Prevention of hypertension and vascular changes by captopril treatment

Treatment of female spontaneously hypertensive rats (SHR) and control Wistar-Kyoto (WKY) rats with captopril was carried out by the addition of the drug in the drinking water throughout pregnancy and lactation and after weaning. At 28 weeks of age, average systolic blood pressure of treated SHR was 113 +/- 3 mm Hg, which was below that of control SHR (188 +/- 3 mm Hg) and WKY rats (124 +/- 3 mm Hg). Body weight and heart rate of the SHR were not affected by the treatment. Tissue level of catecholamines was increased by captopril treatment in the superior cervical ganglia but remained unchanged in the plasma, heart, mesenteric arteries, and the adrenal glands of both SHR and WKY rats. Left ventricular weight, wall thickness, and internal diameter of the left ventricle in the SHR were reduced by the treatment. Morphometric measurements of the mesenteric arteries showed that vascular alterations present in the control SHR were prevented by the treatment. In the superior mesenteric artery and large mesenteric artery, smaller lumen size at maximal relaxation found in the control SHR was normalized to the level of the WKY rats. Hypertrophy of the medial wall in the superior mesenteric, large and small mesenteric arteries, and an increase in the number of smooth muscle cell layers in the large mesenteric artery of the SHR were prevented by the treatment. Perfusion study of the mesenteric vascular bed showed that reactivity of these vessels to norepinephrine was reduced, and sensitivity to norepinephrine (as determined by the effective dose that causes 50% of maximal response) was increased in the SHR by captopril treatment. Sensitivity of the tail artery in response to norepinephrine was not altered by the treatment. We conclude that long-term treatment with captopril of SHR before and after birth prevented the development of hypertension, structural and functional alterations of the mesenteric arteries, and cardiac hypertrophy.     

Combined effect of neonatal sympathectomy and adrenal demedullation on blood pressure and vascular changes in spontaneously hypertensive rats

Neonatal sympathectomy using a combined treatment with antiserum to nerve growth factor and guanethidine during the first 4 weeks after birth was carried out in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. Bilateral adrenal demedullation was performed in 4-week-old sympathectomized SHR and WKY rats. The development of hypertension in SHR was prevented by sympathectomy, but the blood pressure (BP) was still higher than in age-matched WKY rats. Demedullation reduced the BP of sympathectomized SHR to the same level as that of WKY rats. Heart rates of SHR and WKY rats were not affected by the treatments. Morphometric measurements of the mesenteric arteries showed that sympathectomy significantly reduced the medial mass in the mesenteric arteries of SHR, mainly through a reduction in the number of smooth muscle cell layers. In sympathectomized SHR, demedullation increased the lumen size of muscular arteries under maximally relaxed conditions, which might explain the further reduction in BP in these animals. Demedullation in sympathectomized SHR and WKY rats caused a decrease in smooth muscle cell layers in the superior mesenteric artery, but the same treatment resulted in a slight increase in the number of smooth muscle cell layers in the large and small mesenteric arteries of SHR and WKY rats. Adventitial area was increased in some mesenteric arteries of SHR and WKY rats by sympathectomy, and demedullation caused a further increase in the size of adventitia in WKY rats. Heart weight in SHR was normalized to the level found in WKY rats by sympathectomy and demedullation. We conclude that in sympathectomized SHR, the elevated BP was maintained by the adrenal medulla.     

Structural and functional alterations of mesenteric vascular beds in spontaneously hypertensive rats

The morphology and reactivity of mesenteric arteries from spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar Kyoto rats (WKY) were investigated. Isolated, perfused mesenteric vascular beds were prepared from 6-, 11- and 18-week-old SHR and WKY. At these ages, the walls and media of large mesenteric arteries were significantly thicker in SHR than in WKY. The number of smooth muscle cell layers in the media was significantly larger in SHR than in WKY. This difference between SHR and WKY increased as rats grew older, in parallel with differences in the blood pressure. Flow rate-perfusion pressure curves indicated that the vascular basal resistance to flow increased more profoundly in SHR preparations than in WKY preparations as rats grew older. This may be related to the structural alterations of the resistance vessel wall in SHR. The pressor responses to KCl were greater in SHR preparations than in WKY preparations as rats grew older. This may be caused partly by the increase of the number of smooth muscle cell layers in the media of SHR resistance vessels. The pressor response to norepinephrine (NE) was significantly higher in SHR preparations than in WKY preparations at all ages investigated. In marked contrast to the vascular basal resistance and the pressor response to KCl, the pressor response to NE was extremely exaggerated in SHR at the age of 6 weeks. This extremely high NE response in younger SHR may not be caused by the structural alteration in resistance vessels. It may be caused by a functional change, which is regulated by the signal transduction process in smooth muscle cells of resistance vessels. These results suggest that the development of hypertension in SHR may be caused by genetic structural and functional abnormalities of resistance vessels. Both abnormalities may be caused by the hyperreactivity to NE through an altered signal transduction process in smooth muscle cells of resistance vessels in SHR.     

Vascular changes at the prehypertensive phase in the mesenteric arteries from spontaneously hypertensive rats

Morphometric measurements of three categories of mesenteric vessels (representing elastic, muscular and arteriolar vessels) from prehypertensive spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto rats (WKY) were carried out at the light and electron microscope levels. Structural alterations of the blood vessels were already present in the SHR, even though the blood pressure was not yet elevated as compared with age-matched WKY. No change was found in the elastic vessels (superior mesenteric artery). Among the muscular arteries (i.e. large mesenteric arteries), the increase in vessel wall cross-sectional area was due to the increase in the intima, media and adventitia. Increase in media was due to hyperplasia of the smooth muscle cells. The smooth muscle cells were not hypertrophied. Nerve density was also higher in the large mesenteric arteries of SHR. In the arteriolar vessels (i.e. small mesenteric arteries), wall to lumen ratio, as well as media to lumen ratio, were increased in the SHR. The number of smooth muscle cell layers was also increased. In all these vessel types, the cross-sectional area of the lumen under maximal relaxation was similar between SHR and WKY, except in small mesenteric arteries where the lumen was smaller in the SHR. Our results suggest that structural alteration of the blood vessels at the prehypertensive phase may be one of the contributing factors leading to the development of hypertension in the SHR.     

Evaluation of medial hypertrophy in resistance vessels of spontaneously hypertensive rats

The role of smooth muscle cell hypertrophy, hyperploidy, and hyperplasia in medial hypertrophy of mesenteric resistance vessels of 107- to 111-day-old spontaneously hypertensive rats (SHR) was examined using a combination of morphometric, biochemical, and immunological techniques. Mesenteric arteries were classified on the basis of branching order for comparative purposes. Branch level I vessels were those that directly enter the jejunal wall, while Branches II to IV represented more proximal vessels; Branch IV vessels were those that branch from the superior mesenteric artery. Medial hypertrophy was assessed in perfusion-fixed vessels by morphometric evaluation of medial cross-sectional area and smooth muscle content. Medial cross-sectional area and smooth muscle content were significantly increased in larger (Branches III and IV) but not smaller (Branches I and II) mesenteric resistance vessels of SHR compared with control normotensive Wistar-Kyoto rats (WKY). Smooth muscle cell hypertrophy and hyperploidy were evaluated in isolated cells obtained by enzymatic dissociation of mesenteric resistance vessels. Approximately 80% of the cells in these preparations were identified as smooth muscle cells using a smooth muscle-specific isoactin antibody. Feulgen-DNA microdensitometric evaluation of isolated cells showed that polyploid cells were present in mesenteric resistance vessels but at very low frequencies, and no differences were apparent between SHR and WKY. Likewise, no differences in cellular protein content or relative smooth muscle cell size (i.e., area profile) were observed between cells obtained from SHR and WKY vessels. These results demonstrate that the increase in medial smooth muscle content observed in larger mesenteric resistance vessels of SHR cannot be accounted for by smooth muscle hypertrophy and hyperploidy, inferring that hyperplasia must be present. Results indicate that studies of the initiating mechanisms for medial smooth muscle hypertrophy in SHR resistance vessels, at least relatively early in hypertension, should focus on examination of factors that induce true cellular proliferation rather than hypertrophy and hyperploidy.     

Norepinephrine overflow in perfused mesenteric arteries of spontaneously hypertensive rats

We examined the overflow of endogenous norepinephrine with electrical stimulation, the associated pressor response, and rate of initial neuronal uptake of [3H]norepinephrine in perfused mesenteric arteries of 7- and 13-week-old spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. The tissues of two rats, a spontaneously hypertensive and a WKY control rat, were simultaneously processed and subjected to the same electrical stimulation. Both absolute and fractional overflow of endogenous norepinephrine during periarterial nerve stimulation (5 and 10 Hz for 1 minute) in the tissue of 7-week-old SHR was significantly greater whereas overflow of 13-week-old SHR was equivalent as compared with that of the age-matched WKY rats. The tissue content of norepinephrine was 20-25% higher in SHR of both ages. There was significantly enhanced [3H]norepinephrine uptake in the tissues of young SHR, but no difference was observed in the older SHR. The pressor response to periarterial nerve stimulation was significantly enhanced in 7-week-old SHR and much more so at the older age as compared with the WKY control rats. Exogenous norepinephrine dose-response curves in the tissues of 7-week-old SHR exhibited a parallel leftward shift, characteristic of a change in sensitivity, whereas that of 13-week-old SHR showed a much steeper slope as compared with the respective WKY control rats. This finding suggests that in addition to smooth muscle supersensitivity, structural alterations had occurred in vasculature of 13-week-old SHR. These data indicate that in SHR both the exocytotic release of norepinephrine and the responsiveness of the vascular smooth muscle cells are enhanced in the developmental stage of hypertension whereas smooth muscle supersensitivity to norepinephrine and nonspecific structural alterations primarily contribute to the maintenance of hypertension at 13 weeks of age.     

Effect of hydralazine on the mesenteric vasculature of hypertensive rats

To test whether structural alterations observed in the mesenteric vasculature of Wistar-Kyoto spontaneously hypertensive rats (SHR) were dependent on the presence of hypertension, male SHR and Wistar-Kyoto normotensive (WKY) rats were treated in utero and postnatally with hydralazine up to 28 weeks of age. Treated SHR, WKY, and untreated WKY rats had comparable blood pressures that were less than those of untreated SHR. Treatment altered the dimensions of the superior mesenteric, intermediate-sized, and small arteries of the mesenteric vasculature. In the case of the superior mesenteric artery and intermediate vessels, hydralazine treatment increased the lumen and medial cross-sectional areas of the arteries in WKY rats and slightly decreased both parameters in SHR. Within the small arteries, treatment significantly increased the lumen size in SHR but not WKY rats and had no significant effect on the media of the vessels. Despite the above alterations, the media-to-lumen cross-sectional area ratios remained significantly elevated in SHR over WKY rats in both the treated and control groups of animals within all classes of arteries. The results indicate that there is an inherent increase in the quantity of media surrounding the arteries of SHR when compared with WKY rats that cannot be abolished by normalizing the blood pressure in utero and postnatally with hydralazine treatment. In SHR, such changes persist not only in arteries that exhibit an increase in the media-to-lumen ratio before hypertension but also in the superior mesenteric artery in which an increase in the ratio occurs after hypertension development.     

Endothelin-1 and vasopressin signalling in blood vessels of young SHR in comparison to adult SHR.

To examine potential intracellular signalling abnormalities of endothelin-1 (ET-1) and vasopressin (AVP) which may contribute to blood pressure elevation, contractility and inositol phosphate levels in intact arteries and calcium transients in vascular smooth muscle cells were investigated after stimulation with these peptides in pre-hypertensive 5 week-old spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto (WKY) rats. Contractility of aorta in response to ET-1, AVP and norepinephrine (NE) was blunted in SHR relative to WKY. Contraction of mesenteric resistance arteries induced by ET-1 was similar in both groups, whereas sensitivity in response to NE and AVP was greater in SHR. Basal inositol phosphate in aorta and mesenteric arteries was elevated in SHR, but ET-1 and AVP-stimulated inositol phosphate responses were similar in both groups. Calcium transients induced by ET-1 and AVP in vascular smooth muscle cells were similar in young SHR and WKY. In contrast, in adult rats inositol phosphate responses to ET-1 were blunted in aorta of SHR, but were normal in mesenteric arteries. Inositol phosphate responses to AVP were similar in both rat strains of rats both in aorta and mesenteric arteries except for accumulation of inositol trisphosphate, which was enhanced in mesenteric arteries of SHR. Calcium mobilization in vascular smooth muscle cells from adult SHR also exhibited enhanced responses to AVP. In conclusion, in young SHR, blunted ET-1 and AVP-induced contraction in aorta and enhanced AVP-induced mesenteric artery contraction are associated with normal inositol phosphate production and calcium mobilization. Signal transduction in response to ET-1 and AVP is depressed in aorta of pre-hypertensive SHR after the step of inositol phosphate generation and calcium mobilization. Resistance vessel reactivity to AVP is enhanced in young SHR at steps following inositol phosphate generation and calcium mobilization. These results argue against a role of ET-1, but suggest the possible involvement of AVP in the development of this model of genetic hypertension.     

Isolation and characterization of single vascular smooth muscle cells from spontaneously hypertensive rats

To study the properties of vascular smooth muscle in hypertension without the influence of the nerves and endothelium, a procedure was developed to isolate single smooth muscle cells from tail arteries of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) normotensive control rats. Perfusion of intact arteries with a solution of papain and collagenase produced dense populations of viable cells (more than 10(4) cells/ml) that remained relaxed in the presence of physiological levels of calcium. Contractile responses of smooth muscle cells from the SHR were significantly more sensitive to noradrenaline, potassium depolarization, and the calcium channel agonist Bay K 8644 compared with those from WKY rats. Enhanced sensitivity to calcium in the SHR was also observed on readdition of calcium to cells preincubated in noradrenaline or KCl in a calcium-free medium. These results provide evidence for alterations in the properties of vascular smooth muscle in the SHR at the single cell level.     

Involvement of Ras-regulated myosin light chain phosphorylation in the captopril effects in spontaneously hypertensive rats

BACKGROUND: Early treatment with captopril prevents the development of hypertension by inhibiting the generation of angiotensin II and smooth muscle contraction. Although smooth muscle contraction is regulated by myosin light chain phosphorylation (MLC-P), the role of MLC-P in captopril effects in hypertension has not been described. Therefore, we treated spontaneously hypertensive rats (SHR) with captopril and investigated the effects of this agent on downstream signaling. METHODS: Male SHR (n = 12) were treated with captopril (3.7 mmol/L in drinking water) beginning in utero and continuing up to 12 weeks of age. Age- and sex-matched untreated SHR and Wistar-Kyoto (WKY) rats were used as controls. Rats were split into three subgroups and were sacrificed at 12, 18, or 24 weeks of age. Systolic blood pressure, left ventricular weight, and body weight were measured. Mesenteric arteries were removed for histologic and biochemical studies. RESULTS: At 12 weeks, captopril significantly decreased systolic blood pressure (from 198 +/- 10 to 125+/-16 mm Hg), reduced left ventricular weight-to-body weight ratios (from 2.94 +/- 0.06 to 2.17 +/- 0.08 mg/g), and prevented vascular remodeling in mesenteric arteries in SHR. Ras expression, extracellular receptor kinase phosphorylation (ERK-P), myosin light chain kinase (MLCK) expression, and MLC-P were all significantly increased in mesenteric arteries in untreated SHR compared with WKY rats. Early captopril treatment in SHR significantly inhibited Ras and MLCK expression at all ages and decreased ERK-P and MLC-P at 12 and 18 weeks in mesenteric arteries. CONCLUSIONS: These data demonstrate that the antihypertensive effects of captopril are correlated with inhibition of Ras-regulated ERK activation, MLCK expression, and MLC-P.     

High-dose, not low-dose insulin increases the vasoconstrictor effect of norepinephrine in spontaneously hypertensive rats: effects of antihypertensive treatment

The effect of insulin on the vasoconstriction induced by norepinephrine is presently controversial. Therefore, the aims of our study were: (1) to evaluate the effect of low- and high-dose insulin on the concentration-response curve to norepinephrine in small resistance arteries of spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY) before and after the development of hypertension, and (2) to evaluate the effects of antihypertensive treatment on vascular response to insulin and norepinephrine. Fifty-six rats were included in the study. Six SHR were treated with enalapril and 6 with candesartan cilexetil from the 4th to the 12th week of age, while 10 WKY and 14 SHR were kept untreated. Two additional groups of 10 untreated SHR and 10 WKY were killed at 4 weeks of age, in a prehypertensive phase. Mesenteric small arteries were dissected and mounted on a micromyograph. A dose-response curve to norepinephrine was performed at cumulative concentrations in the presence or absence of low- and high-dose insulin. We found that only high-dose insulin increased the vascular response to norepinephrine in 12-week-old SHR, but not in 4-week-old SHR or in age-matched WKY. The increased responsiveness to norepinephrine disappeared after preincubation of the vessels with a selective inhibitor of endothelin-1 type A receptors. After antihypertensive treatment with enalapril or candesartan cilexetil, the potentiation of the vasoconstrictor response to norepinephrine was abolished. In conclusion, insulin at high, nonphysiological doses seems to induce an increase in the reactivity to norepinephrine in mesenteric small arteries of SHR, possibly mediated by a local production of endothelin-1. Antihypertensive treatment with an ACE inhibitor or an angiotensin II receptor blocker may normalize this altered response. This mechanism may be relevant in the development of hypertension in SHR.     

Effect of Insulin on Norepinephrine Overflow at Peripheral Sympathetic Nerve Endings in Young Spontaneously Hypertensive Rats

To determine how the effect of insulin is related to the development of salt-induced hypertension, and whether a hyporesponse to insulin exists in the peripheral sympathetic nerves of a hypertensive model rat, we measured norepinephrine overflow from the periarterial nerve of isolated mesenteric arteries exposed to insulin in spontaneously hypertensive rats (SHR) as well as Wistar-Kyoto rats (WKY) fed diets that were high and low in salt. Salt loading (diet containing 8% salt for 4 weeks) accelerated the development of hypertension in young, spontaneously hypertensive rats (SHR) (157 ± 5 mm Hg υ 198 ± 4 mm Hg, P < .01) but did not affect the blood pressure of Wistar-Kyoto rats (WKY) (102 ± 7 mm Hg υ 104 ± 6 mm Hg, P = NS). Basal norepinephrine overflow did not differ in the SHR and WKY rats, but the overflow of norepinephrine after periarterial electrical stimulation (8 Hz 1 min.) was significantly greater in SHR (0.806 ± 0.079 ng/g) than in WKY (0.723 ± 0.022 ng/g P < .01). Although insulin reduced the norepinephrine overflow by periarterial nerve stimulation in both WKY and SHR, the decrease with insulin was significantly greater in the SHR than in WKY (−18.4% ± 4.0% υ −32.0% ± 4.6%, P < .05). The inhibitory effect of insulin on norepinephrine overflow was reduced by salt loading in SHR (−8.8% ± 4.0%, P < .05), but not in WKY (−32.5% ± 4.7%, P = NS). Cocaine and ouabain completely blocked the effect of insulin in all four groups. In contrast to insulin, direct stimulation of Na⁺-K⁺ ATPase with a high-potassium buffer (12 mmol/L) reduced NE overflow to the same extent among the four groups. These findings show that SHR have a blunted response to the suppression by insulin of norepinephrine overflow. Salt loading reduced the insulin response at peripheral sympathetic nerves of young SHR, but did not affect that of age-matched WKY. Thus, hyporeactivity to insulin may play a role in the development of salt-induced hypertension in young SHR, possibly through a reduced suppression of norepinephrine overflow from sympathetic nerve endings. Am J Hypertens 1996;9:1119–1125     

Structural and reactivity alterations of the renal vasculature of spontaneously hypertensive rats prior to and during established hypertension

The renal vasculature of Wistar Kyoto spontaneously hypertensive rats (SHR), prior to (4-5 week) and during established hypertension (21 week) and those of age-matched Wistar Kyoto normotensive rats (WKY) were morphometrically and pharmacologically studied. Under dilated conditions, the vascular resistances (RVR) of the isolated kidneys of young and adult SHR were similar to WKY. Morphometric measurements of renal vasculature indicated that the cross-sectional area of the intima and adventitia and its subcomponents were similar in adult SHR and WKY. With the exception of the preglomerular arterioles, all the renal arteries of adult SHR exhibited elevated cross-sectional quantities of total media, medial smooth muscle cells (SMCs), and extracellular space. Analysis of the SMCs indicated the presence of increased numbers of SMC layers and/or an increase in the SMC volume-to-surface area ratio in arteries sampled from adult SHR. Vascular contraction produced by infusing norepinephrine, BaCl2, angiotensin II, or by stimulating the renal nerves elevated the RVR to a greater degree in adult SHR than in WKY. The sensitivity of the renal vasculature to the various contractile agents was similar in adult SHR and WKY. When compared with WKY, prehypertensive SHR also exhibited increased cross-sectional quantities of arterial media and elevated amplitudes of RVR change in response to norepinephrine and renal nerve stimulation. However, the vascular contractile sensitivity to norepinephrine was reduced. Our results indicate that renovascular wall thickening and the hypercontractile reactivity associated with such a change precedes hypertension in SHR. In prehypertensive SHR, elevations in RVR might be counterbalanced by a decreased norepinephrine sensitivity. An increase in the norepinephrine contractile sensitivity and further vascular thickening with age could elevate the RVR and establish hypertension.     

Morphometric study of cerebral arteries from spontaneously hypertensive and stroke-prone spontaneously hypertensive rats.

OBJECTIVE: The importance of sympathetic innervation for the development of structural changes in the cerebral arteries of hypertensive animals was studied. DESIGN: Sympathetic denervation was induced with combined treatment from birth of antibody against nerve growth factor and guanethidine. Previous studies from our laboratory showed that this procedure not only caused a permanent denervation of the mesenteric arteries, but also prevented the development of hypertension in spontaneously hypertensive rats (SHR). METHODS: Morphometric measurement of the structural changes was carried out in the basilar, superior cerebellar, posterior cerebral and middle cerebral arteries from 28-week-old SHR, stroke-prone SHR, and normotensive Wistar-Kyoto rats. The results were compared with those obtained from cerebral arteries of sympathectomized rats. RESULTS: Total vascular wall cross-sectional area was significantly larger in the basilar and superior cerebellar arteries from hypertensive rats compared with normotensives. The change was characterized by an increase in the number of smooth muscle cell layers. There were also differences between the two hypertensive groups in some arteries. Sympathetic denervation attenuated the development of hypertension and vascular changes in some arteries. There was a positive linear correlation between blood pressure and medial cross-sectional area, and between blood pressure and the number of smooth muscle cell layers for the four arteries analysed. CONCLUSION: Sympathetic nerves have a trophic influence upon the remodelling of some cerebral arteries during the development of genetic hypertension.     

Influence of cold-induced increases in sympathetic nerve activity on norepinephrine content in the vasculature of the spontaneously hypertensive rat

In spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY), we have examined both the endogenous norepinephrine (NE) contents of caudal arteries, mesenteric arteries and cardiac tissue as well as the rates of decline of NE in these tissues after inhibition of NE synthesis. The endogenous NE contents of caudal and mesenteric arteries from SHR rats were greater than those from WKY rats. In contrast, the NE contents of hearts from SHR and WKY rats were similar. After synthesis inhibition with alpha-methyl-p-tyrosine (300 mg/kg i.p.), the NE contents of hearts and mesenteric arteries decreased in a monoexponential fashion. The rates of decline of NE were similar for corresponding tissues from SHR and WKY rats. Cold stress, reported to selectively activate sympathetic discharge, did not influence the rates of decline of NE in mesenteric arteries of either SHR or WKY animals. In contrast, cold exposure dramatically accelerated the rate of decline of NE in cardiac tissue from both SHR and WKY rats. It is concluded that in mesenteric arteries from SHR rats there is a larger pool of NE with turnover characteristics not dissimilar from that prevailing in vessels from normotensive animals. The failure of cold stress to modify the rates of decline of NE in mesenteric and caudal arteries of SHR and WKY rats suggests that these arteries are under considerable sympathetic influence at ambient temperature. The results support the view that the hypernoradrenergic innervation found in SHR blood vessels, together with normal functioning of the sympathetic nervous system, may have the potential for producing a heightened peripheral vascular resistance in this model.     

In vivo DNA synthesis is not uniformly increased in arterial smooth muscle of young spontaneously hypertensive rats.

We compared the distribution of DNA synthesis over the arterial tree of young normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) with marginally elevated blood pressure. Six-week-old male SHR and WKY rats were therefore infused with 5-bromo-2'-deoxyuridine (BrdUrd) for 2 days and the nuclear incorporation of the thymidine analogue in the media of various arteries was determined by immunohistochemistry. In WKY rats, 2.5% of the arterial smooth muscle nuclei in elastic, muscular and resistance arteries incorporated BrdUrd. In SHR, DNA synthesis was more marked in large arteries than in resistance arteries. It was in addition significantly larger in the aorta, superior mesenteric, renal and femoral arteries of the SHR than in those of the WKY rats. However, nuclear incorporation of BrdUrd in vivo did not differ between SHR and WKY rats in aortic endothelium, carotid arterial smooth muscle, nor in mesenteric or renal resistance arteries. Between 6 and 20 weeks of age, the number of nuclear profiles per media cross-section did not increase in large arteries of WKY rats and SHR. During this period of time, however, carotid artery and thoracic aorta weight and DNA content increased. SHR large arteries gained more DNA than those of WKY rats. These data indicate that DNA synthesis is uniformly distributed over the arterial system in young WKY rats and that DNA synthesis is elevated in the smooth muscle of large arteries of 6-week-old SHR but not in their resistance arteries.     

Elevated nerve growth factor levels in young spontaneously hypertensive rats

It is generally agreed that sympathetic innervation of vascular tissues in spontaneously hypertensive rats (SHR) is greater than that existing in vascular tissues from normotensive Wistar-Kyoto (WKY) rats. One factor responsible for regulation of the growth of peripheral sympathetic nerves is the peptide nerve growth factor, which is released from effector cells. In the present study, an enzyme immunoassay was used to measure nerve growth factor levels in mesenteric arteries (densely innervated) and aortas (sparsely innervated) from both young (20-day-old) and mature (6-month-old) SHR and WKY rats. The nerve growth factor content of mesenteric arteries and aortas from 20-day-old SHR was significantly greater than that present in corresponding tissues from WKY rats. In contrast, the nerve growth factor content found in mesenteric arteries and aortas of adult SHR did not differ significantly from that found in the corresponding adult WKY rat tissues. Moreover, when the tissues were obtained from adult animals, nerve growth factor levels were substantially higher in mesenteric arteries compared with aortas, regardless of the rat strain. These results support the hypothesis that the greater nerve growth factor content of vascular tissues from young SHR is involved in the early increased sympathetic innervation of blood vessels in this animal model of hypertension.     

Enhanced neuroinhibitory effect of diltiazem in blood vessels of spontaneously hypertensive rats

This study investigated the effects of diltiazem (a Ca2(+)-entry blocker) on neuromuscular junctions of blood vessels in hypertension. In isolated perfused mesenteric vasculatures prepared from spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto rats (WKY), the effects of diltiazem on norepinephrine release from vascular adrenergic neurons and pressor responses were examined. The influences of extracellular Ca2(+)-reduction on these responses were also studied. Stimulation evoked pressor responses and norepinephrine release were significantly greater in the mesenteric vasculatures of SHR than in those of WKY. Diltiazem inhibited both pressor responses and norepinephrine release during electrical nerve stimulation in a dose-dependent manner. The suppression of these responses was more pronounced in SHR than in WKY. Reduction of extracellular Ca2(+)-concentration also decreased the responses in SHR and WKY, and the inhibitory degree was significantly greater in SHR than in WKY. These results demonstrate that diltiazem affected the presynaptic site of the mesenteric vasculatures and decreased the stimulation-evoked norepinephrine release from vascular adrenergic neurons with a concomitant reduction of pressor responses of the preparation. Furthermore, the marked inhibition of pressor responses and norepinephrine release by diltiazem or Ca2(+)-depletion in SHR may suggest the increased Ca2(+)-dependency in vascular neurotransmission in this model of hypertension.     

Protection of cavernous tissue in male spontaneously hypertensive rats. Beyond blood pressure control

Male erectile dysfunction is increased in prevalence in patients with hypertension. Previous experiments from our group demonstrated morphologic changes in erectile tissue from male spontaneously hypertensive rats (SHR). The aim of the present study was to determine whether blood pressure (BP) control is enough to preserve cavernous tissue from the deleterious effect of arterial hypertension. Eight-week-old male SHR and normotensive Wistar-Kyoto rats (WKY) were studied during 6 months: Group 1 (n = 10) SHR; group 2 (n = 10) SHR with 7.5 mg/kg/d candesartan (C); group 3 (n = 10) SHR with 100 mg/kg/d atenolol (AT); and group 4 (n = 10) WKY. At the end of the experiment all the animals were killed for microscopic studies. Cavernous tissue was processed by hematoxylin-eosin, Masson's trichrome, monoclonal anti-alpha-smooth muscle actin, and anticollagen type III. Cavernous smooth muscle (CSM) and vascular smooth muscle (VSM) from cavernous arteries and the amounts of collagen type III were evaluated. At the end of the experiment, SHR with C and AT showed similar control in BP (group 2: 131.3 +/- 5.5 mm Hg; group 3: 136.5 +/- 2.9 mm Hg) compared with untreated SHR (group 1: 199.6 +/- 5.1 mm Hg). However, animals with C presented significantly lower values (P <.01) of CSM layer in cavernous space and VSM in cavernous arteries (P <.01), and lower amounts of collagen type III (P <.01) compared to SHR with AT and untreated SHR. We conclude that C provides a significant protective role against structural changes in vessels as well as in cavernous spaces of the erectile tissue, caused by arterial hypertension in SHR, beyond BP control.