Microcirculation of the rat adrenal gland: A scanning electron microscope study of vascular casts

Blood vascular beds of the rat adrenal gland were filled with methacrylate resin and observed with a scanning electron microscope. The classical findings on mammalian adrenal glands of Flint (1900), Bennett and Kilham (1940), and Gersh and Grollman (1941) were confirmed. The cortical capillaries arise from the cortical arteries and converge at the corticomedullary junction into the peripheral venous radicles which flow into the tributaries of the central vein. The medullary capillaries originate from the medullary arteries and drain through the deep venous radicles into the tributaries of the central vein. No direct connection between the cortical and medullary capillaries was noted except for rare communications via the peripheral venous radicles. These findings show that most of the cortical blood, rich in glucocorticoids, flows in the medulla, not through the medullary capillary plexus but exclusively through the radicles of the central vein. Evidence for adrenal portal vessels could not be found.     

胎儿和新生儿肾上腺的血管构筑

本文采用血管复型扫描电镜,注射墨汁切片光镜下观察和注射铅丹乳胶X线照像3种方法,研究了28例胎儿和新生儿肾上腺的血管构筑。发自膈下动脉、腹主动脉和肾动脉的肾上腺上、中、下动脉及其分支,在肾上腺囊表面和穿过囊的过程中逐级分支,最后形成毛细血管。动脉和毛细血管共同构成囊血管丛,从该丛发出的皮质动脉和髓质动脉,分别分支供给皮质和髓质。从囊血管丛发出的“V”型动脉在皮质中行一段距离后又返回囊中分支。永久性皮质毛细血管网是囊毛细血管的直接延续。在胎儿性皮质中,毛细血管有两个来源,其一是永久性皮质毛细血管的延伸;另一来源是由皮质动脉分支构成。它们共同构成胎儿性皮质毛细血管网。在胎儿性皮质的中部,毛细血管汇成小静脉。中央区的髓质由髓质动脉供血。在皮质中,正在迁移的髓质细胞团由与之伴行的动脉供应。在皮质中形成的小静脉呈向心性行走。其中一部分在近中央区又分为毛细血管,这些毛细血管相互吻合,最后入中央静脉的属支中。这种分布特点属于门脉形式的血管;另一部分属于中央静脉的第一级属支,它们逐级汇合后形成中央静脉主干。中央静脉系呈树枝状,其主干在腺的前面穿出腺后为肾上腺静脉。左侧肾上腺静脉人左肾静脉;右侧的人下腔静脉。而与动脉伴行的肾上腺上、中、下静脉的末级属支与囊毛细血管相连。本研究讨论了胎儿和新生儿肾上腺血管的分布规律,为胎儿内分泌学和肾上腺移植等方面提供了血管形态学基础。     

Three-dimensional organization of the collagen fibrillar framework in the rat adrenal gland

The three-dimensional organization of the collagen fibrillar framework in the rat adrenal gland was studied using an alkali-water maceration method and scanning electron microscopy. The structure thus obtained was a continuum of collagen fibril plexuses extending through the adrenal capsule, cortex and medulla. The capsule consisted of finely meshed collagen fibril sheaths and layered, coarsely meshed plexuses of bundles of collagen fibrils. In the cortex, the channels of cortical capillaries were surrounded by thin sheaths of collagen fibrils. Many slender bundles of collagen fibrils extended from these sheaths into intercellular spaces and interconnected adjacent pericapillary sheaths. The collagen fibril sheath tubes precisely reflected the cortical blood vascular architecture; thus the three cortical zones--zona glomerulosa, zona fasciculata and zona reticularis--were also clearly remarked. In the medulla, collagen fibrils were interwoven into more tightly meshed sheaths around the peripheral radicles and venous tributaries of the central veins. Basket-like collagen fibril sheaths divided the spaces among these tree-like perivascular collagen fibril sheath tubes into round compartments which, in intact tissues, contained chromaffin cell nodules and nervous elements. Small tube-like spaces for housing the medullary capillaries were located in the interstices of contiguous collagen fibril baskets. Besides supporting the organization of the gland, the collagen fibrillar framework in the adrenal gland is believed to play important roles in providing three-dimensionally elaborated extravascular spaces for the diffusion of metabolites and physiological messengers, including hormones.     

The blood vascular architecture of the extra-adrenal chromaffin body in the adult rat: a scanning electron microscopic study of corrosion casts

A well developed extra-adrenal chromaffin body with an axis of 200-400 micron was found in seven out of thirty adult male Wistar rats under a stereomicroscope. All seven bodies were located between the left and right kidneys. Blood vascular beds of the five bodies were reproduced with a methacrylate casting medium and observed with a scanning electron microscope. It was revealed that the extra-adrenal chromaffin body contained remarkedly numerous capillaries, which anastomosed with each other to form a conglomerated network. The blood capillaries were of small and uniform caliber and did not represent swollen sinusoids as in the adrenal medulla. The capillary network was denser than that in the adrenal medulla and had no direct vascular linkage with the adrenal cortex or an extra-adrenal cortical body. Histological examination of the two bodies treated with dichromate containing fixatives confirmed that they mainly consisted of chromaffin cells. These findings suggest that in the rat, extra-adrenal chromaffin bodies survive throughout life, actively producing catecholamines.     

Cellular and subcellular immunohistochemical localization of angiotensin-converting enzyme in the rat adrenal gland

Angiotensin-converting enzyme (ACE) was localized by immunocytochemical methods in the rat adrenal gland. The three-layer peroxidase-antiperoxidase method was used with light and electron microscopy. At the cortical level, ACE immunoreactivity occurred only on the luminal side of vascular endothelial cell membranes in the adrenal capsule, whereas no ACE activity was found in the zona glomerulosa, fasciculata, or reticularis. ACE immunoreactivity was found mainly but not exclusively on the luminal side of all the types of vessels in the adrenal medulla such as capillaries, venous sinuses, and arteriae medullae. In addition, ACE was localized on the plasma membrane of chromaffin cells but never in Schwann cells nor in nerve fibers. These results provide evidence for a local production of angiotensin II at the vascular level in the adrenal gland. In addition, the presence of ACE on the plasma membrane of chromaffin cells suggests that angiotensin II or other peptides, such as bradykinin, could be metabolized here.     

Scanning electron microscopy of esophageal microvasculature in human infants and rabbits

Summary The microvasculature of the esophagus was studied by scanning electron microscopy of vascular corrosion casts in human infants and rabbits. In both species, segmental circumferential arteries arise from main longitudinal arteries, the latter giving off numerous perforating arteries. The tunica muscularis is supplied by branches of circumferential and perforating arteries, the submucosa and its glands by branches of perforatings. Terminal arborizations of perforating arteries feed a subepithelial capillary network. These capillaries are drained by a venous plexus in the lamina propria which is connected to a submucosal venous plexus. Perforating veins, running parallel to the corresponding arteries, connect the submucosal plexus with circumferential veins, and finally empty into main longitudinal veins. Valves were not present in any of the veins. Submucosal veins were less numerous in man than in rabbit. The number and caliber of equivalent vessels in human submucosal plexus decreased from the pharyngoesophageal to the gastroesophageal junction, suggesting the latter to be at particular risk in portal hypertension. The subepithelial capillary network reveals a longitudinal arrangement in rabbits, while the same network shows no preferential organization in human infants. The microvascular architecture of the esophagus in humans and rabbits is comparable, especially in the lay-out of the venous plexuses and the absence of venous valves. Therefore the rabbit could serve as an experimental model for studies on portal hypertension. The present results strongly suggest particular significance of the venous plexus in the lamina propria for the genesis of esophageal varices.     

Blood vascular architecture of the rat extra-adrenal cortical body: a scanning electron microscopic study of corrosion casts

A well developed extra-adrenal cortical body with an axis of 200-700 micron was found in eighteen of thirty adult male Wistar rats under a stereomicroscope. All eighteen bodies were located between the kidneys. Blood vascular beds of sixteen of the eighteen bodies were reproduced with a methacrylate casting medium and observed with a scanning electron microscope. The extra-adrenal cortical body was found to contain remarkably numerous capillaries which anastomosed with each other to form a conglomerated network; it received one afferent vessel and issued one to three (usually, one) efferent vessels. The blood capillaries were of sinusoidal and uniform calibers, and resembled those of the adrenal cortex. The network with an axis of 300-700 micron possessed a typical, deep efferent rootlet which corresponds to the central vein of the adrenal gland. Histological examination of the two bodies treated with Orth's or Helley's fixative confirmed that they consisted of non-chromaffin cells similar to those of the adrenal cortex. These findings suggest that in the rat, the extra-adrenal cortical bodies persist throughout life, actively producing cortical hormones.     

Mixed cortical adenoma and composite pheochromocytoma-ganglioneuroma: an unusual corticomedullary tumor of the adrenal gland

Adrenal neoplasms composed of more than one cell type and demonstrating a mixed histologic appearance are exceedingly rare. We report the clinical and pathologic features of a morphologically distinctive tumor of the adrenal gland composed of cortical, chromaffin, and neural cells. Histologically, the tumor consisted of intermixed areas of proliferating cortical cells resembling adrenal cortical adenoma, neoplastic chromaffin cells consistent with pheochromocytoma, and a ganglioneuromatous stroma. The presence of the cortical, medullary, and neural components within the tumor was confirmed by immunohistochemical studies. The present case serves to broaden the morphologic spectrum of mixed tumors that may be encountered in the adrenal gland.     

A review of the anatomy and clinical significance of adrenal veins

The adrenal veins may present with a multitude of anatomical variants, which surgeons must be aware of when performing adrenalectomies. The adrenal veins originate during the formation of the prerenal inferior vena cava (IVC) and are remnants of the caudal portion of the subcardinal veins, cranial to the subcardinal sinus in the embryo. The many communications between the posterior cardinal, supracardinal, and subcardinal veins of the primordial venous system provide an explanation for the variable anatomy. Most commonly, one central vein drains each adrenal gland. The long left adrenal vein joins the inferior phrenic vein and drains into the left renal vein, while the short right adrenal vein drains immediately into the IVC. Multiple variations exist bilaterally and may pose the risk of surgical complications. Due to the potential for collaterals and accessory adrenal vessels, great caution must be taken during an adrenalectomy. Adrenal venous sampling, the gold standard in diagnosing primary hyperaldosteronism, also requires the clinician to have a thorough knowledge of the adrenal vein anatomy to avoid iatrogenic injury. The adrenal vein acts as an important conduit in portosystemic shunts, thus the nature of the anatomy and hypercoagulable states pose the risk of thrombosis. Clin. Anat. 27:1253–1263, 2014. © 2014 Wiley Periodicals, Inc.     

Histological study of intrahepatic cavernous transformation in a patient with primary myelofibrosis and portal venous thrombosis

Summary Cavernous transformation in the liver was examined histologically by serial section observations, in an autopsy case of portal venous thrombosis and primary myelofibrosis. Cavernous transformation was present from the hepatic hilus to medium-sized portal tracts and was composed of dilated and thin-walled vessels. Serial sections disclosed that these vascular channels were anastomotic and occasionally communicated with occluded portal venous radicles. In places they entered directly into the hepatic parenchyma without accompanying biliary or arterial elements, and also drained into the patent portal venous branches beyond the occluded segment. The study demonstrated that cavernous transformation in the liver develops as hepatopetal collaterals secondary to the portal venous obstruction. Periportal and peribiliary capillary plexus may become cavernous in the presence of portal venous occlusion.     

Immunofluorescence microscopic evaluation of the intermediate filament expression of the adrenal cortex and medulla and their tumors.

Normal adrenal glands (10 specimens) and adrenal gland tumors (58 cases) were immunohistochemically evaluated for different types of intermediate filament (IF) proteins. Some of the normal cortical cells showed cytokeratin positivity, and no positivity was seen for epidermal keratin or other types of IF. In the adrenal medulla, neurofilament positivity was seen in nerve axons, some ganglion cells, and chromaffin cells; and cytokeratin-positive cells could not be detected. Only the vascular and connective tissue elements showed vimentin positivity in both cortical and medullary areas. In half of the cortical carcinomas (13/25), cytokeratin-positive tumor cells were found. Furthermore, vimentin-positive tumor cells were present in 10 of 25 cases, in some of them together with cytokeratin-positive cells. Thus, the results show heterogeneity among the adrenal cortical carcinomas. Interestingly, many benign adrenal cortical tissues and some carcinomas lacked immunoreactivity for all types of IF, suggesting a poorly developed IF system in these tissues. In contrast to adrenal cortical tumors, pheochromocytomas contained neurofilamentlike immunoreactivity. These results reflect the different cellular nature of adrenal cortical and medullary tumors, which apparently can be distinguished from each other with antibodies to intermediate filament proteins.     

Local transfer of hormones between blood vessels within the adrenal gland may explain the functional interaction between the adrenal cortex and medulla

The adrenal cortex has a local stimulatory action on synthesis and secretion of adrenaline by the adrenal medulla. This interaction may be based on nervous transmission and/or on glucocorticoids secreted trom the cortex either exerting paracrine effects or reaching the medulla through the local vascular system. The existence of a dual capillary network, a portal system, now seems unlikely. However, a new concept is postulated: the high demand for glucocorticoids in the medulla may be met by local transfer to blood vessels within the adrenal gland, particularly the medullary arteries.     

Relationship between chromaffin cells and blood vessels in the rat adrenal medulla: A transmission electron microscopic study combined with blood vessel reconstructions

The rat adrenal medulla architecture was examined using a combination of medullary blood vessel reconstructions and transmission electron microscopy. The peripheral radicles of the central vein and the medullary capillaries of the medullary arteries were thus precisely identified in the electron microscopic observations. The observations confirmed that the peripheral segments of the central vein were sinusoidal vessels with an attenuated and fenestrated endothelial wall. No ultrastructural differences were observed between segments lined by epinephrine-storing cells and those lined by norepinephrine-storing cells. The findings suggest that these peripheral segments of the adrenal central vein were sites of cortical hormonal effects on the adrenal medulla. The vessel structure does not support the hypothesis that medullary chromaffin-cell development is controlled by selective distribution of adrenal blood vessels.     

Hypophyseal angioarchitecture of common tree shrew (Tupaia glis) revealed by scanning electron microscopy study of vascular corrosion casts

The vascular corrosion cast technique in conjunction with scanning electron microscopy (SEM) was used for the study of pituitary microvascularization in the common tree shrew (Tupaia glis). The pituitary vascular casts were obtained by infusion of low viscosity methyl methacrylate plastic (Batson's no. 17) mixture. It was found that the blood supplies to the pituitary complex were from branches of the circle of Willis and could be divided into two groups. The first group consisted of two to four superior hypophyseal arteries (SHAs) branching off from the internal carotid artery supplying each half of the median eminence (ME), infundibular stalk (IS), and pars distalis (PD). The SHAs supplying the ME branched into internal and external capillary plexi. The internal plexus had a larger capillary size (approximately 15 μm in diameter), was deeper in position, and had denser and more complex capillary loops than those in the external plexus. The capillaries of the external plexus were approximately 10 μm in diameter. The two plexi drained into 15–20 hypophyseal portal veins (HPVs) which were located mainly along the ventral and ventrolateral surfaces of the IS before breaking up into large capillaries (approximately 18 μm in diameter) with an anteroposterior arrangement within the PD. The second group consisted of one inferior hypophyseal artery (IHA) on each side branching off from the internal carotid artery. These arteries gave off branches to pierce the dorsolateral and ventrolateral aspects of infundibular process (IP) before branching off to form a capillary network. They also gave rise to radiating capillaries to supply the pars intermedia (PI) surrounding the cortical area of the IP. The hypophyseal cleft separating the PI from the PD was clearly seen with very few blood vessels. The capillaries in both PD and IP joined to form confluent hypophyseal veins draining the blood into the cavernous sinus.     

Corticomedullary mixed tumor of the adrenal gland with concurrent adrenal myelolipoma

We report the case of a corticomedullary mixed tumor of the adrenal gland in a 55-year-old woman with a left adrenal mass who presented with mild symptoms of Cushing syndrome and an elevated urinary cortisol level. The patient underwent a left adrenalectomy. A well-circumscribed 2.5-cm mass, composed of an admixture of adrenal cortical cells and pheochromocytes, and an incidental 0.7-cm myelolipoma were present in the resected left adrenal gland. The diagnosis of adrenal corticomedullary mixed tumor was confirmed by both immunohistochemistry and electron microscopy. To our knowledge, this is the eighth well-documented report of this rare tumor.     

Postnatal development of the vascular pattern in the rat telencephalic pia-arachnoid

Summary The postnatal changes in arrangement of the vascular system of the pia-arachnoid of rats are described based on scanning electron microscopy of microcorrosion casts and transmission electron microscopy. At birth, the distal arteries and veins are embedded in a dense plexiform network of immature capillaries. Arteries and veins are interconnected by many small capillary anastomoses. The trunks are located above the pial plexus. The underlying plexiform vessels provide the matrix for the formation of additional collateral and precortical segments during further development. During the first postnatal week, the distal pial arteries and veins become visible as separate channels and emerge from the subjacent capillary plexus. The pattern of anastomosing arterial rings is now clearly visible. The pial arterial tree can be subdivided into conductive, collateral, and precortical distributive segments, according to Jokelainen et al. (1982). Subsequently, passive expansion of the vascular system takes place during the period of rapid brain growth. In young adults the majority of the formerly closed arterial rings are interrupted, possibly by regression of single collateral arterial segments (Fig. 6). The dense venous capillary plexus of the pia is maintained during the first eight days in spite of marked brain growth. The process of reduction of this capillary plexus starts at the arterial side and proceeds from proximal to distal segments of the veins during the second and third week. The capillary segments, which provide anastomosis between arterial and venous vessels, disappear at the same time as the regression of the dense venous capillary network. Two processes may biodify the architecture of the pial vasculature during development: brain growth and maturation on the one side and cytodifferentiation of vascular walls on other.This work was presented in part at the Third World Congress for Microcirculation, Oxford, 9–14 September 1984, and was published in abstract form (1984, Int J Microcircul Clin Exp 3:308)     

Angioarchitecture of the coeliac sympathetic ganglion complex in the common tree shrew (Tupaia glis)

The angioarchitecture of the coeliac sympathetic ganglion complex (CGC) of the common tree shrew ( Tupaia glis ) was studied by the vascular corrosion cast technique in conjunction with scanning electron microscopy. The CGC of the tree shrew was found to be a highly vascularised organ. It normally received arterial blood supply from branches of the inferior phrenic, superior suprarenal and inferior suprarenal arteries and of the abdominal aorta. In some animals, its blood supply was also derived from branches of the middle suprarenal arteries, coeliac artery, superior mesenteric artery and lumbar arteries. These arteries penetrated the ganglion at variable points and in slightly different patterns. They gave off peripheral branches to form a subcapsular capillary plexus while their main trunks traversed deeply into the inner part before branching into the densely packed intraganglionic capillary networks. The capillaries merged to form venules before draining into collecting veins at the peripheral region of the ganglion complex. Finally, the veins coursed to the dorsal aspect of the ganglion to drain into the renal and inferior phrenic veins and the inferior vena cava. The capillaries on the coeliac ganglion complex do not possess fenestrations.     

Microvascular architecture of the pampiniform plexus-testicular artery system in the rat: A scanning electron microscope study of corrosion casts

The vascular architecture of the rat pampiniform plexus was studied by scanning electron microscopy of vascular corrosion casts. The plexus consists of a thick bundle of many anastomosing veins that entirely and closely surround the convoluted segments of the testicular artery. This specially developed close contact of the pampiniform plexus with the testicular artery may allow heat exchange between the plexus and the artery to maintain the cooled condition of the testis. The epididymal arteries are also closely surrounded by the networks of the epididymal veins. It is likely that heat exchange may operate even between these epididymal vessels. The ductus deferens is provided with no vascular channels for such heat exchange. A loose or coarse capillary network is always observed between the testicular artery and the pampiniform plexus. This network is supplied by the epididymal arteries and drains into the pampiniform plexus.     

Microradiography of the rabbit's hepatic microcirculation. The similarity of the hepatic portal and pulmonary arterial circulations

Examination of microradiographs of liver indicate that the hepatic arteries supply the richly anastomosing arterial plexus around the biliary ducts. This arterial plexus supplies the portal veins directly and the peripheral hepatic sinusoids. Arterial “boosters” penetrating deep within the lobule were not seen. Hepatic veins receive sinusoids at irregular angles and frequent intervals, whereas portal veins distribute flow through short right angle inlet venules spaced at greater intervals. Pulmonary arteries also distribute flow to capillaries through short right angle precapillaries and pulmonary veins receive capillary drainage at irregular angles and frequent intervals. The location of capillary beds of both liver and lung only 10 to 30 μ from inflow channels appears “ideally” suited for circulations of low vascular resistance. The analogy of liver and lung relates biliary system to airway, hepatic artery to bronchial artery, portal vein to pulmonary artery, hepatic vein to pulmonary vein and ductus venosus to ductus arteriosus. In particular, should the pulmonary artery be considered a “pulmonary portal vein”.     

Membrane potential measurement in cells of the adrenal gland

1. Recordings of transmembrane potentials have been made in vitro from the cells of the adrenal gland using glass micro-electrodes.2. There was only a small species variation in the mean membrane potential of the cortical cells of the rabbit, rat and kitten; 66.2, 70.5, and 71.4 mV respectively.3. The membrane potential of cortical cells was dependent upon the external potassium concentration, [K](o). Raising [K](o) above the normal concentration of 4.7 mM by addition of KCl decreased the membrane potential; lowering [K](o) from normal increased it. The decrease in membrane potential was still evident when chloride was replaced by sulphate. Increasing [K](o) 10-fold decreased the membrane potential of rabbit cortical cells by 44 mV and of kitten cortical cells by 50 mV.4. The mean membrane potential measured in medullary chromaffin cells was for the rabbit 24.2 mV, rat 20 mV, and kitten 31.7 mV. The potentials of medullary cells were much less affected by changes in [K](o) than were cortical cell potentials.5. Age had little influence upon either cortical or medullary membrane potentials of adrenal glands, at least in early life.