Inhibition by Guan-mu-tong (Caulis aristolochiae manshuriensis) of the growth of spontaneous mammary tumors in SHN virgin mice

Multiparous SHN mice with spontaneous mammary tumors (5-10 mm in size) were given water extract of Guan-mu-tong (Gmt; Caulis aristolochiae manshuriensis) (0.5%) ad libitum as drinking water for 10 days. This treatment retarded significantly the growth of mammary tumors compared with the controls. By contrast, normal mammary gland growth, histology of adrenals and ovaries, and body weight were affected little by the Gmt treatment. Gmt appears to be the first agent inhibiting the growth of spontaneous mouse mammary tumors of palpable size by per os treatment.

Endocrine abnormalities in patients with amyloidosis

This study was conducted to examine systematically the endocrine function in 10 patients diagnosed to have renal amyloidosis. Basal and dynamic endocrine tests (GnRh, TRH, and ACTH stimulation tests as well as modified glucose tolerance test) were performed in all patients. Eight patients had advanced renal disease (creatinine clearance < 10 mL/min). Hypofunction of the thyroid gland was present in 5 out of those 8 patients, and thyroid biopsy confirmed amyloid deposition. Of those 5 patients, pituitary and adrenal defects were present in 2. In conclusion, endocrine abnormalities were evident at a later stage of renal amyloidosis. Hypothyroidism was present in all patients who manifested endocrine defects and should be considered as an early sign of endocrine involvement with the disease.

Impact of familial amyloid associated polyneuropathy on duodenal endocrine cells

Duodenal endocrine cells in 11 patients with familial amyloid associated polyneuropathy (FAP) were compared with those in 12 healthy volunteers by means of immunohistochemistry and morphometry. The total endocrine cell content, determined by the argyrophilic reaction and chromogranin A immunoreactivity, was significantly reduced in FAP patients compared with controls. There was a significant reduction in the serotonin, cholecystokinin/gastrin, and secretin immunoreactive cell content. A decreased cell content was also noted for somatostatin and gastric inhibitory polypeptide immunoreactive cells but this was not statistically significant. Amyloid deposits were noted in seven of the 11 biopsy specimens from FAP patients, but otherwise the duodenum was histologically normal in both groups. The reduction in endocrine cell content was not correlated with the degree of amyloid deposit in the duodenum. These findings indicate that patients with FAP have reduced intestinal endocrine cells. This does not seem to be related to amyloid deposits in the mucosa or to villous or crypt abnormalities. The observed changes in endocrine cells may contribute to the development of intestinal motility dysfunction and maldigestion in these patients.

Endocrine and mucous differentiation by a cloned human rectal adenocarcinoma cell line (HRA-19) in vitro: inhibition by TGF-beta 1

Colorectal epithelium is composed of absorptive, mucous and endocrine cells, all of which are considered to arise from a common stem cell located in the crypt base. However, the factors controlling the commitment to differentiate are poorly understood. This is partly due to the lack of in vitro model systems for the study of differentiation in colorectal epithelium. The HRA-19 cell line, established from a human rectal adenocarcinoma, has been shown to have multipotential characteristics with cloned HRA-19 cells able to differentiate into absorptive, mucous and endocrine cells when grown as xenografts. The lack of such differentiated cells in HRA-19 monolayers in vitro suggests that differentiation is controlled by extracellular matrix, stromal cells and/or soluble factors. Such observations show that differentiation in HRA-19 cells can be controlled by extrinsic factors and therefore provide a model system for studying control of differentiation in colorectal epithelium. Unfortunately, the restriction of differentiation to xenografts of the cell line limits the degree to which this differentiation can be manipulated. In this study, the possibility that HRA-19 cells could be induced to differentiate in vitro under appropriate conditions has been investigated. Endocrine and mucous cells were identified by immunocytochemistry with differentiation-related antibodies and histology of monolayers. Preconfluent HRA-19 cells grown in 10% foetal calf serum formed a well polarised monolayer with apical tight junctions and sparse microvilli, but cells with mucous or endocrine phenotypes were only very occasionally observed. However, endocrine and mucous cells could reproducibly be demonstrated in postconfluent monolayers grown in 1% foetal calf serum.(ABSTRACT TRUNCATED AT 250 WORDS)

The consequences of hypergastrinemia

The only gastrin-dependent gastric endocrine cells are the fundic ECL cells. Excessive hypergastrinemia stimulates ECL cell proliferation in animals and man. The growth of other gastric endocrine cells is regulated by the gastric pH. Hypergastrinemia in man results in diffuse and linear hyperplasia of the ECL cells, while micronodular hyperplasia is correlated to the grade of corpus gastritis. ECL cell dysplasia and gastric carcinoids in man have been observed only in patients with gastrinoma as part of the MEN I syndrome and with pernicious anemia. Gastrin dependence of GI adenocarcinoma has not been established. Experimental findings may be explained by the presence of gastrin receptors and the role of gastrin as an autocrine growth factor. Epidemiological data do not support gastrin dependence of carcinoma of the stomach, the pancreas and the colon.

Surgical management of primary hyperparathyroidism in multiple endocrine neoplasia types 1 and 2

BACKGROUND

The surgical management of primary hyperparathyroidism in multiple endocrine neoplasia type 1 (MEN 1) remains controversial. In addition, the rarity of MEN 2A-related hyperparathyroidism has not allowed for a separate strategy for this condition. This study examines our surgical experience with MEN 1- and MEN 2A-related hyperparathyroidism and attempts to define a rational therapeutic approach to each.

METHODS

Between 1970 and 1991, 124 patients underwent surgery for MEN-related hyperparathyroidism at our institution. Primary cervical explorations were performed in 84 patients with MEN 1 and 18 with MEN 2A. An additional 22 patients with MEN 1 underwent reoperative surgery. All patients with MEN 2A underwent concomitant thyroidectomy for medullary thyroid cancer.

RESULTS

Compared with patients with MEN 1, patients with MEN 2A, had a lower preoperative serum Ca2+ level and fewer symptoms or complications of hypercalcemia. Multiple gland disease was evident in 90% and 83%, respectively, of patients with MEN 1 and MEN 2A. Primary explorations in patients with MEN 1 resulted in surgical cure in 94%, persistent hypercalcemia occurring in no patient undergoing subtotal resection compared with 17% of patients in whom more conservative resections were performed (p = 0.005). In patients with MEN 1, 10-year recurrence of hypercalcemia was 16% for primary explorations and 30% for reoperative procedures. In contrast, all patients with MEN 2A, whether treated by total, subtotal, or lesser resections, were cured after surgery and none had recurrence during a median follow-up of 5.8 years.

CONCLUSIONS

In MEN 1 the surgical principles should be (1) identification of all four glands, (2) subtotal resection to ensure cure and facilitate possible reoperation, and (3) excision of supernumerary thymic glands. In MEN 2A we should identify and resect all enlarged glands for cure, but routine subtotal resection need not be performed because this condition is readily cured and recurrence is rare.

The pathology of the gastrointestinal endocrine system

Among endocrine tumors occurring in the gastrointestinal tract, midgut argentaffin EC cell carcinoids, gastric argyrophil ECL cell carcinoids, duodenal gastrin cell tumors, and rectal trabecular L cell carcinoids (in order of decreasing frequency) are those occurring more frequently. Together, they account for more than 80% of such tumors. Duodenal somatostatin cell tumors, gangliocytic paragangliomas, and differentiated neuroendocrine carcinomas are also well-defined tumor entities. The carcinoid syndrome, either classical, with intermittent flushing, hypotension, and diarrhea, or atypical, with persistent histamine-type red flushing, bronchospasm, and no diarrhea, and Zollinger-Ellison syndrome, with severe peptide ulcer disease, are the only hyperfunctional syndromes consistently found in association with these tumors. The carcinoid syndrome occurs in about 10% of gastrointestinal carcinoids, usually in their advanced, metastatic stage. The Zollinger-Ellison syndrome occurs in association with about 40% of intestinal gastrin cell tumors, including small intramural growths. Tumor prognosis depends on the mode and site of presentation, histology, cell type(s), size, level of invasion, metastases (especially distant metastases), and associated clinical syndrome or background disease. Hormones, trophic factors, inherited genetic traits, somatic mutations, and some chronic inflammatory processes are pathogenetically important in a large proportion of cases.

Endocrine cells in diffuse pulmonary fibrosis

BACKGROUND

There is evidence to suggest, particularly from studies in animals, that the products of pulmonary endocrine cells, especially gastrin releasing peptide, may have a role in the pathogenesis of fibrosis in the lung. This study was carried out to examine the morphology, number, distribution, and content of pulmonary endocrine cells in tissue from 49 patients with diffuse pulmonary fibrosis.

METHODS

Twenty patients with interstitial pneumonitis, 17 with early fibrosis, and 12 with frank honeycombing were studied, together with five age matched controls without pulmonary disease. Endocrine cells were immunolabeled by the avidin-biotin complex method for two general markers (protein gene product 9.5 and neuron specific enolase) and a range of normal and aberrant secretory products.

RESULTS

In the early stages, characterised by vigorous pneumonitis, endocrine cells were normal in appearance and distribution but very few in number. They contained only those secretory products normally found in such cells in health; inappropriate substances were not seen. By the time of early fibrosis endocrine cells were even fewer. None were identifiable in the lungs affected by honeycombing, despite the fact that all contained intact, well preserved epithelium.

CONCLUSIONS

It seems unlikely that the products of pulmonary endocrine cells can have any role in the pathogenesis of diffuse pulmonary fibrosis in man, the diminution in their number with advancing fibrosis probably reflecting their loss simply as a consequence of generalised epithelial damage.

Unusual endocervical lesions with endocrine cells

Four cases of unusual lesions of endocervix are presented. They were all incidental findings, showing no obvious infiltrative and metastatic properties to attest their malignant nature. Two lesions were entirely confined to the endocervical mucosa. The main characteristics of these proliferative processes thus were an abnormal architecture with branched or small glands, a hypermucinous benign-appearing epithelium of endocervical type, and stromal smooth-muscle. In contrast with normal endocervical mucosa, all lesions contained prominent and variegated endocrine cells. These 4 cases were quite comparable to 3 other observations previously reported. This homogeneous group of endocervical lesions does not correspond to a well-defined type of endocervical neoplasia. It shares morphological analogies with adenoma malignum. The relationship with adenoma malignum as well as with some other gynaecological neoplasms is discussed. The recognition of these small-sized and highly differentiated lesions is largely facilitated by the use of the Grimelius reaction to detect argyrophilic cells.

Endocrine cells in colorectal adenocarcinomas: incidence, hormone profile and prognostic relevance

The occurrence of endocrine cells in 350 cases of colorectal adenocarcinoma was studied by immunohistochemistry for chromogranin A (CGA). The hormone profile of endocrine tumor cells, the correlation between endocrine differentiation and presence of other colorectal epithelial-cell lineages and the prognostic relevance of endocrine differentiation in colorectal cancer were investigated. CGA-positive tumor cells were found in 30% of cases, 21% showing moderate positivity and 9.0% extensive positivity. Of CGA-positive tumors, 70% additionally produced neurohormones, mainly indigenous to normal colorectal epithelium: 55% showed immunoreactivity for glucagon-like substances, 20% for serotonin and 10% for somatostatin, PYY and HCG. No immunoreactivity was found for various neurohormones not normally produced by colorectal endocrine cells. CGA-positive tumors tended to be more aggressive than CGA-negative tumors. Especially, tumors with extensive CGA positivity showed shorter survival, which was most apparent within Dukes' stage C. In multivariate analysis, extensive CGA positivity was an independent indicator of poor prognosis. CGA immunoreactivity significantly correlated with mucin production, but not with expression of secretory component (SC), a columnar-cell marker. Mucin production significantly correlated with SC expression. Tumors positive for CGA but not for mucin and/or SC showed the worst prognosis. SC expression was a relatively favorable feature, and mucin-producing tumors showed intermediate behavior.

Human Caco-2 cells transfected with c-Ha-Ras as a model for endocrine differentiation in the large intestine

Endocrine cells occur in approximately 30% of all colorectal adenocarcinomas, and this feature appears to correlate with a relatively poor prognosis. To study the factors regulating endocrine differentiation in colorectal cancer, which may bear resemblance to the regulation of endocrine differentiation in normal intestinal mucosa, models in which differentiation can be manipulated are essential. However, endocrine features in colorectal cancer cell lines are scarce and are almost exclusively observed in xenografts, presumably as a result of differentiation induction by stromal components. We attempted to demonstrate endocrine differentiation in the colonic adenocarcinoma cell line Caco-2, which is frequently used as a model for enterocytic differentiation. In vitro endocrine tumor cells were not encountered. In vivo studies were cumbersome, because of the low take rate of Caco-2 cells. We did manage to establish nude mouse xenografts of Caco-2 cells by inoculating cells in collagen gel and by suppressing natural killer cell activity. In an attempt to induce a better take rate and to investigate the effect of Ras oncoprotein overexpression on endocrine differentiation, Caco-2 cells were transfected with a point-mutated c-Ha-Ras gene. The cell line Caco-2 EJ6, generated from these experiments, could be xenografted in nude mice with a high take rate, yielding a moderately well differentiated adenocarcinoma, morphologically identical to the tumors derived from untransfected Caco-2 cells. The xenografts displayed goblet cell, enterocytic, Paneth cell and endocrine differentiation. In vitro endocrine differentiation was observed neither under standard conditions nor with extracellular matrix components as differentiation inducers. We conclude that the Caco-2 cell line and its c-Ha-Ras transfected subline Caco-2 EJ6 in vivo display endocrine differentiation. Ras overexpression does not enhance endocrine differentiation. Due to its favorable growth properties in vivo, Caco-2 EJ6 is a suitable model for studies on endocrine differentiation in colorectal cancer.

Rapid induction of enterochromaffinlike cell tumors by histamine2-receptor blockade

The effect of acid inhibition on gastric endocrine cells was investigated in Praomys (Mastomys) natalensis. Long-term treatment (1 to 32 weeks) with an irreversible histamine 2-receptor blocker (loxtidine) caused a sustained increase in plasma gastrin levels, which was accompanied by a gradual increase in histamine and histidine decarboxylase activity of the gastric oxyntic mucosa. The density of endocrine cells in the oxyntic mucosa increased gradually, doubled by 8 weeks, and was three times that of controls after 24 weeks of treatment. Hyperplastic changes in the endocrine cell population were evident after 2 to 8 weeks in all animals, whereas dysplastic or neoplastic lesions were observed in half the animals after 16, 24, and 32 weeks of treatment. Gross tumors in the oxyntic mucosa were observed in 1/4 of the animals treated for 24 or 32 weeks. Proliferating cells were identified as enterochromaffinlike cells because they were argyrophilic and immunopositive for chromogranin A and histamine. The results demonstrate that histamine 2-receptor blockade initiated by loxtidine promotes a rapid development of enterochromaffinlike cell tumors in Mastomys and suggest a critical role for gastrin in the formation of these tumors. However, the rate and frequency by which carcinoid tumors appeared in Mastomys after acid inhibition was much greater than that reported in other species, indicating that several factors, including hormonal and genetic factors, are important in the development of gastric endocrine tumors.

Extracellular matrix components induce endocrine differentiation in vitro in NCI-H716 cells

Endocrine cells occur in +/- 30% of colorectal adenocarcinomas. The significance of this phenomenon in terms of tumor behavior is still controversial. Endocrine differentiation in colorectal cancer cell lines is almost confined to tumor xenografts in vivo, suggesting that endocrine differentiation might be regulated by epithelial-stromal interactions. This hypothesis was studied in the cecal adenocarcinoma-derived cell line NCI-H716 by comparing the expression of chromogranin A protein and messenger RNA in vivo and in vitro and by attempts to induce differentiation in vitro. We found that chromogranin A expression, which was strongest in vivo, could be significantly enhanced in vitro by culturing tumor cells in the presence of native extracellular matrix, on fibroblast feeder layers, and in a defined medium with basic fibroblast growth factor. The results suggest that the extracellular matrix induces endocrine differentiation through factors (e.g., basic fibroblast-growth factor) that may be produced by stromal cells and after secretion bind to the extracellular matrix.

[Systematic study of the morphology of the immune and endocrine organs during the infectious process]

Immune and endocrine organs of 259 children and adults who had died of sepsis, local purulent-inflammatory affections were studied morphologically and morphometrically. It is established, that compensatory morphological changes in the lymphoid tissue and endocrine organs are integrated into a united system the structural basis of which are numerous inter- and intra-organ correlations. A systemic interaction between the lymphoid and endocrine organs at early age is pronounced much weaker than in the adults. A progressive destruction of this systemic interaction takes place in sepsis and results in an increase of informational entropy and the coefficient of the system disintegration. Inability of the body to fight bacteremia and to localize the infection is secondary to the system destruction this being due to high frequency of previous immuno-endocrinopathies.

Computed tomographic, magnetic resonance, and monoclonal antibody imaging of endocrine tumors

Recent advances in diagnostic imaging with computed tomography, magnetic resonance imaging, and monoclonal antibody imaging in endocrine tumor evaluation are reviewed. Computed tomography is a mature technology whose role has not changed recently. Magnetic resonance imaging is continuing to advance in scan techniques, scan time reduction, and use of intravenous contrast agents; its future role on a routine basis may allow it to supplant computed tomography in endocrine tumor identification. Monoclonal antibody imaging has not yet proven to be as reliably diagnostic for tumor identification as is computed tomography, but continuing technical advances predict an advancing role for diagnosing endocrine tumors with this modality.

[Pathology of experimental hypocobaltosis in goats]

Histological changes in chronic experimental hypocobaltosis manifest as atrophic-degenerative alterations and restructuring of endocrine organs as well as a decrease in systemic resistance (accidental transformation of the thymus, duodenitis and sigmoiditis in some animals). Pronounced fat hepatosis and signs of iron metabolism damage (cheilitis, spleen siderosis) are found as well.

Composite glandular-endocrine cell carcinoma of the extrahepatic bile duct: immunohistochemical study

A composite glandular-endocrine cell carcinoma of the extrahepatic bile duct in a 64 yr old Japanese man is reported. A nodular polyp measuring 1.9 x 1.1 cm was located in the confluence of the extrahepatic bile duct. Histologically, the tumor was composed of well differentiated tubular adenocarcinoma and small cell neuroendocrine carcinoma with a transition between the 2 components. The 2 areas of the tumor immunohistochemically revealed a clear-cut difference in functional differentiation. Tumor cells in the glandular component were immunoreactive to both carcinoembryonic antigen (CEA) and CAM 5.2, while those in the small cell area were immunoreactive to neuroendocrine markers such as neuron specific enolase (NSE), chromogranin A and serotonin. These results suggest that the tumor arose from a multipotential stem cell capable of differentiation in 2 directions.

NCI-H716 cells as a model for endocrine differentiation in colorectal cancer

In colonic neoplasms, endocrine differentiation is encountered not only in carcinoid tumors but also in adenocarcinomas, where endocrine cells may represent a distinct line of differentiation in the tumor. The significance of endocrine differentiation in colorectal cancer is not well established, partly because of the paucity of tumor cell lines which can serve as a model for studying endocrine differentiation. In this report we describe the properties of NCI-H716 cells, a cell line derived from a poorly differentiated adenocarcinoma of the caecum, under various in vitro conditions and as xenografts in athymic mice. Phenotypical properties were immunohistochemically assessed using a panel of differentiation related antibodies, and also by Northern blot analysis and by electron microscopy. Receptors for biogenic amines and peptide hormones were analyzed by ligand binding assay. These studies show that: 1. NCI-H716 cells can be undifferentiated, or show endocrine, mucin-producing or "amphicrine" properties. 2. Endocrine differentiation of NCI-H716 cells preferentially occurs in xenografts in athymic mice, which suggests that mesenchymal elements induce endocrine differentiation. 3. NCI-H716 cells express large amounts of high affinity receptors for gastrin, serotonin and somatostatin and these substances can regulate growth. Thus, NCI-H716 cells form a suitable model for the study of endocrine differentiation in intestinal epithelium and of auto- or paracrine growth regulation in intestinal neoplasia.

Hepatocellular carcinoma containing endocrine cells. An autopsy report of triplecancer involving the liver, kidney and thyroid

An autopsy case of triplecancer (hepatocellular carcinoma of the liver, renal cell carcinoma of the kidney, and papillary carcinoma of the thyroid) was reported. Histological features of primary hepatic tumor suggested undifferentiated hepatocellular carcinoma (Edmondson-Steiner's Grade IV). However, certain tumor cells showed distinctive argyrophilic reactions and electron microscopy revealed small round granules resembling electron dense endocrine secretory granules in their cytoplasm. Immunohistochemistry demonstrated that tumor cells showed a positive reaction for AFP while some others were positive for chromogranin-A. Immunohistochemical demonstration of AFP production by tumor cells indicated their hepatocyte origin. No endocrine syndrome had been present and no alternative primary source of the endocrine tumor was detected. Tumors of the kidney and thyroid were considered to be incidentally combined.

Weaver syndrome

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Bile Duct Adenomas With Endocrine Component

Bile duct adenomas are small nodules that are usually found incidentally on the liver surface at abdominal surgery or autopsy. We recently analyzed two such lesions that, in addition to the typical small caliber ducts, contained periductular nests and clusters of uniform round cells, suggestive of endocrine cell proliferation. Follow-up of these patients did not show endocrine tumors elsewhere. The lesions were studied by immunohistochemistry (avidin-biotin-peroxidase technique) and compared with conventional bile duct adenomas (seven cases). The results showed these cells to decorate with several endocrine markers, namely, neuron-specific enolase, chromogranin, synaptophysin, and Leu-7. Endocrine markers were not seen in the cells of conventional bile duct adenomas. Epithelial markers, that is, cytokeratin (CAM 5.2 antibody) and epithelial membrane antigen, were expressed by the cells composing both conventional bile duct adenomas and those with endocrine-like cells, although with less intensity in the endocrine cell clusters. We suggest that some bile duct adenomas contain endocrine cell proliferations that morphologically may resemble a small carcinoid tumor or the so-called pulmonary tumorlet. Neurosecretory granules have previously been identified in some cholangiocarcinomas and in bile duct proliferation associated with cholestasis. The endocrine clusters in biliary adenomas may constitute a diagnostic pitfall and must be separated from metastases of carcinoids or islet cell tumors.

Pathological findings in horses dying during an outbreak of the paralytic form of Equid herpesvirus type 1 (EHV-1) infection

In 1988 an outbreak of the paralytic form of Equid herpesvirus type 1 (EHV-1) infection occurred on a stud farm and several animals died. This provided an opportunity to perform detailed pathological investigations to gain insights into the pathogenesis of this spontaneous disease. Two paretic mares, three foals, an aborted foetus and its non-paretic dam were examined. The endotheliotropism of the virus was clearly demonstrated by the use of an indirect immunoperoxidase (IP) stain. At autopsy, evidence of viral infection was widespread in the foetus and foals, but limited or absent in the mares, probably reflecting differences in their immune status. Vascular lesions were present in the central nervous system (CNS) of the foals as well as the adults; they resulted in minimal neural lesions in the foals. Severe changes in the upper and lower respiratory tracts were a particular feature in the foals, two of which exhibited extensive vasculitis and thrombosis in the lungs. The IP technique was of great value in locating antigen-containing cells in the CNS of one mare when virus isolation was negative. It also revealed the presence of virus in less well documented sites such as the pancreas, gut, thyroid, uveal tract and the skin of the nares.

Heart and endocrine changes during central hypovolemia in man

Animal experiments have shown that severe haemorrhage often is characterized by an initial general increase in sympathetic activity leading to an increase in heart rate and a subsequent vagally mediated, reversible decrease in heart rate. It is likely that the decrease in heart rate is triggered by mechanoreceptors situated in the left ventricle. The receptors are supposed to be activated by a reduction in end-systolic volume occurring as a result of a decrease in venous return concomitant with the initial increase in heart rate. SA vago-vagal reflex elicited from and returning to the heart is thereby activated, resulting in a slowing of the heart. It has been hypothesized that the left ventricular receptors are activated when the ventricle contracts around an almost bloodless chamber. The decrease in heart rate may allow for an increased filling of the heart and an improved coronary perfusion. However, these experimental observations are in clear contradiction to the general description of the regulatory mechanisms operating during haemorrhagic shock in man as presented by authoritative medical, surgical and anesthesiological textbooks. Until now the (over-simplified) notion has been, that progressive haemorrhage results in an increased activation of the sympathetic nervous system leading to an increase in heart rate and that the occurrence of bradycardia was a sign of irreversible shock. The present systematic measurements in patients in haemorrhagic shock showed that the heart rate during severe haemorrhage often was normal (mean value 73 beats/min, range 46-98 beats/min). Simultaneous measurements of plasma concentrations of pancreatic polypeptide (an index of vagal activity) indicated that organs other than the heart also were exposed to increased vagal activity. A marked increase in the plasma concentration of vasopressin was not a constant finding as it was during the experimental-induced hypotensive central hypovolemia. This difference may be due to a decline in the release of vasopressin during prolonged haemorrhage. In order to elucidate essential regulatory mechanisms behind the clinical observations, central hypovolemia was induced experimentally by "head-up tilt", "lower-body negative pressure", "venous tourniquets of the thighs plus haemorrhage", and by epidural anesthesia. The initial stage of central hypovolemia was characterized by an increase in sympathetic nervous activity resulting in an increase in heart rate. Activation of the renin-angiotensin-aldosterone system occurred prior to marked increases in plasma concentrations of vasopressin. During progression of the central hypovolemia a qualitative shift in the regulatory mechanisms was evident.(ABSTRACT TRUNCATED AT 400 WORDS)