Diabetes mellitus in sand rats (Psammomys obesus). Metabolic pattern during development of the diabetic syndrome.

It has been reported that sand rats, naturally feeding on low-caloric-value plants containing a high concentration of salt, become obese and develop hyperglycemia when fed on a standard laboratory diet. The aim of this study was to examine the long-term effects of a synthetic-chow diet on the metabolic pattern of the diabetic syndrome in a large group of sand rats. While a few animals had a fulminant reaction with markedly decreased glucose tolerance, low plasma insulin levels, and death within 3-4 wk, most sand rats developed obesity and elevated plasma insulin levels. From the third month and forward, 40% of sand rats presented with a diabetic syndrome with hyperinsulinemia, hyperglycemia, markedly decreased glucose tolerance, and insulin resistance. This diabetic syndrome can be compared with maturity-onset (type II) diabetes. When this synthetic-chow diet was given for more than 6 mo, the majority of animals lost considerable weight and showed a major depletion of fat stores. Serum immunoreactive insulin levels fell, while blood glucose rose to above 500 mg/dl with glycosuria and ketonuria. The elevated triglyceride content of plasma and the lipid deposits in the liver were greatly augmented, and no glycogen was present. Animals developed frank insulin-dependent diabetes, and diabetic animals not treated with insulin died in diabetic coma with presumed ketoacidosis. The disease was essentially confined to sand rats showing abnormal glucose tolerance, even before eating laboratory chow. This observation suggests a genetic factor. Thus, the sand rat appears to be a potentially interesting model for investigation of both maturity-onset and insulin-dependent diabetes.

Insulin release from isolated islets of Langerhans after segmental-pancreas autotransplantation in dogs.

Pancreas transplantation is warranted essentially by the quality of glucose regulation. Although the fasting blood glucose is invariably normal, this may not be the case during glucose load tests. The purpose of this study was to examine dysregulation within the isolated islet originating from a segmental-pancreas autograft in the dog. Results show an increased basal insulin secretion by the graft islets in static incubation compared with that of islets originating from the head of the pancreas and left in situ. This abnormal secretion may be accounted for by various factors intervening within the graft or the isolated islet, thus suggesting a possible improvement in the surgical model.

S15261 antagonises amylin-induced impaired glucose tolerance.

Amylin has been postulated to antagonise or inhibit the action of insulin in peripheral rat tissues and thus contribute to, or be responsible for, the development of insulin resistance. We have recently reported that S15261 is a compound capable of increasing insulin sensitivity in ageing insulin resistant rats. In order to assess whether S15261 had any effects on amylin induced insulin resistance we used a model where amylin causes an impairement in glucose tolerance in an acute manner, by means of an intraportal infusion of the hormone in normal rats. We report here that S15261 can antagonise this amylin-induced impaired glucose tolerance.

780 SE: a new type of hypolipemic agent. Comparative assays in rats.

The effect of 1-(m-trifluoromethylphenyl)-2-(beta-benzoyloxyethyl)-amino- propane hydrochloride (780 SE) on serum lipids, blood glucose and liver weight was studied in 4 experimental models, and compared with that of clofibrate and tiadenol. When rats were given a daily oral dose of 25 mg/kg or 50 mg/kg of 780 SE for 5 days a marked reduction of serum triglycerides and liver weight was observed. The decreases were more pronounced than those in rats treated with 50 mg/kg or 100 mg/kg of clofibrate or tiadenol. On the other hand, a reduction of serum cholesterol was only observed in the groups given clofibrate and tiadenol. These differences could be explained on the basis of the mechanism of action of the different drugs. Only 780 SE induced a decrease in blood sugar level, a reduction of plasma insulin concentration and restored the insulin sensitivity to a normal value in obese animals. There was a significant decrease in liver weight of 780 SE treated rats, whereas clofibrate and tiadenol cause hepatomegaly.

Development of macroangiopathy in sand rats (Psammomys obesus), an animal model of non-insulin-dependent diabetes mellitus: effect of gliclazide.

The risk of developing macroangiopathy associated with diabetes led us to study in sand rats the long-term consequences of non-insulin-dependent diabetes on the development of arterial lesions promoted by feeding a high-cholesterol diet. Gliclazide, an agent whose preventive effect has previously been suggested in other experimental models of atheroma, was also investigated in these diabetic and hypercholesterolemic animals. Sand rats were fed a natural diet (ND group), a standard laboratory feed (StD group), or a high-cholesterol feed (HCD group) for 15 months. Biologic parameters were monitored throughout the period of the study, and histologic and histochemical examinations were conducted when the animals were killed (month 15). One StD group and one HCD group were treated with gliclazide from month 3 to month 15. The StD group developed a syndrome of obesity, hyperglycemia, hyperinsulinemia, and triglyceridemia. The high cholesterol feed further increased hypercholesterolemia. These biologic abnormalities were accompanied by arterial lesions (thickening of the intima, deposition of glycosaminoglycans). Foam cells were seen in the intima, and microthrombi were present in the lumen of the arteries of animals in the HCD group. Long-term gliclazide medication at doses that normalized serum glucose levels also reduced the obesity, hyperinsulinemia, lipid disorders, and it prevented or retarded the appearance of arterial lesions.

Hyperoxia/normoxia-driven retinal angiogenesis in mice: a role for angiotensin II.

PURPOSE: To examine a possible role for the angiotensin system in a rodent model of retinopathy of prematurity. METHODS: A previously described model was used in which oxygen cycling (5 days hyperoxia and 5 days hypoxia) induced retinal alterations in newborn mice. An angiotensin-converting enzyme inhibitor (perindopril), or angiotensin receptor antagonists AT1 (losartan) or AT2 (PD123319) were administered subcutaneously for 5 days after the hyperoxia exposure. According to histologic methods, the endothelial cell count within the anterior part of the ganglion cell layer was used for the evaluation of the compound effect. RESULTS: Histologic evaluation showed an increased number of endothelial cells in retinas of hypoxic pups compared with hyperoxic or normoxic pups. Hypoxic animals treated with perindopril (4 mg/kg) showed a significant decrease (29%, P < or = 0.001) in endothelial cell number (163 +/- 7) compared with hypoxic control animals (231 +/- 10). Losartan also decreased the endothelial cell number (14%, P < or = 0.05), whereas the AT2 antagonist had no effect. CONCLUSIONS: The data showed a protective effect of an angiotensin-converting enzyme inhibitor and of an AT1 receptor antagonist on hyperoxia- and normoxia-induced neovascularization in newborn mice. The results suggest a role for the angiotensin system in this model and that such compounds may be of interest in the prevention of proliferative retinopathies such as proliferative diabetic retinopathy.

Glucose and insulin modulate the capacity of endothelial cells (HUVEC) to express P-selectin and bind a monocytic cell line (U937).

Diabetes mellitus is associated with increased prevalence of endothelial cell dysfunction and vascular diseases. Mechanisms leading to alterations in endothelial cell function are poorly understood. We report here that hyperglycaemia results in the expression of endothelial adhesion molecules involved in leukocyte adhesion and extravasation. Incubation of human umbilical cord endothelial cells (HUVEC) with 25 mM glucose induced the expression of P-selectin. This effect was reversed by the addition of 1 nM insulin. Moreover, increased ICAM-1 expression was observed upon HUVEC incubation with 25 mM glucose. Increased adhesion of U937 cells (a monocytic cell line) to endothelial cells cultured with 25 mM glucose was observed. High glucose-induced monocytes cell adhesion was inhibited by an anti-P-selectin monoclonal antibody (LYP20). These results show that high glucose concentration activates endothelial cells leading to monocytes adhesion providing further evidence that hyperglycaemia might be implicated in vessel wall lesions contributing to diabetic vascular disease.

Vascular endothelial growth factor and the in vivo increase in plasma extravasation in the hamster cheek pouch.

1. The purpose of this study in the hamster cheek pouch was to determine whether or not vascular endothelial growth factor (VEGF) induced changes in plasma extravasation and if so, the mechanism(s) involved. 2. The cheek pouch microcirculatory bed of the anaesthetized hamster was directly observed under microscope and the number of vascular leakage sites, as shown by fluorescein isothiocyanate (FITC-dextran, 150 kD) extravasation, was counted. Drugs and VEGF were applied topically. VEGF from 0.05 to 0.5 microg ml(-1) (1.2 to 12 nM) produced a dose-dependent increase in the number of microvascular leakage sites from virtually none in basal conditions to up to 250 in some pouches. The effects of VEGF (0.1 microg ml(-1) or 2.4 nM) were blocked in a concentration-dependent manner by the non-specific heparin growth factor antagonist TBC-1635 (0.1, 1 and 3microM). The placenta growth factor (PlGF-1: 0.1 and 0.5 microg ml(-1) or 3.4 and 17 nM) did not increase plasma extravasation, per se, but abolished the effects of VEGF (2.4 nM). 3. The increases in microvascular leakage produced by VEGF (2.4 nM) were partially but significantly (P<0.05) inhibited by genistein (5 and 10 microM, up to 33% inhibition), LY 294002 (30 microM, 41%), bisindolylmaleimide (1 microM, 65%) and virtually abolished by indomethacin (3 microM, 88%) and L-nitro-arginine (10 microM, 95%), these drugs being inhibitors of tyrosine kinase, phosphatidylinositol-3-kinase, protein kinase C, cyclo-oxygenase and nitric oxide synthase respectively. None of these inhibitors, at the concentration tested, induced alone an increase in plasma extravasation. 4. These results indicate that the VEGF-induced plasma extravasation may involve the stimulation of VEGF-R2 (Flk-1/KDR) and the activation of phosphatidylinositol-3-kinase and protein kinase C. The production of both nitric oxide and prostaglandin is required to observe an increase in vascular leakage.

Epoxyeicosatrienoic acids, potassium channel blockers and endothelium-dependent hyperpolarization in the guinea-pig carotid artery.

1. Using intracellular microelectrodes, we investigated the effects of 17-octadecynoic acid (17-ODYA) on the endothelium-dependent hyperpolarization induced by acetylcholine in the guinea-pig isolated internal carotid artery with endothelium. 2. In the presence of Nomega-nitro-L-arginine (L-NOARG, 100 microM) and indomethacin (5 microM) to inhibit nitric oxide synthase and cyclo-oxygenase, acetylcholine (1 microM) evoked an endothelium-dependent hyperpolarization which averaged -16.4 mV starting from a resting membrane potential of -56.8 mV. There was a negative correlation between the amplitude of the hyperpolarization and the absolute values of the resting membrane potential. 3. The acetylcholine-induced endothelium-dependent hyperpolarization was not altered by charybdotoxin (0.1 microM) or iberiotoxin (30 nM). It was partially but significantly reduced by apamin (0.5 microM) to -12.8+/-1.2 mV (n=10) or the combination of apamin plus iberiotoxin (-14.3+/-3.4mV, n=4). However, the combination of charybdotoxin and apamin abolished the hyperpolarization and under these conditions, acetylcholine evoked a depolarization (+ 7.1+/-3.7 mV, n = 8). 4. 17-ODYA (10 microM) produced a significant hyperpolarization of the resting membrane potential which averaged -59.6 mV and a partial but significant inhibition of the acetylcholine-induced endothelium-dependent hyperpolarization (-10.9 mV). 5. Apamin did not modify the effects of 17-ODYA but in the presence of charybdotoxin or iberiotoxin, 17-ODYA no longer influenced the resting membrane potential or the acetylcholine-induced hyperpolarization. 6. When compared to solvent (ethanol, 1% v/v), epoxyeicosatrienoic acids (EpETrEs) (5,6-, 8,9-, 11,12- and 14,15-EpETrE, 3 microM) did not affect the cell membrane potential and did not relax the guinea-pig isolated internal carotid artery. 7. These results indicate that, in the guinea-pig internal carotid artery, the involvement of metabolites of arachidonic acid through the cytochrome P450 pathway in endothelium-dependent hyperpolarization is unlikely. Furthermore, the hyperpolarization mediated by the endothelium-derived hyperpolarizing factor (EDHF) is probably not due to the opening of BK(Ca) channels.

Role of endothelial cell hyperpolarization in EDHF-mediated responses in the guinea-pig carotid artery.

1. Experiments were performed to identify the potassium channels involved in the acetylcholine-induced endothelium-dependent hyperpolarization of the guinea-pig internal carotid artery. Smooth muscle and endothelial cell membrane potentials were recorded in isolated arteries with intracellular microelectrodes. Potassium currents were recorded in freshly-dissociated smooth muscle cells using patch clamp techniques. 2. In single myocytes, iberiotoxin (0.1 microM)-, charybdotoxin (0.1 microM)-, apamin (0.5 microM)- and 4-aminopyridine (5 mM)-sensitive potassium currents were identified indicating the presence of large- and small-conductance calcium-sensitive potassium channels (BK(Ca) and SK(Ca)) as well as voltage-dependent potassium channels (K(V)). Charybdotoxin and iberiotoxin inhibited the same population of BK(Ca) but a conductance specifically sensitive to the combination of charybdotoxin plus apamin could not be detected. 4-aminopyridine (0. 1 - 25 mM) induced a concentration-dependent inhibition of K(V) without affecting the iberiotoxin- or the apamin-sensitive currents. 3. In isolated arteries, both the endothelium-dependent hyperpolarization of smooth muscle and the hyperpolarization of endothelial cells induced by acetylcholine or by substance P were inhibited by 5 mM 4-aminopyridine. 4. These results indicate that in the vascular smooth muscle cells of the guinea-pig carotid artery, a conductance specifically sensitive to the combination of charybdotoxin plus apamin could not be detected, comforting the hypothesis that the combination of these two toxins should act on the endothelial cells. Furthermore, the inhibition by 4-aminopyridine of both smooth muscle and endothelial hyperpolarizations, suggests that in order to observe an endothelium-dependent hyperpolarization of the vascular smooth muscle cells, the activation of endothelial potassium channels is likely to be required.

Potassium ions and endothelium-derived hyperpolarizing factor in guinea-pig carotid and porcine coronary arteries.

Experiments were designed to determine in two arteries (the guinea-pig carotid and the porcine coronary arteries) whether or not the endothelium-derived hyperpolarizing factor (EDHF) can be identified as potassium ions, and to determine whether or not the inwardly rectifying potassium current and the Na+/K+ pump are involved in the hyperpolarization mediated by EDHF. The membrane potential of vascular smooth muscle cells was recorded with intracellular microelectrodes in the presence of N(omega)-L-nitro-arginine (L-NA) and indomethacin. In vascular smooth muscle cells of guinea-pig carotid and porcine coronary arteries, acetylcholine and bradykinin induced endothelium-dependent hyperpolarizations (-18+/-1 mV, n = 39 and -19+/-1 mV, n = 7, respectively). The hyperpolarizations were not affected significantly by ouabain (1 microM), barium chloride (up to 100 microM) or the combination of ouabain plus barium. In both arteries, increasing extracellular potassium concentration by 5 or 10 mM induced either depolarization or in a very few cases small hyperpolarizations which never exceeded 2 mV. In isolated smooth muscle cells of the guinea-pig carotid artery, patch-clamp experiments shows that only 20% of the vascular smooth muscle cells expressed inwardly rectifying potassium channels. The current density recorded was low (0.5+/-0.1 pA pF(-1), n = 8). These results indicate that, in two different vascular preparations, barium sensitive-inwardly rectifying potassium conductance and the ouabain sensitive-Na+/K+ pump are not involved in the EDHF-mediated hyperpolarization. Furthermore, potassium did not mimic the effect of EDHF pointing out that potassium and EDHF are not the same entity in those arteries.

Acetylcholine-induced relaxation in blood vessels from endothelial nitric oxide synthase knockout mice.

1. Isometric tension was recorded in isolated rings of aorta, carotid, coronary and mesenteric arteries taken from endothelial nitric oxide synthase knockout mice (eNOS(-/-) mice) and the corresponding wild-type strain (eNOS(+/+) mice). The membrane potential of smooth muscle cells was measured in coronary arteries with intracellular microelectrodes. 2. In the isolated aorta, carotid and coronary arteries from the eNOS(+/+) mice, acetylcholine induced an endothelium-dependent relaxation which was inhibited by N(omega)-L-nitro-arginine. In contrast, in the mesenteric arteries, the inhibition of the cholinergic relaxation required the combination of N(omega)-L-nitro-arginine and indomethacin. 3. The isolated aorta, carotid and coronary arteries from the eNOS(-/-) mice did not relax in response to acetylcholine. However, acetylcholine produced an indomethacin-sensitive relaxation in the mesenteric artery from eNOS(-/-) mice. 4. The resting membrane potential of smooth muscle cells from isolated coronary arteries was significantly less negative in the eNOS(-/-) mice (-64.8 +/- 1.8 mV, n = 20 and -58.4 +/- 1.9 mV, n = 17, for eNOS(+/+) and eNOS(-/-) mice, respectively). In both strains, acetylcholine, bradykinin and substance P did not induce endothelium-dependent hyperpolarizations whereas cromakalim consistently produced hyperpolarizations (- 7.9 +/- 1.1 mV, n = 8 and -13.8 +/- 2.6 mV, n = 4, for eNOS(+/+) and eNOS(-/-) mice, respectively). 5. These findings demonstrate that in the blood vessels studied: (1) in the eNOS(+/+) mice, the endothelium-dependent relaxations to acetylcholine involve either NO or the combination of NO plus a product of cyclo-oxygenase but not EDHF; (2) in the eNOS(-/-) mice, NO-dependent responses and EDHF-like responses were not observed. In the mesenteric arteries acetylcholine releases a cyclo-oxygenase derivative.

Cannabinoid CB1 receptor and endothelium-dependent hyperpolarization in guinea-pig carotid, rat mesenteric and porcine coronary arteries.

1. The purpose of these experiments was to determine whether or not the endothelium-dependent hyperpolarizations of the vascular smooth muscle cells (observed in the presence of inhibitors of nitric oxide synthase and cyclo-oxygenase) can be attributed to the production of an endogenous cannabinoid. 2. Membrane potential was recorded in the guinea-pig carotid, rat mesenteric and porcine coronary arteries by intracellular microelectrodes. 3. In the rat mesenteric artery, the cannabinoid receptor antagonist, SR 141716 (1 microM), did not modify either the resting membrane potential of smooth muscle cells or the endothelium-dependent hyperpolarization induced by acetylcholine (1 microM) (17.3 +/- 1.8 mV, n = 4 and 17.8 +/- 2.6 mV, n = 4, in control and presence of SR 141716, respectively). Anandamide (30 microM) induced a hyperpolarization of the smooth muscle cells (12.6 +/- 1.4 mV, n = 13 and 2.0 +/- 3.0 mV, n = 6 in vessels with and without endothelium, respectively) which could not be repeated in the same tissue, whereas acetylcholine was still able to hyperpolarize the preparation. The hyperpolarization induced by anandamide was not significantly influenced by SR 141716 (1 microM). HU-210 (30 microM), a synthetic CB1 receptor agonist, and palmitoylethanolamide (30 microM), a CB2 receptor agonist, did not influence the membrane potential of the vascular smooth muscle cells. 4. In the rat mesenteric artery, the endothelium-dependent hyperpolarization induced by acetylcholine (1 microM) (19.0 +/- 1.7 mV, n = 6) was not altered by glibenclamide (1 microM; 17.7 +/- 2.3 mV, n = 3). However, the combination of charybdotoxin (0.1 microM) plus apamin (0.5 microM) abolished the acetylcholine-induced hyperpolarization and under these conditions, acetylcholine evoked a depolarization (7.7 +/- 2.7 mV, n = 3). The hyperpolarization induced by anandamide (30 microM) (12.6 +/- 1.4 mV, n = 13) was significantly inhibited by glibenclamide (4.0 +/- 0.4 mV, n = 4) but not significantly affected by the combination of charybdotoxin plus apamin (17.3 +/- 2.3 mV, n = 4). 5. In the guinea-pig carotid artery, acetylcholine (1 microM) evoked endothelium-dependent hyperpolarization (18.8 +/- 0.7 mV, n = 15). SR 141716 (10 nM to 10 microM), caused a direct, concentration-dependent hyperpolarization (up to 10 mV at 10 microM) and a significant inhibition of the acetylcholine-induced hyperpolarization. Anandamide (0.1 to 3 microM) did not influence the membrane potential. At a concentration of 30 microM, the cannabinoid agonist induced a non-reproducible hyperpolarization (5.6 +/- 1.3 mV, n = 10) with a slow onset. SR 141716 (1 microM) did not affect the hyperpolarization induced by 30 microM anandamide (5.3 +/- 1.5 mV, n = 3). 6. In the porcine coronary artery, anandamide up to 30 microM did not hyperpolarize or relax the smooth muscle cells. The endothelium-dependent hyperpolarization and relaxation induced by bradykinin were not influenced by SR 141716 (1 microM). 7. These results indicate that the endothelium-dependent hyperpolarizations, observed in the guinea-pig carotid, rat mesenteric and porcine coronary arteries, are not related to the activation of cannabinoid CB1 receptors.

NPY receptor subtype in the rabbit isolated ileum.

1. The purpose of this work was to verify the hypothesis that the rabbit ileum is a selective preparation for the NPY Y5 receptor by using new selective antagonists recently synthesized. Spontaneous contractions of the rabbit isolated ileum were recorded and binding experiments were performed in cells expressing the human NPY Y1, Y2, Y4 or Y5 receptor subtype. 2. NPY analogues produced a concentration-dependent transient inhibition of the spontaneous contractions of the rabbit ileum with the following order of potency hPP > rPP > PYY > or = [Leu31,-Pro34]-NPY > NPY >> NPY13-36. Pre-exposure to rPP, PYY, [Leu31,Pro34]-NPY or NPY (but not NPY13-36) inhibited the effect of subsequent administration of hPP suggesting cross-desensitization of the preparation. The apparent affinity of the various agonists studied was correlated to the affinity reported for the human Y4 receptor subtype (and to a lesser extent for the rat Y4 subtype) but not to the affinity for the Y5 receptor subtype. 3. BIBO 3304, a selective NPY Y1 receptor antagonist, and CGP 71683A, a selective NPY Y5 receptor antagonist, did not affect the response to hPP. JCF 109, another NPY Y5 receptor antagonist, produced an inhibition of the response to hPP but only at the highest dose tested (10 microM) which also, by itself, produced intrinsic inhibitory effects. 4. 1229U91, a non-selective ligand for Y1, Y2, Y4 and Y5 receptors with high affinity toward the Y1 and Y4 receptor subtypes, produced a concentration-dependent transient inhibition of the spontaneous contractions of the rabbit ileum and a dose-dependent inhibition of the response to hPP (apparent pKB: 7.2). 5. These results suggest that in the rabbit ileum, the NPY receptor involved in the inhibition of the spontaneous contractile activity is a NPY Y4 receptor subtype.

Monoaminergic regulation of growth hormone in the rat.

The administration of gamma-hydroxybutyrate (GHB) induced a consistent secretory episode of growth hormone (GH) in the morning followed by basal levels of secretion of GH for several hours. The measurement of endogenous noradrenaline, dopamine and serotonin (5-HT) following infusion of GHB showed that dopamine concentrations were significantly increased in the striatum; at the level of the hypothalamus, however, no significant differences were observed between control and GHB-treated animals. The data reported in this study are consistent with the interpretation that the neurotransmitter regulation of GH release and the modulation of hypothalamic glucoreceptor systems are not fundamentally different in rodents and primates. Clonidine, and alpha-adrenergic agonist, enhanced the peak of GH observed in the morning and caused a rapid increment of GH during the period when it was normally at basal levels. Under the same experimental conditions, dopamine agonists, apomorphine and levodopa, had no effect on GH secretion. The inhibition of catecholamine synthesis by alpha-methyl-p-tyrosine blocked the secretory episode of GH following administration of GHB and after insulin hypoglycaemia whereas the GH rise induced by clonidine was unchanged. The inhibition of 5-HT synthesis by p-chlorophenylalanine also suppressed the secretory episode of GH seen in the morning and the release of GH induced by hypoglycaemia; both being partly restored in animals pretreated with 5-hydroxytryptamine.

NPY receptor subtypes involved in the contraction of the proximal colon of the rat.

Experiments were designed to determine the receptor subtype(s) involved in the contraction of the rat proximal colon to NPY. In this tissue, mRNA of Y2 and Y4 NPY receptor subtypes were highly expressed, whereas Y5 mRNA levels were very low and Y1 mRNA levels were intermediate. NPY analogues induced contractions with the following order of potency: rPP > hPP = PYY = NPY = [Leu31,Pro34]NPY > NPY(2-36) = [D-Trp32]NPY > NPY(33-36). Responses to NPY, PYY and NPY(13-36) were not or partially affected by tetrodotoxin, in contrast to the responses to [Leu31,Pro34]NPY, rPP, hPP and [D-Trp32]NPY which were fully blocked. Atropine did not inhibit the contractions to NPY, PYY and [Leu31,Pro34]NPY but significantly affected those to NPY(13-36), [D-Trp32]NPY, rPP and hPP. The specific Y1 receptor antagonist BIBP 3226 was ineffective but JCF 104 and JCF 105 (two compounds with preferential affinity toward the hY5 receptor versus the hY1 or hY2 receptor) abolished the contractions provoked by the NPY analogues. These results suggest that NPY activates three receptor subtypes, a Y2 subtype possibly by a direct action on the smooth muscle cells, as well as a Y4 and a Y5 (or 'Y5-like') subtype which, respectively, release acetylcholine and an unknown neurotransmitter.

Fenfluramine long-term administration and brain serotonin.

Long-term administration of fenfluarmine induced a decrease of brain 5-HT to the same extent as did an acute dose. 48 h after drug withdrawal, the brain serotonin level returned to the control value. The present study provides evidence to suggest that a degenerative lesion of 5-HT neurons is not involved in fenfluramine activity.

8-OH-DPAT induces a selective increase in protein intake in ageing overweight animals.

We have examined the effects of a 5-HT1A receptor agonist (8-hydroxy-2-(di-n-propylamino)tetralin, 8-OH-DPAT) on food preference in ageing rats that had been given a 'palatable' meal 15 min before administration of the drug. Ageing rats consumed a greater amount of the 'palatable' pre-meal than the young rats. In young rats lipids were the predominant source of calories, but in old animals lipid and protein consumption was similar. Administration of 8-OH-DPAT resulted in an increase in total caloric intake in both groups. Concomitant with this there was a significant increase in protein intake in both groups, which was most important in ageing rats, where proteins became the predominant source of calories.

History and evolution of the concept of oral therapy in diabetes.

The object of diabetes treatment is to restore adequate carbohydrate, protein and lipid metabolism. The cornerstone of this treatment has been diet since the end of the 18th century, but true antidiabetic therapy started only with the identification and purification of insulin. Pressure for oral therapy then quickly built up. The hypoglycemic effect of guanidines was discovered in 1919, leading to their therapeutic use, but they were withdrawn in 1932 due to their hepatotoxic effects. The related biguanides appeared in the 1950s but have since diminished in importance so that metformin is practically the only representative still used today. Work in the 1940s and 1950s led to the discovery and development of hypoglycemic sulfonylureas (SU), a therapeutic class unique for its specificity and safety. These products were found to stimulate insulin secretion by the endocrine pancreas. In vitro studies have shown that they bind specifically to an ATP-dependent K+ channel of the beta cell membrane. This binding closes the channel so that K+ outflow ceases, the beta cell membrane depolarizes and voltage-dependent Ca2+ channels open to allow an influx of extracellular calcium. The result is migration and extrusion of insulin granules. Although this mechanism of action has been demonstrated in vitro, it cannot account for all the clinical actions of various SU. They thus appear to have extrapancreatic actions, probably potentiating the peripheral effects of insulin at a postreceptor site in target cells. Other effects involve fibrinolytic activity of the blood, platelet behavior and vascular reactivity. The future of oral diabetes therapy thus seems to lie with the sulfonylureas.

Vascular responsiveness in young, diabetic, and aging hyperinsulinemic rats.

The purpose of this study was to compare vascular responsiveness in young (12 week old), aging hyperinsulinemic-glucose intolerant (52 weeks old) and diabetic (streptozotocin; 14 weeks old) rats. Aortic rings with and without endothelium were maintained in organ chambers for isometric tension recording. The contractile response to KCl was significantly enhanced in aortae from diabetic animals when compared to the responses obtained in young and old ones. The contractile response to norepinephrine or U46619, was significantly shifted to the right in the aortae from aging animals, however the aortae from these hyperinsulinemic rats were hyperresponsive to serotonin. Acetylcholine and ADP provoked an endothelium-dependent relaxation which was markedly depressed in the aortae from diabetic animals. The relaxation to ADP was selectively inhibited in the aging animals. The effect of sodium-nitroprusside was not significantly different in the three groups. Isoproterenol and forskolin induced endothelium-independent relaxation. Isoproterenol responses were inhibited in aging and diabetic animals, however the forskolin-relaxation was inhibited only in the aortae from aging animals. These results suggest that in two models of diabetes (i.e. Type I insulin-dependent and type II non insulin-dependent) vascular responsiveness is differently affected. Aging hyperinsulinemic animals present a selective hyperresponsiveness to serotonin, a selective dysfunction of ADP-induced endothelium-dependent relaxation and smooth muscle adenylate cyclase deficit. In diabetic animals a beta adrenergic hyporesponsiveness, not linked to adenylate-cyclase dysfunction, and non-selective depression of endothelium-dependent responses can be observed.