Fluorescence microscopical studies on noradrenaline in the peripheral blood vessels of spontaneouly hypertensive rats

Hepatic expression of spermatogenic genes and their transiently remarkable downregulations in Wistar-Kyoto rats in response to lead-nitrate administration: strain-difference in the gene expression patterns

Administration of lead ion (Pb) to rats and mice affects hepatic functions such as the induction of hepatic cell proliferation and upregulation of cholesterol biosynthesis. To identify the genes for which expression changes in response to Pb-administration, we analyzed hepatic gene expression patterns in stroke-prone spontaneously hypertensive rat (SHRSP), its normotensive control, Wistar-Kyoto rat (WKY), and Spraque-Dawley (SD) rat strains, 3, 6, and 12 hr later after single i.v. injection of lead nitrate (LN) at a dose of 100 µmol using a DNA microarray technique. The data analysis demonstrated that the expression of a great number of genes was transiently and remarkably downregulated 3 hr after LN-injection, and then recovered to control levels only in LN-injected WKY. These normal hepatic expression levels in WKY and SHRSP were much higher than those in SD rats. Furthermore, most of these genes were ones thought to be expressed specifically in the spermatids and/or testes; i.e. genes encoding protamin 1, transition protein 1, and transition protein 2. These findings suggest that the regulation system common to expression of all of these genes could be a target site of Pb-toxic action, at least, in the liver of WKY, and that this system might be similar to the system essential for spermatogenesis, especially spermiogenesis, in the testis. In addition, it appears that clarifying the cause of the difference between the systems of WKY and SHRSP might aid in identifying the pathologic genes in SHRSP. Finally, it will be an important to clarify how the products of the genes related to spermatogenesis, including spermiogenesis, are functional in the livers of WKY and SHRSP.

No involvement of the nerve growth factor gene locus in hypertension in spontaneously hypertensive rats

Sympathetic hyper-innervation and increased levels of nerve growth factor (NGF), an essential neurotrophic factor for sympathetic neurons, have been observed in the vascular tissues of spontaneously hypertensive rats (SHRs). Such observations have suggested that the pathogenesis of hypertension might involve a qualitative or quantitative abnormality in the NGF protein, resulting from a significant mutation in the gene's promoter or coding region. In the present study, we analyzed the nucleotide sequences of the cis-element of the NGF gene in SHRs, stroke-prone SHRs (SHRSPs), and normotensive Wistar-Kyoto (WKY) rats. The present analyses revealed some differences in the 3-kb promoter region, coding exon, and 3' untranslated region (3'UTR) for the NGF gene among those strains. However, the observed differences did not lead to changes in promoter activity or to amino acid substitution; nor did they represent a link between the 3'UTR mutation of SHRSPs and elevated blood pressure in an F2 generation produced by crossbreeding SHRSPs with WKY rats. These results suggest that the NGF gene locus is not involved in hypertension in SHR/ SHRSP strains. The present study also revealed two differences between SHRs and WKY rats, as found in cultured vascular smooth muscle cells and in mRNA prepared from each strain. First, SHRs had higher expression levels of c-fos and c-jun genes, which encode the component of the AP-1 transcription factor that activates NGF gene transcription. Second, NGF mRNAs prepared from SHRs had a longer 3'UTR than those prepared from WKY rats. Although it remains to be determined whether these events play a role in the hypertension of SHR/SHRSP strains, the present results emphasize the importance of actively searching for aberrant trans-acting factor(s) leading to the enhanced expression of the NGF gene and NGF protein in SHR/SHRSP strains.

Persistent reduction in renal nerve growth factor mRNA after perindopril treatment of young spontaneously hypertensive rats

Nerve growth factor (NGF) determines sympathetic innervation of target tissues, and NGF levels are increased in young spontaneously hypertensive rats (SHR). Angiotensin can affect NGF levels, and the persistent reduction in blood pressure after brief angiotensin-converting enzyme inhibition in young SHR may involve long-term changes in NGF and sympathetic innervation. We measured the relative abundance of renal NGF mRNA by reverse transcription-polymerase chain reaction in SHR during and after treatment from 6 to 10 weeks of age with vehicle, perindopril (3 mg/kg per day), the bradykinin B2 antagonist Hoe 140 (0.5 mg/kg per day), both perindopril and Hoe 140, or angiotensin II (Ang II; 200 ng/kg per minute). Glomerular filtration rates were estimated at 10 and 20 weeks of age. At 10 weeks of age, Ang II caused a significant (P<.01) increase and perindopril caused a significant (P<.01) decrease in renal NGF mRNA levels. Blockade of the bradykinin B2 receptor during perindopril treatment attenuated (P<.05) the reduction in NGF mRNA levels. Renal NGF mRNA (P=.005) and blood pressure (P<.001) remained significantly lower than control 10 weeks after perindopril treatment was stopped. The partial reduction in blood pressure at 20 weeks of age in rats that had received perindopril and Hoe 140 was not associated with any difference in renal NGF mRNA. Perindopril-induced long-term reduction in renal NGF mRNA levels may decrease sympathetic innervation and thereby contribute to the long-term posttreatment blood pressure reduction.

Mutation of low affinity nerve growth factor receptor gene is associated with the hypertensive phenotype in spontaneously hypertensive inbred rat strains

We previously reported a missense mutation in the low affinity nerve growth factor receptor (LNGFR) gene of spontaneously hypertensive rats (SHR), proposing this gene as a promising candidate in genetic hypertension. In this study we provide further support for implicating this gene in genetic hypertension using two new inbred strains, WKHT and WKHA rats. These strains originated from crossbreeding SHR rats with normotensive Wistar-Kyoto rats (WKY): WKHT rats are hypertensive but not hyperactive, and WKHA rats are hyperactive but not hypertensive. Nucleotide sequence analysis of the LNGFR gene revealed that WKHT has the same mutation as SHR, whereas WKHA has the normal sequence, as seen in WKY. These results support our original hypothesis that the mutated LNGFR gene is linked to hypertension, since the mutation had co-segregated with the hypertensive trait, and not hyperactivity trait of SHR.

Pathophysiology of smooth muscle in hypertension

Structural changes of the arteries in hypertension are determined by the unique genetics of the animals and by various growth promoters and growth inhibitors. Vascular smooth muscle cell growth promoting factors include fibroblast growth factor, platelet-derived growth factor, and vasoactive peptides such as norepinephrine, angiotensin II, and endothelin. Endothelial cells secrete three types of growth inhibiting factors. These are heparin--heparan sulfate, transforming growth factor beta, and nitric oxide. The effect of sympathetic innervation on vascular growth is probably dependent on its interaction with the renin-angiotensin system. In the mesenteric vascular bed, the elevated resistance in the arterial system is present in both the macroarteries and in the more distal microarteries and veins. Changes in resistance arteries include hypertrophy and reduction in outer diameter (remodelling). In the resistance arteries from human essential hypertensives, remodelling is the predominant finding. Long-term treatment with an angiotensin I converting enzyme inhibitor but not with a beta-blocker was effective in reversing this type of vascular change. Studies have suggested that in addition to angiotensin II, endothelin may play a role in vascular remodelling of resistance arteries.

Mutation of low affinity nerve growth factor receptor gene in spontaneously hypertensive and stroke-prone spontaneously hypertensive rats: one of the promising candidate genes for hypertension

There is evidence that abnormal formation of the sympathetic nervous system might be important for pathogenesis of hypertension. In the present study we analyzed nucleotide sequences of low affinity nerve growth factor receptor (LNGFR) genes in the spontaneously hypertensive rat and its stroke-prone substrain. There was a point mutation generating an amino acid substitution in signal peptide of these LNGFRs. This result suggested that the mutated LNGFR gene is one of the promising candidate genes for hypertension.

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.

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.

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.

Histochemically demonstrable catecholamines in sympathetic ganglia and carotid body of spontaneously hypertensive and normotensive rats

The catecholamine content and morphology of the superior cervical and the hypogastric ganglion and the carotid body were studied in Spontaneously Hypertensive Rats (SHR) before (at the age of 6 weeks) and after (at the age of 20 weeks) becoming hypertensive, with Wistar Kyoto (WKY) rats as controls. The study was performed by formaldehyde-induced fluorescence method combined with quantitative microfluorimetry of catecholamines. At the age of 6 weeks the only significant difference observed between the rat strains was a greater number of small intensely fluorescent (SIF) cells in the superior cervical ganglion of SHR. At the age of 20 weeks the fluorescence intensity was higher in the principal neurons of the superior cervical ganglion and in glomus cells of the carotid body of SHR compared to WKY. The volumes of superior cervical ganglion and carotid body were larger in 20-week-old SHR compared to WKY. In the hypogastric ganglion differences were not found between SHR and WKY rats. The present results show differences in the superior cervical ganglion and in the carotid body of adult SHR compared to controls. These differences develop during the time period when the SHR become hypertensive, and might be functionally significant in the regulation or maintenance of the increased blood pressure in SHR rats.

Evidence for an increase in adrenergic nerve function in blood vessels from experimental hypertensive rabbits

The possibility of changes in the adrenergic innervation of blood vessels in experimental hypertension was investigated by measuring arterial norepinephrine content, neuronal uptake of norepinephrine, and the neurogenic contractile response in rabbits made hypertensive by partial constriction of the abdominal aorta proximal to the kidneys. Two to 3 weeks after surgery, norepinephrine content was increased in the arteries above the ligature, where arterial blood pressure was increased, but not in the arteries below the ligature, where arterial blood pressure was normal, in the heart, or in the veins. Neuronal norepinephrine uptake per unit length of vessel and the neurogenic contractile response increased with the rise in arterial blood pressure. The neurogenic contractile response can be taken as an indication of an increase in transmitter release. The results taken together suggest an increase in the function and possibly the amount of the adrenergic neuroneal terminal in hypertension. Since the distributions of the changes in the adrenergic innervation and the increases in smooth muscle cell proliferation in hypertension are similar, these two processes may be interrelated.