The correlation between the development of sympathetic innervation and the development of medial hypertrophy in jejunal arteries in normotensive and spontaneously hypertensive rats

Elevated Vascular Sympathetic Neurotransmission and Remodelling Is a Common Feature in a Rat Model of Foetal Programming of Hypertension and SHR

Hypertension is of unknown aetiology, with sympathetic nervous system hyperactivation being one of the possible contributors. Hypertension may have a developmental origin, owing to the exposure to adverse factors during the intrauterine period. Our hypothesis is that sympathetic hyperinnervation may be implicated in hypertension of developmental origins, being this is a common feature with essential hypertension. Two-animal models were used: spontaneously hypertensive rats (SHR-model of essential hypertension) and offspring from dams exposed to undernutrition (MUN-model of developmental hypertension), with their respective controls. In adult males, we assessed systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), sympathetic nerve function (3H-tritium release), sympathetic innervation (immunohistochemistry) and vascular remodelling (histology). MUN showed higher SBP/DBP, but not HR, while SHR exhibited higher SBP/DBP/HR. Regarding the mesenteric arteries, MUN and SHR showed reduced lumen, increased media and adventitial thickness and increased wall/lumen and connective tissue compared to respective controls. Regarding sympathetic nerve activation, MUN and SHR showed higher tritium release compared to controls. Total tritium tissue/tyrosine hydroxylase detection was higher in SHR and MUN adventitia arteries compared to respective controls. In conclusion, sympathetic hyperinnervation may be one of the contributors to vascular remodelling and hypertension in rats exposed to undernutrition during intrauterine life, which is a common feature with spontaneous hypertension.

Impaired inhibitory function of presynaptic A1-adenosine receptors in SHR mesenteric arteries

In hypertension, vascular reactivity alterations have been attributed to numerous factors, including higher sympathetic innervation/adenosine. This study examined the modulation of adenosine receptors on vascular sympathetic nerves and their putative contribution to higher noradrenaline spillover in hypertension. We assessed adenosine receptors distribution in the adventitia through confocal microscopy, histomorphometry, and their regulatory function on electrically-evoked [(3)H]-noradrenaline overflow, using selective agonists/antagonists. We found that: i) A1-adenosine receptor agonist (CPA: 100 nM) inhibited tritium overflow to a lower extent in SHR (25% ± 3%, n = 14) compared to WKY (38% ± 3%, n = 14) mesenteric arteries; ii) A2A-adenosine receptor agonist (CGS 21680: 100 nM) induced a slight increase of tritium overflow that was similar in SHR (22% ± 8%, n = 8) and WKY (24% ± 5%, n = 8) mesenteric arteries; iii) A2B- and A3-adenosine receptors did not alter tritium overflow in either strain; iv) all adenosine receptors were present on mesenteric artery sympathetic nerves and/or some adventitial cells of both strains; and v) A1-adenosine receptor staining fractional area was lower in SHR than in WKY mesenteric arteries. We conclude that there is an impaired inhibitory function of vascular presynaptic A1-adenosine receptors in SHR, likely related to a reduced presence of these receptors on sympathetic innervation, which might lead to higher levels of noradrenaline in the synaptic cleft and contribute to hypertension in this strain.

ß-adrenoceptor blockers increase cardiac sympathetic innervation by inhibiting autoreceptor suppression of axon growth

β-Adrenoceptor antagonists are used widely to reduce cardiovascular sympathetic tone, but withdrawal is accompanied by sympathetic hyperactivity. Receptor supersensitivity accounts for some but not all aspects of this withdrawal syndrome. Therefore, we investigated effects of β-blockers on sympathetic innervation. Rats received infusions of adrenergic receptor blockers or saline for 1 week. The nonselective β-blocker propranolol and the β(1)-antagonist metoprolol both increased myocardial sympathetic axon density. At 2 d after propranolol discontinuation, β-receptor sensitivity and responsiveness to isoproterenol were similar to controls. However, tyramine-induced mobilization of norepinephrine stores produced elevated ventricular contractility consistent with enhanced sympathetic neuroeffector properties. In addition, rats undergoing discontinuation showed exaggerated increases in mean arterial pressure in response to air puff or noise startle. In sympathetic neuronal cell cultures, both propranolol and metoprolol increased axon outgrowth but the β(2)-blocker ICI 118551 did not. Norepinephrine synthesis suppression by α-methyl-p-tyrosine also increased sprouting and concurrent dobutamine administration reduced it, confirming that locally synthesized norepinephrine inhibits outgrowth via β(1)-adrenoceptors. Immunohistochemistry revealed β(1)-adrenoceptor protein on sympathetic axon terminations. In rats with coronary artery ligation, propranolol reversed heart failure-induced ventricular myocardial sympathetic axon depletion, but did not affect infarct-associated sympathetic hyperinnervation. We conclude that sympathetic neurons possess β(1)-autoreceptors that negatively regulate axon outgrowth. Chronic β-adrenoceptor blockade disrupts this feedback system, leading to ventricular sympathetic axon proliferation and increased neuroeffector gain, which are likely to contribute to β-blocker withdrawal syndrome.

Enhanced neuropeptide Y immunoreactivity and vasoconstriction in mesenteric small arteries from the early non-obese diabetic mouse

The present study investigated whether sympathetic neurotransmission is altered at an early stage of diabetes in mesenteric small arteries isolated from female non-obese diabetic (NOD) and control animals without diabetes from the same mouse strain. The NOD diabetic mice had increased plasma glucose and hypertension. Confocal microscopy showed distribution of nerve terminals was similar, but immunoreaction intensity for neuropeptide Y (NPY) and tyrosine hydroxylase was higher in small arteries from NOD diabetic compared with NOD control mice. In the presence of prazosin and activated with vasopressin, electrical field stimulation evoked contractions which were more pronounced in mesenteric arteries from NOD diabetic versus NOD control mice and inhibited by the NPY Y(1) receptor antagonist, BIBP 3226. NPY concentration-response curves were leftward shifted in arteries from NOD diabetic versus NOD control both in arteries with and without endothelium, but not in the presence of the BIBP 3226. The present findings suggest that enhanced NPY content and vasoconstriction to NPY by activation of NPY Y(1) receptors in arteries from diabetic mice may contribute to the enhanced sympathetic nerve activity and vascular resistance in female non-obese early diabetic animals.

Structural and neurochemical features of postganglionic sympathetic neurons in the superior mesenteric ganglion of spontaneously hypertensive rats

Postganglionic sympathetic neurons, which are exquisitely sensitive to small changes in levels of target-derived nerve growth factor (NGF), express two transmembrane receptors: 1) the trkA receptor mediates neuron survival and neurite outgrowth; and 2) the p75 neurotrophin receptor (p75NTR) enhances neuronal responsiveness of trkA to NGF. Elevating levels of NGF induces several morphological and neurochemical alterations in sympathetic neurons, including axonal sprouting, increased levels of p75NTR mRNA relative to trkA mRNA, and increased accumulations of NGF in hypertrophied somata. Spontaneously hypertensive rats (SHR) display both elevated NGF levels and increased sympathetic axonal innervation of the mesenteric vasculature. In this investigation we assessed whether sympathetic neurons innervating the mesenteric vasculature of SHR display other features indicative of increased levels of target-derived NGF. In 5-week-old SHR, levels of both p75NTR and trkA mRNA in mesenteric sympathetic neurons were significantly elevated compared to levels in age-matched control rats. By 15 and 30 weeks of age, levels of p75NTR mRNA expression in mesenteric sympathetic neurons were similar between SHR and control rats. Accumulations of NGF were depleted in the sympathetic somata of 15- and 30-week-old SHR compared to age-matched control rats. Moreover, sympathetic neurons in SHR were not hypertrophied, as the sizes of somata were comparable between SHR and control rats. Our data illustrate that despite having augmented levels of NGF in the mesenteric vasculature, SHR do not display many of the morphological and neurochemical features that are associated with an enhanced responsiveness by sympathetic neurons to elevated levels of target-derived NGF.

Enhanced neuropeptide Y immunoreactivity and vasoconstriction in mesenteric small arteries from spontaneously hypertensive rats

Enhanced sympathetic nerve activity is thought to play a role in the pathogenesis of hypertension. The purpose of the present study was to investigate the mechanisms underlying the enhanced vasocontractile response to perivascular stimulation of mesenteric arteries isolated from female spontaneously hypertensive rats (SHR). Innervation of mesenteric small arteries was evaluated by immunohistochemistry and confocal microscopy while functional studies were conducted in a microvascular myograph. The distribution of nerve terminals immunoreactive for tyrosine hydroxylase (TH) and neuropeptide Y (NPY) was similar in mesenteric small arteries from Wistar-Kyoto (WKY) and SHR rats. However, immunointensity of TH or NPY immunoreactivities were much higher in small arteries from SHR compared to WKY. Expressed as percentage of contractions elicited by 124 mM K(+), concentration-response curves for noradrenaline (NA) and NPY were shifted leftward in SHR compared with WKY rats. The combination of noradrenaline (1 microM) and NPY (10 nM) contracted mesenteric arteries from WKY and SHR to higher levels than compared to either contractile agent added alone. The NPY Y(1) receptor antagonist, BIBP 3226, inhibited these contractions with 87 +/- 0.7 and 80 +/- 1.3% (p < 0.05, n = 6) in arteries from WKY and SHR rats, respectively. In arteries incubated with the alpha(1)-adrenoceptor antagonist, prazosin, and preactivated with vasopressin, electrical field stimulation evoked contractions which were more pronounced in mesenteric arteries from SHR compared to WKY rats. BIBP 3226 partially inhibited these contractions. In vasopressin-activated arteries BIBP 3226 caused rightward shifts of the concentration-response curves for NPY in mesenteric arteries from SHR rats, but in addition it also abolished the maximal NPY contraction in arteries from WKY rats. In the presence of BIBP 3226, low concentrations (1 pM to 10 nM) of NPY caused relaxations in arteries from WKY, but not in segments from SHR rats. Mechanical removal of the endothelium abolished NPY relaxation in arteries from WKY. In arteries activated with vasopressin and exposed to either forskolin or sodium nitroprusside, the addition of NPY evoked contractions which were more pronounced in arteries from SHR compared to WKY arteries. The present study suggests that enhanced NPY content and vasoconstriction to NPY in arteries from hypertensive rats can contribute to the enhanced sympathetic nerve activity and vascular resistance in female hypertensive rats. Endothelial cell dysfunction as well as alterations in smooth muscle response to NPY seem to contribute to the enhanced vasoconstriction in arteries from hypertensive animals.

Ontogenetic aspects of hypertension development: analysis in the rat

In this review, we attempt to outline the age-dependent interactions of principal systems controlling the structure and function of the cardiovascular system in immature rats developing hypertension. We focus our attention on the cardiovascular effects of various pharmacological, nutritional, and behavioral interventions applied at different stages of ontogeny. Several distinct critical periods (developmental windows), in which particular stimuli affect the further development of the cardiovascular phenotype, are specified in the rat. It is evident that short-term transient treatment of genetically hypertensive rats with certain antihypertensive drugs in prepuberty and puberty (at the age of 4-10 wk) has long-term beneficial effects on further development of their cardiovascular apparatus. This juvenile critical period coincides with the period of high susceptibility to the hypertensive effects of increased salt intake. If the hypertensive process develops after this critical period (due to early antihypertensive treatment or late administration of certain hypertensive stimuli, e.g., high salt intake), blood pressure elevation, cardiovascular hypertrophy, connective tissue accumulation, and end-organ damage are considerably attenuated compared with rats developing hypertension during the juvenile critical period. As far as the role of various electrolytes in blood pressure modulation is concerned, prohypertensive effects of dietary Na+ and antihypertensive effects of dietary Ca2+ are enhanced in immature animals, whereas vascular protective and antihypertensive effects of dietary K+ are almost independent of age. At a given level of dietary electrolyte intake, the balance between dietary carbohydrate and fat intake can modify blood pressure even in rats with established hypertension, but dietary protein intake affects the blood pressure development in immature animals only. Dietary protein restriction during gestation, as well as altered mother-offspring interactions in the suckling period, might have important long-term hypertensive consequences. The critical periods (developmental windows) should be respected in the future pharmacological or gene therapy of human hypertension.

Augmented sensory-motor vasodilatation of the rat mesenteric arterial bed after chronic infusion of the P1-purinoceptor antagonist, DPSPX

1. The effect of long-term antagonism of P1-purinoceptors on vascular function was examined in the perfused mesenteric arterial bed isolated from rats which had received constant infusion of either the non-selective P1-purinoceptor antagonist, 1-3-dipropyl-8-sulphophenylxanthine (DPSPX, 30 micrograms kg-1 h-1, i.p.) or saline for seven days. Sympathetic and sensory-motor neurotransmission, smooth muscle and endothelial function were assessed. 2. Basal tone was similar in mesenteric arterial preparations from control and DPSPX-treated rats. Continuous perfusion with methoxamine (7-70 microM) induced similar increases in tone in control and DPSPX-treated preparations. In the presence of guanethidine (5 microM), electrical field stimulation (EFS; 1-12 Hz, 60V, 0.1 ms, 30 s) elicited frequency-dependent vasodilatation due to activation of sensory-motor nerves. In tissues from DPSPX-treated rats the nerve-mediated vasodilator responses were markedly augmented at all frequencies. Maximal relaxation at 8 Hz was 38.34 +/- 4.76% (n = 5) in controls and 65.92 +/- 3.68% (n = 5) after DPSPX-treatment (P < 0.01). Adenosine (3 microM) inhibited the frequency-dependent sensory-motor neurotransmission similar in preparations from controls and DPSPX-treated rats. 3. In raised-tone preparations calcitonin gene-related peptide (CGRP; 5,15 and 50 pmol), the principal vasodilator transmitter of sensory-motor nerves in rat mesenteric arteries, produced similar relaxations in control and DPSPX-treated preparations. Vasodilator responses to the sensory neurotoxin capsaicin (50 and 500 pmol) were also similar between the groups. 4. Assay of tissue CGRP levels of the superior mesenteric artery by enzyme-linked immunosorbent assay showed no significant difference in tissue levels of CGRP in controls, 120.25 +/- 26.34 pmol g-1 tissue (n = 6) and with DPSPX-treatment, 82.12 +/- 24.42 pmol g-1 tissue (n = 6). 5. In raised-tone preparations dose-dependent endothelium-dependent vasodilatation to acetylcholine and ATP, and endothelium-independent vasodilatation to sodium nitroprusside were similar in control and DPSPX-treated preparations. 6. EFS (4-32 Hz, 90V, 1 ms, 30 s) elicited frequency-dependent vasoconstriction due to activation of sympathetic nerves which was similar in controls and in DPSPX-treated preparations. Adenosine (10 and 30 microM) inhibited sympathetic neurotransmission similarly in control and DPSPX-treated preparations. Dose-dependent vasoconstriction to noradrenaline (NA) and ATP, and to KCI (0.15 mmol) was similar between the groups. 7. High performance liquid chromatographic analysis of tissue NA showed no significant difference in NA content of the superior mesenteric artery from DPSPX-treated (1.38 +/- 0.09 ng mg-1, n = 6) and control rats (1.46 +/- 0.17 ng mg-1, n = 6). 8. In conclusion, in rats with hypertension due to 7 days treatment with the P1-purinoceptor antagonist, DPSPX, there is an increase in sensory-motor vasodilatation of the mesenteric arterial bed. There is no change in sympathetic nerve, endothelial or smooth muscle function. Augmented sensory-motor neurotransmission, which does not involve a change in postjunctional responsiveness to CGRP or in the CGRP content of sensory-motor nerves, could be a compensatory change in response to the DPSPX- induced hypertension.

Severe cardiovascular disease and Alzheimer's disease: senile plaque formation in cortical areas

The main objectives of this study were to analyze the distribution of senile plaques (SP) and neurofibrillary tangles (NFT) in different cortical areas of patients suffering from severe cardiovascular diseases (CVD) and to compare them with Alzheimer's disease (AD) cases. Forty brains were divided into three groups: an AD group (n = 12), a CVD group (n = 17), and a nonheart disease control group (n = 11). The cortical areas examined were the middle frontal gyrus, the superior and inferior watershed areas, the hippocampal formation with the transentorhinal cortex, and the primary visual cortex. SP and NFT were counted in Bielschowsky-stained sections from all cortical areas and from the hippocampal formation and the transentorhinal cortex, respectively. Patients with severe CVD occupied an intermediate position in the spectrum of SP formation between AD and nonheart disease patients. The CVD group showed a higher prevalence of SP than the control group, and SP counts were significantly larger in the inferior watershed area, dentate gyrus, subiculum, and transentorhinal cortex. The distribution of SP was similar in CVD and AD patients. Control and CVD patients showed no difference regarding the number of NFT. The existence of a possible cardiovascular component in the genesis of SP is discussed.

Enhanced vascular neuropeptide Y-immunoreactive innervation in two hypertensive rat strains

Considerable evidence indicates an enhanced sympathetic innervation of resistance arterial smooth muscle in the spontaneously hypertensive rat (SHR) compared with its normotensive Wistar-Kyoto (WKY) control. In addition to sympathetic hyperinnervation, an increased vascular innervation by neuropeptide Y-containing fibers, which are known to exert a vasoconstrictive and trophic action in vascular smooth muscle, has also been described. In addition to genetic hypertension, the SHR expresses hyperactive behavior and hyperreactivity to stress. To determine whether the enhanced neuropeptide Y-immunoreactive vascular innervation is specifically associated with hypertension and/or these behavioral abnormalities, four genetically related, inbred rat strains were used: SHR, which are hypertensive and hyperactive; WKY rats, which are neither hypertensive nor hyperactive; WKHA, which are hyperactive but normotensive; and WKHT, which are hypertensive but not hyperactive. The present study demonstrated that whereas the hypertensive strains (SHR and WKHT) exhibited smooth muscle hypertrophy in both superior mesenteric and caudal arteries in adulthood (10 months) but not at a prehypertensive age (1 month), both arteries exhibited significantly increased neuropeptide Y-immunoreactive innervation at both ages. It was further observed that the mesenteric artery in WKHA, a normotensive strain, had significant smooth muscle hypertrophy at 10 months; however, neuropeptide Y innervation in this artery was no different from that of WKY controls. The findings indicate that there is a cosegregation of neuropeptide Y hyperinnervation of the vasculature with the hypertensive phenotype, evident as early as 1 month of life in the hypertensive strains, and this should be considered further as a contributory factor in genetic hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced excitatory junction potentials in mesenteric arteries from spontaneously hypertensive rats

Excitatory junction potentials (EJPs) were examined using intracellular recording techniques in mesenteric arteries isolated from 12- to 15-week-old spontaneously hypertensive (SHR), Wistar Kyoto (WKY) and Sprague Dawley (SD) rats. The amplitudes of EJPs evoked by single supramaximal stimuli were larger in arteries from SHRs (12.9 +/- 0.7 mV, n = 16) than in arteries from either WKYs (5.2 +/- 0.5 mV, n = 24) or SDs (8.6 +/- 0.8 mV, n = 15). The time constant of decay of EJPs did not differ significantly, suggesting that the passive electrical properties of the vascular smooth muscle are similar in the three rat strains. Spontaneous EJPs recorded in tissues from SHRs and WKYs had similar amplitude frequency distributions, suggesting that the quantal size is also similar between strains. In some arteries from SHRs, EJPs evoked by single stimuli triggered muscle action potentials (MAPs). Visible constriction only occurred following a MAP. In tissues from all three strains, summation of EJPs triggered MAPs. As EJPs are generated by the sympathetic co-transmitter adenosine 5'-triphosphate (ATP), the findings of the present study indicate that purinergic transmission is enhanced in mesenteric arteries from SHRs, probably as a result of an increase in quantal release. A consequence is that when nerves are activated SHR arteries more readily undergo constriction that is dependent on voltage-activated Ca2+ influx.

Enhanced sympathetic neurotransmission in the tail artery of 1,3-dipropyl-8-sulphophenylxanthine (DPSPX)-treated rats

1. Sympathetic neurotransmission and noradrenaline content of the tail artery of Wistar rats treated for 7 days with the adenosine antagonist, 1,3-dipropyl-8-sulphophenylxanthine (DPSPX), were examined. 2. Systolic blood pressure of the DPSPX-treated rats (164.0 +/- 2.9 mmHg; n = 6) was significantly greater than saline-treated controls (140.0 +/- 2.8 mmHg; n = 5) after 7 days treatment. 3. The pressor responses of the arterial rings to transmural nerve stimulation (65 V, 0.1 ms, 4-64 Hz, for 1 s) were markedly enhanced in the DPSPX-treated compared with the saline-treated animals. Both noradrenergic and purinergic components of perivascular sympathetic neurotransmission were enhanced during DPSPX-induced hypertension. 4. Vasoconstrictor responses to exogenous noradrenaline (0.1-300 microM) and adenosine 5'-triphosphate (0.01-3 mM) were unaffected after DPSPX treatment, indicating prejunctional alteration of sympathetic cotransmission during DPSPX-induced hypertension. 5. Acute exposure to DPSPX (10 microM) did not modify vasoconstrictor responses to transmural nerve stimulation, thus supporting the claim that the enhancement of sympathetic neurotransmission only results from long-term DPSPX treatment. 6. The noradrenaline content of the tail arteries of DPSPX-treated (4.498 +/- 0.26 ng cm-1; n = 4) was significantly greater than saline-treated (3.440 +/- 0.30 ng cm-1; n = 5) animals. 7. These findings show that chronic inhibition of the actions of endogenous adenosine by DPSPX results in an elevation of systolic blood pressure accompanied by enhanced sympathetic cotransmission and enhanced noradrenaline content of the rat tail artery.

In vivo hypothalamic release and synthesis of catecholamines in spontaneously hypertensive rats

Juvenile spontaneously hypertensive rats (SHR) have higher plasma levels of catechols and markedly larger catechol responses to yohimbine than do normotensive Wistar-Kyoto rats, indicating increased sympathoadrenal outflow and increased alpha 2-adrenergic receptor-mediated restraint of peripheral catecholamine release during hypertension development in SHR. Yohimbine-induced catecholamine release and metabolism in the posterolateral hypothalamus of the brain were assessed in juvenile (6 to 7 weeks) and adult (15 to 16 weeks) SHR and Wistar-Kyoto rats. In vivo microdialysis was used to obtain samples for measurements of norepinephrine, dihydroxyphenylglycol, methoxyhydroxyphenylglycol, and dihydroxyphenylacetic acid in conscious animals before and after yohimbine injection (1 mg/kg IV) beginning 24 hours after probe implantation. Catecholamine synthesis was examined from elevations of 3,4-dihydroxyphenylalanine levels after probe perfusion with NSD-1015, an inhibitor of L-aromatic acid decarboxylase. In adults, SHR had higher dialysate norepinephrine (277 +/- 38 versus 181 +/- 35 pg/mL), dihydroxyphenylglycol (3260 +/- 509 versus 2231 +/- 201 pg/mL), methoxyhydroxyphenylglycol (2659 +/- 369 versus 1890 +/- 144 pg/mL), and dihydroxyphenylacetic acid (46,312 +/- 5512 versus 13,187 +/- 1963 pg/mL) levels and markedly larger increases in 3,4-dihydroxyphenylalanine levels after NSD-1015 than Wistar-Kyoto rats. In juveniles, SHR had larger proportionate increments in microdialysate norepinephrine levels after yohimbine than Wistar-Kyoto rats (85% versus 25%). Although juvenile SHR and Wistar-Kyoto rats had similar NSD-1015-elicited increments in 3,4-dihydroxyphenylalanine levels, systemic yohimbine enhanced the NSD-1015-elicited 3,4-dihydroxyphenylalanine elevations in juvenile SHR but not in Wistar-Kyoto rats. These findings suggest augmented norepinephrine release and catecholamine synthesis in the posterolateral hypothalamus of adult SHR and augmented alpha 2-adrenergic receptor restraint of both norepinephrine release and catecholamine synthesis in juvenile SHR.

Elevated concentrations of nerve growth factor in heart and mesenteric arteries of spontaneously hypertensive rats

Considerable evidence indicates an enhanced sympathetic innervation of muscular resistance arteries in the spontaneously hypertensive rat (SHR) compared with its normotensive Wistar-Kyoto (WKY) control. Since nerve growth factor (NGF) is known to affect the growth of sympathetic nerves, we have utilized a sensitive two-site enzyme linked immunoassay for NGF to compare the NGF content of hearts and mesenteric arteries of developing SHR and WKY rats. NGF levels in hearts revealed similar, although not identical, patterns of expression. In both strains, NGF levels declined from postnatal day 15, the earliest age examined, to stabilize at adult levels by postnatal day 32. Adult SHR concentrations were similar to those in age matched WKY controls. In contrast, in the mesenteric vascular bed, NGF levels of SHR were greater than those of WKY controls at all ages above 15 days. Moreover, these changes in NGF occurred concomitantly with increases in vascular mass and medial smooth muscle hyperplasia in the SHR. Whether abnormal NGF levels are a cause or consequence of vascular smooth muscle growth has yet to be determined. These results are consistent with the hypothesis that the hyper-noradrenergic innervation of SHR vascular tissues results from an early elevation of NGF gene expression.

Postnatal development of the rat portal vein: correlation with occurrence of peptidergic innervation

The portal vein of the rat is immature at birth, and is composed of an endothelium surrounded by undifferentiated cells of mesenchymal origin. Three days after birth, these cells have begun to differentiate and aggregate around the lumen to form two separate layers of perpendicularly oriented myoblasts, while a rich calcitonin gene-related peptide (CGRP) innervation is present around the vessel. In the internal circular muscle layer of the media myofibrils first develop on the endothelial side of the myoblasts, and then progressively reach the other side. In the longitudinal muscular layer of the media, which is separated from the circular layer by a connective lamina as early as 3 days after birth, myofibrils develop randomly in the cells. At the time of the enlargement of the longitudinal layer, long close contacts and intermediate junctions between external myoblasts and adventitial fibroblast-like cells were noted, suggesting that recruitment of this cell type is necessary for the maturation of the vessel wall. At about 28 days, the vein has reached its final structure and the smooth muscle cells are fully differentiated. The dense CGRP perivascular innervation already present at birth persists for the first 14 days of postnatal life when most of the cells have not yet acquired their complete contractile differentiation and are still capable of division. This innervation decreases transiently between 15-17 days, when the vessel acquires its spontaneous contractile activity, then rises to a peak between 20 and 25 days, and falls again. CGRP innervation, which is very scarce at 28 days, slowly increases during the peripubescent stage, by which time the adult structure of the vessel is established. Similar fluctuations in the density of peptidergic innervation were observed for substance P and neuropeptide Y, although these peptides were not yet present at birth and occurred only after 5 days. Vasoactive intestinal polypeptide- and bombesin-immunoreactive fibres were not found at any stage investigated. In addition to a description of the different cell-to-cell contacts which could play a role in the maturation of the vessel wall, we discuss the possible implication of the different peptides in the differentiation, maturation or maintenance of the vessel wall.

Pharmacology of smooth muscle cell replication

The suggestion that smooth muscle cell proliferation contributes to hypertension, atherosclerosis, and restenosis after angioplasty has led to a growing interest in the use of drugs to inhibit this process. This review summarizes pharmacological studies of smooth muscle cell proliferation in vitro and in vivo and identifies specific mediators of proliferation that are implicated by drugs binding with high affinity to enzymes or receptors.

Increased density of fluorescent adrenergic fibers around the middle cerebral arteries of stroke-prone spontaneously hypertensive rats

The distribution of fluorescent adrenergic nerve fibers in the proximal portion (horizontal segment, Hs) and the three distal portions (major branches) of the middle cerebral arteries (MCA) was examined in stroke-prone spontaneously hypertensive rats (SHRSP) aged 10, 30, 60, 90, and 180 days, by the glyoxylic acid method. The results were compared with those in age-matched normotensive Wistar Kyoto (WKY) rats. While the distribution pattern of fluorescent nerve fibers in the proximal portion of WKY rats changed from a straight linear arrangement at 10 and 30 days of age to a network-like arrangement after 60 days, those from SHRSP showed a constant meshwork pattern throughout the entire examination period. In the distal portions of the MCA of both SHRSP and WKY rats at all ages examined, fluorescent nerve fibers formed a coarse network. The distribution densities of adrenergic nerve fibers in the proximal and distal portions of the MCA of SHRSP were significantly higher (P less than 0.01 and 0.05) than those of WKY rats at all ages examined, except in the proximal portion at 90 and 180 days of age. The difference in nerve fiber density between SHRSP and WKY rats reached a peak at 30 days of age in both proximal and distal portions, and then gradually decreased with age. The present study suggests that sympathetic hyperinnervation is an important factor in the development of hypertension, and is involved in its maintenance in SHRSP.

The microvasculature in skeletal muscle. VI. Adrenergic innervation of arterioles in normotensive and spontaneously hypertensive rats

A microanatomical study of the adrenergic nerve plexus on the arterioles in the spinotrapezius muscle of normotensive and spontaneously hypertensive rats was carried out. The spinotrapezius muscle was selected since its microvasculature has been reconstructed in previous studies of this series. A modified glyoxylic acid amine densification technique was used to visualize the major portion of the microvascular nerve plexus. The nerve plexus density was quantified in the form of fiber length per unit area of vascular smooth muscle media. The adrenergic innervation was found to be limited to the arterial/arteriolar side of the microcirculation and positioned in close vicinity to vascular smooth muscle, in line with previous reports. Substantial variations of the nerve plexus density could be detected along the arterioles. Arcade arterioles show a significant reduction of the adrenergic innervation compared to that of the thoracodorsal supply artery. There was a significant elevation of the nerve plexus density at the origin of the transverse arterioles at the arcade arterioles, a site that in the past has been shown to exhibit the highest microvascular tonus in all arterioles of this organ. Distal to this site, transverse arterioles exhibit a progressive reduction of adrenergic plexus density toward their capillary endings, in line with the termination of vascular smooth muscle in these small branches. Sporadic fiber extensions were encountered leading from some of the transverse arterioles into the capillary network per se, but no regular innervation was detected in capillaries or in venules. These results suggest that the transverse arterioles may play a central role in nervous control of blood flow to the capillaries of muscle. Compared with the Wistar and Wistar-Kyoto strain, the spontaneously hypertensive rats exhibit qualitatively a similar pattern, but show quantitatively a significantly higher plexus density in the thoracodorsal artery and the arcade arterioles, a factor that may contribute to the elevated arteriolar tone.

Effect of α1-adrenoceptor blockade on the development of hypertension in the spontaneously hypertensive rat

There is a large body of evidence to suggest that the sympathetic nervous system plays a critical role in the development of hypertension and vascular medial hypertrophy in the spontaneously hypertensive rat (SHR). The synthesis of a water soluble, specific alpha 1-adrenoceptor antagonist (terazosin) has permitted an examination of the influence of alpha 1-adrenoceptors on those two phenomena. Thus, in the present study, terazosin (43 mg/kg per day) was administered to SHR and Wistar-Kyoto (WKY) rats from 4.5 to 12 weeks of age, and a number of assessments made in vitro and in vivo. In the SHR, the development of hypertension was not prevented by terazosin. The drug did not influence blood pressure in the WKY. This was despite the fact that animals which had been chronically treated with terazosin displayed marked alpha-adrenoceptor blockade in vivo. The response of systolic blood pressure to tyramine and noradrenaline was significantly reduced in animals which had been chronically treated with terazosin. In both the SHR and WKY, chronic administration of terazosin did not influence vascular concentrations of 3-methylhistidine, a biochemical marker for contractile proteins and vascular medial hypertrophy. The results therefore argue against a role of alpha 1-adrenoceptors in the development of hypertension and vascular medial hypertrophy in the SHR.

Arterial neuroeffector responses in early and mature spontaneously hypertensive rats

Intramural sympathetic neuroeffector responses and presynaptic regulation of neurotransmission by amine uptake and alpha 2-adrenergic receptors were examined in young (5-week-old) and mature (12-week-old) spontaneously hypertensive rats (SHR) and were compared with those of age-matched Wistar-Kyoto (WKY) control rats. Electrical field stimulation (20 V, 0.2-msec pulse width, 3-second pulse train each minute, 5-100 Hz) elicited contractile responses from isolated mesenteric arteries mounted in a myograph. There was a significant difference between the sensitivity of arteries to electrical field stimulation in the two age groups, with arteries from 12-week-old rats being more sensitive than arteries from 5-week-old animals. Also, there was a significant age-strain interaction: the sensitivity of arteries from SHR to electrical field stimulation increased dramatically with age compared with that of WKY rat arteries. Cocaine significantly increased the sensitivity to electrical field stimulation after inhibition of presynaptic alpha 2-adrenergic receptors, and had a significantly greater effect in arteries from 5-week-old SHR compared with WKY controls. This would reflect an overactive neuronal amine uptake mechanism in young SHR. At 12 weeks there was no significant interstrain difference in the effect of cocaine. Yohimbine increased the sensitivity to electrical field stimulation both before and after inhibition of neuronal amine uptake, but there was no difference in its effect with age or strain. Therefore, although sensitivity to sympathetic nerve stimulation varies with age in the SHR, there is no evidence that this can be ascribed to alpha 2-adrenergic receptor function.

Chronic nerve growth factor treatment of normotensive rats

The objectives of this study were to examine the effects of chronic nerve growth factor (NGF) administration on vascular innervation and blood pressure in neonatal rats. Newborn Wistar-Kyoto (WKY) rats bred from normotensive parents were chronically treated with NGF for 8 weeks. Littermate controls received saline. Sympathetic ganglia of treated animals were greatly enlarged and in the superior cervical ganglion neuronal numbers were increased 200% and nuclear areas by 46%. The catecholamine contents of several sympathetically innervated tissues were determined biochemically and found to be significantly elevated in mesenteric arteries, aorta, ileum, adrenal and salivary glands from treated compared to control animals. The catecholamine concentrations were similar to, or exceeded those of the spontaneously hypertensive rat. Histochemically, an aberrant nerve supply was evident occupying a greater volume of the adventitia of the caudal artery and mesenteric arteries. In addition, nerve fibres could be seen penetrating the vessel wall to emerge within the lumen of mesenteric blood vessels. Analysis of the smooth muscle wall of the caudal artery revealed that a small but significantly hyperplastic response had been induced. Systolic blood pressures of NGF-treated and control animals were taken at one week intervals from 5 to 8 weeks of age utilizing the tail cuff method. The blood pressure of treated animals were within the normotensive range. It is concluded that chronic NGF treatment leads to changes in vascular innervation and muscle thickness that are similar to those seen in hypertensive animals. Furthermore, the results suggest the elevated levels of NGF seen in peripheral tissues of the spontaneously hypertensive rat are likely to be responsible for the hyperinnervation and resulting hyperplastic responses within vascular tissues, but not exclusively responsible for the elevated blood pressure.

Relationship between the sympathetic nervous system and vascular smooth muscle: a morphometric study of adult and juvenile spontaneously hypertensive rat/Wistar-Kyoto rat caudal artery

The relationship between the sympathetic nervous system and vascular smooth muscle has been assessed in adult and juvenile spontaneously hypertensive rats (SHR) and compared with age-matched Wistar-Kyoto rats (WKY) using ultrastructural and light microscopic morphometric analysis of the caudal artery. The absolute volume of smooth muscle in the caudal artery of adult SHR (14-19) months was 169% greater than that in WKY vessels. As well, the axonal volume was 89% greater than that in the WKY. There was also a 51% increase in the number of vesicles per volume of varicosity in SHR compared to WKY. At 3 weeks of age the volume of both smooth muscle and axons within the caudal artery of SHR and WKY was not significantly different. However, there was a significantly greater number of vesicles (25%) per unit volume of varicosity in the SHR compared to the WKY. Thus, in the caudal artery there appears to be a relationship between smooth muscle cell volume and axonal volume. An increase in arterial smooth muscle volume (whether it be due to growth or hypertrophy) is accompanied by an increase in axonal volume, or vice versa. The significant increase in the number of vesicles per unit volume of varicosity in the SHR, compared to the WKY reported here, is consistent with other published data indicating an increased availability or turnover of transmitter in these animals. Since the blood pressures of the SHR and WKY are similar at 3 weeks, the apparent increase in sympathetic nerve activity observed suggests that this may be an initiating factor in the development of high blood pressure in SHR.

Neuropeptide Y in rat sympathetic neurons is altered by genetic hypertension and by age

We have used immunocytochemistry to quantitate neuronal neuropeptide Y in superior cervical ganglia of a strain of normotensive Wistar-Otago rats and a related genetically hypertensive strain over the age range 1-60 weeks. The numbers of neuropeptide Y-immunoreactive cells and total ganglionic cell numbers were both greater in ganglia of young normotensive than in those of hypertensive rats. Between 10 and 60 weeks of age, peptide immunoreactivity and total cell numbers both fell in normotensive rat ganglia but remained constant in ganglia from hypertensive rats. Densitometric analysis showed that the concentrations of neuropeptide Y were similar in neurons of age-matched individuals of both strains, but during aging there was a substantial decline in neuronal peptide content that was similar in both strains and that was not accompanied by any decline in neuronal immunoreactivity for tyrosine hydroxylase. Our results suggest that there is a developmental abnormality of neuropeptide Y in sympathetic neurons of this strain of genetically hypertensive rat and that, furthermore, the aging process is accompanied by a selective loss of neuronal neuropeptide Y that is independent of blood pressure status.

Analysis of cerebrovascular sympathetic nerve density in relation to stroke development in spontaneously hypertensive rats

Previous studies have shown that elevating the K+ levels from 0.75% to 2.11% in the diet of stroke-prone spontaneously hypertensive rats significantly retards the development of stroke and increases their lifespan. On the other hand, stroke-resistant spontaneously hypertensive rats fail to develop stroke even if they are fed the low-K+ version of this diet. Since sympathetic nerves surrounding the cerebral vasculature play an important role in protecting the brain from stroke during hypertension, I studied whether changes in sympathetic nerve density accounted for the differing incidences of stroke in stroke-prone spontaneously hypertensive rats fed high- and low-K+ diets and in stroke-resistant and stroke-prone spontaneously hypertensive rats fed a low-K+ diet. At 14 weeks of age, all 11 stroke-prone rats fed the low-K+ diet had evidence of cerebral hemorrhage while such lesions were virtually absent in the 11 littermates fed the high-K+ diet and totally absent in the eight stroke-resistant rats fed the low-K+ diet. Stroke-prone (regardless of diet) but not stroke-resistant rats exhibited greater sympathetic nerve densities in the left hemisphere than in the right. When stroke-prone rats were compared, in some areas of the cerebrovasculature, rats fed the high-K+ diet had greater mean sympathetic nerve densities than those fed the low-K+ diet. On the other hand, stroke-resistant and stroke-prone rats fed the low-K+ diet exhibited comparable sympathetic nerve densities in most cerebral arteries studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Perivascular innervation of the mesenteric artery in spontaneously hypertensive rats

Perivascular innervation of the mesenteric arteries of 7-week-old and 6-month-old spontaneously hypertensive rats and normotensive Wistar-Kyoto rats was examined. The densities of neuropeptide Y-containing nerve fibers and adrenergic nerve fibers were increased in the distal regions of mesenteric arteries of spontaneously hypertensive rats as compared with findings in Wistar-Kyoto rats. However, the densities of cholinergic nerve fibers, vasoactive intestinal polypeptide-containing, and substance P-containing nerve fibers in the mesenteric arteries of the spontaneously hypertensive rats were unchanged in comparison with findings in the Wistar-Kyoto rats. Thus, not only adrenergic nerve fibers but also neuropeptide Y-containing nerve fibers may play an important role in the development and maintenance of hypertension in spontaneously hypertensive rats.

Morphometric study of the superior cervical and stellate ganglia of spontaneously hypertensive rats during the prehypertensive stage

To compare the functional state of the superior cervical (SCG) and stellate sympathetic ganglia (SG) of spontaneously hypertensive rats (SHR) with those of age-matched normotensive Wistar Kyoto rats (WKY), ganglion cell volume and area occupied by ganglion cells relative to each whole ganglionic area were morphometrically examined using the Texture Analyse System (TAS) in rats at 0, 10 and 30 days of age. The weight of each ganglion relative to animal weight was also measured. The ganglion cell volume and the relative area of ganglionic cells in both ganglia of SHR were significantly larger (P less than 0.05) than those of age-matched WKY at ages 0 and 10 days after birth. The relative ganglionic weights of SHR were significantly larger (P less than 0.01) compared with those of WKY at all ages examined, except for SG at 0 days after birth. These results show that the relative volume of sympathetic ganglion cells is greater in both SCG and SG of SHR than that of WKY, suggesting that hyperfunction of sympathetic ganglia occurs at the prehypertensive stage as a primary factor in the development of hypertension in SHR.

Increased density of perivascular adrenergic innervation in tibial and vagus nerves of spontaneously hypertensive rats

Adrenergic innervation of epiperineurial arterioles and of the endoneurium of the tibial and vagus nerves of spontaneously hypertensive rats (SHR) and normotensive controls (WKY) was studied by glyoxylic acid-induced fluorescence and paraformaldehyde-induced fluorescence methods. Adrenergic perivascular innervation of epiperineurial arterioles in both nerves was denser in SHR than in controls. Mean density in the endoneurium also was higher in SHR in both nerve types. These results suggest that adrenergic perivascular innervation, which may influence nerve blood flow, becomes greater in density in peripheral nerves during chronic hypertension.

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.

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.

Image analysis of the sympathetic innervation of the myenteric plexus in the small intestine of mammalian species

1. The arrangement of the sympathetic innervation of the myenteric plexus varies between mammalian species. 2. In larger mammals the density of sympathetic innervation of the myenteric plexus is significantly less than in small (less then 1 kg) species. 3. The number of varicosities on the terminal parts of sympathetic neurons innervating the gut is significantly less in larger mammals.

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.

Increased density of perivascular nerves to the major cerebral vessels of the spontaneously hypertensive rat: differential changes in noradrenaline and neuropeptide Y during development

Fluorescence and immunohistochemical techniques were used to study the pattern and density of perivascular nerves containing noradrenaline (NA) and neuropeptide Y (NPY) supplying the major cerebral arteries of 4-, 6-, 8- and 12-week-old spontaneously hypertensive rats (SHR) and normotensive Wistar (WIS) controls. Levels of NA and NPY in the superior cervical ganglia were measured. The density of nerves containing NA and NPY was greater in the hypertensive animals at all ages studied. However, the developmental changes in the density of innervation showed similar trends in both SHR and WIS groups. With few exceptions, there was a significant increase in the density of nerves containing NA from 4 to 6 weeks and from 8 to 12 weeks of age. This was in contrast to a low expression, and in some vessels a significant decrease in the number of NPY-containing nerves from 4 to 6 weeks. The density of nerve fibres containing NPY increased significantly in almost all vessels between 6 and 8 weeks of age and then stabilized. Thus there is a differential time course for the appearance of NA and NPY during development. Furthermore, the hyperinnervation of cerebral vessels in SHR by nerves containing NA and NPY precedes the onset of hypertension and associated medial hypertrophy. High-performance liquid chromatography and enzyme-linked immunosorbant assays show that the NA and NPY contents of the superior cervical ganglion do not reflect the changes in innervation pattern seen in the terminal fibres in the cerebral arteries. This tends to support the view that a local neurovascular mechanism is involved in the maintenance of hypertension. The possibility that increase in NPY as well as NA in cerebral perivascular nerves of hypertensive animals is involved in the protection of the blood-brain barrier against oedema and cerebral haemorrhage is raised.

Vascular innervation in human skeletal muscle with and without neuromuscular disease. A quantitative ultrastructural study with references to the effects of age and different blood pressure

A quantitative ultrastructural study has been made of the innervation of 461 arterioles in 114 skeletal muscle biopsies of patients with or without neuromuscular disease excluding diabetes and autonomic neuropathy. In 18 controls the number of nerves and Schwann cells around each vessel was related to the size of the vessel, whether the vessel was within a muscle fascicle or between muscle fascicles. The innervation of arterioles increased with increased diastolic blood pressure. There was no statistically significant change in innervation with increased systolic blood pressure or with age, from 4 to 85 years. In 96 cases of neuromuscular disease and especially in motor neurone disease, axonal varicosities in cross section tended to be larger, more often contained no vesicles or only a few and had altered satellite cell cover depending on the location of the arteriole. Whilst the numerical density of Schwann cells did not change with disease, fewer varicosities were identified within Schwann cells in motor neurone disease, metabolic myopathy and neuropathy and myopathy due to toxins or vascular disease. Preterminal axons in nerve fascicles adjacent to arterioles were lost in polymyositis and muscle disease due to toxins or vascular disease. In polymyositis, metabolic myopathy and motor neurone disease there was some evidence of compensatory nerve sprouting, either in the nerve fascicles or in the adventitia of the arterioles. These structural changes may be related to the changes in blood flow or vascular reactivity described by others in motor neurone disease, polymyositis and metabolic myopathy. It is concluded that the ultrastructure of the vascular innervation of human skeletal muscle is similar to that in other mammals and is changed more with increased diastolic blood pressure and neuromuscular disease than with age.

Autoradiographic study of 3H-DOPA uptake by superior cervical and stellate ganglia of spontaneously hypertensive rats during the prehypertensive stage

The functional state of sympathetic ganglia in spontaneously hypertensive rats (SHR) was compared with that of ganglia in normotensive Wistar Kyoto rats (WKY) by examining catecholamine synthetic activity by light microscopic autoradiography 3H-L-dihydroxyphenyl alanine (3H-DOPA). The number of silver grains over the perikarya of ganglion cells in the superior cervical (SCG) and stellate ganglia (SG) of newborn, 10-day-old and 30-day-old animals was counted on photographic enlargements. There were significantly more silver grains over ganglion cells in SHR compared with those in age-matched WKY at almost all incorporation times at all ages examined in SCG, at all incorporation times in newborn rats, and at incorporation times of 15 and 60 min in SG of 10-day-old rats. The increased incorporation of the label by both sympathetic ganglia was more marked in newborn than in 30-day-old animals. These results indicate that catecholamine synthetic activity in these ganglion cells is increased in SHR from the newborn stage, suggesting that a congenital hyperfunction of sympathetic ganglia occurs in SHR.

Structural and functional consequence of neonatal sympathectomy on the blood vessels of spontaneously hypertensive rats

Neonatal sympathectomy of spontaneously hypertensive rats (SHR) and control Wistar-Kyoto rats (WKY) was performed by a combined treatment with antiserum to nerve growth factor and guanethidine during the first 4 weeks after birth. The development of hypertension was completely prevented in the treated SHR: at 28 to 30 weeks of age, systolic blood pressure of treated SHR was 139 +/- 2 mm Hg as compared with 195 +/- 8 mm Hg in untreated SHR. The extent of sympathectomy was verified by histofluorescence. Fluorescence histochemistry for catecholamine-containing nerves showed a complete absence of adrenergic nerves in the mesenteric arteries of treated rats. A supersensitivity to norepinephrine was exhibited by mesenteric arteries, anococcygeus muscle, and tail arteries from the treated SHR and WKY. In the mesenteric vascular bed, maximal response to norepinephrine was significantly reduced by sympathectomy. Sympathectomy also abolished the responses (e.g., generation of excitatory junctional potentials) of tail arteries to electrical stimulation of perivascular nerves. Morphometric measurements of three categories of mesenteric arteries showed that sympathectomy had no effect on the hypertrophic change of smooth muscle cells in the conducting vessels, but it prevented the hyperplastic changes of the muscle cells from reactive, muscular arteries and small resistance vessels. These results suggest that one of the primary roles of the overactive sympathetic nervous system in the development of hypertension in SHR is manifested through its trophic effect on the arteries of SHR. This trophic effect appears to cause a hyperplastic change in the smooth muscle cells in the reactive and resistance vessels, thereby contributing to the development of hypertension in older SHR.

Autoradiographic study of 3H-lysine uptake by superior cervical and stellate ganglia in prehypertensive spontaneously hypertensive rats

In order to compare the functional state of sympathetic ganglia in spontaneously hypertensive (SHR) with those in normotensive Wistar Kyoto rats (WKY), protein synthetic activity was examined by light microscopic autoradiography with 3H-lysine. The number of silver grains over the cytoplasm of ganglion cells in the superior cervical and stellate ganglia of newborn and 30-day-old animals were counted on photographic enlargements. In both sympathetic ganglia there were significantly more silver grains over ganglion cells in SHR compared with age-matched WKY at 15, 60, and 120 min after injection of 3H-lysine. The increased incorporation of the label by both sympathetic ganglia was more marked in newborn than in 30-day-old animals. This result shows that protein synthetic activity in these ganglion cells is increased in SHR from the newborn stage. It is suggested that a congenital hyperfunction of sympathetic ganglia occurs in SHR.

Effect of chronic sympathetic denervation on cerebrovascular hypertrophy during the development of hypertension in rats

The present study was designed to examine the trophic effect of sympathetic nerves on cerebrovascular hypertrophy in developmental hypertension. Unilateral superior cervical ganglionectomy was performed in spontaneously hypertensive rats at 4 weeks of age, and wall-to-lumen ratios of cerebral arteries were determined at 5 weeks, 2 months or 5 months after denervation. To estimate the thickness of the vessel wall, a freeze substitution technique was used for the preparation of cerebral arteries. Basal mean arterial blood pressure measured through cannulated femoral artery was 127 +/- 2, 146 +/- 7 and 168 +/- 6 mm Hg (mean +/- S.E.M.) at 9 weeks, 3 months and 6 months of age, respectively. The wall-to-lumen ratios in the denervated and innervated hemispheres were 0.124 +/- 0.004 and 0.129 +/- 0.005 at 9 weeks, 0.127 +/- 0.003 and 0.169 +/- 0.004 (P less than 0.02 vs denervated) at 3 months, and 0.194 +/- 0.007 and 0.222 +/- 0.006 (P less than 0.05 vs denervated) at 6 months. The effect of denervation was more significant in downstream vessels (diameter less than or equal to 100 microns) than larger ones. We conclude that wall-to-lumen ratio is correlated well with a rise in basal blood pressure, and chronic interruption of the sympathetic nerves attenuates normal occurrence of vascular hypertrophy during the development of hypertension.

The adrenergic innervation of pulmonary vasculature in the normal and pulmonary hypertensive rat

It would appear that susceptibility to chronic proliferative pulmonary hypertension in response to chronic alveolar hypoxia is most severe in species in which adrenergic innervation of pulmonary arteries is reduced or lacking. Intrapulmonary arteries of the rat have been reported to lack adrenergic innervation by some workers but not others. Since the rat develops severe proliferative pulmonary hypertension in response to prolonged alveolar hypoxia, the different divisions of the lung vasculature of Sprague-Dawley rats were thoroughly examined to determine the presence or absence of an adrenergic innervation. The degree of innervation in normal rats was compared with that of rats developing pulmonary hypertension. Both in normal and experimental pulmonary hypertensive rats the pulmonary arteries, all their branches and the small pulmonary veins with a smooth muscle media were found to be devoid of adrenergic innervation. In contrast, the cardiac-like muscle in the media of large pulmonary veins, the bronchial arteries and the vasa vasorum of larger vessels were richly innervated by adrenergic nerves. Thus the increase in medial smooth muscle which occurs in pulmonary arteries during chronic alveolar hypoxia is independent of a pre-existing adrenergic innervation or of such an innervation newly derived from that of adjacent vessels or structures. This is in contrast to systemic vessels where it has been suggested that increased adrenergic activity and density of innervation may augment hypertrophy of the media in hypertensive animals. Adrenergic nerves are suggested to have a protective action on pulmonary vessels.

Upper limit of cerebral autoregulation during development of hypertension in spontaneously hypertensive rats--effect of sympathetic denervation

The upper limit of cerebral autoregulation was studied in pre- or early established hypertension in spontaneously hypertensive rats (SHR). Cerebral blood flow (CBF) was measured with the hydrogen clearance method, and wall/lumen ratio of cerebral arteries was morphometrically measured with the freeze-substitution technique. To test autoregulation, phenylephrine was intravenously infused to cause stepwise increments of blood pressure. Unilateral superior cervical ganglionectomy was carried out to examine the effects of sympathetic denervation on CBF autoregulation and thickness of vascular wall. Resting blood pressure at 4 weeks, 3 months and 6 months of age were 89 +/- 3 mm Hg (mean +/- SEM), 140 +/- 6 and 165 +/- 6, respectively. Baseline CBF was slightly diminished with age; 50.6 +/- 9.2 ml/100 g/min at 4 weeks, 49.8 +/- 8.1 at 3 months and 44.1 +/- 5.6 at 6 months. The upper limit of autoregulation was markedly raised with age; 118 +/- 5 mm Hg at 4 weeks, 180 +/- 7 at 3 months and 208 +/- 10 at 6 months. Acute sympathetic denervation lowered the upper limits to 105 +/- 2, 162 +/- 4 and 185 +/- 7 mm Hg, respectively. On the other hand, in chronic denervation which was made at 4 weeks of age, the upper limit of autoregulation in the denervated hemisphere was slightly lower than that in innervated hemisphere at 2 months (165 +/- 5 and 178 +/- 6 mm Hg), and at 5 months (202 +/- 8 and 215 +/- 8 mm Hg) after ganglionectomy.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chronic hypertension and sympathetic nerves on the cerebral microvasculature of stroke-prone spontaneously hypertensive rats

The purpose of this study was to examine hemodynamic mechanisms which protect cerebral vessels against chronic hypertension, and contribute to protective effects of sympathetic nerves in the cerebral circulation. We studied stroke-prone spontaneously hypertensive rats and normotensive Wistar-Kyoto rats. At 3-4 weeks of age, all rats underwent removal of one superior cervical sympathetic ganglion. Approximately 1 year later, we cut the superior cervical sympathetic nerve contralateral to the chronic ganglionectomy and exposed pial arterioles on the cerebral cortex ipsilateral or contralateral to the chronic ganglionectomy. We measured aortic, pial arteriolar, and venous pressures with a servo-null technique, and cerebral blood flow with microspheres. Large artery resistance and small vessel resistance were calculated. During control conditions, pressure in pial arterioles was higher in stroke-prone spontaneously hypertensive rats (83 +/- 6 mm Hg) (mean +/- SE) than in Wistar-Kyoto rats (60 +/- 3 mm Hg, P less than 0.05), even though large artery resistance was almost two-fold greater in stroke-prone spontaneously hypertensive rats than in Wistar-Kyoto rats (P less than 0.05). During maximal dilation produced by seizures, large artery resistance was almost three-fold higher in stroke-prone spontaneously hypertensive rats than in Wistar-Kyoto rats (P less than 0.05). Small vessel resistance also was increased in stroke-prone spontaneously hypertensive rats. During seizures in stroke-prone spontaneously hypertensive rats, large artery resistance was 29% lower in chronically denervated vessels than in acutely denervated vessels (P less than 0.05). Three stroke-prone spontaneously hypertensive rats had pial vessels with a "sausage string" appearance.(ABSTRACT TRUNCATED AT 250 WORDS)