Protein kinase C activity in brain tissue of spontaneously hypertensive rats

Central Research Laboratory, Ministry of Health of the USSR, Moscow. Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 108, No. 7, pp. 42–44, July, 1989.     

丝裂原活化蛋白激酶参与胰岛素对自发性高血压大鼠血管平滑肌细胞的增殖研究

目的:探讨高血压血管平滑肌细胞(VSMC)在胰岛素作用下胞内信号转导途径之一丝裂原活化蛋白激酶(MAPK)的影响,及其与VSMC增殖的关系。方法:选用6周龄自发性高血压大鼠(SHR)和WKY大鼠,无菌分离主动脉,体外纯化培养VSMC至6~8代,加胰岛素干预和蛋白激酶C(PKC)抑制剂,采用胶内髓磷脂碱性蛋白原位磷酸化法测定VSMC中MAPK活性,并用Western Blot检测VSMC中MAPK的含量, [³H]-TdR测定VSMC的DNA合成量。结果:胰岛素作用后,SHR组的DNA合成量显著增加,MAPK活性及蛋白含量也显著增加,PKC抑制剂可明显降低MAPK活性。结论:SHR体外培养的VSMC增殖与MAPK活性增加有关,胰岛素可影响其活性,并且可能存在胰岛素-PKC-MAPK轴。     

Renomedullary interstitial cells in the spontaneously hypertensive rat.

Renomedullary interstitial cells (RIC) are known to synthesize and release prostaglandins which may play a significant role in the development or severity of hypertension. The medulla of the spontaneously hypertensive rat contains RIC which are morphologically very similar to those previously described in the normotensive rat. The granularity of the RIC, however, was increased in the spontaneously hypertensive rat compared to normotensive Wistars (9.6 +/- 2.34 versus 5.3 +/- 2.05 granules per cell, respectively, p less than 0.001) or treated spontaneously hypertensive rats (7.2 +/- 1.65 granules per cell, p less than 0.001). Granule counts also increased in the presence of mild and moderate degrees of renal arteriolar sclerosis, but decreased in long standing hypertension with more severe and extensive lesions involving both arteries and arterioles. These results are consistent with the hypothesis that the RIC respond to an elevation of blood pressure in the spontaneously hypertensive rats by increased release of antihypertensive substances. In addition, the decrease in granularity of the RIC in the presence of extensive renal arteriolar and arterial damage suggests reduced ability to compensate for the elevated blood pressure and thus may contribute to the acceleration of hypertension.     

Vascular prostaglandin synthesis in the spontaneously hypertensive rat.

Vascular prostaglandin synthesis was studied in tissues (aorta and inferior vena cava) obtained from spontaneously hypertensive rats (SHRs) of the Aoki-Okamoto strain and age-matched Wistar-Kyoto (WKYs) controls. PGE2 synthesis in aortas from SHRs was significantly enhanced at 10 wk of age (5.3 +/- 0.7 nmol PGE2/mg protein per 10 min vs. 1.9 +/- 0.03 nmol PGE2/mg protein per min in the WKYs, P less than 0.001) and increased progressively until 22 wk of age; PGE2alpha synthesis in SHRs was not significantly different from WKYs. In the venous walls from SHRs, PGF2alpha was the prostaglandin predominantly synthesized (7.1 +/- 0.6 vs. 1.9 +/- 0.05 nmol PGE2alpha/mg protein per 10 min in the WKY controls, P less than 0.01). The activities of 15-hydroxy prostaglandin dehydrogenase and PGE 9-ketoreductase were also compared in the two groups of animals. The only difference detected was a significant increase in venous PGE 9-ketoreductase of SHR's (7.3 +/- 0.06 vs. 4.8 +/- 0.04 nmol PGF2alpha/mg per min, P less than 0.01). The results suggest that increased vascular synthesis of prostaglandins accompanies the development of spontaneous hypertension and may serve to attenuate the effects of blood pressure elevation.     

Renal vascular resistance and reactivity in the spontaneously hypertensive rat.

Renal vascular resistance is elevated in spontaneously hypertensive rats (SHR) when compared to normotensive control Wistar-Kyoto rats (WKY). The present study examined possible determinants of this raised vascular resistance in in situ autoperfused kidneys of pentobarbital-anesthetized, 12- to 16-wk-old SHR and WKY. Over a wide range of arterial pressures (30--100 mmHg) renal blood flow was consistently higher in WKY than in SHR. This relative flow difference was unchanged by acute renal denervation, with renal vascular resistance decreasing approximately 20% in both strains. Changes in renal vascular resistance to renal nerve stimulation and the administration of intra-arterial vasoactive hormones also were assessed. Vascular responses to renal nerve stimulation, tyramine, angiotensin II, and acetylcholine were similar in kidneys of the two strains, but reactivity to norepinephrine was significantly less in kidneys of SHR. It was concluded that elevated renal vascular resistance in the SHR does not result from an excessive neurogenic influence on the renal vasculature or from vascular hyperreactivity to norepinephrine or angiotensin II.     

Cardiac function and morphology with aging in the spontaneously hypertensive rat.

To determine the effects of a chronic pressure load on cardiac function and morphology, spontaneously hypertensive rats (SHR) and two normotensive strains of Wistar rats (WKY and NWR) were studied under ether anesthesia at 13, 25, 52, and 90 wk of age. Although resting cardiac index of the SHR was comparable to that of WKY and NWR at all ages, the peak cardiac output and peak stroke volume per gram of left ventricle determined during a rapid intravenous infusion of Tyrode solution was markedly reduced in the SHR only at 90 wk of age. Autonomic inhibition did not alter the peak stroke volume attained, but reduced peak cardiac output at all ages in each of the strains. Absolute left ventricular dimensions in the SHR increased out of proportion to body growth, consistent with concentric hypertrophy. As peak pumping ability markedly declined from 52 to 90 wk of age in the SHR, the free wall of the left ventricle greatly thickened whereas the septum remained unchanged. At this time the right ventricle also hypertrophied. This disproportionate thickening of the walls of the left ventricle and the hypertrophy of the right ventricle were reflected in measurements of their fiber diameters. These alterations in ventricular architecture may contribute to the decrease in pumping ability observed in long-standing hypertension.     

Immune response modulation in the spontaneously hypertensive rat

Spontaneously hypertensive male and female rats (SHR) were compared with Wistar/Kyoto (W/K) controls at 15 wk and 80 wk of age. Treatment of the young and old hypertensives with thymosin, fraction 5, lowered the blood pressure within 4 wk of the start of treatment. Following 10 wk of injections, the blood pressures of the hypertensive rats remained at a depressed level for about 6 wk. The thymic hormone raised the depressed spontaneous T-cell rosette formation of the aged hypertensive rat and increased the lymph node T-cell response to the mitogens, Con A and PHA. Thymosin administration over a period of 7 wk increased the size of the aged hypertensive thymus. No similar effect was observed in the W/K. Spleen cell production of prostaglandin E (PgE) was markedly higher in the young hypertensive and immune complex deposition was found in the glomeruli and tubules of the aged SHR kidneys. Thymosin lowered the high level of PgE to normal and decreased the immune complex deposition in the kidney. IgG1 levels were considerably depressed in the SHR as compared to the W/K. Following thymosin administration levels of IgG1 increased 2-fold in both rat strains. Plaque-forming cells from the spleens of the untreated SHR were about 3-fold less than those of the age-matched W/K. Following treatment with thymosin the number of plaque-forming cells of both groups demonstrated a substantial further decrease. Spontaneous hypertension in rats is similar, in certain respects to autoimmune-like diseases in humans with a depression in T-cell activity as well as immune complex deposition; both conditions being altered by exposure to a thymic extract.     

Relationship between intracellular Ca2+ store and protein kinase C in agonist-induced contraction of hypertensive rat aortae.

The roles of intracellular Ca2+ store and protein kinase C (PKC) in vascular contractile responses independent of Ca2+ influx were studied using aortic rings from spontaneously hypertensive rat (SHR) and Wistar-Kyoto rat (WKY). The functional sizes of agonist-sensitive intracellular Ca2+ store were estimated as the peak response to agonist after PKC inhibition with calphostin C (Cal-C), a PKC inhibitor. The participation of PKC in 5-hydroxytryptamine-, phenylephrine-, and endothelin-1 (ET-1)-induced contractions in aortae of SHR was equal to, or greater than that in WKY. In contrast, compared with WKY, SHR aortae possessed a greater size of endothelin-1-sensitive Ca2+ store, a similar size of 5-hydroxytryptamine-sensitive Ca2+ store, and a smaller size of phenylephrine sensitive Ca2+ store. Based on these data, both PKC activation and functional size of intracellular Ca2+ store differ between SHR and WKY and these differences are selective among agosists.     

Temporal characteristics of cardiomyocyte hypertrophy in the spontaneously hypertensive rat.

BACKGROUND: The spontaneously hypertensive rat (SHR) is frequently used as model of cardiovascular disease, with considerable disparity in reported parameters of hypertrophy. The aim of this study was to assess the temporal changes occurring during the development and progression of cardiomyocyte hypertrophy in SHR, subsequent to pressure overload, compared to changes associated with normal aging using the normotensive Wistar-Kyoto (WKY) rat. METHODS: Ventricular cardiomyocytes were isolated from rats at 8, 12, 16, 20 and 24 weeks, and parameters of hypertrophy (cell dimensions, protein mass, de novo protein synthesis, and gene expression) and function (contraction and hypertrophic responsiveness in vitro) were assessed. RESULTS: Hypertension was evident at > or =7 weeks in SHRs. Heart:body mass ratio, cardiomyocyte protein mass and width were elevated (P<.05) in SHRs at 16-20 weeks compared to WKYs. In SHRs compared to WKYs at 16 weeks, there was a transient increase (P<.05) in protein synthesis, enhanced hypertrophic responsiveness to phorbol-12-myristate-13-acetate, and induced hypertrophic responsiveness to isoprenaline. Skeletal-alpha-actin mRNA was detected in SHR but not WKY cells at all ages. ANP mRNA was lower in SHR than in WKY cells at 8-20, but progressively increased (P<.05) from 12 to 24 weeks within SHRs. Contractile function increased (P<.05) at 20 weeks in SHR compared to WKY rats. CONCLUSION: Structural and functional changes occurring at the cellular level in the myocardium of SHR follow a distinct pattern, such that pressure overload was initially accompanied by expressional changes (8-12 weeks), followed by active hypertrophic growth and enhanced function (16-20 weeks), which subsequently decelerated as stable compensation was attained.     

The evolution of vascular changes in the spontaneously hypertensive rat.

A longitudinal study on the development of vascular lesions was carried out in the spontaneously hypertensive rat (SHR) of the Aoki-Okamoto strain. The aorta and intrarenal arterial vessels were examined at different ages, from 5 to 48 weeks, by light and electron microscopy. Endothelial permeability to injected horseradish peroxidase (HRP) was evaluated in 20-week-old animals. Morphologic differences between vessels of SHRs and age-matched normotensive controls (Wistar-Kyoto strain) were first noted at 10 weeks of age and became more pronounced with time. Vascular pathology involved both intima and media. Medial thickening was seen in both aorta and peripheral arteries and, in the latter, was associated with decreased luminal diameters. These medial changes may contribute to the maintenance of the elevated blood pressure. Intimal lesions affected predominantly the aorta and were characterized by an expansion of the subendothelial space with deposition of acid mucopolysaccharides. There was increased accumulation of tracer HRP in the expanded subendothelium, which suggested enhanced permeability and/or retention of the tracer. In animal species susceptible to atherosclerosis, these intimal changes could serve as the structural basis for the higher propensity for atheromatous lesions in hypertensive individuals. In the SHR, despite stabilization of systolic blood pressure at about 20 weeks of age, both intimal and medial lesions continue to progress and become more extensive and severe; this suggests that not only the severity of hypertension but also its duration are significant determinants of the degree of vascular damage.     

Modification of aortic barorecptor resetting in the spontaneously hypertensive rat.

Aortic barorecptor function was studied in spontaneously hypertensive rats (SHR) of various ages and normotensive Wistar rats. The aortic arch was isolated and perfused, and the activity of the left aortic nerve was recorded. The threshold pressure to elicit barerecptor firing was 80-120 mmHg in normotensive Wistar rats. Resetting of barorecptors (threshold pressure 160-180 mmHg) was found in all untreated SHR of 35-70 wk of age. Resetting of barorecptors was prevented in SHR by starting treatment with antihypertensive agents at the age of 11 wk. Treatment of 32-wk old SHR with antihypertensive agents for 4-6 wk resulted in reversal of barorecptor resetting in 50% animals. The percentage of SHR showing complete reversal of resetting did not increase even when the duration of treatment was tripled. In 52- to 64-wk old SHR, treated with antihypertensive agents, reversal of baroceptor resetting was seen in only 30% animals. It was concluded that baroceptor resetting in SHR was secondary to hypertension. Hypertension, in turn, induced hypertrophy of the tunica media of the aorta. Histological studies showed a close correlation between aortic hypertrophy resetting. Aortic hypertrophy may, therefore, be one of the important factors involved in baroceptor resetting.     

The renal medulla and mechanisms of hypertension in the spontaneously hypertensive rat.

A significant number of offspring from brother-sister matings of NIH-Okamoto-Aoki spontaneously hypertensive rats (SHRs) were found to be normotensive at 20 weeks of age. Over 20% of the animals that were hypertensive at this age had mild-to-moderate unilateral hydronephrosis at the time of sacrifice. In over 90% of the rats that did not develop hypertension spontaneously, ligation of one ureter raised blood pressure above 150 mm Hg within 2 weeks. In those rats made hypertensive by obstructing one ureter and in those that developed hypertension with accompanying naturally occurring hydronephrosis, subcutaneous implants of fragmented renal medulla from unrelated normal rats decreased blood pressure to normotensive levels. In contrast, medullary implants had no significant effect in rats developing hypertension spontaneously without hydronephrosis. Renal inner medullary plasma flow was low in the obstructed kidneys of hydronephrotic hypertensive SHRs but was elevated in the kidneys of nonhydronephrotic hypertensive SHRs. The hypertension in hydronephrotic SHRs appears to be related to an impairment of the antihypertensive function of the renal medulla. Such an impairment of medullary antihypertensive function does not appear to play a significant role in the hypertension in SHRs without hydronephrosis.     

Nocturnal food-related hyperdipsia in the adult spontaneously hypertensive rat

Male adult spontaneously hypertensive rats (SHR) ate the same but drank more and had a higher water to food ratio (W:F) than did Wistar-Kyoto (WKY) rats in 24-hr when they had continuous access to standard laboratory pellets and tap water. When rats ate in the day phase of a 12:12 light/dark cycle after 24-hr food deprivation, SHR rats ate and drank the same as did WKY rats in a 60-min test. When the same rats ate at night after 24-hr food deprivation, however, SHR rats were hyperdipsic: They ate the same as did WKY rats, but SHR rats drank more and had a higher W:F. This relative hyperdipsia reflected the increased ability of ingestion of food to stimulate drinking in SHR, because when food was absent for a 60-min test at night SHR drank the same as did WKY rats. Three dipsogens which are candidate components for eating-elicited drinking in the rat, cellular dehydration, histamine and angiotensin II, elicited drinking differentially in SHR and WKY rats: SHR drank more than did WKY rats in response to (1) cellular dehydration produced by IP hypertonic saline, (2) large doses of SC histamine, and (3) SC angiotensin II. These results demonstrate that SHR exhibit a nocturnal food-related hyperdipsia which may reflect differential sensitivity to stimuli important for eating-elicited drinking such as increased osmolality and endogenous histamine or angiotensin.     

Patterns of maternal behavior in the spontaneously hypertensive rat

Maternal behavior of spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) normotensive rats was assessed over the preweanling period (days 1-21). Ten litters of each strain were observed during the dark phase of the light:dark cycle using a scan sampling technique. Cages were observed periodically throughout the day and the momentary behavior of the dam was recorded on a checklist of 9 different behaviors. These behaviors included: nursing entire litter, nursing part of litter, contact with entire litter, contact with part of litter, pup carrying/retrieval, licking pups, sniffing pups, nest building, and away from litter. A second set of ten litters per strain was observed in the same manner during the light phase of the light:dark cycle thus providing around the clock data throughout the entire preweanling period. For purposes of data analysis, the 21-day preweanling period was divided into 7 3-day blocks. The mean relative frequency with which each behavior was observed from SHR and WKY mothers was determined for each block and for each phase of the light:dark cycle separately. SHR mothers were with their pups and nursing them more frequently than WKY mothers during the light phase of the circadian cycle. Complimentary to this finding, WKY mothers were observed away from their pups more frequently than SHR mothers during both light and dark phases. Finally, SHR mothers were observed to lick their pups more often than WKY mothers during both phases of the light:dark cycle. These findings were consistent across the entire preweanling period.(ABSTRACT TRUNCATED AT 250 WORDS)     

Arterial myogenic properties of the spontaneously hypertensive rat

When subject to a transmural pressure gradient resistance arteries develop a spontaneous, intrinsically initiated contraction which varies according to the pressure stimulus and occurs in the absence of vasoconstrictor agonists. Such pressure-dependent active changes in vascular tone are indicative of the vascular myogenic response and contribute to autoregulation and the setting of total peripheral resistance and hence blood pressure regulation. The myogenic behaviour of blood vessels provides the background tone upon which other vasomotor influences act. Hypertension is associated with a raised vascular resistance and in this article the evidence for increased myogenic activity contributing to the raised vascular resistance is reviewed. Although there are some cases that provide evidence for exaggerated myogenic responsiveness in resistance arteries taken from hypertensive animals it is not possible to conclude that enhanced myogenic contractile responses within normal pressure ranges contribute to the raised total peripheral resistance. However, the myogenic tone of the resistance arteries of the various vascular beds is subject to differing modulatory influences in hypertensive animals and their normotensive controls which may contribute to the aetiology of hypertension.     

The juxtaglomerular apparatus of the spontaneously hypertensive rat

Spontaneously hypertensive rats (SHR) are used to study the pathogenesis of essential hypertension. This study investigates the role of the renin-angiotensin system (RAS) in the pathogenesis of hypertension in SHRs and the morphometry of the JGA by a three-dimensional computer reconstruction program "GLOM" and electron microscopy. Systolic blood pressure (SBP) (tail cuff method) was higher in SHRs compared to controls (P less than 0.001). Plasma renin concentration (PRC) was lower in SHRs than in controls (P less than 0.001). Reconstruction of the JGA revealed granulated JG cells in the afferent and efferent arterioles and in the vascular tree away from the JGA area. Electron microscopy showed granulated JG cells in the afferent and efferent arterioles. The percentage volume of the granulated JG cells in SHR was significantly higher than in controls (P less than 0.01). A relationship was found between the percentage volume of granulated JG cells and the SBP in SHRs (r = 0.933, P less than 0.05). The wall/lumen perimeter ratio was also significantly higher in the SHRs compared to the controls (P less than 0.05). Low PRC in SHRs has been reported by several workers. The apparent hyperactivity of the JGA may indicate failure of renin release or an abnormal synthesis/secretion rate.     

自发性高血压大鼠苯丙氨酸代谢动力学异常

目的和方法：自发性高血压大鼠（ＳＨＲ）及相应的正常血压对照大鼠（Ｗｉｓｔａｒ Ｋｙｏｔｏ大鼠,ＷＫＹ）静注［＾３Ｈ］苯丙氨酸后的药物动力学及组织摄取。结果：苯丙氨酸在大鼠的药物动力学符合二室开放模型。与ＷＫＹ相比,ＳＨＲ中苯丙氨酸消除半衰期延长,清除率缩小,药时曲线下面积增加,中央室表观分布容积增加,心脏对苯丙氨酸摄取增加。结论：高血压药可能是一种与遗传性氨基酸代谢异常有关的疾病。