Change In Basal Release Research Articles

Aging influences steroid hormone release by mink ovaries and their response to leptin and IGF-I.

ABSTRACTThe aim of our study was to understand whether ovarian steroid hormones, and their response to the metabolic hormones leptin and IGF-I leptin, could be involved in the control of mink reproductive aging via changes in basal release of ovarian progesterone and estradiol. For this purpose, we compared the release of progesterone and estradiol by ovarian fragments isolated from young (yearlings) and old (3-5 years of age) minks cultured with and without leptin and IGF-I (0, 1, 10 or 100 ng/ml). We observed that isolated ovaries of older animals produced less progesterone but not less estradiol than the ovaries of young animals. Leptin addition stimulated estradiol release by the ovarian tissue of young animals but inhibited it in older females. Leptin did not influence progesterone output by the ovaries of either young or older animals. IGF-I inhibited estradiol output in young but not old animals, whereas progesterone release was inhibited by IGF-I irrespective of the animal age. Our observations demonstrate the involvement of both leptin and IGF-I in the control of mink ovarian steroid hormones release. Furthermore, our findings suggest that reproductive aging in minks can be due to (a) reduction in basal progesterone release and (b) alterations in the response of estradiol but not of progesterone to leptin and IGF-I.

Attenuation of insulin secretion by insulin-like growth factor binding protein-1 in pancreatic β-cells

IGFBP-1 is involved in glucohomeostasis, but the direct action of IGFBP-1 on the β-cell remains unclear. Incubation of dispersed mouse β-cells with IGFBP-1 for 30min inhibited insulin secretion stimulated by glucose, glucagon-like peptide 1 (GLP-1) or tolbutamide without changes in basal release of insulin and in cytosolic free Ca2+ concentration ([Ca2+]i) and NAD(P)H evoked by glucose. In contrast, IGFBP-1 augmented glucose-stimulated insulin secretion in intact islets, associated with a reduced somatostatin secretion. These results suggest a suppressive action of IGFBP-1 on insulin secretion in isolated β-cells through a mechanism distal to energy generating steps and not involving regulation of [Ca2+]i. In contrast, IGFBP-1 amplifies glucose-stimulated insulin secretion in intact islets, possibly by suppressing somatostatin secretion. These direct modulatory influences of IGFBP-1 on insulin secretion may imply an important regulatory role of IGFBP-1 in vivo and in the pathogenesis of type 2 diabetes, in which loss of insulin release is an early pathogenetic event.

In vivo monitoring of dopamine overflow in the central nervous system by amperometric techniques combined with carbon fibre electrodes

Electrochemical techniques are extensively used to investigate in vivo and in vitro events associated with neurotransmission, particularly dopamine (DA) transmission. In vivo amperometric measurements only concern evoked extracellular neurochemical events over short time periods independently of changes in basal release. In this context, DA release is evoked either by brief and low electrical or by chemical stimulation, which, respectively, mimics or elicits the physiological discharge rates of DA neurones. The combination of electrochemically treated carbon fibre electrodes with differential pulse amperometry (DPA) has been extensively used to monitor DA overflow on a 1-s time scale. The more recent in vivo combination of untreated carbon fibre electrodes with continuous amperometry gives better temporal information allowing the precise description of the kinetic parameters of the mechanisms which regulate DA overflow. The results obtained in rats extended by the results obtained in mice lacking a protein involved in DA transmission demonstrate that DA autoregulation and DA uptake: (i) contributes to the operational properties of DA terminals in converting action potentials into DA release as a high pass filter which favours short bursts of action potentials and (ii) inhibits excessive DA release which might result from prolonged and large increases in the impulse flow.

Decreased antigen-induced eicosanoid release in conjugated linoleic acid-fed guinea pigs.

This study investigated the capacity of conjugated linoleic acids (CLA) to reduce ex vivo antigen-induced release of eicosanoids in a type I hypersensitivity model. Guinea pigs were fed a diet containing 0.25% safflower oil (control) or 0.25% CLA [43% trans (t)10, cis (c)12; 41% c9, t11/t9, c11 18:2] for 2 wk before and during sensitization to ovalbumin (OVA). Lungs, tracheas, and bladders were incubated in physiological saline solution (PSS) for 1 h (basal mediator release) and challenged with OVA (0.01 g/l PSS) for 1 h (mediator release in response to antigen). Eicosanoids were quantified by HPLC/tandem mass spectrometry or enzyme immunoassay. CLA feeding resulted in no change in basal release but decreased eicosanoid release from sensitized tissues in response to antigen challenge in the following manner: thromboxane B(2), 6-keto-prostaglandin (PG)F(1alpha), PGF(2alpha), PGD(2), PGE(2) by 57-75% in lung, 45-65% in trachea, and 38-60% in bladder; and leukotriene C(4)/D(4)/E(4) by 87, 90, and 50% in lung, trachea, and bladder, respectively. These data indicate that feeding CLA reduces lipid-derived inflammatory mediators produced by this type I hypersensitivity model.

Diminished basal nitric oxide release after myocardial ischemia and reperfusion promotes neutrophil adherence to coronary endothelium.

We measured changes in basal release of nitric oxide and its effect on polymorphonuclear leukocyte (PMN) adherence to endothelial cells (ECs) in a feline model of myocardial ischemia (90 minutes) and reperfusion. Basal release of nitric oxide from the left anterior descending coronary artery (LAD) after myocardial ischemia/reperfusion and from the control left circumflex coronary artery (LCX) was assessed by NG-nitro L-arginine methyl ester (L-NAME)-induced vasocontraction. L-NAME induced a significant EC-dependent vasocontraction in control LCX rings (0.28 +/- 0.04 g), which was fully reversed by L-arginine but not D-arginine. L-NAME-induced vasocontraction of LAD rings was not significantly changed after 90 minutes of myocardial ischemia without reperfusion. However, 10 minutes of reperfusion reduced the L-NAME-induced vasocontraction to 0.13 +/- 0.04 g (p < 0.05), and this was restored by addition of 3 mM L-arginine but not D-arginine. Longer periods of reperfusion progressively decreased L-NAME-induced vasocontraction. After 270 minutes of reperfusion, L-NAME-induced vasocontraction was virtually abolished. Myocardial ischemia without reperfusion did not increase PMN adherence to ECs. However, PMN adherence to LAD ECs was significantly increased after 20 minutes of reperfusion (39 +/- 6 to 105 +/- 9 PMNs/mm2, p < 0.01), and incubation of LAD segments with L-arginine significantly attenuated this increase in PMN adherence. After 270 minutes of reperfusion, PMN adherence to LAD ECs was further increased to 224 +/- 10 PMNs/mm2 (p < 0.001). This increase in PMN adherence was almost completely blocked by MAb R15.7, a monoclonal antibody against CD18 of PMNs, and was significantly attenuated by MAb RR1/1, a monoclonal antibody against intercellular adhesion molecule-1 of ECs (p < 0.01). These results indicate that decreased basal release of endothelium-derived relaxing factor after myocardial ischemia/reperfusion precedes enhanced PMN adherence to the coronary endothelium, which may lead to PMN-induced myocardial injury.

Ethanol-induced increase in endogenous dopamine release may involve endogenous opiates.

The effect of opiate peptides on basal and potassium-stimulated endogenous dopamine (DA) release from striatal slices was studied in vitro. Dual stimulation of the striatal slices gave a reproducible increase in DA release that was calcium dependent. Addition of the delta-opiate receptor agonists Met5-enkephalin, [D-Ala2,D-Leu5]enkephalin (DADLE), and [D-Ser2]Leu-enkephalin-Thr (DSLET), increased the basal DA release without affecting potassium-stimulated release in a dose-dependent manner. The effect of DADLE was antagonized by the addition of naloxone. In contrast, the mu-opioid receptor agonist [D-Ala2,N-MePhe4,Gly-ol5]enkephalin (DAGO) and the epsilon-opioid agonist beta-endorphin inhibited the stimulated DA release without changing the basal release. The inhibitory effect of DAGO on potassium-stimulated release was antagonized by naloxone. The addition of ethanol (75 mM) to the incubation media produced a delayed increase of both the basal and stimulated DA release. There was no change in stimulated DA release when the change in basal release was subtracted, suggesting that ethanol produced a dose-dependent, selective increase in basal DA release. Naloxone and the selective delta-opiate antagonist ICI 174864 inhibited the ethanol-induced increase in basal DA release. Naloxone and ICI 174864 added alone did not alter either basal or stimulated DA release. We therefore suggest that the ethanol-induced increase in basal DA release is an indirect effect involving an endogenous delta-opiate agonist.

Raised [ 3H]-5-HT release and 45Ca 2+ uptake in diazepam withdrawal: Inhibition by baclofen

The effect of diazepam withdrawal (2 mg/kg/day) on release of [ 3H]-5-hydroxytryptamine(5-HT) and [ 14C]-GABA from rat cortical and hippocampal slices was studied. No changes in [ 14C]-GABA release (basal, K +-evoked, uptake) from slices of either region were observed. Similarly, all parameters of [ 3H]-5-HT release were unchanged in cortical slices. However, during diazepam withdrawal, depolarised [ 3H]-5-HT release from hippocampal slices was raised with no changes in basal release or uptake into the slices being found. This increase could be prevented by in vivo administration of 1 mg/kg baclofen—this dose having no significant effect on [ 3H]-5-HT release from hippocampal slices of control rats. To further investigate this effect, 45Ca 2+ uptake into hippocampal synaptosomes was examined and found to be increased during withdrawal. This was blocked by in vitro addition of 10 μM (−)baclofen, which had no effect on 45Ca 2+ uptake in controls. Inhibition of 45Ca 2+ uptake by (−)baclofen was also enhanced in nonwithdrawn diazepam-treated rats, but not in rats treated acutely with diazepam. The results from both studies indicate that chronic diazepam treatment increases neuronal sensitivity to baclofen. These results are discussed with reference to the anxiogenic state during diazepam withdrawal and a recent report of reversal of this behaviour by baclofen.

Handling habituation and ehlordiazepoxide have different effects on GABA and 5-HT function in the frontal cortex and hippocampus

In slices of frontal cortex and hippocampus from rats that had been habituated to handling for 21 days, there was significantly less 20 mM K +-evoked release of [ 14C]GABA ([ 14C]7-aminobutyric acid) compared with rats naive to handling. Handling for 21 days also significantly increased the uptake of [ 14C]GABA into frontal cortex and hippocampus. The change in uptake in the hippocampus was independent of any changes in release and could account for the apparent change in evoked release; in the cortex there were no independent changes in uptake and K +-evoked release. When the changes in uptake were taken into account, there were no independent changes in basal release of GABA in either region. HPLC analysis showed the change in uptake was not due to differences between the groups in endogenous GABA concentrations. Acute administration of chlordiazepoxide (CDP 7.5 mg/kg i.p.) to handling naive rats also significantly reduced K +-evoked [ 14C]GABA release from the cortex and hippocampus, but basal release and GABA uptake were unchanged. Neither handling nor CDP administration significantly changed the K +-evoked [ 3H]5-HT release, however the uptake of 5-HT and its basal release in both regions were both significantly and independently increased in animals habituated to handling, compared with handling naive animals. In the hippocampus, the endogenous 5-HT concentrations were significantly lower in the rats that had received 21 days of handung, compared with handling naive rats. In the cortex the endogenous 5-hydroxyindoleacetic acid concentrations were significantly lower in the group that had been handled for 21 days. Thus both the GABA and 5-HT systems were responsive to handling habituation.

Modulation of adrenal catecholamine release by DA2 dopamine receptors in the anaesthetized dog.

1. The effects of DA2 agonist, quinpirole (50 micrograms/kg, i.v.) and a DA2 antagonist, domperidone (50 micrograms/kg, i.v.) on the release of adrenal catecholamines were evaluated in the anaesthetized and vagotomized dog. 2. Stimulations (5 V pulses of 2 ms duration for 3 min) of the splanchnic nerve at frequencies of 1, 3 and 5 Hz were applied randomly before and after injection of the drug. 3. The results show that quinpirole reduces significantly the release of adrenaline at 1 and 3 Hz but not at 5 Hz, while the release of noradrenaline is reduced at 1 Hz but not at 3 and 5 Hz. Inversely, domperidone potentiates significantly the release of both catecholamines at 3 and 5 Hz, but not at 1 Hz. 4. There was no change in basal release of adrenal catecholamines, adrenal blood flow or heart rate after both drug treatments. 5. The mean arterial pressure was not affected by domperidone treatment but there was a significant reduction in basal mean arterial pressure after the injection of quinpirole. 6. There was no change in any of these parameters during electrical stimulation. 7. Therefore, these results strongly suggest that DA2 dopamine receptors are present at the level of the adrenal medulla and that their activation could mediate an inhibitory modulation on the adrenal catecholamines release within a certain range of electrical stimulation.

Effect of extracellular manganese on amylase release from dispersed pancreatic acini.

In dispersed acini from guinea pig pancreas, adding extracellular manganese increased amylase release. A significant effect could be detected with 0.25 mM manganese, and maximal stimulation occurred with 1 mM manganese. When manganese was added, the rate of amylase release did not change during the first 20 min of incubation and then gradually increased to a new steady state by 80 min, which with 1 mM manganese represented a fourfold increase in the rate of enzyme release. Extracellular manganese inhibited the stimulation of amylase release caused by those secretagogues that mobilize cellular calcium but augmented the stimulation caused by those secretagogues whose actions are mediated by cellular cAMP. The mechanism by which manganese altered stimulated amylase secretion differed from the mechanism by which manganese stimulated basal amylase release because the change in stimulated release was maximal within 10 min, whereas the change in basal release did not occur until after 20 min. The actions of manganese on secretagogue-stimulated amylase release were not attributable to manganese-induced changes in secretagogue-stimulated calcium outflux or cAMP and, instead, appear to result from actions of manganese on one of the later steps in the mechanisms for stimulating the secretory process.