Age-related structural characteristics of the adrenal medulla in hypertensive NISAG rats

Structural characteristics of the adrenal medulla in hypertensive NISAG rats (hereditary stress-induced arterial hypertension) were studied during various periods of postnatal ontogeny. Signs of hyperplasia of the adrenal medulla were most pronounced in adult hypertensive animals with persistent arterial hypertension, as well as during the period of late ontogeny. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 142, No. 12, pp. 604–606, December, 2006     

自发性高血压大鼠交感神经节与肾上腺髓质内NPY的表达及超微结构的变化

目的:通过对自发性高血压大鼠(SHR)颈上神经节、肾上腺髓质内神经肽酪氨酸(NPY)表达及超微结构变化的研究,探讨NPY在高血压发生和发展中的作用。方法:随机选取成年大鼠60只,分成SHR组和正常对照组,每组各30只,采用Real-Time PCR技术和免疫组织化学法,检测两组大鼠颈上神经节、肾上腺髓质内NPYmRNA和蛋白的表达;应用透射电镜技术观察上述两种组织内超微结构的改变。结果:与同周龄的正常组大鼠相比,SHR大鼠的血压明显增高(P<0.05),RT-PCR和免疫组织化学方法检测到颈上神经节、肾上腺髓质内NPYmRNA和蛋白质的表达均增高(P<0.05),NPY免疫阳性神经元的数量和阳性细胞的光密度亦增加(P<0.05)。电镜结果示SHR大鼠两种组织内异染色质、线粒体、粗面内质网等数量均明显增加(P<0.05)。结论:SHR颈上神经节、肾上腺髓质内的NPY通过复杂的机制可能参与了高血压的形成。     

Sympathetic-adrenal medullary responses to acute stress in Dahl hypertensive (S/JR) rats

Sympathetic-adrenal medullary responses to acute footshock stress were assessed in inbred Dahl salt-sensitive (S/JR) and salt-resistant (R/JR) rats by measuring plasma levels of norepinephrine (NE) and epinephrine (EPI). Ten-week-old S/JR and R/JR rats were surgically prepared with indwelling tail artery catheters which permitted direct measurements of mean arterial pressure (MAP, mmHg) and heart rate (HR, beats/min) and remote sampling of blood. Two days after surgery, S/JR and R/JR rats were subjected to an acute stress paradigm. Blood samples were collected before and 3 minutes after transfer of rats to a shock chamber, after 1 minute of intermittent footshock, and again 5 minutes later. S/JR rats had significantly higher resting MAP's compared to R/JR rats. In contrast, baseline heart rates were similar for rats of the two strains. Basal plasma levels of NE and EPI were also similar in S/JR and R/JR rats. Upon transfer from the home cage to a shock chamber, S/JR rats exhibited significant increases in plasma levels of both catecholamines, while R/JR rats maintained circulating levels of NE and EPI that were near baseline values. However, S/JR and R/JR rats had similar increments in plasma NE and EPI following acute footshock stress. Five minutes after footshock, levels of NE and EPI returned toward baseline values for R/JR's, but remained significantly elevated above baseline in hypertensive S/JR rats. These data suggest that S/JR rats are more responsive than R/JR controls to the mild stress of transfer, but exhibit comparable responses to the more intense stress of inescapable footshock.(ABSTRACT TRUNCATED AT 250 WORDS)     

The role of the adrenal medulla in cardiovascular responses to hypertonic saline in haemorrhaged conscious rats

The aim of this study was to determine if the adrenal medulla plays a role in mediating haemodynamic effects of hypertonic saline (HTS) resuscitation during haemorrhagic hypotension in conscious rats. Wistar-Kyoto rats were either adrenomedullectomized (ADMX, n = 11) or sham-operated (SHAM, n = 10) and implanted with intravascular catheters. Pre-haemorrhage resting mean arterial pressure (MAP) was lower in the ADMX than in the SHAM group. Haemorrhage was performed by withdrawal of blood through the venous catheter, and a MAP of 50 mmHg was maintained for 1 h by further withdrawal when necessary. Both groups responded to haemorrhage with marked bradycardia. Plasma adrenaline (A) rose 10-fold in response to hypotension in the SHAM group, while remaining at pre-haemorrhage levels in the ADMX group, indicating successful adrenal demedullation. Infusion of 2.0 ml kg^-1 HTS (NaCl 8.0 mg ml^-1 i.v.) produced an immediate increase in MAP and heart rate (HR) in both groups, to pre-haemorrhage values or higher. Plasma noradrenaline (NA) increased in both groups after HTS, while the high levels of A in the SHAM group slowly returned toward baseline. Plasma glucose and rate of haemodilution was higher in the SHAM group during and after hypotension. The maintenance of MAP above 60 mmHg was less effective in the SHAM group during the first 2 h after HTS, but after 24 h, pre-haemorrhage MAP was established in both groups. In conclusion, the adrenal medulla does not play a major role in the response to HTS resuscitation.     

Plasma catecholamines in salt-sensitive hypertensive (Dahl) rats

We examined the effects of low (0.4%) and high (8.0%) salt diets on basal and stress-induced increments in plasma levels of norepinephrine (NE) and epinephrine (EPI) in the Dahl lines of salt-sensitive (DS) and salt-resistant (DR) rats. DS rats develop sustained increases in blood pressure when maintained on a high salt diet while DR rats remain normotensive. For this study, blood samples were obtained via a chronic tail artery catheter from DS and DR rats under resting conditions or following exposure to stress. Plasma samples were later assayed for content of NE and EPI by a radioenzymatic assay. Basal plasma levels of both catecholamines were similar in DS and DR rats, irrespective of dietary salt content and mean arterial blood pressure. The mild stress of handling and transfer of rats to a different cage resulted in greater increments in plasma NE but not EPI in DS rats fed a high salt diet compared to DS rats fed a low salt diet. There was a significant effect of line and an interaction of line and diet with respect to the effects of immobilization stress on plasma catecholamines. DS rats had greater immobilization-induced increments in plasma NE and EPI compared to DR rats when both lines were fed a low salt diet. Maintenance on a diet high in salt resulted in lesser immobilization-induced increments in plasma catecholamines for DS rats and greater immobilization-induced increments in plasma catecholamines for DR rats when compared to their respective controls on a low salt diet. There was a significant effect of diet on plasma levels of both catecholamines when blood samples were obtained by decapitation. DS and DR rats that were fed a high salt diet had lower plasma levels of NE and EPI following decapitation compared to rats of the two lines that were fed a low salt diet. These findings demonstrate that dietary salt and genetic factors are important in regulating the activity and responsiveness of the sympathetic-adrenal medullary system to a variety of stressors. Our findings do not provide evidence for a critical role of the sympathetic nervous system in maintaining the diet-induced increase in the arterial blood pressure of DS rats.     

Mismatch between peripheral and central demands in salt-sensitive hypertensive Dahl rats

Sympathetic nerve activity in essential hypertension, which accounts for 90% of all hypertension cases, is in general thought to be elevated regardless of whether there is salt sensitivity or insensitivity. The cause is thought to be an abnormality in the sympathetic center. On the other hand, neuronal nitric oxide synthase-expressing neurons that function to inhibit the sympathetic center are clearly activated in the salt-sensitive hypertensive Dahl rat model. How is this related to sympathetic hyperactivity and hypertension? Also, how is hypertension associated with peripheral vessel contractility and renal function? Human life is supported by the body's various essential functions. The circulatory system links all these functions into one system that cannot be separated. Blood pressure is the driving force of this circulatory system, and both the central and peripheral demands determine the output. We examined the ‘mismatch’ between these two sides and its association with hypertension.     

Dysfunction of paracellin-1 by dephosphorylation in Dahl salt-sensitive hypertensive rats

A high-salt diet reduced the levels of renal cAMP content and serine-phosphorylated paracellin-1 in Dahl salt-sensitive hypertensive rats. In MDCK cells expressing paracellin-1, protein kinase A inhibitor reduced the serine-phosphorylated paracellin-1 and transepithelial Mg(2+) transport, suggesting that a dephosphorylation of paracellin-1 induces the reduction of Mg(2+) reabsorption in salt-sensitive hypertension.     

Sympathetic nerve function and vascular reactivity in Doca-salt hypertensive rats

The present study was conducted to measure norepinephrine release during sympathetic nerve stimulation and to evaluate vascular reactivity in the isolated perfused mesenteric vasculature of normotensive and Doca-salt hypertensive rats. Significantly greater vasoconstrictor responses to periarterial nerve stimulation, norepinephrine, and vasopressin, but not to barium chloride, were observed in the mesenteric vasculature of the hypertensive rats in comparison with the control normotensive group. Norepinephrine release, measured as total tritium overflow, during periarterial nerve stimulation at 4 Hz for 2 min, was identical in both normotensive and hypertensive animals. Phentolamine (5.3 micro M) significantly increased tritium overflow, but to the same extent in the normotensive and the hypertensive mesenteric vasculature, suggesting that the negative feedback presynaptic alpha-adrenoceptor mechanism, which has been proposed to modulate transmitter release, was unaltered in this form of hypertension. These results indicate that hyperresponsiveness of the mesenteric vasculature to periarterial nerve stimulation in the hypertensive rats is due to increased sensitivity of the vascular alpha-adrenoceptor and not facilitation of the transmitter release. The increased vascular reactivity to norepinephrine and vasopressin may be involved in the maintenance of Doca-salt hypertension.     

自发性高血压大鼠延髓microRNA差异表达分析

目的　探讨自发性高血压大鼠延髓microRNA（miRNA）差异表达谱及其靶基因生物信息学分析。 方法　采用自发性高血压大鼠模型（SHR组）,同周龄SD大鼠为对照组（Control组）。利用miRNA芯片检测大鼠延髓中miRNAs差异表达谱。 结果　与对照组比较,SHR组尾动脉收缩压显著升高（P＜0.0001）;SHR组延髓组织miRNAs有显著差异表达谱,16个miRNAs表达上调和7个miRNAs表达下调（1.5-fold change cutoff, P<0.05）。qRT-PCR验证结果显示,与对照组比较,SHR组延髓miR-153、miR-193及miR-301a表达显著下降,与芯片结果一致。生物信息学分析显示,差异表达miRNAs可能调控2775个靶基因（target score≥83）。这些靶基因主要富集在12个信号通路,包括磷脂酰肌醇3-激酶（Phosphatidylinositide3-kinase,PI3K）通路等。 结论　自发性高血压大鼠延髓组织中miR-153、miR-193及miR-301a明显下调,且生物信息学分析提示PI3K通路介导神经炎症可能作为高血压中枢相关差异表达miRNAs调控靶基因介导的主要致病通路。     

Effect of the adrenal inhibitor trilostane on the morphology of the adrenocortical cells of Dahl salt-sensitive and Dahl salt-resistant rats.

The effects of trilostane on the adrenal cortex of Dahl salt-sensitive (DS) and Dahl salt-resistant (DR) rats were investigated morphometrically, histochemically, ultrastructurally and biochemically. The statistical analysis indicated that trilostane induced a significant increase in the adrenal weight and the surface area of cells and nuclei in the zona fasciculata (ZF) of the adrenal cortex of DS and DR rats (P less than O.OI). DS rats treated with trilostane revealed marked accumulation of large amounts of lipid droplets and a decrease in the activity of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) in the ZF. Ultrastructurally, the mitochondria of the ZF in DS rats treated with trilostane revealed swelling of matrix with a loss of cristae and occasional interruption of the membranes of mitochondria. Some of them had a continuity with lipid vacuoles or SER, presenting a characteristic 'feather'-like appearance. Other characteristic findings in DS rats treated with trilostane were a marked villous proliferation of plasma membranes with numerous dense bodies, occasional coated pits, and pinocytic vesicles in the outer portion of the ZF. In DS and DR rats the plasma level of ACTH increased, and corticosterone decreased significantly (P less than O.OI) after treatment with trilostane. These morphological alterations were considered to be an expression of the inhibitory effects of trilostane on the adrenal steroidogenesis in DS and DR rats, more especially in DS rats. Simultaneously there were confirmed morphological alterations in the cells of the ZF, reflecting the feedback stimulation of endogenous ACTH. The cells of the ZF of DS rats were more responsive to suppression by trilostane than those of DR rats.     

Sympathetic nervous system and adrenal medullary responses to ischemic injury in mice

Acute, severe injury is frequently attended by hypotension, hypothermia, and decreased metabolic rate despite elevated urine and plasma catecholamine levels. Because the combination of sympathetic nervous system (SNS) suppression and adrenal medullary stimulation documented in several other situations could account for these observations, SNS and adrenal medullary function were examined independently in mice in the hindlimb ischemia model of acute injury. SNS activity was assessed by the measurement of [3H]norepinephrine (NE) turnover in heart and adrenal medullary secretion by depletion of adrenal catecholamine content. In nine separate experiments during the first 10 h after termination of a 2.5-h period of hindlimb ischemia, cardiac NE turnover was reduced an average of 23% (P less than 0.05) in injured mice. At the same time, adrenal catecholamine content fell 37% (P less than 0.05) in injured animals but not in controls. In contrast to the acute reaction, SNS activity in mice surviving 3 days was 59% greater than in controls. Thus, the reduction in NE turnover and depletion of adrenal catecholamine content suggest that SNS suppression and adrenal medullary stimulation constitute the acute sympathoadrenal response in this model of severe injury. Because survival within the first 24 h after injury was decreased in adrenalectomized mice despite glucocorticoid treatment, adrenal medullary catecholamines may contribute to survival in severely injured animals. Furthermore, because the SNS plays an important role in the regulation of blood pressure and heat production, the diminution in SNS activity in the hours after injury may contribute to posttraumatic hypotension and hypometabolism.     

Effect of vagotomy on morphology and function of the adrenal medulla in rats

Marked dilatation of the venous sinusoids, a decrease in area of the chromaffin tissue, and a stronger chromaffin reaction in the adrenal medulla were found 7 and 45 days after bilateral subdiaphragmatic vagotomy in male albino rats. Considerable changes were found in the ultrastructural organization of the secretory cells and endothelium. Injection of glucose into these animals caused only slight fluctuations in the adrenalin content in the chromaffin cells.Department of Histology and Embryology, Therapeutic Faculty, N. I. Pirogov Second Moscow Medical Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR Yu. M. Lopukhin.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 85, No. 3, pp. 370–373, March, 1978.     

Sympathetic and metabolic mechanisms of the cerebrovasomotor function of the caudal ventrolateral medulla in rats.

We attempted to elucidate the cerebrovasomotor function of the caudal ventrolateral medulla. Sixty-one rats were anaesthetized, paralysed and artificially ventilated. The microsphere method was employed for the measurement of blood flow. Microinjection of an antagonist of excitatory amino acids, kynurenate (2 nmol), into functionally identified depressor sites within the caudal ventrolateral medulla produced arterial hypertension of about 140 mmHg. We found that the cerebral blood flow was substantially increased, but was maintained at the same level (17 rats) as that observed under phenylephrine-induced hypertension (26 rats). Bilateral severing of the cervical sympathetic trunks resulted in a further increase in blood flow in all brain regions studied (18 rats). The response was most significant in the cerebral parasagittal cortex (164 +/- 31% of baseline without, and 211 +/- 43% with sympathectomy; mean +/- S.D.; P < 0.001). The contributions of the cerebral metabolic mechanism to this flow increase under denervation was minimal, as evidenced by the observation of disproportionately smaller changes in cerebral metabolic rate for oxygen during any type of hypertension. We conclude that the cerebrovasomotor functions of the caudal ventrolateral medulla may operate to keep an equilibrium between simultaneously working tonic inhibitions against sympathetic vasoconstriction as well as against vasodilatation. This dual effect is mediated by excitatory amino acid receptors located within this particular brain area. The vasodilator mechanism may be of neurogenic origin. When the function of the brain area is suppressed, the subsequently disinhibited vasodilator mechanism dominates the cerebrovascular autoregulatory function.(ABSTRACT TRUNCATED AT 250 WORDS)     

Sympathetic hyperresponsiveness to hypothalamic stimulation in young hypertensive rats.

The possible occurrence of central sympathetic dysfunction during development of spontaneous hypertension was studied by recording aortic pressure and sympathetic nerve activity concurrently during electrical stimulation of the posterior hypothalamus in 9-wk-old Kyoto-Wistar rats. Even at this early age, basal levels for both measurements were already elevated significantly in those with spontaneous hypertension. Increases in sympathetic neural firing induced by graded hypothalamic stimulation were always followed by corresponding increases in blood pressure; magnitude of both effects was appreciably larger in spontaneously hypertensive than in normotensive rats, as was the vasodepression caused by blocking autonomic ganglia with pentolinium. By contrast, pressor responses to injected norepinephrine were almost equal thereby suggesting that cardiovascular reactivity was unaltered and that enhanced responsiveness to hypothalamic stimulation was directly due to the concomitant increase in sympathetic nerve activity. Although the exact site from which sympathetic hyperactivity originates was unidentified, our results support the interpretation that sympathetic mechanisms involving the posterior hypothalamus participate in elevating blood pressure during development of spontaneous hypertension in rats.     

Diseases of the adrenal medulla

The adrenal glands are vital in the organism's response to environmental stress. The outer cortex releases steroid hormones: glucocorticoids, mineralocorticoids and sex hormones, which are crucial to metabolism, inflammatory reactions and fluid homeostasis. The medulla is different developmentally, functionally and structurally. It co-releases catecholamines (primarily adrenaline and to some extent noradrenaline) as well as peptides by the all-or-none process of exocytosis from chromaffin granules, to aid in blood pressure and blood flow regulation, with regulated increments during the activation of the sympathetic nervous system. The co-released peptides function to regulate catecholamine release, blood vessel contraction and innate immune responses. Pathology within the adrenal medulla and the autonomic nervous system is primarily because of neoplasms. The most common tumour, called phaeochromocytoma when located in the adrenal medulla, originates from chromaffin cells and excretes catecholamines, but may be referred to as secreting paragangliomas when found in extra-adrenal chromaffin cells. Neoplasms, such as neuroblastomas and ganglioneuromas, may also be of neuronal lineage. We will also briefly discuss the catecholamine deficiency state.     

Role of TRPV1 channels in renal haemodynamics and function in Dahl salt-sensitive hypertensive rats

This study tests the hypothesis that dysfunction of transient receptor potential vanilloid type 1 (TRPV1) channels occurs and contributes to the decrease in the glomerular filtration rate (GFR) and sodium/water excretion in Dahl salt-sensitive hypertensive rats. Recirculating Krebs-Henseleit buffer added with inulin was perfused at a constant flow in the isolated kidneys of Dahl salt-sensitive (DS) or Dahl salt-resistant (DR) rats fed a high-salt (HS) or low-salt (LS) diet for 3 weeks. Perfusion pressures (PP) were pre-adjusted to three levels ( approximately 100, approximately 150 or approximately 190 mmHg) with or without phenylephrine. Capsaicin, a selective TRPV1 agonist, in the presence or absence of capsazepine, a selective TRPV1 antagonist, was perfused. Basal GFR, urine flow rate (UFR) and Na(+) excretion (U(Na)V) were significantly lower in DS-HS than in DR-HS, DS-LS and DR-LS rats. Capsaicin caused pressure-dependent decreases in PP and increases in GFR, UFR and U(Na)V in all groups, with less magnitude of decreases in PP and increases in GFR, UFR and U(Na)V in DS-HS than in DR-HS, DS-LS and DR-LS rats. Capsazepine completely blocked the effect of capsaicin on PP, GFR, UFR and U(Na)V in all groups. Thus, these results show that TRPV1 function is impaired in the kidney of DS rats fed a high-salt diet, which may contribute to the decrease in GFR and renal excretory function in DS rats in the face of salt challenge.