Involvement of corticotropin-releasing factor in restraint stress-induced anorexia and reversion of the anorexia by somatostatin in the rat

The mechanism by which restraint stress induces suppression of food intake and the influence of intracerebroventricular (icv) administration of somatostatin on the anorexia induced by restraint stress were examined in the rat. Ninety minutes of restraint stress reduced food intake of rats to approximately 60% that of control. Anorexia induced by 90 min restraint stress was partially reversed by icv administration of alpha-helical CRF (9-41), a corticotropin-releasing factor (CRF) antagonist, and completely reversed by anti-CRF gamma-globulin. These results provide further evidence in support of the theory that CRF is involved in the inhibitory mechanism of food intake in restraint stress. ICV administration of somatostatin 14 and SMS 201-995, an analog of somatostatin, also reversed restraint stress-induced anorexia. It is, therefore, suggested that somatostatin may counteract the suppressive action of CRF on food intake in stress.     

Effects of adrenergic blockers on corticotropin-releasing factor-induced behavioral changes in rats

The effects of adrenoreceptor blocking agents on corticotropin-releasing factor (CRF)-induced behavioral changes in rats were examined. The i.c.v. injection of 1 micrograms ovine CRF significantly increased the grooming frequency, number of occurrences of rearing and total distance moved. I.c.v. administered phentolamine at a dose of 10 nmol completely suppressed the increase in rearing and total distance moved induced by CRF without affecting the grooming frequency, whereas 100 nmol phentolamine significantly decreased the grooming frequency as well as the rearing and total distance moved. In contrast, propranolol reduced the increase in rearing induced by CRF only at a dose which induced ataxia in rats. The increases in rearing and total distance moved induced by CRF were reduced by 10 nmol of yohimbine and 100 nmol of prazosin. S.c. injection of caffeine (10 mg/kg) produced a significant increase in grooming frequency, rearing, and total movement. Administration of 10 nmol phentolamine and yohimbine did not affect these behavioral changes induced by caffeine, while 100 nmol prazosin suppressed them. Therefore, prazosin depressed the behavior of rats non-specifically. These results suggest that CRF-induced behavioral hyperactivity is mediated at least in part by alpha-noradrenergic, mainly alpha 2-noradrenergic, systems in the brain.     

Antagonistic effect of scutellarin on the toxicity of selenium in rat livers

Selenium has both nutritional function and toxicity according to its concentration and species. To counteract the toxicity of selenium, scutellarin was investigated. Wistar rats were supplemented with 40 μg Se/kg/d as sodium selenite, 40 μg Se/kg/d with 20 mg/kg/d scutellarin, and 20 mg/kg/d scutellarin, respectively, for 15 d. The mRNA levels and activities of glutathione peroxidase (GSH-Px) and thioredoxin reductase (TR), and the malondialdehyde (MDA) contents were measured. Reactive oxygen species (ROS) were detected by chemiluminescence assay, and tissue conformation was investigated by histological study. The results showed significant decreases of mRNA levels and activities of GSH-Px and TR and a significant increase of MDA content in livers of the Se-treated rats (p<0.05, compared with the control). Supplementation of scutellarin to the Se-treated group significantly inhibited the decreases of mRNA levels and activities, and the increase of MDA content (p<0.05, compared with the Setreated group). Meanwhile, scutellarin-scavenged ROS generated in the mixture of sodium selenite, reduced glutathione, and oxygen. Liver injury was displayed in slices exposed to selenium at the present dose. The groups treated with both selenium and scutellarin or only scutellarin did not show significant tissue damage. Thus, scutellarin had an antagonistic effect against the toxicity of selenium.     

Dorsomedial hypothalamic corticotropin-releasing factor mediation of exercise-induced anorexia

Running wheel access and resulting voluntary exercise alter food intake and reduce body weight. The neural mechanisms underlying these effects are unclear. In this study, we first assessed the effects of 7 days of running wheel access on food intake, body weight, and hypothalamic gene expression. We demonstrate that running wheel access significantly decreases food intake and body weight and results in a significant elevation of CRF mRNA expression in the dorsomedial hypothalamus (DMH) but not the paraventricular nucleus. Seven-day running wheel access also results in elevated arcuate nucleus and DMH neuropeptide Y gene expression. To assess a potential role for elevated DMH CRF activity in the activity-induced changes in food intake and body weight, we compared changes in food intake, body weight, and hypothalamic gene expression in rats receiving intracerebroventricular (ICV) CRF antagonist alpha-helical CRF or vehicle with or without access to running wheels. During a 4-day period of running wheel access, we found that exercise-induced reductions of food intake and body weight were significantly attenuated by ICV injection of the CRF antagonist. The effect on food intake was specific to a blockade of activity-induced changes in meal size. Central CRF antagonist injection further increased DMH CRF mRNA expression in exercised rats. Together, these data suggest that DMH CRF play a critical role in the anorexia resulting from increased voluntary exercise.     

Stimulatory effect of acetylcholine on immunoreactive corticotropin-releasing factor release from the rat hypothalamus in vitro

Effects of acetylcholine (Ach) and gamma-aminobutyric acid (GABA) on immunoreactive corticotropin-releasing factor (CRF) release from the rat hypothalamus were examined using a rat hypothalamic perifusion system and a rat CRF RIA in vitro. Ach stimulated CRF release in a dose-dependent manner (1 pM-1 nM). One nM Ach-induced CRF release was inhibited by atropine in a dose-dependent manner (1-100 nM), but was inhibited by only a high concentration (100 nM) of hexamethonium. In addition, such Ach-induced CRF release was inhibited by norepinephrine. GABA did not influence basal CRF release. These results suggest that Ach stimulates CRF release mainly through muscarinic receptors at least under our conditions.     

Inhibitory effect of norepinephrine on immunoreactive corticotropin-releasing factor release from the rat hypothalamus in vitro

Effects of catecholamines on immunoreactive corticotropin-releasing factor (I-CRF) release from the rat hypothalamus were examined using a rat hypothalamic perifusion system and a rat CRF RIA in vitro. Norepinephrine had a potent inhibitory effect on I-CRF release in a dose-dependent manner at 0.1 nM-1 microM concentrations, but dopamine did not. This inhibitory effect of norepinephrine was completely blocked by propranolol, but only partially blocked by phentolamine. Isoproterenol also had a potent inhibitory effect at 0.01-100 nM concentrations, and a high dose of phenylephrine (10 nM) inhibited I-CRF release. Clonidine did not influence I-CRF release. These results suggest that norepinephrine inhibits I-CRF release mainly through the beta-adrenergic receptor and partially through the alpha 1-receptor.     

Inhibitory effect of nociceptin on somatostatin secretion of the isolated perfused rat stomach

The heptadecapeptide nociceptin/orphanin FQ (N/OFQ) has recently been isolated from porcine and rat brain and identified as the endogenous ligand of the N/OFQ receptor (NOP). It shows structural similarity with opioid peptides. N/OFQ has also been demonstrated in the gastrointestinal tract, where it inhibits gastrointestinal motility. The effect of N/OFQ on gastric neuroendocrine function is unknown as yet.In the isolated perfused rat stomach, N/OFQ 10(-6) M shows a small, but not significant decrease of basal somatostatin (SRIF) secretion. At the doses of 10(-12) M, 10(-10) and 10(-8) M N/OFQ has neither an effect on basal SRIF nor on basal vasoactive intestinal polypeptide (VIP), gastrin, substance P or bombesin secretion, respectively. However, gastric inhibitory polypeptide (GIP) 10(-9) M prestimulated SRIF secretion is significantly inhibited by N/OFQ 10(-8) M (-45+/-11%; p<0.05 vs. GIP). During concomitant infusion of the specific competitive NOP receptor antagonist [Nphe(1)]nociceptin(1-13)NH(2) 10(-6) M, the effect of N/OFQ is abolished (6+/-11%; p<0.05 vs. GIP and N/OFQ) while the opiate receptor antagonist naloxone 10(-6) M has no significant effect (-32+/-9%; ns vs. GIP and N/OFQ). At the higher concentration of N/OFQ 10(-6) M, the inhibition of prestimulated SRIF secretion (-58+/-6%; p<0.05 vs. GIP) is not influenced by the NOP receptor antagonist at the concentration of 10(-6) M (-49+/-9%; ns vs. GIP and N/OFQ) and 10(-5) M (-69+/-10%; ns vs. GIP and N/OFQ), respectively. On the other hand, infusion of naloxone 10(-6) M attenuates the inhibitory effect of N/OFQ 10(-6) M significantly (-21+/-6%; p<0.05 vs. GIP and N/OFQ).Thus, N/OFQ is an inhibitor of gastric somatostatin secretion. At the lower dose, this effect is transmitted via NOP receptors, while at the higher dose of 10(-6) M, the effect is at least in part mediated via opiate receptors.     

Antagonistic effect of methadone on steroidogenesis and the adenylate cyclase system in isolated rat adrenocortical cells

Methadone exhibits an antagonistic effect toward steroidogenesis which lies prior to progesterone in the biosynthetic pathway in isolated rat adrenal cells. Levels of adenosine cyclic 3′–5′ monophosphate are depressed in a dose dependent fashion in ACTH stimulated cells as is steroidogenesis in cells stimulated with N⁶O²-dibutyryl adenosine cyclic 3′–5′ monophosphate. Stimulation produced by the ACTH analog, O-nitrophenyl sulfenyl ACTH, is also inhibited by methadone. The participation of adenosine cyclic 3′–5′ monophosphate as an obligatory messenger in ACTH stimulated steroidogenesis is discussed with respect to the pharmacological properties of methadone in this system.     

Stimulatory effect of somatostatin on norepinephrine release from rat brain cortex slices

The effect of somatostatin (SRIF) on norepinephrine (NE) release from the brain tissue was determined on the superfused rat cerebral cortex slices preloaded with ³HNE. SRIF (0.38 μM–1.53 μM) was found to stimulate dose-dependently tritium (³H) overflow evoked electrically by 30%—116% although SRIF did not affect on the spontaneous ³H overflow. SRIF at the concentrations which exhibited the stimulatory effect inhibited scarecely the uptake of ³HNE by cortex slices, while the reference drug, cocaine (50 μM, 10 μM) markedly depressed the uptake. The stimulatory effect of SRIF was not reduced by phentolamine (3.14 μM), α-adrenoceptor blocker, which increased the evoked ³H overflow from the slices itself. These results suggest that SRIF does not produce its stimulatory effect by inhibiting the NE reuptake mechanisms or by interacting with the presynaptic α-adrenoceptors. Elevating of Ca²⁺ concentrations from 0.75 mM to 2.25 mM in the superfusion fluid reduced the stimulatory effect of SRIF. It is possible that SRIF stimulates NE release by facilitating the availability of Ca²⁺ for the release mechanisms.     

Effects of chlordiazepoxide on footshock- and corticotropin-releasing factor-induced increases in cortical and hypothalamic norepinephrine secretion in rats

Noradrenergic and corticotropin-releasing factor (CRF) neuronal systems within the brain have been implicated in stress and anxiety. Synaptic release of cerebral norepinephrine (NE) is increased during stress, and following intracerebral CRF administration. Benzodiazepines are commonly used anxiolytic drugs but information on their effects on the stress- and CRF-related release of NE is limited. We have used in vivo microdialysis to test the effects of the benzodiazepine, chlordiazepoxide (CDP) on the noradrenergic responses to footshock and intracerebroventricular CRF in the medial hypothalamus and the medial prefrontal cortex (PFM) of freely moving rats. Footshock (60 x 0.1-0.2 mA shocks in 20 min) significantly increased microdialysate concentrations of NE in the first sample collected after initiating the footshock. In the hypothalamus, microdialysate NE was augmented 64% above baseline. A second footshock session (100 min after the first footshock) increased microdialysate NE to 313% of the baseline. Thus the noradrenergic responses to footshock were enhanced by preceding footshocks. CRF (100 ng) administered into the locus coeruleus (LC) almost tripled microdialysate concentrations of NE in the PFM. CDP (5mg/kg, i.p.) had no statistically significant effects on the basal dialysate concentrations of NE, but it significantly attenuated both footshock- and CRF-induced increases in dialysate NE. CDP may exert a direct inhibitory effect on the noradrenergic neurons, alter the input to LC noradrenergic neurons, or alter the ability of CRF to activate the LC noradrenergic system.     

Adrenergic receptors are not mediators in the lipolytic effect of somatostatin in rat adipocytes

Beta-adrenergic receptors have been purported to act as possible mediators in the lipolytic effect of somatostatin in vivo. Investigations with isolated rat adipocytes studying the lipolytic activity of somatostatin (1.7 x 10(-7) M), glucagon (8.1 x 10(-8 M) and norepinephrine (10(-6) M), have shown that the lipolytic effect stimulated by somatostatin is not altered by 10(-5) M propranolol (beta-antagonist); is significantly enhanced by 10(-5) M isoproterenol (beta-agonist) and is not altered by the addition of 10(-6) M phenoxybenzamine (alpha-antagonist) or 10(-6) M phenylephrine (alpha-agonist). Similar results were found when lipolysis was stimulated by glucagon, whereas the lipolytic effect stimulated by norepinephrine was blocked by propranolol. These results indicate that the direct lipolytic effect of somatostatin on isolated rat adipocytes does not seem to be mediated through mechanisms involved with adrenergic receptors.     

Age dependence of somatostatin levels and somatostatin binding in the rat brain

1. Somatostatin-like immunoreactivity (SLI) and 125I-Tyrl-somatostatin binding were measured from the brains of rats aged 1, 8 and 18 months. 2. Somatostatin binding was reduced in the striatum, frontal cortex, hypothalamus and hippocampus of the 8-month-old rats compared to the 1-month-old group. 3. Somatostatin binding was reduced in the striatum, frontal cortex and hippocampus of the 18-month-old rats compared to the 1-month-old group. 4. The reduction (40%) was most striking in the frontal cortex. 5. In no area of the brain did changes in SLI differ significantly between the different age groups.     

Inhibitory effect of somatostatin on the growth and steroidogenic capacity of rat adrenal zona glomerulosa

Chronic administration of somatostatin induced atrophy of zona glomerulosa cells of rat adrenals and lowering of plasma aldosterone concentration. Zona fasciculata cells did not display any significant change and corticosterone plasma concentration was not significantly affected. These findings are interpreted to indicate that somatostatin exerts a direct inhibitory effect on the growth and steroidogenic capacity of rat adrenal zona glomerulosa.     

Adrenocortical responses to corticotropin-releasing factor in the rat

The time course of plasma corticosterone was measured in male Sprague-Dawley rats whose endogenous release of ACTH had been blocked following rapid i.v. injections of doses ranging from 0.003 to 10 micrograms corticotropin-releasing factor (CRF) per rat and during i.v. infusions at rates ranging from 0.001 to 20 ng CRF X min-1 X 100 g body weight-1. The range of the dose-response curve, following rapid injection, extends from 0.01 to 0.37 micrograms CRF, whereas it extends over a 20 000-fold range from 0.001 to 20 ng CRF X min-1 X 100 g body weight-1 during a continuous infusion. The delayed response to a small rate of CRF could be ascribed to a relatively long time of residence of CRF in the plasma which implies that a relatively long period of time is required until a minimal plasma CRF concentration is reached after the onset of a continuous infusion of CRF at a small rate. When presented with a prolonged infusion of CRF at a large rate, the pituitary secretion of ACTH is rapidly turned on at a rate which exhibits the characteristics of a prolonged secretion at a constant large magnitude.     

Distribution and metabolism of corticotropin-releasing factor in the rat

To develop a mathematical model of the distribution and metabolism of rat corticotropin-releasing factor (rCRF), the time course of 125I-labelled rCRF in plasma was measured in male Sprague-Dawley rats (i) following a rapid injection of 24 ng rCRF/100 g body weight (BW), or (ii) following a rapid injection of 424 ng rCRF/100 g BW, or (iii) during an infusion at a rate ranging from 0.28 to 0.73 ng rCRF X min-1 X 100 g BW-1. The comparison of the one-, two-, and three-compartment models shows that the two-pool structure fits better to the dynamics of CRF in plasma as measured in each rat. Following a rapid injection the decay curve occurs in a biphasic manner; the early phase of disappearance is 25 times faster than the late one. There is no significant difference between the estimates of the metabolic clearance rate following both amplitudes of injection (0.40 +/- 0.06 and 0.48 +/- 0.05 mL X min-1 X 100 g BW-1). The volume of the first pool, 16.8 +/- 1.1 mL/100 g BW, is four times larger than the plasma volume. It would thus appear that CRF is rapidly distributed from plasma into several tissues which are represented in the first pool of the model. The mean residence time of every CRF molecule in the second compartment, from the moment of secretion to its elimination, is from three to four times longer than in the first one. It stays, on average, between 140 min and 3 h in the system before an irreversible exit.(ABSTRACT TRUNCATED AT 250 WORDS)