Dawley rats, 38.9 +/- 2.0). Intralymphocytic potassium content was not significantly altered in any of the forms of hypertension. Lymphocytes from spontaneously hypertensive stroke-prone rats and deoxycorticosterone acetate-treated rats exhibited elevated net sodium fluxes (millimoles per kilogram of dry weight per hour) as compared with those of controls (spontaneously hypertensive stroke-prone rats, 7.00 +/- 0.99 vs Wistar-Kyoto rats, 4.89 +/- 0.63; deoxycorticosterone acetate-treated rats, 7.58 +/- 0.97 vs Sprague-Dawley rats, 5.6 +/- 0.64). Net potassium fluxes were significantly elevated only in the spontaneously hypertensive stroke-prone rats (14.07 +/- 1.70 vs 8.23 +/- 1.04 in Wistar-Kyoto rats). Sodium and potassium fluxes in lymphocytes from two-kidney, one clip rats and Sprague-Dawley rats were not significantly different.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet serotonin content and uptake in spontaneously hypertensive rats

Platelet serotonin (5-HT) content and uptake were studied in male SHR and WKY at various ages. Blood was withdrawn from the carotid artery under anesthesia and 5-HT levels determined from platelet rich plasma (PRP) using a HPLC technique coupled with an electrochemical detection method. Platelet 5-HT uptake was studied by incubating PRP at 37 degrees C for 10 sec with increasing concentrations of 3H-5HT. Lineweaver- Burk plots of 3H-5HT uptake were linear suggesting simple Michaelis- Menten uptake kinetics. The SHR had more platelets than age-matched controls and consequently a higher blood circulating pool of 5-HT. Nevertheless, the 5-HT platelet levels were similar to those of their age-matched rats. The 5 week-old SHR and WKY had greater numbers of platelets and higher 5-HT platelet levels than the older rats of both strains. The affinity constants (Km) and the maximal velocities (Vmax) of platelet 5-HT uptake did not differ significantly between the 12 week- and the 6 month-old SHR and WKY. These data suggest that the SHR do not show the same impairment in platelet 5-HT metabolism as observed in essential hypertension in man.

Temperature dependence and bidirectional cation fluxes in red blood cells from spontaneously hypertensive rats

The net passive influx of Na+ and efflux of K+ (orthodirection) through the red blood cell membranes from spontaneously hypertensive rats (SHR) were observed to be significantly higher (p less than 0.05) than those of three strains of normotensive rats when the measurements were made at 4 degrees C. Similar comparative studies, carried out at 37 degrees C, in the absence or presence of ouabain, showed no difference in these fluxes through this membrane from SHR compared to those from Wistar-Kyoto (WKY) rats, one of the normotensive strains. A study was undertaken to determine the temperature at which the greater cation fluxes in SHR red blood cells occurred. The net fluxes of Na+ and K+ decreased as the temperature was reduced from 37 degrees to 15 degrees C, but a paradoxical increase in the fluxes was observed as the temperature was decreased from 15 degrees to 4 degrees C. Only with this temperature shift (15 degrees to 4 degrees C) was the increase in flux significantly greater in SHR than in WKY cells. Subsequent studies were designed to determine whether the difference in the transport systems of red blood cells of SHR and WKY could be observed in fluxes of these cations in either direction across the membrane. For "reverse direction" flux studies, red blood cells were loaded with Na+ (to 130 mEq/liter cell water) and depleted of K+ (to 30 mEq/liter cell water) by incubation with the ionophore monensin.(ABSTRACT TRUNCATED AT 250 WORDS)

Intrinsic difference in erythrocyte membrane in spontaneously hypertensive rats characterized by Na+ and K+ fluxes

The goal of this study was to determine whether the elevated flux of sodium and potassium through the erythrocyte membrane of spontaneously hypertensive rats (SHR) is due to an intrinsic difference in the cell membrane or to a humoral factor present in the plasma. Isolated and washed erythrocytes from SHR and normotensive Wistar Kyoto (WKy) and Sprague-Dawley (SD) rats, were incubated in 1) a physiological salt solution, 2) WKy or SD plasma and 3) SHR plasma. Incubations were performed at 4 degrees C for 23 h. Erythrocytes from SHR incubated in physiological salt solution had significantly greater Na+ and K+ fluxes than those from normotensive WKy and SD rats (P less than 0.005). Plasma from any of the three strains of rats, as compared to physiological salt solution, increased Na+ influx in the following order: SD greater than WKy greater than SHR. Erythrocyte K+ efflux was not altered by plasma. We conclude that the elevated flux of Na+ and K+ in SHR erythrocytes is due to an intrinsic difference in the cell membrane. The greater Na+ influx in plasma from any strain of rats is not correlated with the blood pressure of the rat. The lesser increase in Na+ influx in erythrocytes incubated in plasma from SHR masks the greater intrinsic membrane permeability in the SHR erythrocyte when Na+ fluxes are studied in whole blood. The elevated flux of Na+ and K+ through the erythrocyte membrane of SHR may reflect a general membrane defect that underlies the pathogenesis of elevated arterial pressure.

Kidney function and sodium handling in the pregnant spontaneously hypertensive rat

Effects of gestation on volume homeostasis and renal function were studied in awake spontaneously hypertensive rats (SHR). Systolic blood pressure was similar to that of virgin littermates during most of SHR pregnancy but decreased near term (p less than 0.005). Plasma renin activity was lower in SHR than in age-matched Wistar-Kyoto (WKY) rats (p less than 0.001), but values were similar in gravid and nonpregnant animals from each strain. Renal renin content and lipid volume fractions of papillary interstitial granules were significantly greater in pregnant animal of each strain and those of the gravid WKY were also greater than both pregnant and virgin SHR. Saralasin had no effect on mean arterial pressure in gravid and virgin rats from either group. Plasma volume increased significantly near term in animals of both strains. Kidney weight, glomerular filtration rate (GFR), and renal blood flow were lower in SHR compared to WKY, and the hypertensive rats failed to demonstrate an increase in GFR during gestation, unlike the WKY. All SHR and pregnant WKY excreted infused sodium better than the virgin WKY. Also, regular Wistar animals excreted a salt load better than the virgin WKY. Finally, uterine blood flow, pup number and conceptus weight were similar in SHR and WKY. We conclude that pregnancy induces a decrease in blood pressure in SHR, and that angiotensin II does not seem to play an important role in maintaining blood pressure during gestation in either SHR or WKY. Despite a lower GFR and its failure to increase during pregnancy, renal sodium handling is not impaired in the SHR. The virgin WKY has a decreased ability to excrete sodium which is ameliorated during gestation.

Capillary pressure gradients in cremaster muscle of normotensive and spontaneously hypertensive rats

The purpose of this investigation is to test the hypothesis that capillary pressure gradients are elevated in spontaneously hypertensive rats (SHR) and to determine the mechanism for the elevation. The cremaster muscle was prepared for microscopic examination under chloralose-urethane anesthesia in seven SHR and eight Wistar-Kyoto (WKY) rats 4-6 weeks of age. Capillary hematocrit, diameter, and red cell velocity were measured. Capillary flow induced by a time-varying pressure gradient was treated mathematically. A finite Hankel transformation was applied to the Navier-Stokes equation for capillary vessels. The solution was expressed as a Fourier-Bessel series, and the fluctuation of capillary flow induced by a time-varying pressure gradient was studied. It was shown that if the velocity fluctuation depended only on the pressure gradient, then the velocity fluctuation would be diminished almost instantly after the capillary started to flow. Capillary pressure gradient and shear stress were evaluated according to two different flow models, Newtonian and Casson. The capillary viscosity was obtained from the capillary hematocrit based on the empirical correlation of viscosity vs hematocrit. Calculations based on both flow models indicate that the capillary pressure gradient and shear stress of SHR is higher than in WKY, especially in vessels near 6 microns in diameter. The elevated pressure gradient is due to a combination of reduced capillary density, causing a higher red cell velocity and a tendency toward smaller capillary diameters in the SHR. Capillary hematocrit and viscosity were not elevated in the SHR.

Analysis of calcium handling in erythrocyte membranes of genetically hypertensive rats

Calcium handling by erythrocyte membranes was compared in genetically hypertensive (SHR) and normotensive (WKR) rats by direct measurement of calcium binding, passive influx, and adenosine triphosphate (ATP)-dependent extrusion. The SHR erythrocyte membranes exhibited the following abnormalities: 1) the binding capacity of the high affinity Ca2+-binding sites located on the inner side of the membrane was 0.84 +/- 0.07 nmole/mg protein compared with 1.17 +/- 0.08 nmole/mg protein in WKR, 2) ATP-dependent Ca2+ extrusion, measured as the Ca2+ influx into inside-out vesicles, was also lower than the WKR, as was the La3+ -sensitive, Ca2+ -dependent hydrolysis, indicating reduced activity of the calcium pump; 3) the passive calcium influx into ATP-depleted red blood cells was slightly accelerated. these abnormalities in Ca2+ binding and transport probably enhanced intracellular Ca2+ concentration, and were observed under both prehypertensive an hypertensive conditions, in 3-week-old and adult SHR respectively. Similar membrane defects in excitable cells may help to explain the pathogenesis of hypertension, since they may increase vascular tone and/or catecholamine release.

Renal function of conscious spontaneously hypertensive rats

Renal clearance studies were performed in conscious 13-week-old spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) before and during volume expansion by intravenous infusion of isotonic saline. Mean arterial pressure and filtration fraction were greater in SHR, whereas fractional and absolute excretion of sodium and water, glomerular filtration rate, and renal plasma flow in SHR and WKY were not statistically different. This was the case during hydropenia and volume expansion. We did not observe as exaggerated natriuresis after intravenous loading when unanesthetized SHR were compared with the response of WKY. These observations suggest that the kidneys of genetically hypertensive rats of the Okamoto-Aoki strain have adapted to an elevated renal perfusion pressure or that hypertension is required to normalize renal function so that excretion is appropriately matched with intake.

Increased erythrocyte permeability to Li and Na in the spontaneously hypertensive rat

Red blood cells incubated in a physiological medium in which Li replaces Na (LiPSS) gain Li in exchange for Na and K. The rate of Li uptake is modestly but significantly increased in the spontaneously hypertensive rat (SHR) at 37 degrees C and at 22 degrees C. The slow rate of Na gain and K loss during cooling at 2 degrees C was about doubled in unmodified whole blood samples from the SHR.

The role of the kidney in spontaneous hypertension

There is direct and indirect evidence that the kidneys are involved in the onset of hypertension in spontaneously hypertensive animals. In the Dahl strain, rather convincing evidence exists for a primary, inherent renal defect that is worsened by high dietary salt. In the Okamoto and New Zealand strains, an intrinsic defect may be provoked by increased sympathetic nerve activity. Similarities between all of these strains and Goldblatt hypertension suggest a fluid volume abnormality, but the gradual onset of elevated pressure and continuing growth during development of hypertension may obscure critical volume changes. Theoretically, arterial pressure, somewhat independent of intermediate steps, will reach the level which is dictated by renal function as being necessary for the maintenance of salt and water homeostasis. While widespread use of different spontaneously hypertensive strains may currently be complicating our understanding of the intermediate steps, studies of dissimilar strains should, in time, enhance our understanding of the many different facets of long-term blood pressure control.

Renin in rats with spontaneous hypertension

An age-dependent study of plasma renin activity (PRA), kidney renin activity (KRA), and plasma renin substrate was carried out in rats with spontaneous hypertension during the prehypertensive, the early hypertensive, and the established hypertensive phases of their disease. PRA and KRA were both significantly elevated before and during the initial phase of hypertension and normal or subnormal during the established phase. In normal controls, neither KRA nor PRA was significantly different during the entire growth period. Plasma renin substrate was elevated throughout the growth period in rats with hypertension. This relationship between renin and blood pressure suggests that renin may play a primary role, possibly along with other factors, in the initiation of hypertension in rats with spontaneous hypertension.