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

Summary 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.     

Alterations in plasma catecholamines and behavior during acute stress in spontaneously hypertensive and Wistar-Kyoto normotensive rats

The responsiveness of the sympathoadrenal system to stress was assessed in spontaneously hypertensive (SHR) and Wistar-Kyoto normotensive (WKY) rats at 6, 18, and 48 weeks of age. Two days after insertion of a tail arterial catheter, each rat was transferred from its home cage to a shock chamber, and after 5 min received 60 footshocks over a 5 min interval. Blood samples were taken from undisturbed rats when in the home cage, 3–5 min after transfer to the shock chamber, and at the end of shock. An additional group of naive SHR and WKY rats was exposed to footshock and behavioral responses were recorded. There were no strain differences in levels of norepinephrine (NE) or epinephrine (EPI) while rats were undisturbed in their home cages. Transfer to the shock chamber resulted in a greater increase in plasma levels of both catecholamines in SHRs of each age. A similar pattern was evident after footshock; SHR rats had significantly higher post-shock levels of plasma NE and EPI than age-matched WKY rats. During shock, SHR rats were more active and jumped and reared more frequently than WKYs. These results demonstrate that the sympathoadrenal system of SHR rats is more responsive than normotensive rats to stressful stimuli and that this hyper-responsitivity is independent of increases in blood pressure. The excessive discharge of NE and EPI into plasma during stress may contribute to the development and maintenance of high blood pressure in SHR rats.     

Histochemically demonstrable increase in the catecholamine content of the carotid body in adult rats treated with methylprednisolone or hydrocortisone

Synopsis Carotid bodies of adult albino rats were examined using the formaldehyde-induced fluorescence (FIF) method for the demonstration of fluorogenic monaomines and staining with I% Toluidine Blue for morphological observations.In the carotid body of normal controls, most glomus (principal or type I) cells exhibited a FIF presumably due to catecholamines. The intensity of the fluorescence was weak in most cells, while some glomus cells were non-fluorescent and others exhibited a moderate or intense FIF. The sustentacular (satellite, supporting or type II) cells were essentially non-fluorescent.One week after the administration of a single intraperitoneal injection of the long-acting glucocorticoid 6-methylprednisolone sypionate (400 mg/kg) or after seven intraperitoneal injections of the water-soluble glucocorticoid hydrocortisone sodium succinate (40 mg/kg daily for a week), a distinct increase was observed in the FIF of the glomus cells. No non-fluorescent glomus cells were observed after treatment with either glucocorticoid, and the intensity of most fluorescent glomus cells was moderate or intense.It is concluded that glucocorticoids cause an increased storage of catecholamines in the glomus cells of the carotid body of the adult rat, an observation of interest in view of the fact that such changes due to glucocorticoids have as yet been reported only in catecholamine-storing cells of newborn rats.     

Histochemically demonstrable catecholamines and cholinesterases in nerve fibres of rat dorsal skin

Summary Histochemically demonstrable cholinesterases of rat skin and cutaneous nerves hydrolyze acetylthiocholine iodide and butyrylthiocholine iodide. Cholinesterase activity of the skin was located in the epidermis, in the hair follicles at the level of the sebaceous glands, in adjacent parts of the sebaceous glands, in erector pili muscles and their nerves, in cutaneous and subcutaneous nerves and nerve trunks, including some nerves accompanying cutaneous blood vessels, and in the membranes of fat cells. No encapsulated nerve endings were found. In the nerves of erector pili muscles there was some neurilemmal non-specific cholinesterase activity, demonstrated in the presence of 10^–5 M BW 284C 51, and specific acetylcholinesterase activity resistant to 10^–5 M iso-OMPA. The cholinesterase activity in other cutaneous nerves was inhibited by 10^–5 M iso-OMPA but was resistant to 10^–5 M BW284 C 51, thus representing mainly non-specifc cholinesterase (nsChE) activity.The adrenergic nerves of the dorsal skin, as revealed by glyoxylic acid-induced fluorescence (GIF), were located in association with erector pili muscles and surrounded arteries and arterioles. Small fluorescent nerves were situated in subcutaneous nsChE-positive nerve trunks.Using GIF and cholinesterase techniques performed either simultaneously or consecutively, it was found that the nsChE-positive, probably sensory, nerves accompanying blood vessels were fewer in number than the fluorescent adrenergic nerves and ran a course independent of them. No cholinesterase reaction was seen in the fluorescent adrenergic nerves when short incubation times were used. When the incubation time was prolonged overnight, the nsChE reaction closely followed the course of fluorescent adrenergic nerves.     

Morphological characteristics and peptidergic innervation in the carotid body of spontaneously hypertensive rats

We examined morphological characteristics of the carotid body of spontaneously hypertensive rats (SHR), those of age-matched normotensive Wistar rats (NWR), and age-matched genetically comparable Wistar Kyoto rats (WKY). We examined the distribution and abundance of four different regulatory neuropeptides: substance P (SP), calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), and neuropeptide Y (NPY) in the carotid bodies of these three strains of rats. The carotid bodies of SHR were larger than those of NWR and WKY. The values of the long axis of the carotid bodies of SHR were significantly larger (1.3 times) than those of NWR and WKY. In the carotid bodies of SHR, the percentage of relatively large vessels was similar to that of the carotid bodies of WKY, although the carotid bodies themselves were significantly larger than in WKY. The density of VIP varicose fibers in the carotid bodies of SHR was lower than in the carotid bodies of WKY, although the density of SP, CGRP and NPY fibers was similar to that of the carotid bodies of NWR and WKY. These findings suggested that VIP was unrelated to enlargement of the carotid body of SHR, but it might modify the sensitivity of chemoreceptors in the carotid body.     

Beta-adrenoceptors in kidney tubules of spontaneously hypertensive and normotensive rats

Beta-adrenoceptor binding characteristics were determined in different fractions of rat kidney tubules using a [125Iodo]-(-)-cyanopindolol (ICYP) binding assay. The highest amount of binding sites was found in a fraction containing predominantly distal tubular fragments. In a separate series of experiments the ICYP binding characteristics were compared in whole tubular fractions from spontaneously hypertensive (SHR) and normotensive Wistar Kyoto rats (WKY) of different ages. The maximum number of binding sites was significantly higher both in young (3 weeks) and adult (14 weeks) SHR when compared to age-matched WKY. These studies showed the presence of beta-adrenoceptor binding sites in rat kidney tubules and support the potential importance of tubular beta-adrenoceptors in the development of spontaneous hypertension and in the mechanism of antihypertensive action of beta-blockers.     

Comparison of somatosympathetic reflex in normotensive and spontaneously hypertensive rats

In chloralose anaesthetized and paralyzed normotensive (Wistar, Wistar--Kyoto) and spontaneously hypertensive rats (SHR), a somatosympathetic reflex in the cervical sympathetic trunk elicited by a single electrical shock to forelimb afferent fibres in the median nerve was recorded. It has been shown that the elicited response of SHR is similar to the response of normotensive rats. Amplitude of somatosympathetic reflex in SHR is larger than that of somatosympathetic reflex in normotensive animals. It is supposed that somatosympathetic reflex in hypertensive and normotensive rats is formed in the same way. However, reflex excitability of sympathetic nervous system in SHR is greater.     

Cold-restraint induced gastric lesions in normotensive and spontaneously hypertensive rats

Spontaneously hypertensive (SHR) rats and normotensive Wistar-Kyoto (WKY) rats were subjected to 2 hr of cold-restraint stress at 2–6°C following a 24 hr fast. WKY rats had a significantly greater incidence and degree of ulceration of the gastric glandular mucosa than did SHR rats. Mean arterial pressure, obtained from a chronic arterial cannula, fell during 2 hr of cold-restraint stress in both SHR and WKY rats. Heart rate was unchanged in WKY but fell significantly in SHR. Plasma norepinephrine (NE) and epinephrine (E), determined by radioenzymatic assay, increased significantly following stress. Increased levels of NE remained similar for both SHR and WKY rats, while post-stress levels of E for the SHR rats greatly exceeded E levels for WKY rats. A greater degree of hypothermia was also noted in SHR rats. Decreased stress induced ulcerogenesis in the SHR may be due to the well-known altered hemodynamic and autonomic nervous system reactivity in this strain or other factors not yet discovered.     

Plasma catecholamines and dopamine-beta-hydroxylase activity in spontaneously hypertensive rats.

Levels of plasma norepinephrine and total catecholamines in spontaneously hypertensive rats bred from a normotensive Kyoto strain of Wistar rats increase between their 8th to 12th week post utero concomitant with the development of hypertension, but levels of plasma norepinephrine are not significantly different between the spontaneously hypertensive strain, a normotensive Kyoto strain and a N.I.H. strain of Wistar rats at either 8 or 12 weeks of age. Plasma total catecholamine levels in the spontaneously hypertensive strain are significantly higher at 12 weeks of age than those in either control strain, while plasma levels of dopamine-β-hydroxylase show no consistant relationship between the three strains. It, therefore, appears unlikely that increased sympathetic neuronal activity is an etiological factor in this form of hypertension.     

Pressor responses to endothelin-1 in normotensive and spontaneously hypertensive rats

In freely moving rats, endothelin-1 (0.0135–4.5 nmol/kg) administered as an intravenous bolus injection, produced an immediate, short-lasting, dose-related fall in blood pressure followed by a long-lasting, dose-related increase in blood pressure. There was a higher sensitivity in the pressor responses to endothelin-1, in spontaneously hypertensive (SH) rats (ED₅₀ = 0.11 ± 0.02 and 0.28 ± 0.02 nmol/kg, in SH and normotensive rats, respectively), but no change in the maximal pressor effect of endothelin-1 in SH rats.

In rat isolated aorta, endothelin-1 induced a greater vasocontractile effect in SH rats than in normotensive rats. In both rat strains, removal of the endothelium did not change the concentration-effect curves obtained in endothelium-intact preparations. These data add further support to the hypothesis that endothelin-1 could play a role in genetic hypertension, at least in the maintenance of high blood pressure.     

Tissue distribution of acebutolol in mature normotensive and stroke-prone spontaneously hypertensive rats

Tissue distribution of acebutolol was studied in 33-week-old normotensive (WKY) and Okamoto stroke-prone (SHR-SP) rats, 30 min after an i.v. administration, by using 14C-acebutolol. Plasma level of acebutolol was higher in WKY than in SHR-SP. Aorta, kidney, liver and muscle radioactivity/plasma radioactivity ratios were higher in SHR-SP than in WKY. The brain/plasma radioactivity ratio was very low and similar in the two groups. The drug distribution was the same in the two groups except in medulla + corpus trapezoides where drug concentration was greater in SHR-SP. These results, compared with previous ones, show an age-related evolution in pathological state in SHR-SP. They point out a specific concentration of the beta-blocking drug in a defined part of the brain, namely medulla + corpus trapezoides.     

Norepinephrine concentration in kidneys of normotensive Wistar-Kyoto and spontaneously hypertensive rats.

Renal norepinephrine (NE) concentration was measured in normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) at 7, 9, 11, and 13 weeks of age. Although the weight of kidneys was similar in the two strains of rats, renal NE concentration was significantly lower in SHR at all ages (147 +/- 9 to 175 +/- 13 ng/g for SHR, and 216 +/- 8 to 262 +/- 17 ng/g for WKY rats). The difference in renal NE concentration during this time of rapidly increasing arterial pressure in the SHR suggests that renal NE may in some way be related to the development of hypertension.     

Calcitonin gene-related peptide (CGRP) in normotensive and spontaneously hypertensive rats

With the techniques of specific radioimmunoassay and gel filtration it was found that CGRP was distributed in various tissues of normotensive (WKY) and spontaneously hypertensive rats (SHR) with the highest concentration in the lumbar spinal cord (1197 +/- 94.8 pg/mg tissue) and the lowest in the auricle (15.0 +/- 2.1 pg/mg tissue). In comparison with WKY, CGRP concentration in the plasma was decreased and in the abdominal aorta and hypothalamus was increased in SHR. Gel filtration revealed only one major CGRP molecular form in the tissues. In addition, CGRP reduced the mean arterial pressure (MAP) in SHR in a dose-dependent manner. These data suggest that CGRP may play an important role in the pathogenesis of hypertension and its possible therapy.