Histamine release from Weibel-Palade bodies of toad aortas induced by endothelin-1 and sarafotoxin-S6b

Hypertension meets osteoarthritis - revisiting the vascular aetiology hypothesis

Osteoarthritis (OA) is a whole-joint disease characterized by subchondral bone perfusion abnormalities and neovascular invasion into the synovium and articular cartilage. In addition to local vascular disturbance, mounting evidence suggests a pivotal role for systemic vascular pathology in the aetiology of OA. This Review outlines the current understanding of the close relationship between high blood pressure (hypertension) and OA at the crossroads of epidemiology and molecular biology. As one of the most common comorbidities in patients with OA, hypertension can disrupt joint homeostasis both biophysically and biochemically. High blood pressure can increase intraosseous pressure and cause hypoxia, which in turn triggers subchondral bone and osteochondral junction remodelling. Furthermore, systemic activation of the renin-angiotensin and endothelin systems can affect the Wnt-β-catenin signalling pathway locally to govern joint disease. The intimate relationship between hypertension and OA indicates that endothelium-targeted strategies, including re-purposed FDA-approved antihypertensive drugs, could be useful in the treatment of OA.

Flavin adenine dinucleotide may release preformed stores of nitrosyl factors from the vascular endothelium of conscious rats

This study determined whether flavin adenine dinucleotide (FAD) may elicit vasodilation in conscious rats via release of preformed endothelium-derived nitrosyl factors. Injections 1-6 (inj(1-6)) of FAD (2.5 micromol/kg, IV) elicited pronounced and equivalent vasodilator responses in saline-treated rats. Inj(1) of FAD elicited pronounced vasodilation in L-NAME-treated rats pretreated with the nitric oxide (NO) synthesis inhibitor, NG-nitro-L-arginine (L-NAME; 50 micromol/kg, IV), whereas Inj(2-6) elicited progressively smaller responses such that inj(6) elicited minor responses. The vasodilator responses elicited by the endothelium-dependent agonist, acetylcholine, were markedly attenuated in L-NAME-treated rats that had received inj(1-6) of FAD but not in saline-treated rats that had received inj(1-6) of FAD. The vasodilator actions of L-S-nitrosocysteine and the NO donor, sodium nitroprusside, were not diminished after the injections of FAD in saline- or in L-NAME-treated rats. Binding studies demonstrated that the densities of muscarinic M3 receptors were increased in thoracic aorta endothelium of rats treated with L-NAME + inj(1-6) of saline or L-NAME + inj(1-6) of FAD as compared to rats treated with saline + inj(1-6) of saline or saline + inj(1-6) of FAD. The progressive loss of response to injections of FAD in L-NAME-treated rats coupled with the loss of response to acetylcholine suggests that FAD elicits the use-dependent depletion of vesicular pools of nitrosyl factors in endothelial cells that cannot be replenished in the absence of NO synthesis.

Bulbus arteriosus of the antarctic teleosts. I. The white-blooded Chionodraco hamatus

The bulbus arteriosus of teleost fish is a thick-walled chamber that extends between the single ventricle and the ventral aorta. The functional importance of the bulbus resides in the fact that it maintains a steady blood flow into the gill system through heart contraction. Despite of this, a thorough study of the structure of the bulbus in teleost fish is still lacking. We have undertaken a morphologic study of the bulbus arteriosus in the stenothermal teleosts of the Antarctic sea. The structural organization of the bulbus arteriosus of the icefish Chionodraco hamatus has been studied here by conventional light, scanning, and transmission electron microscopy. The inner surface of the bulbus shows a festooned appearance due to the presence of longitudinal, unbranched ridges that extend between the ventricle and the arterial trunk. The wall of the bulbus is divided into endocardial, subendocardial, middle, and external layers. Endocardial cells show a large number of moderately-dense bodies. The endocardium invaginates into the subendocardium forming solid epithelial cords that contain numerous secretory vacuoles. Cells in the subendocardium group into small domains, have some of the morphological characteristics of smooth muscle cells, and appear enmeshed in a three-dimensional network of matrix filaments. Cells in the middle layer are typical smooth muscle cells. They appear arranged into layers and are surrounded by a filamentous meshwork that excludes collagen fibers. Orientation of this meshwork occurs in the vicinity of the smooth muscle cells. Elastin fibers are never observed. The external layer is formed by wavy collagen bundles and fibroblast-like cells. This layer lacks blood vessels and nerve fibers. The endocardium and the endocardium-derived cords are secretory epithelia that may be involved in the formation ofmucins or glycosaminoglycans. These mucins may have a protecting effect on the endocardium. The subendocardium and the middle layer appear to be formed by the same cell type, smooth muscle, with a gradient of differentiation from the secretory (subendocardium) to the contractile (middle layer) phenotype. Despite the absence of elastin fibers, the filamentous matrix could maintain the elastic properties of the bulbus wall. Smooth muscle cells appear to be actively involved in bulbus wall dynamics. The restriction of collagen to the external layer suggests that it may control wall dilatation and bulbus compliance. When comparison was possible, structural differences between C. hamatus and temperate teleosts seemed to be not species-related, but of phenotypic adaptative significance. This is remarkable since Antarctic fishes have lived isolated in freezing waters for the last two million years.

Evidence using immunoelectron microscopy for regulated and constitutive pathways in the transport and release of endothelin

We investigated the distribution of endothelin (ET)-like immunoreactivity in the human coronary artery and examined sites linked to the storage and release of intracellular proteins. Intense ET-like immunoreactivity was observed at the light-microscope level in luminal coronary artery endothelial cells. A low level of staining also was detected in the outer medial smooth-muscle layer and diffusely within the adventitia. Immunoelectron microscopy was used to determine the ultrastructural localisation of ET in the endothelium. Positive ET-like immunoreactive staining was detected in secretory vesicles at the ultrastructural level. Quantitative immunoelectron microscopy revealed that ET-like immunoreactivity was predominantly localised to the cytoplasmic matrix (including secretory vesicles) and Weibel-Palade bodies (endothelial cell-specific storage granules). Labelling was detected in 44% of Weibel-Palade body profiles positively identified by using antisera to von Willebrand factor and in cytoplasm surrounding these structures. A low level of immunoreactive staining was associated with mitochondria, whereas the cell nucleus and Golgi complex showed little or no positive staining. These findings indicate that ET is released from human coronary artery endothelial cells via two distinct secretory pathways. We propose that ET is continuously transported in and released from secretory vesicles by the constitutive secretory pathway. ET may also be stored in Weibel-Palade bodies and released after an appropriate stimulus by the regulated pathway. Positive immunoreactivity was also observed in plasmalemmal vesicles (50- to 60-nm diameter), indicating a role for these structures in endocytosis.

Weibel-Palade bodies as a storage site of calcitonin gene-related peptide and endothelin-1 in blood vessels of the rat carotid body

BACKGROUND

The vasculature of the carotid body has been considered to play a role in the regulation of blood flow into this organ. This light and electron microscope immunocytochemistry deals with endothelium-dependent vasomotion by vasodilatory calcitonin gene-related peptide (CGRP) and vasoconstrictive endothelin-1 (ET-1).

METHODS

After adult male rats were perfused with a solution of periodate-lysine-paraformaldehyde through the left ventricle, the carotid artery bifurcations were isolated and utilized for light and electron microscope immunolabelings with CGRP and ET-1 primary antisera.

RESULTS

By light microscope immunocytochemistry, immunoreactions to CGRP were seen along the endothelium of the carotid body artery (CBA) and its branches, and those of ET-1 were observed along the endothelium of the intralobular capillaries in addition to the above vessels. By immunoelectron microscopy, immunoreactive gold particles of CGRP and ET-1 were identified in the rough endoplasmic reticulum (rER) and in the Weibel-Palade (WP) bodies of endothelial cells of the CBA and its branches. Colocalization of both immunoreactive gold particles was observed in the same WP body. Immunoreactive gold particles of CGRP were also identified in the rER, Golgi apparatus, and specific granules of the dark glomus cells.

CONCLUSIONS

Conceivably, CGRP and ET-1 are synthesized in the rER of these endothelial cells and are stored in the WP bodies for the autoregulation of blood flow.

Increase in number of Weibel-Palade bodies and endothelin-1 release from endothelial cells in the cadmium-treated rat thoracic aorta

Male rats received daily intraperitoneal injections of cadmium sulphate (2.0 mg/kg) for 3 (Cd-3 group), 6 (Cd-6 group) and 8 days (Cd-8 group). The blood samples were prepared for endothelin (ET)-1 assay, and the thoracic aorta was investigated by both electron microscopy and immunoelectron microscopy using anti ET-1 sera. The plasma ET-1 concentrations of both Cd-6 and Cd-8 groups increased significantly in a cumulative dose-dependent manner. The cadmium-treated rat aorta showed an increase in the number of Weibel-Palade (WP) bodies in endothelial cells, and degranulation and exocytosis of WP bodies occurred exclusively in the Cd-8 group. Immunoreaction for ET-1 was localized preferentially in WP bodies of both cadmium-treated and control groups, and in the rough endoplasmic reticulum of the cadmium-treated groups only. Reactivity was also found on the WP bodies undergoing exocytosis in the Cd-8 group. Cadmium intoxication induces an increase in number of ET-1-storing WP bodies in the rat aorta endothelium. The enhancement of extracellular release of their contents by exocytosis results in elevation of the plasma ET-1 concentration.