A study of brain and serum brain-derived neurotrophic factor protein in Wistar and Wistar-Kyoto rat strains after electroconvulsive stimulus.

BACKGROUND: Serum brain-derived neurotrophic factor (BDNF) protein has been related to depression and less consistently to its treatments in human studies. However, animal studies have failed to demonstrate a clear link between BDNF protein in serum and brain tissue. METHODS: Serum and brain tissue levels of BDNF protein were measured with ELISA in the Wistar-Kyoto (WKY) and Wistar strains at 1 and 7 days after 5 daily electroconvulsive stimulus sessions or sham treatments. RESULTS: The WKY strain showed lower baseline serum BDNF protein relative to Wistar controls. After 5 electroconvulsive stimuli, BDNF protein density was significantly increased in hippocampus and cortical regions, but not in the cerebellum or in serum. A clear correlation between brain and serum BDNF was not observed in either strain or treatment group. DISCUSSION: Despite lower baseline serum BDNF protein in the WKY strain, a lack of change in serum BDNF after electroconvulsive stimulus and a lack of correlation between brain and serum BDNF protein calls into question the relevance of serum BDNF as a measure of depression and treatment response.

Baseline serum cardiac troponin I concentrations in Sprague-Dawley, spontaneous hypertensive, Wistar, Wistar-Kyoto, and Fisher rats as determined with an ultrasensitive immunoassay.

Cardiac troponins have proved to be reliable blood biomarkers for identifying a variety of myocardial alterations in humans and animals. Recently, an ultrasensitive cTnI assay (Erenna IA) has been used to demonstrate increases in baseline cTnI resulting from drug-induced myocardial injury in rats, dogs, and monkeys, as well as to document baseline cTnI ranges in Sprague-Dawley (SD) rats. The present study was initiated to use the Erenna cTnI assay to further document baseline cTnI concentrations in normal control animals from multiple strains, including SD, Spontaneous Hypertensive (SHR), Wistar, Wistar-Kyoto (WKY), and Fisher strains. Baseline cTnI concentrations were quantified in all rats tested, and males had higher mean cTnI concentrations than females of the same strain. SHR males had the highest mean cTnI concentrations and the largest cTnI variability. Interestingly, cTnI concentrations increased in castrated SHR compared with unaltered male SHR, whereas cTnI concentrations decreased in ovariectomized SHR compared with unaltered female SHR. These results show significant differences in cTnI concentrations between strains, sexes, and noncardiac surgical alterations in control animals, and identify these as potential contributing factors to cTnI baseline variability that should be taken into account when using ultrasensitive cTnI as a biomarker to assess preclinical cardiotoxicity.

Platelet lipoxygenase in spontaneously hypertensive rats.

We have previously reported that the nonselective lipoxygenase inhibitor phenidone is a potent hypotensive agent in the spontaneously hypertensive rat (SHR). In the present study, we examined the relationship between production of platelet 12-hydroxyeicosatetraenoic acid (12-HETE) and intra-arterial blood pressure in SHR and Wistar-Kyoto rats (WKY) using both a cross-sectional analysis and an acute pharmacological intervention. Basal generation rate of 12-HETE by platelets collected from the SHR was approximately 3.7-fold higher than in the WKY (0.86 +/- 0.24 versus 0.23 +/- 0.05 nmol/mL per 10 minutes, respectively; P < .01). Systolic arterial pressure was positively related to platelet 12-HETE formation rate when the entire rat population was considered (r = .70, P < .001). The specific 12-lipoxygenase inhibitor cinnamyl-3,4-dihydroxycyanocinnamate induced lowering of both arterial blood pressure and platelet 12-lipoxygenase activity in SHR. At 15 mg/kg, cinnamyl-3,4-dihydroxycyanocinnamate elicited a marked hypotensive effect in SHR but not in WKY. This reduction in arterial pressure was accompanied by an approximate 70% inhibition in platelet 12-HETE production rate. The return of high blood pressure to basal levels was associated with a significant rise in the production of platelet 12-HETE toward control values (baseline, 0.97 +/- 0.33 nmol/mL per 10 minutes; nadir of blood pressure, 0.19 +/- 0.03; resumption of basal pressure, 0.42 +/- 0.14). In contrast, captopril (15 mg/kg) induced a quantitatively similar decrease in blood pressure but had no effect on platelet 12-HETE generation rate. Thus, hypertension in SHR is linked to increased production rate of platelet 12-HETE. Acute blood pressure reduction attained during lipoxygenase inhibition but not by angiotensin converting enzyme inhibition leads to a concomitant reduction in the production of platelet 12-HETE. We speculate that since rat arterial tissue produces 12-HETE, increased 12-lipoxygenase activity in SHR may contribute to the maintenance of elevated arterial pressure in this strain.

[Ectacytometry of the erythrocytes in rats of the SHR, WKY and Wistar strains]. / Ektatsitometriia éritrotsitov krys linii SHR, WKY i Vistar.

Deformation properties of erythrocytes have been studied using osmotic gradient ectacytometric procedure in rats with spontaneous hereditary hypertension (SHR), normal tension rats from Wistar-Kyoto strain and albino rats from Wistar strain. It was shown that high intrinsic viscosity and, to a less extent, changes in their form account for the increased rigidity of the erythrocytes from SHR rats. No significant changes in visco-elastic properties of the membrane were found. The degree of hydration of haemoglobin significantly increases in the order SHR-WKY-Wistar.

Vascular conversion of angiotensin I in stroke-prone spontaneously hypertensive and Wistar-Kyoto rats.

OBJECTIVE: Linkage studies have shown that the gene locus for angiotensin converting enzyme (ACE) is associated with the expression of hypertension in stroke-prone spontaneously hypertensive rats (SHRSP). We tested the hypothesis that the conversion of angiotensin I (Ang I) to angiotensin II (Ang II) in blood vessels is elevated in SHRSP. DESIGN: We measured the conversion rate of Ang I to Ang II during one pass through an isolated resistance vessel bed. We used the same substrains of SHRSP and Wistar-Kyoto control rats (WKY) that had been employed in the earlier linkage studies. METHODS: Isolated hindquarters from young and adult (10- to 12- and 36- to 38-week-old) rats were perfused with an artificial medium and then infused with Ang I at 0.5 and 2 pmol/ml. Ang I and II were measured with high-performance liquid chromatography and radioimmunoassay in hindquarter effluent and in blank control channels. Conversion and extraction rates were calculated from angiotensin levels in hindquarter and blank perfusion channels, respectively. RESULTS: The conversion rates of Ang I to Ang II did not differ between SHRSP and WKY in young or in adult rats. Captopril completely abolished the formation of Ang II in all groups of rats. During infusion at the higher dose of Ang I, the extraction of Ang I was significantly decreased in SHRSP compared with WKY. CONCLUSIONS: Our results are consistent with the notion that the metabolism of angiotensin is decreased in spontaneously hypertensive rats. However, we found no support for the hypothesis that vascular ACE is responsible for high blood pressure in SHRSP. These findings suggest that other genes close to the ACE locus or the hyperexpression of the enzyme in other areas may contribute to hypertension in these rats.

Evidence from comparative investigations that impaired platelet activation is not specific for stroke-prone spontaneously hypertensive rats.

BACKGROUND AND PURPOSE: Platelet behavior of Sprague Dawley (SD), Wistar (WI), Wistar-Kyoto (WKY), spontaneously hypertensive (SHR), and stroke-prone spontaneously hypertensive rats (SHRSP) was studied in vivo to evaluate the importance of hypertension-related hemostatic disorders. METHODS: The study was based on the model of stimulus-induced pulmonary microembolization of labeled platelets. After injection of 51Cr-labeled homologous platelets into urethane-anesthetized rats, the organ distribution of the platelets was continuously monitored by gamma detectors. Count rates of two detectors--one placed above the animals' thoraxes (C1), the other above their abdomens (C2)-and the ratio of C1:C2 were calculated. The following platelet activators were applied intravenously: adenosine diphosphate (ADP; 50 micrograms/kg), collagen (100 micrograms/kg), and thrombin (50 IU/kg). RESULTS: All three substances caused a reversible pulmonary accumulation of the labeled platelets and hence an increase in C1/C2 (delta C1/C2%). ADP induced a shift of 75% in SD, 52% in WI, 32% in WKY, 30% in SHR, and 31% in SHRSP. Thrombin-mediated shift was 79% in SD, 64% in WI, 58% in WKY, 48% in SHR, and 54% in SHRSP. Collagen induced a shift of 85% in SD, 96% in WI, 84% in WKY, 56% in SHR, and 62% in SHRSP. CONCLUSIONS: Because indistinguishable results were observed in both hypertensive strains, we conclude that impaired platelet aggregation is not specific for SHRSP. Hence, it may not primarily be responsible for the increased occurrence of stroke in these animals.

[The activity and properties of K-pNPphosphatase in membrane preparations of erythrocytes with different polypeptide compositions in Wistar, Wistar-Kyoto and SHR strain rats]. / Aktivnost' i svoistva K-pNFfosfatazy v membrannykh preparatakh éritrotsitov s razlichnym polipeptidnym sostavom u krys linii Vistar, Vistar--Kioto i SHR.

A higher K-pNPPase activity was found in erythrocyte membrane preparations from the SHR as compared with the Wistar rats. Removal of peripheral proteins from the membrane skeleton depressed the K-phosphatase activity and eliminated the difference between the SHR and Wistar rats. No activating effect of the ATP and Ca on the enzyme was found. The data obtained suggest that the proteins of the erythrocyte membrane skeleton are connected with regulation of the enzyme transport in the erythrocyte membranes of the SHR via a modulating effect of intracellular ATP and Ca.

Increased plasma level of endothelin-1 in the Okamoto spontaneously hypertensive rat.

The objectives of this study were to determine plasma levels of endothelin (ET) in a genetic model of hypertension and in control rats during control conditions and in response to short-term volume expansion with saline. Okamoto spontaneously hypertensive rats (SHR) and control Wistar-Kyoto (WKY) rats were used in this study. One group of each strain served as control animals, and another group of each strain underwent volume expansion with saline (5% of body weight infused during a period of 30 minutes). The levels of ET-1 and ET-3 were measured in plasma by using a double-antibody radioimmunoassay. In the control groups of SHR and WKY rats, plasma ET-1 levels were 72.5 +/- 14.9 pg/ml (N = 8) and 40.2 +/- 7.5 pg/ml (N = 12), respectively (P < 0.05). In the volume-expanded SHR group (N = 8), the plasma ET-1 level was 45.5 +/- 11.1 pg/ml (approximately 37% less than that of the control SHR group), whereas it was 40.6 +/- 10.2 pg/ml in the volume-expanded group of WKY rats (N = 10) (almost identical to that of the control WKY group). Plasma levels of ET-3 were similar in control and in volume-expanded groups of SHR and WKY rats. These data show that basal levels of plasma ET-1 are significantly higher in the SHR than in the WKY rat.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Purification of parathyroid hypertensive factor from plasma of spontaneously hypertensive rats.

Parathyroid hypertensive factor (PHF) is a newly described hypertensive factor that may be related to elevation of blood pressure in 30-40% of North American essential hypertensive patients. PHF is also found in several animal models of hypertension, including spontaneously hypertensive rats, and deoxycorticosterone acetate salt hypertensive rats. Plasma collected from spontaneously hypertensive rats (SHR) was used in the present study for purification of PHF. Plasma was dialyzed at a molecular mass cutoff of 1 kDa, and then ultrafiltered at a molecular mass cutoff of 5 kDa. PHF activity, as determined by bioassay (characteristic delayed hypertensive response in normotensive rat) was retained in the fraction that was greater than 1 kDa and less than 5 kDa. Dialyzed and ultrafiltered SHR plasma was fractionated by molecular-exclusion chromatography, either with Bio-Gel P-6 liquid chromatography, or TSK 2000 SW HPLC. The biological activity was detected in a discrete region corresponding to a molecular mass of 2.5-3 kDa. When the molecular-exclusion fraction was subsequently fractionated by reverse-phase HPLC, biological activity was located in a single discrete peak, which did not occur in plasma from normotensive rats prepared in a similar manner. The biologically active fraction of PHF was inactivated by trypsin; this and its UV spectrum indicate the presence of a peptide structure.

Reduced calcium binding capacity is an intrinsic abnormality of red blood cell membrane in spontaneously hypertensive rats.

Reduced calcium (Ca) binding capacity is a widespread and primary abnormality in SHR. It was reported that in red blood cell (RBC) membranes it is detectable only in membrane preparations containing sealed inside-out vesicles, the formation of which implies the partial removal of cytoskeletal proteins from the RBC membrane. The present study compares the Ca binding capacity of RBC membrane preparations with normal (+CS) and reduced (-CS) cytoskeleton content in SHR and normotensive WKY control rats. In addition to Ca binding capacity and protein content, the cholesterol content and the acetylcholinesterase (ACE) activity were measured as having a quantitative measure of integral membrane components in the different membrane preparations. In both strains the cholesterol/protein ratio, the ACE activity per mg of membrane protein, and the Ca binding capacity were all significantly higher in -CS compared to +CS membrane preparations (P less than .001). A statistically significant difference in Ca binding capacity between SHR and WKY was observed only using -CS membranes preparation. The results support the concept of a reduced membrane Ca binding capacity in rat genetic hypertension: this abnormality is detectable only in membrane preparations with reduced cytoskeletal content.

Effects of a fructose-enriched diet on plasma insulin and triglyceride concentration in SHR and WKY rats.

Significant increases (P less than 0.001) in plasma insulin and triglyceride concentrations and in blood pressure were seen when SHR and WKY rats ate a fructose-enriched diet for 14 days. However, all of the changes were significantly accentuated (P less than 0.02-0.001) in SHR rats. Specifically the increment in plasma insulin concentration following the fructose-enriched diet was 42 +/- 4 microU/ml in SHR as compared to 25 +/- 4 microU/ml in WKY rats (P less than 0.001). Plasma triglyceride concentrations also increased to a greater degree in response to fructose in SHR rats (260 +/- 24 vs. 136 +/- 20 mg/dl, P less than 0.001). Finally, the fructose-induced increase in blood pressure of 29 +/- 4 mm of Hg in SHR rats was greater (P less than 0.02) than that seen in WKY rats (19 +/- 2 mm of Hg). There was no change in plasma glucose concentration in response to the fructose diet. WKY rats gained more weight than did the SHR rats. Thus, although plasma triglyceride and insulin concentration and blood pressure increased when either WKY or SHR rats consumed a fructose enriched diet, the magnitude of these changes was greater in SHR rats.

Chronic antihypertensive drug treatment decreases protein kinase C activity in platelets from SHR.

There is evidence that protein kinase C activity in platelets from adult SHR is significantly higher than this activity in age-matched WKY. In the present study, protein kinase C activity in the SHR was measured following antihypertensive drug treatment. Chronic administration of enalapril to SHR for 2 weeks decreased both systolic blood pressure and protein kinase C activity to the levels seen in the WKY. Similar results were obtained in case of chronic treatment of SHR with hydralazine or nifedipine. These results suggest that enhanced protein kinase C activity of SHR can be suppressed by lowering blood pressure by antihypertensive drugs.

Plasma and pituitary thyroid-stimulating hormone and their responses to bromocriptine in the Japanese strains of hypertensive and normotensive rats and the F2 generation of the hybrid.

Plasma thyroid-stimulating hormone (TSH) concentration and pituitary TSH content were examined in bromocriptine (BRC)- and vehicle-treated male Spontaneously Hypertensive Rat (SHR), its normotensive control, the Wistar-Kyoto (WKY) rat and the F2 generation of the SHR/WKY hybrid. The hybrid rats were divided into three groups according to their systolic blood pressures (BP) as follows--group I: BP less than 140 mmHg; group II: BP = 140-160 mmHg and group III: BP greater than 160 mmHg. Plasma TSH concentrations were not significantly different between the vehicle-treated SHR and WKY nor between the three groups of vehicle-treated hybrid rats. The pituitary TSH content was significantly higher in the vehicle-treated SHR than in the vehicle-treated WKY while it was not significantly different between the three groups of vehicle-treated hybrid rats. Plasma TSH concentrations in the BRC-treated SHR, WKY and three groups of hybrid rats were significantly lower than the concentrations in the corresponding vehicle-treated rats. Pituitary TSH content were significantly lower in the BRC-treated SHR, group I and group III rats but not in the BRC-treated WKY and group II rats when compared to their respective vehicle-treated controls. The results of this study suggest that TSH is not involved in the maintenance of systolic BP in the SHR, WKY and hybrid rats.

Effect of serum from spontaneously hypertensive rats on 86Rb washout in cultured vascular smooth muscle cells.

In addition to the known genetic abnormalities affecting the membrane permeability of vascular smooth muscle cells (VSMC) of spontaneously hypertensive rats (SHR), serum humoral factors may also play some role in the alteration of permeability of VSMC and possibly contribute to the pathogenesis of hypertension in SHR. To test this hypothesis, the passive K permeability described as the washout rate constant (Ke) was measured based on 86Rb washout from cultured VMC in response to serum from SHR, Wistar-Kyoto rats (WKY), and Wistar rats (W). Serum from the three rat strains produced a substantial increase in the Ke of 86Rb washout from 9.6 +/- 1.7 for the control (C) of 17.3 +/- 2.0 for SHR. 15.3 +/- 0.9 for WKY, and 16.0 +/- 2.4 for W (x 10(-3)/min) (p less than 0.001 comparing C with SHR, W and p less than 0.01 comparing C with WKY respectively). However, comparison of the Ke of 86Rb washout among the three rats strains revealed no significant differences. It is concluded that serum increased passive K permeability of VSMC in culture. However, the data do not support the suggestion that some unknown humoral factors in the serum from SHR are involved in the abnormal alterations of membrane permeability to cations and thus contributing to the pathogenesis of hypertension in the SHR.

Congenital changes of platelet functions in stroke-prone SHR: aggregability of gel-filtered platelets, PRP and whole blood, and effects of hypotensive treatment.

Platelet aggregation in whole blood, platelet rich plasma, and gel-filtered platelets were markedly attenuated in SHRSP compared with those in age-matched normotensive WKY. The result was consistent with the previous report of washed platelets. Despite prevention of high blood pressure, a long duration of hypotensive treatment only slightly improved aggregability of washed platelets but did not restore it to the range of age-matched WKY platelets. Blood pressure, heart ratios and thrombin-induced washed platelet aggregation were examined in SHRSP, WKY, and the cross (F1: WKY x SHRSP). The higher blood pressure and heart ratios the lower platelet aggregability was observed in the three strains, and there was no overlapping distribution of these values. F1 progeny exhibited intermediate values in blood pressure, heart ratio and platelet aggregability between the parental values. These results suggested that hypofunctions of SHRSP platelet were not secondary changes due to high blood pressure, but primary changes which are genetically linked to high blood pressure.

Defective protein phosphorylation associated with hypofunctions in stroke-prone spontaneously hypertensive rat platelets.

The mechanism of platelet dysfunctions in stroke-prone spontaneously hypertensive rats (SHRSP) was investigated. Platelet aggregation was inversely correlated with blood pressure or heart weight/body weight ratios in various strains of spontaneously hypertensive rats (SHR), indicating genetic defects. Thrombin-induced 47 kDa protein phosphorylation was markedly reduced in platelets of SHRSP compared with that in Wistar-Kyoto (WKY) rat platelets, accompanying reduced aggregation and secretion, but in 20 kDa protein phosphorylation was unchanged. Ca2+ ionophore A23187-induced responses were also significantly decreased in SHRSP, and the degrees of the changes were greater than those by thrombin. However, 12-O-tetradecanoylphorbol 13-acetate-induced responses in SHRSP were similar to those in WKY rats, suggesting that protein kinase C activity and its substrate were normally present in SHRSP platelets. Phosphatidylinositol content in platelets of SHRSP was 20% less than that in WKY rat platelets, but the contents of other phospholipids, including phosphatidylinositol-4-monophosphate and phosphatidylinositol-4,5-bisphosphates, were unaltered. Thrombin-induced formation of diacylglycerols and phosphatidic acid did not differ from each other at the low concentrations. In the absence of Ca2+, thrombin-induced responses occurred to a similar degree in both platelets, whereas the enhancements by Ca2+ were much greater in WKY rats than in SHRSP. These results suggested that defective Ca2+ functions in receptor-mediated activation of protein kinase C and postkinase-mediated events appear to be an underlying mechanism for the hypofunctions in SHRSP platelets.

Adenylate cyclase of platelets from spontaneously hypertensive rats: reduction of the inhibition by GTP.

We have compared the effects of Gpp[NH]p on adenylate cyclase activity of platelet membranes in SHR and WKY rats. In the presence of 50 microM forskolin, low concentrations of Gpp[NH]p (0.01 to 0.3 microM) inhibited the enzyme activity in both strains, but the maximal level of inhibition was significantly lower in SHR (- 20%). In the absence of forskolin, 0.1 microM Gpp[NH]p was inhibitory only in WKY and the adenylate cyclase activity was greater in hypertensive rats at this nucleotide concentration. Increasing Gpp[NH]p from 0.1 to 3 microM induced the same increase of enzyme activity in both strains. In SHR, GTP itself induced a lower inhibition of the enzyme stimulated by 50 microM forskolin or 0.1 microM prostaglandin E1. These results suggest that the modulatory effect of the guanine nucleotide inhibitory protein on adenylate cyclase may be reduced in platelets from SHR.

Effects of chronic alcohol consumption and alcohol withdrawal on blood pressure in stroke-prone spontaneously hypertensive rats.

The development of blood pressure was monitored by the tail-cuff method in normotensive (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP) receiving ethanol (alcohol) in drinking water from weaning (approximately 1 month of age). Alcohol administration over a 3-month period attenuated the development of hypertension in SHRSP and also caused a small reduction of the initial blood pressure rise in WKY. This was accompanied by a reduction of fluid intake and an increase of circulating antidiuretic hormone (arginine vasopressin; AVP). Circulatory volume remained constant. Direct measurement of arterial blood pressure in conscious rats before and after autonomic blockade confirmed the antihypertensive effect of alcohol in SHRSP and indicated that it is at least partly dependent on altered activity of neural mechanisms. Sudden withdrawal of alcohol caused an immediate increase of fluid intake followed by a rise of blood pressure lasting several days in both WKY and SHRSP. This withdrawal hypertension could not be attributed to changes in plasma catecholamines or AVP.

Endogenous digoxin-like material in normotensive and hypertensive strains of rats.

We measured the concentration of endogenous digoxin-like materials (EDLM) in the serum of spontaneously hypertensive rats (SHR) and three normotensive rat strains at four stages during growth using a sensitive RIA. In the SHR, there was a significant peak in the EDLM level between 0.057-0.087 ngE/mL at 6 to 8 weeks of age, shortly after the onset of hypertension. The EDLM concentration returned to normal levels by 20 weeks of age. Sprague-Dawley and Wistar-Kyoto rats had EDLM levels below 0.050 ngE/mL at all time points studied. In contrast, Fischer 344 rats displayed persistently elevated serum EDLM concentrations that exceeded 0.124 ngE/mL from 3 to 20 weeks of life. We conclude that (1) there are significant interstrain differences in serum EDLM levels in rats; and (2) the SHR has a unique peak in serum EDLM levels at 6 to 8 weeks of age, indicating a possible role for the substance in the inception of hypertension.