Glucocorticoid anorexia in rats

Conventional Vasopressor and Vasopressor-Sparing Strategies to Counteract the Blood Pressure-Lowering Effect of Small Interfering RNA Targeting Angiotensinogen

Background

A single dose of small interfering RNA (siRNA) targeting liver angiotensinogen eliminates hepatic angiotensinogen and lowers blood pressure. Angiotensinogen elimination raises concerns for clinical application because an angiotensin rise is needed to maintain perfusion pressure during hypovolemia. Here, we investigated whether conventional vasopressors can raise arterial pressure after angiotensinogen depletion.

Methods and Results

Spontaneously hypertensive rats on a low‐salt diet were treated with siRNA (10 mg/kg fortnightly) for 4 weeks, supplemented during the final 2 weeks with fludrocortisone (6 mg/kg per day), the α‐adrenergic agonist midodrine (4 mg/kg per day), or a high‐salt diet (all groups n=6–7). Pressor responsiveness to angiotensin II and norepinephrine was assessed before and after siRNA administration. Blood pressure was measured via radiotelemetry. Depletion of liver angiotensinogen by siRNA lowered plasma angiotensinogen concentrations by 99.2±0.1% and mean arterial pressure by 19 mm Hg. siRNA‐mediated blood pressure lowering was rapidly reversed by intravenous angiotensin II or norepinephrine, or gradually reversed by fludrocortisone or high salt intake. Midodrine had no effect. Unexpectedly, fludrocortisone partially restored plasma angiotensinogen concentrations in siRNA‐treated rats, and nearly abolished plasma renin concentrations. To investigate whether this angiotensinogen originated from nonhepatic sources, fludrocortisone was administered to mice lacking hepatic angiotensinogen. Fludrocortisone did not increase angiotensinogen in these mice, implying that the rise in angiotensinogen in the siRNA‐treated rats must have depended on the liver, most likely reflecting diminished cleavage by renin.

Conclusions

Intact pressor responsiveness to conventional vasopressors provides pharmacological means to regulate the blood pressure–lowering effect of angiotensinogen siRNA and may support future therapeutic implementation of siRNA.

Quercetin Ameliorates Lipid and Apolipoprotein Profile in High-Dose Glucocorticoid Treated Rats

Background Glucocorticoids (GCs) are widely prescribed for the treatment of numerous clinical disorders due to their anti-inflammatory and immune-modulatory properties and one of the most common untoward effects of these drugs is dyslipidemia. Objective To evaluate the effect of quercetin, a plant-derived flavonoid, on the lipid profile of high-dose glucocorticoid treated rats. Methods A total of 32 Sprague-Dawley rats, were randomly distributed among four groups (8 rats per group) and treated for 6 weeks with one of the following: (i) normal saline; (ii) 40 mg/kg methylprednisolone sodium succinate (MP); (iii) MP + 50 mg/kg quercetin; (iv) MP + 150 mg/kg quercetin. MP was injected subcutaneously, and quercetin was administered by oral gavage 3 days a week. At the end of the study, the animals' lipid profile was measured by enzymatic kits. Data were analyzed and statistical significance was set at p<0.05. Results The mean serum total cholesterol (TC), triglyceride (TG) and LDL levels were drastically increased in GC-treated animals compared with the control group. Both doses of quercetin (50 and 150 mg/kg) ameliorated TC (43% and 45%), LDL (56% and 56%) and TG (46% and 55% respectively). Apo B/A1 ratio decreased more than 20% following quercetin intake and the decline in TC/HDL, TG/HL, LDL/HDL ratios were significant. Conclusions These data suggest that quercetin intake with both doses of 50 and 150 mg/kg could be considered as a protective agent for glucocorticoid-induced dyslipidemia. (Arq Bras Cardiol. 2020; 115(1):102-108.).

Quercetin prevents experimental glucocorticoid-induced osteoporosis: a comparative study with alendronate

Glucocorticoid-induced osteoporosis (GIO) is the most common type of secondary osteoporosis. The aim of this study was to compare the efficacy of quercetin, a plant-derived flavonoid, with alendronate in the prevention of GIO. Fifty-six Sprague–Dawley rats were randomly distributed among 7 groups (8 rats per group) and treated for 6 weeks with one of the following: (i) normal saline; (ii) 40 mg methylprednisolone sodium succinate (MP)/kg body mass; (iii) MP + 40 μg alendronate/kg; (iv) MP + 50 mg quercetin/kg; (v) MP + 40 μg alendronate/kg + 50 mg quercetin/kg; (vi) MP + 150 mg quercetin/kg; and (vii) MP + 40 μg alendronate/kg + 150 mg quercetin/kg. MP and alendronate were injected subcutaneously and quercetin was administered by oral gavage 3 days a week. At the end of the study, femur breaking strength was significantly decreased as a consequence of MP injection. This decrease was completely compensated for in groups receiving 50 mg quercetin/kg plus alendronate, and 150 mg quercetin/kg with or without alendronate. Quercetin noticeably elevated osteocalcin as a bone formation marker, while alendronate did not show such an effect. In addition, administration of 150 mg quercetin/kg increased femoral trabecular and cortical thickness by 36% and 22%, respectively, compared with the MP-treated group. These data suggest that 150 mg quercetin/kg, alone or in combination with alendronate, can completely prevent GIO through its bone formation stimulatory effect.

Inhibition of dehydration-induced water intake by glucocorticoids is associated with activation of hypothalamic natriuretic peptide receptor-A in rat

Atrial natriuretic peptide (ANP) provides a potent defense mechanism against volume overload in mammals. Its primary receptor, natriuretic peptide receptor-A (NPR-A), is localized mostly in the kidney, but also is found in hypothalamic areas involved in body fluid volume regulation. Acute glucocorticoid administration produces potent diuresis and natriuresis, possibly by acting in the renal natriuretic peptide system. However, chronic glucocorticoid administration attenuates renal water and sodium excretion. The precise mechanism underlying this paradoxical phenomenon is unclear. We assume that chronic glucocorticoid administration may activate natriuretic peptide system in hypothalamus, and cause volume depletion by inhibiting dehydration-induced water intake. Volume depletion, in turn, compromises renal water excretion. To test this postulation, we determined the effect of dexamethasone on dehydration-induced water intake and assessed the expression of NPR-A in the hypothalamus. The rats were deprived of water for 24 hours to have dehydrated status. Prior to free access to water, the water-deprived rats were pretreated with dexamethasone or vehicle. Urinary volume and water intake were monitored. We found that dexamethasone pretreatment not only produced potent diuresis, but dramatically inhibited the dehydration-induced water intake. Western blotting analysis showed the expression of NPR-A in the hypothalamus was dramatically upregulated by dexamethasone. Consequently, cyclic guanosine monophosphate (the second messenger for the ANP) content in the hypothalamus was remarkably increased. The inhibitory effect of dexamethasone on water intake presented in a time- and dose-dependent manner, which emerged at least after 18-hour dexamethasone pretreatment. This effect was glucocorticoid receptor (GR) mediated and was abolished by GR antagonist RU486. These results indicated a possible physiologic role for glucocorticoids in the hypothalamic control of water intake and revealed that the glucocorticoids can act centrally, as well as peripherally, to assist in the normalization of extracellular fluid volume.

Glucocorticoids increase salt appetite by promoting water and sodium excretion

Glucocorticoids [e.g., corticosterone and dexamethasone (Dex)], when administered systemically, greatly increase water drinking elicited by angiotensin and sodium ingestion in response to mineralocorticoids [e.g., aldosterone and deoxycorticosterone acetate (DOCA)], possibly by acting in the brain. In addition, glucocorticoids exert powerful renal actions that could influence water and sodium ingestion by promoting their excretion. To test this, we determined water and sodium intakes, excretions, and balances during injections of Dex and DOCA and their coadministration (DOCA+Dex) at doses commonly employed to stimulate ingestion of water and sodium. In animals having only water to drink, Dex treatment greatly increased water and sodium excretion without affecting water intake, thereby producing negative water and sodium balances. Similar results were observed when Dex was administered together with DOCA. In animals having water and saline solution (0.3 M NaCl) to drink, Dex treatment increased water and sodium excretion, had minimal effects on water and sodium intakes, and was associated with negative water and sodium balances. DOCA treatment progressively increased sodium ingestion, and both water and sodium intakes exceeded their urinary excretion, resulting in positive water and sodium balances. The combination of DOCA+Dex stimulated rapid, large increases in sodium ingestion and positive sodium balances. However, water excretion outpaced total fluid intake, resulting in large, negative water balances. Plasma volume increased during DOCA treatment and did not change during treatment with Dex or DOCA+Dex. We conclude that increased urinary excretion, especially of water, during glucocorticoid treatment may explain the increased ingestion of water and sodium that occurs during coadministration with mineralocorticoids.

The somatostatin subtype-2 receptor antagonist, BIM-23627, improves the catabolic effects induced by long-term glucocorticoid treatment in the rat

BIM-23627 is a synthetic peptide with "in vitro" and "in vivo" properties consistent with a pure sst2 antagonist. The aim of the present study was to evaluate the effects of long-term administration of BIM-23627 and the combined effects of BIM-23627 and dexamethasone (DEX) on the somatotropic axis, including growth, epididymal fat accumulation, glucose homeostasis and insulin activity, in young male rats. Beginning on day 23 of age, 16 animals were treated daily with saline or DEX (40 microg/kg/daily). Each group was subdivided into two paired groups and treated with either vehicle or BIM-23627 (0.5 mg/kg, t.i.d.). The treatment period lasted 31 days. The animals were killed by decapitation; trunk blood and pituitaries were collected for the determination of hormone concentrations and GH mRNA expression, respectively. Based on plasma GH and IGF-I concentrations and GH mRNA expression in the pituitary, BIM-23627 was able to counteract the inhibitory effects of DEX on the somatotropic axis; however, only a partial reversal of somatic growth inhibition was observed. DEX-treated rats remained euglycemic, but their insulin levels were significantly increased, indicating an incipient insulin resistance. Although BIM-23627 itself tended to increase insulin concentration in saline-treated rats, its administration to DEX-treated rats reduced insulin levels (saline: 25+/-3; DEX: 55+/-16*; DEX+BIM-23627: 34+/-5; BIM-23627: 38+/-7 microIU/ml; *P<0.05 vs. saline), apparently improving the degree of insulin sensitivity. DEX administration significantly reduced circulating ghrelin, whereas the sst2 antagonist had no significant effect. An inverse correlation was found between ghrelin concentrations and plasma insulin levels. Both rats receiving DEX and rats receiving BIM-23627 had decreased plasma concentration of total testosterone (P<0.05); however, the effects of DEX and BIM-23627 were not additive. In conclusion, BIM-23627 may represent a new pharmacological agent to reduce the suppression of the GH-IGF-I axis in long-term GC treated patients and enhance insulin sensitivity. Further studies are required in order to fully optimize the SSTR-2 antagonist-induced reversal of DEX-induced somatic growth inhibition.

Neural and hormonal consequences of neonatal 5,7-dihydroxytryptamine may not be associated with serotonin depletion

The neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) is often used in neonatal rats to induce specific, rapid, and permanent depletion of brain serotonin (5-HT). One assumed benefit of using this drug in neonates is that it is well-tolerated, with pups exhibiting few side effects normally attributed to 5-HT depletion. Here, we present evidence that 5,7-DHT administered neonatally induces seizure-like behavior, decreases weight gain, and increases plasma corticosterone without depletion of brain 5-HT.

Differential action of ondansetron and dexamethasone to modify cisplatin-induced acute and delayed kaolin consumption ("pica") in rats

The ability of cisplatin to induce acute (0-24 h) and delayed (24-48 and 48-72 h) phases of kaolin ingestion (pica) was investigated in the rat. Cisplatin 3 mg/kg, i.p., induced kaolin consumption during the 0-24- (P<0.001) and 48-72-h (P<0.05) periods that was antagonised by dexamethasone 1 mg/kg, i.p., administered every 12 h alone or in combination with ondansetron 2 mg/kg, i.p., administered every 12 h (P<0.05). As a single treatment, ondansetron 2 mg/kg, i.p., administered every 12 h potentiated cisplatin-induced kaolin consumption by 41% (P<0.05) during the 0-24-h period but had no action to modify the delayed response (P>0.05). Dexamethasone 1 mg/kg, i.p., administered every 12 h and cisplatin 3 and 6 mg/kg, i.p., but not ondansetron 2 mg/kg, i.p., administered every 12 h (P>0.05) reduced food consumption and decreased rat weight. The highest dose of cisplatin 6 mg/kg, i.p., induced acute (P<0.001) but not delayed kaolin ingestion (P>0.05). The action of cisplatin to induce acute and delayed pica is complicated and may be affected by drugs that modify appetite.

Sodium depletion and maternal separation in the suckling rat increase its salt intake when adult

To establish whether neonatal sodium depletion increases the adult's avidity for NaCl, 12-day-old suckling pups were injected with the natriuretic-diuretic furosemide (1 mg) while with their dams. The injections surged plasma aldosterone, and when the rats were adult (70 days), their spontaneous intake of 3% NaCl was increased. Additional experiments investigated whether maternal separation has a similar effect and could thus be a source of individual variation in salt intake of the adult. Fifteen-day-old pups were separated from their dams for 24 h in an incubator. When adult, their intake of 3% NaCl was increased. Availability of saline during maternal separation obviated the effect. The increase in adult intake of 3% NaCl was specific insofar as drinking of water was not increased similarly. The results show that the adult rat's avidity for sodium can be increased by postnatal natriuresis and possibly stress. The implications of the findings are discussed.

Effects of the glucocorticoid agonist, RU28362, and the antagonist RU486 on lung phosphatidylcholine and antioxidant enzyme development in the genetically obese Zucker rat

The biochemical maturation of the lung in late gestation and in the young animal is regulated by glucocorticoids. The present study was aimed at dissociating the different glucocorticoid receptor sites involved in these regulatory functions. The obese Zucker rat was selected as a model for this study as it exhibits hypersensitivity to glucocorticoid hormone action by virtue of its elevated receptor numbers and activity. Two synthetic steroid analogues were administered to obese animals; RU28362, a specific type II receptor agonist, and the type II antagonist RU486. RU28362 promoted a strong catabolic effect, which was associated with reduced food intake and the abolition of growth in the rats. The agonist, RU28362, attenuated developmental increases in antioxidant enzyme activities, and altered the growth of the tissue. At the age studied, development of the lung phosphatidylcholine (PC) system was almost complete, but RU28362 increased disaturated PC 16:0/16:0 concentrations by almost 2-fold, and altered the molecular composition of total pulmonary PC. RU486 attenuated the growth of the rats and reduced their food intake. Treatment with the type II antagonist attenuated lung growth and increased the activities of pulmonary copper zinc (Cu/Zn) and manganese (Mn) superoxide dismutases. RU486 had no effect on lung PC concentrations and molecular composition. The data suggest a role for type I glucocorticoid receptors in the regulation of the antioxidant enzyme system in the lung, as type II antagonism will channel endogenous glucocorticoid binding to the type I site. Type II receptor binding would appear to play a role in regulating the lung PC content.

Mimicking corticosterone's daily rhythm with specific receptor agonists: effects on food, water, and sodium intake

The endogenous pattern of type I and II corticosteroid receptor stimulation was systematically assembled from specific agonists in order to detect any unique receptor interactions in the control of ingestive behavior. The type II agonists dexamethasone (0, 5, or 25 micrograms/kg) or RU28362 (0, 5, or 25 micrograms/kg) were injected daily in the final hour of the light phase of the illumination cycle of adrenalectomized rats. This was carried out in the presence or absence of continuous aldosterone (type I agonist) infusion. Additional comparisons were made with sham-operated groups and animals receiving type II agonists by continuous infusion. Type II agonists increased the intake of 2% saline and the proportion of food taken at night, but had negligible effects on total food intake. Type II agonists did not interact with the type I agonist. Type II effects were greatly potentiated by continuous infusion, though administered at the same doses as acute injection. When the effects of type II receptor stimulation emerged, they always consisted of an exacerbation of the adrenalectomy syndrome, not a return to normal quantities or patterns. In contrast, type I receptor stimulation restored both the quantities and unique day-night patterns of saline, water, and food intake to values matching intact animals. The findings suggest that the behavioral significance of corticosterone's nocturnal peak of type II stimulation is small, and that its most important function may lie in the metabolic processes it instigates during its steady rise in the light phase.

Acute, chronic, and interactive effects of type I and II corticosteroid receptor stimulation on feeding and weight gain

Type I (aldosterone) and/or type II (dexamethasone or RU28362) corticosterone receptor agonists were continuously infused in adrenalectomized Sprague-Dawley rats for 28 days at doses of 3.4, 17.2, or 86.2 nmol/day. Additional groups received combined agonist infusions, blank infusions, or sham operations. The type I agonist stimulated body weight gain, and the type II agonists were both suppressive, differing mainly in degree. Although there were a few early effects of these hormones (usually a stage of exaggerated activity), once passed, chronic stimulation was marked by steady or slightly increasing steroid influence on body weight. Throughout the chronic phase of this study there was no departure from a simple opponent model of type I and II ligand actions, and their combination approximated an arithmetic summation of the two separate agonists. This was generally true of feeding as well, although steroid effects on intake were always less pronounced. In contrast to chronic administration, acute combinations of these agonists were highly interactive, producing slight losses than large gains for the aldosterone and RU28362 combinations, but a large gain then small loss for the aldosterone and dexamethasone combination. These results imply that RU28362 and dexamethasone differ in more respects than potency. Because normal endogenous type II stimulation is acute and occurs against a background of type I receptor occupation, mixed agonist interactions are probably the rule for everyday physiological activity, not the exception.

Glucocorticoids potentiate the dipsogenic action of angiotensin II

The effect of a short-term, acute treatment with a glucocorticoid, dexamethasone sodium phosphate, on the drinking induced by angiotensin II (AII) was investigated in a series of experiments. Initial studies indicated that a single injection of dexamethasone (700-750 micrograms/kg, i.p.) reduced food intake, body weight and water intake for up to 48 h, but had little effect on blood pressure when it was measured 6 h subsequent to the injection. The drinking elicited by peripherally administered AII (200 micrograms/kg, s.c.) was enhanced if the glucocorticoid (700 micrograms/kg, i.p.) was given 3 h or 6 h prior to the dipsogen. There was no effect of pretreatment with the steroid if the drinking test was delayed by 24 h. The subsequent experiment showed that the glucocorticoid effect on AII-stimulated drinking was dose dependent (100 micrograms-1600 micrograms/kg). The drinking stimulated by intracerebroventricular (i.c.v.) AII (2.5 ng) was enhanced in terms of volume and total duration by prior treatment with dexamethasone, but i.c.v. carbachol (200 ng)-induced drinking remained unaffected. The final study showed that binding of AII to its receptors in five different areas of the rat brain was not affected by prior treatment with dexamethasone.

Corticosterone's dual metabolic actions

Corticosterone possesses two distinctly opposite metabolic actions. The actions are strictly dose-dependent and are linked to type I and type II corticosteroid receptor binding. These conclusions are drawn from continuous infusion studies where corticosterone yields a bitonic dose-response curve for body weight gain and feeding efficiency. Anabolic at low serum levels, corticosterone concentrations above 2 micrograms/dl bring about an opponent catabolic process that intensifies and eventually masks the anabolic action. Relatively pure type I (aldosterone) and type II (RU28362 and dexamethasone) corticosterone receptor agonists produce opposite monotonic functions that respectively mimic the ascending and descending arms of the corticosterone dose-response curve. Stimulation of either receptor increases the proportion of carcass fat to lean body mass by either increasing carcass lipids (type I) or by reducing protein (type II).

Reductions in maternal food and water intake account for prenatal stress effects on neurobehavioral development in B6D2F2 mice

This study evaluated the role of stress-induced reductions in food intake in pregnant B6D2F1 mice in the production of developmental abnormalities in the offspring. One group of dams underwent one hour of physical restraint stress twice daily from days 12 to 17 of gestation. A second group was not restrained but, during this period, each dam was pair-fed to a weight-matched partner in the stressed group. A third group was left undisturbed and allowed unlimited access to lab chow and water. The restraint stress procedure reduced the average daily food and water intake in the dams, resulting in lower maternal weights, with the unstressed pair-fed group being affected more severely than the stressed group. The offspring of both the stressed and pair-fed dams were lighter than the offspring of the dams fed ad lib on day 20 postconception, and exhibited lower brain weights on day 32 postconception. Neurobehavioral development, as assessed on a battery of sensorimotor tests on day 32 postconception, was retarded in the prenatally stressed pups in comparison to the ad lib pups, while the pair-fed pups did not differ from either group. There were no differences among any of the groups on day 50 body or brain weight, body or tail length, anogenital distance, or locomotion, rearing and defecation in the open field.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevention of adrenalectomy-induced brain growth stimulation by corticosterone treatment

Previous research in our laboratory has shown that adrenalectomizing rats on day 11 postnatal leads to subsequent increases in brain weight, cellularity (measured in terms of DNA content), and myelination. The present study was designed to determine whether these effects are due to removal of circulating glucocorticoids. Male and female albino rats were adrenalectomized (ADX) on day 11 and then injected daily with either 7.0 mg/kg corticosterone in a steroid suspension vehicle or vehicle alone. A third group of animals was sham-operated (SHAM) and given daily vehicle injections. Subjects were sacrificed at 60 days of age for measurement of brain and body weights, cerebral DNA content, and the activity of 2',3'-cyclic nucleotide phosphodiesterase (CNP), a myelin marker enzyme. As expected from our earlier findings, brain weights and DNA and CNP levels were all significantly elevated in ADX-untreated rats compared to SHAMs. More importantly, all of these changes were completely prevented by chronic corticosterone administration. These results are consistent with previous reports that corticosterone treatment blocks increased brain growth in ADX weanling rats and support our hypothesis that the brain growth stimulating effects of day-11 adrenalectomy are likewise mediated by the removal of glucocorticoids. It appears that glucocorticoid hormones exert a tonic inhibition of at least some growth related processes in the brains of intact developing organisms.

Hypophysectomy disturbs the noradrenergic feeding system of the paraventricular nucleus

Injection of norepinephrine (NE) into the hypothalamic paraventricular nucleus (PVN) of satiated rats is known to stimulate eating behavior. In addition, drinking behavior is potentiated just prior to the onset of eating, followed by a strong inhibition of water intake. To understand the relationship between these PVN noradrenergic phenomena and endocrine processes associated with the PVN, chronically hypophysectomized animals were tested for their behavioral responsiveness to PVN NE injection. Pituitary ablation was found to abolish the NE-elicited eating response and the NE drinking suppressive effect. However, hypophysectomy had no impact on the NE-elicited preprandial drinking response, nor did it affect drinking produced by carbachol, angiotensin, and histamine, or the feeding and drinking responses induced by insulin. These results demonstrate that hypophysectomy disturbs PVN noradrenergic mechanisms in a behaviorally and pharmacologically specific specific manner.

Opioid modulation of appetite

The discovery of opiate receptors and endogenous opioid peptides within the central nervous system has resulted in a number of speculations concerning the physiological significance of these peptides. In the present article, we review the evidence suggesting a primary role for some of the opioid peptides as regulators of ingestive behavior. In particular, we elaborate a hypothesis in which we suggest that in some species opioid peptides may play a role as a tonic inducer of ingestive behaviors, held in check by a variety of neuropeptides and monoamines. This review explores in detail the role of the opioid peptides as major mediators of the reward system and as a link between reward and feeding behaviors. Finally, a teleological role for opioid peptides in species preservation, which may explain the discrepancies in the role of the opioid peptides in feeding behavior in different species is proposed. It is suggested that the feeding profile of the animal provides important clues as to whether or not the animal has an opiate-sensitive feeding system. We stress that interactions with ingested nutrients and the milieu interieur provide an important means by which animals modulate the opiate-entrained feeding drives.