Comparative pyrogenic potency of endogenous prostanoids and of prostanoid-mimetics injected into the anterior hypothalamic/preoptic region of the cat

Intracerebroventricular injection of prostaglandin E(1) changes concentrations of biogenic amines in the posterior hypothalamus of the rat

Since the posterior hypothalamus (PH) plays a key role in the control of body temperature, the aim of this study was to evaluate the changes in adrenaline, noradrenaline and dopamine levels in the PH during the hyperthermia induced by prostaglandin E(1) (PGE(1)). The concentration of adrenaline, noradrenaline and dopamine in the PH, the firing rate of the sympathetic nerves innervating interscapular brown adipose tissue (IBAT), IBAT and colonic temperatures (T(IBAT) and T(C)) were monitored in 12 urethane-anaesthetized male Sprague-Dawley rats before and after an intracerebroventricular injection of 500 ng PGE(1) dissolved in 2 microl of 0.9% NaCl saline solution or only saline. The catecholamines were collected using a microdialysis probe and quantified by HPLC. The results showed that PGE(1) caused a significant increment in the concentration of adrenaline from 15. 83+/-2.69 to 34.95+/-3.9 ng ml(-1) and of dopamine from 35.15+/-4.48 to 55.68+/-6.21 ng ml(-1). A significant decrease in the level of noradrenaline from 18.75+/-2.05 to 8.56+/-2.26 ng ml(-1) was registered. The firing rate of sympathetic nerves to IBAT was increased from 100+/-0% to 204.83+/-15.22% by PGE(1). T(IBAT) and T(C) rose respectively from 36.91+/-0.15 degrees C to 38.88+/-0.29 degrees C, and from 36.7+/-0.15 degrees C to 38.13+/-0.36 degrees C after the injection of PGE(1). The changes in adrenaline and noradrenaline occurred during the first 20 min as did the changes in temperature and firing rate, while the change in dopamine was delayed until 21-60 min after the PGE(1) injection. No significant change of analyzed variables was found in the control rats. These findings suggest that these biogenic amines of the PH are involved in the control of the sympathetic and thermogenic changes induced by PGE(1).

Prostanoid receptors: structures, properties, and functions

Prostanoids are the cyclooxygenase metabolites of arachidonic acid and include prostaglandin (PG) D(2), PGE(2), PGF(2alpha), PGI(2), and thromboxne A(2). They are synthesized and released upon cell stimulation and act on cells in the vicinity of their synthesis to exert their actions. Receptors mediating the actions of prostanoids were recently identified and cloned. They are G protein-coupled receptors with seven transmembrane domains. There are eight types and subtypes of prostanoid receptors that are encoded by different genes but as a whole constitute a subfamily in the superfamily of the rhodopsin-type receptors. Each of the receptors was expressed in cultured cells, and its ligand-binding properties and signal transduction pathways were characterized. Moreover, domains and amino acid residues conferring the specificities of ligand binding and signal transduction are being clarified. Information also is accumulating as to the distribution of these receptors in the body. It is also becoming clear for some types of receptors how expression of their genes is regulated. Furthermore, the gene for each of the eight types of prostanoid receptor has been disrupted, and mice deficient in each type of receptor are being examined to identify and assess the roles played by each receptor under various physiological and pathophysiological conditions. In this article, we summarize these findings and attempt to give an overview of the current status of research on the prostanoid receptors.

Cortical spreading depression reduces paraventricular activation induced by hippocampal neostigmine injection

The firing rate of the neurons of the hypothalamic paraventricular nucleus, the temperatures of the interscapular brown adipose tissue and of the colon (TIBAT and Tc) were monitored in 24 urethane-anesthetized male Sprague-Dawley rats divided into four groups. These variables were measured before and after hippocampal injection of neostigmine (5x10(-7) mol) in the 1st and 2nd groups or of saline in the 3rd and 4th groups. The hippocampal injection was preceded by cortical spreading depression in the 1st and 3rd groups, while the cortical depression was not induced in the 2nd and 4th groups. The results show an increase of firing rate, TIBAT and Tc after neostigmine injection in the rats without cortical depression. Cortical spreading depression significantly reduces these enhancements. These findings demonstrate that: (1) the paraventricular nucleus plays a significant role in the hyperthermia induced by neostigmine injection into the hippocampus; and (2) the cerebral cortex is involved in the control of the paraventricular activity.

Norepinephrine Injection into the Paraventricular Nucleus Induces a Reduced Modification of Eating Behavior and Thermogenesis in Brattleboro Rats

Intake of carbohydrates, lipids, proteins and total calories, temperature of interscapular brown adipose tissue, and oxygen consumption were monitored in vasopressin-containing and vasopressin-deficient rats. These variables were measured after a 20 nmol norepinephrine (NE) or saline injection into the paraventricular nucleus (PVN) of the hypothalamus. NE increased the intake of carbohydrates, lipids and total calories, decreased brown adipose tissue temperature and oxygen consumption in vasopressin-containing rats. NE reduced the intake of carbohydrates, while it increased the consumption of lipids in vasopressin-deficient rats. These findings indicate that vasopressin is involved in the modifications of eating behavioral and thermogenesis induced by NE injection into the hypothalamic PVN.

Procaine injection into the paraventricular nucleus reduces sympathetic and thermogenic activation induced by frontal cortex stimulation in the rat

These experiments were designed to test the effect of procaine injection into the paraventricular nucleus on the sympathetic and thermogenic changes induced by frontal cortex stimulation. Oxygen consumption, firing rate of the sympathetic nerves to interscapular brown adipose tissue (IBAT), along with IBAT and colonic temperatures (T(IBAT) and T(C)) were monitored in fasted male Sprague-Dawley rats before and 25 min after an electrical stimulation of the frontal cortex. The same variables were monitored in rats with administration of procaine into the paraventricular nucleus. The results show that cortical stimulation raises oxygen consumption, sympathetic neuron firing rates, T(IBAT), and T(C). This increase is reduced by procaine injection. These findings suggest that the paraventricular nucleus plays a key role in the sympathetic and thermogenic changes induced by cortical stimulation.

Aspartic and glutamic acids increase in the frontal cortex during prostaglandin E1 hyperthermia

The aim of the present experiment was to evaluate the role played by aspartic acid and glutamic acid of frontal cerebral cortex during the hyperthermia induced by prostaglandin E1. Two groups of six Sprague Dawley male rats were anaesthetized with ethyl-urethane. The frontal cortical concentrations of aspartic and glutamic acids, the firing rate of the sympathetic nerves to the interscapular brown adipose tissue, the colonic and interscapular brown adipose tissue temperatures were monitored both before and after an intracerebroventricular injection of prostaglandin E1 (500 ng) or saline. Aspartic and glutamic acids were collected using a microdialysis probe placed in the frontal cortex. Concentrations of aspartic and glutamic acids were measured by high-pressure liquid chromatography with fluorescence detector. Prostaglandin E1 induced an increase in the concentrations of aspartic and glutamic acids, in the firing rate of sympathetic nerves and in the colonic and interscapular brown adipose tissue temperatures. The findings of the present experiment indicate that an intracerebroventricular injection of prostaglandin E1 causes release of aspartic and glutamic acids in the frontal cortex.

A selective inhibitor of cyclooxygenase-2 reverses endotoxin-induced pyretic responses in non-human primates

The anti-pyretic effect of a selective cyclooxygenase-2 inhibitor, DFU (5,5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulfonyl)phenyl-2(5H)-furano ne), was examined in conscious, un-restrained squirrel monkeys (Saimiri sciureus) using a radio telemetric system. Injection of bacterial endotoxin (lipopolysaccharide, 6 microg kg(-1), i.v.) in squirrel monkeys caused a gradual increase in core body temperature reaching a plateau of 2.07 +/- 0.17 degrees C above baseline at 2 h post-injection. Oral administration of DFU (1 mg kg(-1)) reduced, and DFU (3 mg kg(-1)) completely reversed the lipopolysaccharide-induced pyretic responses. The onset of action of DFU (about 30 min) is in good agreement with the pharmacokinetic profile of this compound in squirrel monkeys. The effect of DFU is comparable to that of a conventional non-selective non-steroidal anti-inflammatory drug (NSAID), diclofenac (3 mg kg(-1)). Since the plasma levels achieved for DFU at the dose employed in the present study are below the threshold required for inhibition of cyclooxygenase-1, it is concluded that the anti-pyretic effect of DFU can be attributed predominantly to an inhibitory action on cyclooxygenase-2. Thus, lipopolysaccharide-induced pyresis in squirrel monkeys can be used as a model for evaluation of anti-pyretic activity of cyclooxygenase inhibitors.

Effects of centrally administered prostaglandin EP receptor agonists on febrile and adrenocortical responses in the prepubertal pig

Febrile and adrenocortical responses to central (lateral ventricle) injections of prostaglandin E2 (PGE2) and E-series prostanoid receptor agonists (EP1, EP2, EP3, subtypes) were investigated in prepubertal pigs. In Experiment 1, administration of PGE2, (1.4, 5.6 nmol) produced dose-related increases in core temperature and plasma cortisol concentrations. In Experiment 2, approximately equimolar (1.2 to 1.4 nmol) amounts of EP1, EP2, and EP2/EP3 agonists were compared. The EP2 and EP2/EP3 prostanoids raised core temperature, whereas the increase induced by the EP1 agonist was not significant. Similarly, although all of the agonists appeared to stimulate cortisol release, these results were also not significant. In Experiment 3, pigs treated with an EP3 agonist (1.3 nmol) showed marked febrile and adrenocortical responses. The results of these experiments are compared with data from the rat using the same agonists and route of administration. The findings are also discussed in relation to the distribution of receptor populations in vascular and synaptosomal compartments of the porcine brain.

Iloprost, a stable analogue of PGI2, potentiates the hyperthermic effect of PGE2 in rats

Centrally mediated effects of iloprost, a stable analogue of PGI2, on rectal temperature have been investigated in conscious rats. ICV administration of iloprost (100-1,000 ng, ICV) produced a dose-dependent, monophasic hyperthermic response that was not inhibited by indomethacin. When injected into the preoptic anterior hypothalamic (POAH) region, iloprost (2-50 ng/POAH) induced a biphasic increase in rectal temperature. While the first phase was inhibited by AH 6809, an E1-type prostaglandin (EP1) receptor antagonist, the second phase was abolished by indomethacin pretreatment. Iloprost was found not to alter rectal temperature when injected into the ventromedial hypothalamic area. Administration of iloprost into the POAH in a dose that had no effect on rectal temperature significantly potentiated the hyperthermic effect of PGE2 (50 ng, ICV). These findings suggest that the pyrogenic effect of iloprost is partly mediated by EP1 receptors located on the POAH. Regarding the similarities of iloprost and PGI2, it is further proposed that endogenous PGI2 might act to modulate hyperthermic effect of PGE2 released during arachidonic acid- or endogenous pyrogen-induced fever.

Localization of central prostaglandin E2 antisecretory effects

Intracerebroventricular prostaglandin E2 (PGE2) inhibits stimulated gastric acid secretion; however, the central site of action is unknown. Specific PGE2 binding sites have been localized to the ventromedial hypothalamic nucleus and central amygdala (A). The nuclear accumbens has been shown to play a role in central neurotensin-induced antisecretory effects. These studies tested the hypothesis that microinjections of PGE2 into the ventromedial hypothalamic nucleus, central amygdala, and nuclear accumbens inhibit stimulated gastric acid secretion. The hippocampus served as a cerebral control region. Two days before the experiments, metal cannulas were stereotaxically positioned bilaterally into specific areas of the brain, and metal gastric cannulas were operatively implanted, under nembutal anesthesia, in male 250-g Sprague-Dawley rats. On the experimental day, the rats, fasted for 14 hours, were given saline or PGE2 (0.1-1.0 micrograms in 0.2 microL/side) through the central cannulas 10 minutes before administering pentagastrin (40 micrograms/kg SC). Gastric secretion was measured at 30-minute intervals and expressed as acid output, micromoles per hour. Acid output (mean +/- SE) in control animals was 161 +/- 14 mumol/h. Prostaglandin E2 administration at doses of 0.10, 0.50, and 1.0 micrograms/side (a) into ventromedial hypothalamic nucleus reduced acid output to 53 +/- 11,* 36 +/- 10,* and 27 +/- 11* mumol/h regularly; (b) into NACB reduced acid output to 157 +/- 36, 60 +/- 12,* and 38 +/- 12* mumol/h; and (c) into A reduced acid output to 144 +/- 31, 141 +/- 26, and 90 +/- 19* mumol/h, respectively (*P less than 0.05 by Neuman-Keuls test). Prostaglandin E2 (0.50 micrograms/side) administration into hippocampus had no significant effect on acid output (134 +/- 28 mumol/h). Although central PGE2 administration was associated with hyperthermia, this occurred at lower doses than those required to inhibit acid secretion. Prostaglandin E2 administration into specific brain areas known to have PGE2 receptors, the central amygdala and ventromedial hypothalamic nucleus, and into nuclear accumbens inhibits stimulated gastric acid secretion. These observations suggest that PGE2 may have a physiological role in the central control of gastric acid secretion.