Sequential morphological and permeability changes in the rete capillaries during hyperglycaemia.

With the rete model of the eel swimbladder, we have studied the appearance and development of a microangiopathy during a 2-year period of hyperglycaemia. Hyperglycaemia was induced in the eel by chronic exposure to cold water. At 3-5 months, basement membrane thickness was twice the normal value and increased only slightly thereafter. Diffusion coefficients of permeability were measured in counter-current perfusion experiments for a variety of tracers that are believed to use different pathways of transcapillary transport. The permeability to sucrose was the first to significantly increase, at 6-8 months, followed by that of albumin, insulin, and inulin, at 9-11 months and that of sodium, at 18-24 months. The permeability to water and antipyrine remained stable throughout the study. The results indicate that in the rete model, chronic hyperglycaemia induces a rapid thickening of the capillary basement membrane and selective permeability increments in the various paths of transcapillary transport.

The rete mirabile of the eel: a useful model for the study of transcapillary passage of MR contrast agents.

Our purpose was to study the capillary leakage of MR contrast media using a pure capillary model, the rete mirabile of the eel. The rete is a countercurrent-exchange organ composed of an arterial and a venous capillary system that can be catheterized and perfused. Substances are introduced at the arterial input by a constant infusion, and their steady-state concentrations are measured at the arterial and venous outputs. The capillary leakage of four MR contrast agents--Gd-DOTA(MW = 561 D), carboxymethyldextran-Gd-DTPA (MW = 38,900 D), albumin-Gd-DTPA (MW = 92,000 D), AMI-227 (400,000 D

Evidence of a tubular system for transendothelial transport in arterial capillaries of the rete mirabile.

The arterial endothelial cells of the rete capillaries of the eel were examined by transmission electron microscopy on thin sections, on freeze-fracture replicas, by scanning electron microscopy, after cytochemical osmium impregnation and perfusion with peroxidase. The study revealed the existence of membrane-bound tubules and vesicles that open at both the luminal and abluminal poles of the cell and at the level of the intercellular space. The tubules are straight or present successive dilations and constrictions. They branch in various directions and intrude deeply into the cell cytoplasm, forming a complex tubular network within the cell. Immunocytochemical techniques were applied on immersion-fixed tissues and on perfusion of the capillaries with albumin and insulin. These demonstrated that the tubular-vesicular system is involved in the transport of circulating proteins. Furthermore, protein A-gold immunocytochemistry has revealed the association of actin with the membranes of this system. On the basis of these results, we suggest that the transendothelial transport of serum proteins takes place by a transcytotic process through a membrane-bound tubular-vesicular system and is equivalent to the large pore system presumed from functional studies.

Hypothalamic-pituitary-adrenal axis in abdominal obesity: effects of dexfenfluramine.

OBJECTIVE: Hyperactivity of the HPA axis is a possible mechanism underlying abdominal obesity. We aimed to evaluate in premenopausal women with abdominal obesity, (i) the hypothalamic-pituitary-adrenal (HPA) axis responses to direct pituitary stimulation with corticotrophin releasing hormone (CRH) and to opioid blockade with naloxone, and (ii) the interaction between short-term serotoninergic activation with dexfenfluramine (dF), a serotonin-release agonist, and these responses. DESIGN AND SUBJECTS: Eight obese women (mean BMI, 35 kg/m2) with waist to hip ratio (WHR) > 0.85 were tested with CRH (1 microgram/kg i.v.) and naloxone (125 micrograms/kg i.v.) before and at the end of two treatment periods with dF (15 mg twice daily for 7 days) and placebo (washout 7 days) in a cross-over design. Eight normal weight control women were tested with CRH and naloxone. RESULTS: Prior to treatment, ACTH and cortisol responses to naloxone (areas under the curve) were significantly higher in obese women then in control women (P = 0.027 and P = 0.035 respectively) dF treatment resulted in significant (P < 0.05) reduction of ACTH and cortisol increments. In contrast, ACTH and cortisol responses to CRH were not significantly different in obese and control subjects and were unaffected by dF treatment. CONCLUSION: We conclude that women with abdominal obesity have hyperreactivity of the HPA axis to opiod blockage and that dexfenfluramine treatment reduces this hyperactivity.

Transport of insulin and albumin by the microvascular endothelium of the rete mirabile.

Vascular permeability for albumin and insulin in the continuous capillary network of the rete mirabile of the eel swimbladder was evaluated by ultrastructural immunocytochemistry and countercurrent perfusion experiments. Upon perfusion of the rete capillaries with a buffer solution containing albumin and insulin, these serum proteins were revealed at the electron microscope level, by the Protein A-gold immunocytochemical technique on a post-embedding step. For the simultaneous detection of both proteins, the double labeling technique with different sized gold particles was used. Furthermore, labeling was performed with the mixture of anti-albumin and anti-insulin anti-bodies. The labelings obtained were morphometrically evaluated and demonstrate that: (1) serum proteins such as albumin and insulin are transported by the endothelial cells through their plasmalemmal vesicular system; (2) insulin is transported preferentially to albumin; and (3) this transport involves different populations of plasmalemmal vesicles. Measurements of diffusion permeability coefficients have confirmed the preferential transport of insulin, its coefficient being higher than that of albumin. Conversely, when compared to that of insulin or sucrose, which are assumed to be markers of the paracellular diffusion, it was found to be much lower, indicating that transcytosis through the vesicular system is less efficient than diffusion along the intercellular junctions. These results indicate that transcytosis of insulin and albumin occurs via different sets of plasmalemmal vesicles, probably through receptor-mediated mechanisms, and that the overall rate of transport across the rete capillaries, with respect to paracellular diffusion, is higher for insulin than for albumin.

Effects of second messengers on the permeability and morphology of eel rete capillaries.

The effects of second-messenger concentration changes on capillary diffusion capacity (permeability-surface area product [PS]) to cellular and paracellular tracers and on capillary ultrastructure were studied during countercurrent perfusion of the rete of the eel swim bladder. Cyclic nucleotide effects were investigated with isoproterenol, forskolin, and dibutyryl cAMP. Isoproterenol (5 x 10(-6) mol/L) did not modify water and solute permeability or capillary structure. Forskolin (10(-4) mol/L) immediately raised the concentrations of cAMP in the rete and produced interstitial edema but did not change permeability. The addition of dibutyryl cAMP (10(-6) mol/L) to the perfusate had rapid effects: it reduced the PS of [3H]water and oxygen and increased the PS of [125I]albumin, [14C]sucrose, and 22Na. No structural changes were observed. Phosphoinositide effects were studied with 1,2-dioctanoyl-sn-glycerol (DG) and phorbol 12-myristate 13-acetate (PMA). DG (10(-5) mol/L) had no effect on the permeability of the rete to water and solutes, while inducing cell membrane vacuolization. PMA (10(-5) mol/L) progressively reduced the PS of [3H]water. In contrast, PS values of [125I]albumin, [14C]sucrose, and 22Na rose gradually. Membrane vacuoles bulging into the lumen and in the cytoplasm were a common feature. The Ca2+ effect was investigated with the Ca2+ ionophore A23187. At 5 x 10(-6) mol/L, unsteady permeability changes and extensive cytolysis were observed. At 5 x 10(-7) mol/L, the PS of [125I]albumin, [14C]sucrose, and 22Na rapidly increased. The PS values for water were not modified. No structural changes were identified.(ABSTRACT TRUNCATED AT 250 WORDS)

[Effect of ranitidine on blood alcohol and glucose levels after ingestion of alcohol]. / Effet de la ranitidine sur l'alcoolémie et la glycémie après ingestion d'alcool.

Are alcohol and glucose blood levels modified in fasting subjects taking ranitidine? This experience tries to simulate normal life conditions. Nine men, volunteer, aged from 24 to 29 years old, without any digestive symptoms, ate a standard lunch after five hours of fasting, took 0.35 g of alcohol per kg. Ethanol blood levels, glycemia and blood levels of insulin and glucagon were taken at regular intervals every 10 to 15 minutes during all the experiment (120 minutes). After the initial experiment, all subjects took 150 mg of ranitidine p.o. b.i.d. during seven days. Afterward they were submitted to the same protocol. Between both experiments no differences were found on blood levels of ethanol. Peak concentration, decreasing rate, and biodisponibility (estimated by area under the curve) did not change. There was a tendency to have a faster decrease in glucose blood level (p < 0.05). This study does not show any significant modification of ethanol metabolism after taking ranitidine p.o.; those results are differing from data already found with studies using cimetidine.

[The treatment of Cushing's disease]. / Le traitement de la maladie de Cushing.

The differential diagnosis of Cushing's disease remains difficult to establish. The selective transsphenoidal adenomectomy is the initial treatment of choice. In a group of 65 patients, 50 (77%) initially responded to surgery with correction of their hypercortisolism. Forty-three out of 51 (84%) patients with small pituitary tumors responded favourably to surgery, but recurrency occurred in 10% of the cases. Medical treatment with steroids inhibitors or antagonists is only an adjuvant treatment. In case of surgery failure or recurrency, bilateral adrenalectomy is usually performed. Conventional radiotherapy may be used after surgery in presence of macroadenomas or invasive adenomas. Correction of the hypercortisolism, after a second surgery, was achieved in 50% of the cases and was always associated with a panhypopituitarism.

[The treatment of acromegaly]. / Le traitement de l'acromégalie.

Acromegaly is a rare disease which can significantly reduce life expectancy. Clinical features are diverse and the patient may consult a variety of medical and surgical specialists before the diagnosis is suspected. However, the disease is easily confirmed by the appropriate laboratory tests, namely GH and IGF1 measurements. In most cases, acromegaly is secondary to a micro or macrosomatotrope pituitary adenoma. Those lesions are easily visualized by a pituitary CT Scan or Magnetic Resonance Imaging. Visual fields have to be evaluated by a neuro-ophthalmologist, and a thorough evaluation of other pituitary functions have to be performed. Selective removal of the adenoma by the transsphenoidal route is the treatment of choice for acromegaly. When performed by an experienced neurosurgeon, normalization of GH secretion can be expected in approximately 75% of cases. The surgical outcome is modulated by the volume, the extension of the tumor and the preoperative GH level. Octreotide, radiotherapy or bromocriptine are indicated whenever the patient remains with an elevated level of GH with persistency of symptoms.

[Treatment of the non-functioning hypophyseal adenoma]. / Le traitement de l'adénome hypophysaire non fonctionnel.

Non-functioning pituitary adenoma is a lesion usually large enough to produce loss of vision and often loss of libido. Transsphenoidal microsurgery is the treatment of choice of these patients. Postoperative radiation therapy should be performed in patients with significant residual pituitary adenoma. Some studies have recently reported that somatostatin analogue may be useful as adjuvant medical therapy, at least in order to improve visual field defects.

[The treatment of prolactinoma]. / Le traitement du prolactinome.

Prolactinoma is the most common type of secretory pituitary tumor. The clinical presentation varies with age and sex, and the size of the adenoma. The differential diagnosis with nonfunctioning adenoma and hyperprolactinemia is particularly important in selecting an appropriate therapy. The choice of therapy depends on a number of factors including the patient's preference. In cases of radiologically undetectable microprolactinomas, we prefer observation only. However, hypogonadic patients are treated with bromocriptine. Generally, it is our recommendation that almost all of the patients with micro--and macroprolactinomas undergo a primary medical therapy, provided they are willing to continue such therapy on a long term basis. We recommend transsphenoidal surgery for patients who refuse long term medical therapy and in rare cases of prolactinomas which are unresponsive to medical therapy. We also consider surgery as a valuable alternative to medical therapy in patients with microprolactinomas and prolactin below 200 micrograms/L.

Effects of dexfenfluramine treatment on body weight and postprandial thermogenesis in obese subjects. A double-blind placebo-controlled study.

The purpose of this study was to determine the effects of dexfenfluramine on body weight and post-prandial thermogenesis in obese subjects. Thirty obese subjects, men and women, with an excess weight between 20 and 80% of the ideal weight and aged from 20 to 60 years, participated in this double-blind, placebo-controlled study. During the treatment period, the subjects were not submitted to caloric restriction. Basal metabolic rate and postprandial thermogenesis (following a 400 kcal test meal) measurements were made by indirect calorimetry. Metabolic parameters such as glucose, insulin, thyroid hormones, free fatty acids, beta-hydroxybutyrate, total cholesterol and triglycerides were also measured before the test meal. These measurements were done at baseline, after one week and after three months of treatment. Following the three month treatment period, the mean weight loss of the dexfenfluramine group was 4.6 +/- 1.6 kg (s.e.) (P < 0.01) whereas the placebo group maintained the initial weight. The mean weight loss in the dexfenfluramine group represented 15% of the initial overweight. There was no significant change in either group in basal metabolic rate and postprandial thermogenesis following one week and three months of treatment (P > 0.05). The caloric intake after the treatment period was significantly reduced in the dexfenfluramine group (from 1631 +/- 103 kcal (s.e.) to 1353 +/- 109 kcal (s.e.); P < 0.05); in the placebo group, the changes were not significant (P > 0.05). The plasma concentrations of tri-iodothyronine, total cholesterol and triglycerides were significantly reduced in the dexfenfluramine group (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of temperature change on the permeability of eel rete capillaries.

The changes in the permeability properties of the rete capillaries of the eel in response to temperature shifts were studied during countercurrent perfusion at constant flow and pressure. Tracers and oxygen were added to the arterial perfusate. From the ratio of end concentrations of arterial to venous capillaries divided by surface area, calculated from rete weight, a value for the ratio of permeability to flow, P/F, with dimensions in centimeters-2 was estimated. Because flow and surface area are constant, this provides an index of how permeability varies with time. A group of paracellular (albumin, sucrose, and sodium) and cellular (antipyrine, water, and oxygen) probes were used. When the temperature of the perfusate was raised abruptly from 25 degrees C to 35 degrees C, P/F values rose continuously and irreversibly from 0.042 +/- 0.009 to 0.281 +/- 0.112 cm-2 (mean +/- SEM) for 125I-albumin, from 0.082 +/- 0.006 to 1.74 +/- 0.070 cm-2 for [14C]sucrose, and from 0.32 +/- 0.06 to 2.78 +/- 0.62 cm-2 for 22Na, whereas they were not modified for [14C]antipyrine, [3H]water, and O2. Gradual increase of temperature was accompanied by a smaller rise in sucrose and sodium permeability and no change in albumin permeability; with decrease, the change was reversible.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of phalloidin on structure and permeability of rete capillaries in the normal and hypoxic state.

The effects of 10(-6) M phalloidin on reperfusion-injured blood capillary structure and permeability were studied in the countercurrent perfused rete mirabile of the eel swim bladder. In the normal rete, the addition of phalloidin to the perfusion medium did not induce morphological or functional changes. When flow was arrested for 30 minutes, during which time the capillaries were exposed to inhibitors of ATP generation, and flow was then resumed with an oxygenated medium, cell membrane blebs and vacuolization, mitochondrial swelling, pericyte shrinkage, and interstitial space edema were observed. The permeability coefficients for labeled albumin, sucrose, and sodium increased to three to four times baseline values, whereas the permeability to water was not significantly modified. When the same protocol was repeated with phalloidin present in the medium throughout the experiment, the structural integrity of the endothelial cells was completely preserved and pericyte shrinkage was abolished, but interstitial space edema still occurred. The permeability to albumin, sucrose, and sodium increased only to 1.5 times baseline values, a significantly decreased increment in comparison with the experiments performed without phalloidin. We concluded that although phalloidin does not improve the capillary barrier of the normal rete, it provides protection against the structural and functional damage induced by hypoxia and reperfusion.

Effect of reduced energy metabolism and reperfusion on the permeability and morphology of the capillaries of an isolated rete mirabile.

The effects of reduction in energy metabolism were explored in the eel rete mirabile, an organ composed predominantly of capillaries. In vitro experiments showed that glycolysis is the major pathway of energy production in this capillary tissue, and that iodoacetate, KCN, and low PO2 in combination markedly reduce its ATP generation. When in situ energy generation was inhibited by this combination during countercurrent perfusion of the arterial and venous capillaries of the rete, an approximate doubling of the intercapillary barrier permeability for human [125I]albumin, [14C]sucrose, and 22Na was found. Structural damage was evident, but the intercellular junctions remained intact. The effect of cessation of flow for 30 minutes, followed by reperfusion, was then explored. Stasis alone altered the structure, chiefly of the venous capillary endothelium, but not the permeability of the intercapillary barrier. Stasis with a hypoxic medium containing the inhibitors of energy generation, followed by reperfusion with oxygenated control medium, resulted in a progressive breakdown of the intercapillary barrier, with a threefold to fourfold increase in solute (labeled albumin, sucrose, and sodium) permeability, evolving during early reperfusion, but no change for labeled water permeability. Morphologically, the endothelial cells, especially those in venous capillaries, showed substantial damage; they appeared vacuolated, their cytoplasm was extracted, and cytoplasmic and membrane debris were found in the lumen; intercellular junctions remained intact. Local pericyte detachment with interstitial edema also appeared. Thus, stasis and reperfusion amplified the effects of reduction in energy generation and hypoxia on both permeability and morphological change.

Clinical pancreas transplantation: a learning curve of its management.

In this evolving experience, acceptable patient and graft survival after PTX appear best secured by the use of whole duodenopancreatic grafts, enteric drainage, triple immunosuppression induced by OKT3, and the monitoring of postprandial blood glucose and serum amylase for detection of rejection.

Growth hormone-releasing factor increases serum prolactin concentrations in normal subjects and in patients with pituitary adenomas.

We have examined the serum growth hormone (GH) and prolactin (PRL) response to growth hormone releasing factor (hGRF-(1-44)NH2 (GRF) 1 microgram/kg i.v. bolus) in 16 acromegalic patients (eight of whom were hyperprolactinaemic), 13 patients with microprolactinoma, and 14 healthy subjects. The GH responses to TRH and to the somatostatin analogue SMS 201-995 were also studied in acromegalic patients. In these, and in patients with microprolactinoma, GH responses after GRF (P less than 0.001 vs saline) were variable. The absolute GH increase (calculated as area under the curve) in acromegalic patients (2489 +/- 920 micrograms/l min), or in patients with microprolactinoma (1322 +/- 279 micrograms/l min) was not different from that in controls (2238 +/- 633 micrograms/l min). In addition, a significant increase in PRL release was observed after GRF in comparison to saline in acromegalic patients (P less than 0.01), in patients with microprolactinoma and in normal subjects (P less than 0.001). The PRL increase was significantly correlated with basal PRL levels in acromegalic patients (r = 0.99, P less than 0.001) and in patients with microprolactinomas (r = 0.61, P less than 0.05). Furthermore, a significant correlation was found between GH rise after GRF and basal GH, and between GH rise after GRF and GH decrement after SMS in patients with acromegaly. These results suggest that GRF can stimulate PRL release by actions on the normal pituitary and on pituitary adenomas, including microprolactinomas. Moreover, the data suggest that in acromegaly there is a relative functional deficiency of hypothalamic somatostatin.

Temporal changes in prolactin and corticosterone response during chronic treatment with d-fenfluramine.

In order to elucidate the mechanism of development of tolerance to the anorectic effect during chronic treatment with d-fenfluramine (d-F), we examined the temporal changes induced by d-F in food intake and prolactin (PRL) and corticosterone secretion. Male Sprague-Dawley rats were treated for 14 days with d-F (2.5 mg/kg i.p.) or saline twice daily and were given free access to food and water. Groups of 8 rats were sacrificed 30 min after d-F or saline injection at days 1, 4 and 14 for measurements of serum PRL and corticosterone. Food intake and weight gain were reduced significantly by d-F during the first 2-3 days of treatment but not thereafter. Compared with saline, d-F initially increased PRL (57 +/- 9 vs. 7 +/- 0.7 ng/ml) and corticosterone (42 +/- 2 vs. 14 +/- 3 micrograms/dl) serum concentrations. At 4 days, PRL was still significantly increased (43 +/- 5 vs. 10 +/- 4 ng/ml) but corticosterone returned to basal levels. At 14 days, PRL and corticosterone concentrations in the d-F group were not different from corresponding values in the saline group. To verify whether the loss of corticosterone and PRL responses to d-F was not due to a depletion of hormone stores, direct stimulation of corticosterone with corticotrophin and of PRL with metoclopramide were made at days 4 and 14, respectively. Corticotrophin (0.25 mg/kg i.p.) increased corticosterone concentrations similarly in d-F-treated (45 +/- 8 micrograms/dl) and in saline-treated rats (51 +/- 7 micrograms/dl).(ABSTRACT TRUNCATED AT 250 WORDS)