Pivotal role of nitric oxide in the control of blood pressure after leptin administration.
Leptin administration has been shown to increase renal, adrenal, and lumbar sympathetic nerve activity. However, this generalized sympathoexcitatory activity is not always followed by an increase in arterial pressure. The present study tested the hypothesis that leptin induces a release of nitric oxide (NO) that opposes the pressor effect of sympathoexcitation. The effect of intravenous administration of leptin (10, 100, and 1,000 microg/kg body wt) or vehicle on blood pressure (BP), heart rate (HR), and serum nitrite/nitrate concentrations of anesthetized Wistar rats was examined. At 90 min after injection, the three leptin doses tested increased serum NO concentrations 20.5, 33.1, and 89.5%, respectively (P < 0.001 vs. baseline). The effect of leptin on NO concentrations was significantly dose-dependent on linear trend testing (P = 0.0001). In contrast, leptin did not change serum nitrite/nitrate concentrations of fa/fa rats. Leptin administration to Wistar rats under NO synthesis inhibition (N(omega)-nitro-L-arginine methyl ester [L-NAME]) produced a statistically significant increase (P < 0.05) in both systolic BP and mean arterial pressure as well as in HR (P < 0.01). Injection of leptin into rats with pharmacologically induced ganglionic blockade (chlorisondamine) was followed by a decrease in BP and HR to values significantly lower (P < 0.01) than those observed with chlorisondamine treatment alone. The leptin-induced hypotension observed in the setting of ganglionic blockade was blocked by L-NAME. These findings raise the possibility that the leptin-induced release of NO may contribute to the homeostasis of BP. (+info)
Thermogenic effects of sibutramine and its metabolites.
1. The thermogenic activity of the serotonin and noradrenaline reuptake inhibitor sibutramine (BTS 54524; Reductil) was investigated by measuring oxygen consumption (VO2) in rats treated with sibutramine or its two pharmacologically-active metabolites. 2. Sibutramine caused a dose-dependent rise in VO2, with a dose of 10 mg kg(-1) of sibutramine or its metabolites producing increases of up to 30% that were sustained for at least 6 h, and accompanied by significant increases (0.5-1.0 degrees C) in body temperature. 3. Based on the accumulation in vivo of radiolabelled 2-deoxy-[3H]-glucose, sibutramine had little or no effect on glucose utilization in most tissues, but caused an 18 fold increase in brown adipose tissue (BAT). 4. Combined high, non-selective doses (20 mg kg(-1)) of the beta-adrenoceptor antagonists, atenolol and ICI 118551, inhibited completely the VO2 response to sibutramine, but the response was unaffected by low, beta1-adrenoceptor-selective (atenolol) or beta2-adrenoceptor-selective (ICI 118551) doses (1 mg kg(-1)). 5. The ganglionic blocking agent, chlorisondamine (15 mg kg(-1)), inhibited completely the VO2 response to the metabolites of sibutramine, but had no effect on the thermogenic response to the beta3-adrenoceptor-selective agonist BRL 35135. 6. Similar thermogenic responses were produced by simultaneous injection of nisoxetine and fluoxetine at doses (30 mg kg(-1)) that had no effect on VO2 when injected individually. 7. It is concluded that stimulation of thermogenesis by sibutramine requires central reuptake inhibition of both serotonin and noradrenaline, resulting in increased efferent sympathetic activation of BAT thermogenesis via beta3-adrenoceptor, and that this contributes to the compound's activity as an anti-obesity agent. (+info)
AV3V lesions attenuate the cardiovascular responses produced by blood-borne excitatory amino acid analogs.
Systemic injections of the excitatory amino acid (EAA) analogs, kainic acid (KA) and N-methyl-D-aspartate (NMDA), produce a pressor response in conscious rats that is caused by a centrally mediated activation of sympathetic drive and the release of arginine vasopressin (AVP). This study tested the hypothesis that the tissue surrounding the anteroventral part of the third ventricle (AV3V) plays a role in the expression of the pressor responses produced by systemically injected EAA analogs. Specifically, we examined whether prior electrolytic ablation of the AV3V region would affect the pressor responses to KA and NMDA (1 mg/kg iv) in conscious rats. The KA-induced pressor response was smaller in AV3V-lesioned than in sham-lesioned rats (11 +/- 2 vs. 29 +/- 2 mmHg; P < 0.05). After ganglion blockade, KA produced a pressor response in sham-lesioned but not AV3V-lesioned rats (+27 +/- 3 vs. +1 +/- 2 mmHg; P < 0.05). The KA-induced pressor response in ganglion-blocked sham-lesioned rats was abolished by a vasopressin V1-receptor antagonist. Similar results were obtained with NMDA. The pressor response to AVP (10 ng/kg iv) was slightly smaller in AV3V-lesioned than in sham-lesioned ganglion-blocked rats (45 +/- 3 vs. 57 +/- 4 mmHg; P < 0.05). This study demonstrates that the pressor responses to systemically injected EAA analogs are smaller in AV3V-lesioned rats. The EAA analogs may produce pressor responses by stimulation of EAA receptors in the AV3V region, or the AV3V region may play an important role in the expression of these responses. (+info)
Opposing adrenergic actions of intravenous metformin on arterial pressure in female spontaneously hypertensive rats.
OBJECTIVE: Intravenous (i.v.) injection of the antidiabetic drug metformin rapidly lowers mean arterial pressure (MAP) in spontaneously hypertensive rats (SHR). However, if autonomic ganglia or alpha-adrenoceptors are first blocked then metformin rapidly raises MAP in SHR. This study was conducted to further characterize the adrenergic mechanisms of these opposing i.v. actions of the drug. METHODS: Conscious, undisturbed female SHR with indwelling vascular catheters were used to measure acute effects of i.v. metformin (100 mg/kg; before and after sustained ganglionic blockade, GB, with chlorisondamine, 5 mg/kg) on: (1) circulating levels of catecholamines, (2) MAP after pharmacologic modulation of beta- as well as alpha-adrenoceptors and (3) all the above in the absence as well as presence of the adrenal medulla. RESULTS: Plasma norepinephrine (NE) and epinephrine (E) levels (pg/ml) were rapidly increased by i.v. metformin (8 SHR, p < 0.05) both before GB (delta NE = +146 +/- 41; delta E = +119 +/- 31) and after GB (delta NE = +79 +/- 24; delta E = +120 +/- 32). Similar increases in plasma NE (though not E) were seen in SHR without adrenal medullae. Blockade of beta-adrenoceptors with propranolol (pro; 3 mg/kg, 8 SHR) enhanced the rapid depressor response to i.v. metformin before GB (delta MAP, mmHg: -38 +/- 4 with pro vs -17 +/- 3 without pro; p < 0.05) and attenuated the rapid pressor response to i.v. metformin after GB (delta MAP, mmHg: +8 +/- 3 with pro vs +30 +/- 4 without pro; p < 0.05). Results were similar in SHR without adrenal medullae. Finally, if baseline MAP under GB was raised back to hypertensive levels with i.v. infusion of either NE or phenylephrine then i.v. metformin did not raise but rather reduced MAP in SHR. CONCLUSION(S): The acute depressor action of i.v. metformin in female SHR (1) is most likely due to a direct vasodilator action which includes inhibition of alpha-receptor-mediated vasoconstriction and (2) is buffered by an acute beta-receptor-mediated pressor action likely due to a direct metformin-induced release of NE from postganglionic sympathetic nerve endings. (+info)
Reward and somatic changes during precipitated nicotine withdrawal in rats: centrally and peripherally mediated effects.
The negative affective aspects of nicotine withdrawal have been hypothesized to contribute to tobacco dependence. In the present studies in rats, brain stimulation reward thresholds, conditioned place aversions, and somatic signs of withdrawal were used to investigate the role of central and peripheral nicotinic acetylcholine and opioid receptors in nicotine withdrawal. Rats prepared with s.c. osmotic mini-pumps delivering 9.0 mg/kg/day nicotine hydrogen tartrate or saline were administered various doses of the nicotinic antagonists mecamylamine (s.c.), chlorisondamine (s. c. or i.c.v.), dihydro-beta-erythroidine (s.c.), or the opiate antagonist naloxone (s.c.). Nicotine-treated rats receiving mecamylamine or i.c.v. chlorisondamine exhibited elevated thresholds and more somatic signs than saline-treated rats. Nicotine-treated rats receiving s.c. chlorisondamine, at doses that do not readily cross the blood-brain barrier, exhibited more somatic signs than saline-treated rats with no threshold elevations. Naloxone administration produced threshold elevations and somatic signs only at high doses that induced similar magnitude effects in both nicotine- and saline-treated subjects. Mecamylamine or dihydro-beta-erythroidine administration induced conditioned place aversions in nicotine-treated rats but required higher doses than those needed to precipitate threshold elevations. In contrast, naloxone administration induced conditioned place aversions at lower doses than those required to precipitate threshold elevations and somatic signs. These data provide evidence for a dissociation between centrally mediated elevations in reward thresholds and somatic signs that are both centrally and peripherally mediated. Furthermore, threshold elevations and somatic signs of withdrawal appear to be mediated by cholinergic neurotransmission, whereas conditioned place aversions appear to be primarily mediated by the opioid system. (+info)
Effects of nicotine and chlorisondamine on cerebral glucose utilization in immobilized and freely-moving rats.
Chlorisondamine blocks central nicotinic receptors for many weeks via an unknown mechanism. Intracerebroventricular administration of [(3)H]-chlorisondamine in rats results in an anatomically restricted and persistent intracellular accumulation of radioactivity. The initial aim of the present study was to test whether nicotinic receptor antagonism by chlorisondamine is also anatomically restricted. Male adult rats were pretreated several times with nicotine to avoid the disruptive effects of the drug seen in drug-naive animals. They then received chlorisondamine (10 microg i. c.v.) or saline, and local cerebral glucose utilization (LCGU) was measured 4 weeks later after acute nicotine (0.4 mg kg(-1) s.c.) or saline administration. During testing, rats were partially immobilized. Nicotine significantly increased LCGU in the anteroventral thalamus and in superior colliculus. Chlorisondamine completely blocked the first of these effects. Chlorisondamine significantly reduced LCGU in the lateral habenula, substantia nigra pars compacta, ventral tegmental area, and cerebellar granular layer. The second experiment was of similar design, but the rats were not pre-exposed to nicotine, and were tested whilst freely-moving. Acute nicotine significantly increased LCGU in anteroventral thalamus, superior colliculus, medial habenula and dorsal lateral geniculate. Overall, however, nicotine significantly decreased LCGU. Most or all of the central effects of nicotine on LCGU were reversed by chlorisondamine given 4 weeks beforehand. These findings suggest that chlorisondamine blocks nicotinic effects widely within the brain. They also indicate that in freely-moving rats, nicotine can reduce or stimulate cerebral glucose utilization, depending on the brain area. British Journal of Pharmacology (2000) 129, 147 - 155 (+info)
Activation of antigen-specific CD4+ Th2 cells and B cells in vivo increases norepinephrine release in the spleen and bone marrow.
The neurotransmitter norepinephrine (NE) binds to the beta 2-adrenergic receptor (beta 2AR) expressed on various immune cells to influence cell homing, proliferation, and function. Previous reports showed that NE stimulation of the B cell beta 2AR is necessary for the maintenance of an optimal primary and secondary Th2 cell-dependent Ab response in vivo. In the present study we investigated the mechanism by which activation of Ag-specific CD4+ Th2 cells and B cells in vivo by a soluble protein Ag increases NE release in the spleen and bone marrow. Our model system used scid mice that were reconstituted with a clone of keyhole limpet hemocyanin-specific Th2 cells and trinitrophenyl-specific B cells. Following immunization, the rate of NE release in the spleen and bone marrow was determined using [3H]NE turnover analysis. Immunization of reconstituted scid mice with a cognate Ag increased the rate of NE release in the spleen and bone marrow 18-25 h, but not 1-8 h, following immunization. In contrast, immunization of mice with a noncognate Ag had no effect on the rate of NE release at any time. The cognate Ag-induced increase in NE release was partially blocked by ganglionic blockade with chlorisondamine, suggesting a role for both pre- and postganglionic signals in regulating NE release. Thus, activation of Ag-specific Th2 cells and B cells in vivo by a soluble protein Ag increases the rate of NE release and turnover in the spleen and bone marrow 18-25 h after immunization. (+info)
Possible contribution of central gamma-aminobutyric acid receptors to resting vascular tone in freely moving rats.
Previous studies have shown that central administration of GABA (gamma -aminobutyric acid), an inhibitory neurotransmitter, preferentially reduces hindquarters and carotid vascular resistances but not renal and coeliac vascular resistances in conscious rats. This study tested the hypothesis that these preferential actions of central GABA receptors are related to differences between vessels in resting autonomic vascular tone in freely moving rats. Rats were chronically implanted with intracisternal cannulas and/or electromagnetic probes to measure regional blood flows. In response to GABA administration, the changes in vascular resistance (arterial blood pressure/regional blood flow) of the hindquarters (n = 23) and carotid (n = 12) vascular beds were significantly and negatively correlated with basal vascular resistance. No such relationship was found for the renal (n = 21), coeliac (n = 13) and superior mesenteric (n = 23) vascular beds. This finding indicates that the responsiveness to GABA of brainstem pathways controlling the hindquarters and carotid vascular beds co-varies with resting resistance in hindquarters and carotid vessels. A similar analysis was performed, correlating the ongoing vascular resistance of each vessel with its response to ganglionic blockade by chlorisondamine. In this case, a significant negative correlation was also found for the hindquarters (n = 26) and carotid (n = 15) vascular beds, but not for the coeliac (n = 17) or superior mesenteric (n = 19) vessels. Together, these findings suggest that central GABA receptors accessible from the cisterna magna preferentially affect two vascular beds which, in the freely moving rat, show resting autonomic vascular tone. (+info)