Search

We determined whether deficiency of neuronal SOCS3 (suppressor of cytokine signaling 3)-a potential negative regulator of leptin signaling-amplifies the chronic effects of leptin on food intake, energy expenditure, glucose, and blood pressure (BP) and protects against adverse cardiometabolic effects of obesity. BP and heart rate were recorded by telemetry, and oxygen consumption (VO 2 ) was monitored in 22-week-old mice with nervous system SOCS3 deficiency (SOCS3-Nestin-Cre) and control mice (SOCS3 flox/flox ) fed normal or high-fat-high-fructose diet from 6 to 22 weeks of age. Compared with controls, SOCS3-Nestin-Cre mice had lower plasma glucose (124±7 versus 146±10 mg/dL), consumed less food (3.0±0.4 versus 3.6±0.2 g/d), and had similar VO 2 (77±6 versus 73±3 mL/kg per minute) and BP (103±3 versus 107±3 mm Hg) but higher heart rate (666±15 versus 602±17 bpm). In mice fed the normal diet, leptin infusion for 7 days caused similar reductions in food intake (2.3±0.1 versus 2.4±0.2 g) but greater increases in BP (15±3 versus 7±2 mm Hg) in SOCS3-Nestin-Cre compared with controls. Leptin reduced blood glucose concentrations in both groups. Male or female SOCS3-Nestin-Cre fed high-fat-high-fructose diet exhibited less weight gain, body fat, and liver steatosis and greater energy expenditure and heart rate compared with controls. Female SOCS3-Nestin-Cre mice fed high-fat-high-fructose diet had higher BP compared with controls. Thus, neuronal SOCS3 seems to play an important role in cardiometabolic regulation because neuronal SOCS3 deficiency reduced body weight and food intake while amplifying leptin's effects on appetite and BP and attenuating the adverse metabolic effects of high-fat-high-fructose diet., (© 2018 American Heart Association, Inc.)

Diabetes mellitus and hypertension are major risk factors for chronic kidney injury, together accounting for >70% of end-stage renal disease. In this study, we assessed interactions of hypertension and diabetes mellitus in causing kidney dysfunction and injury and the role of endoplasmic reticulum (ER) stress. Hypertension was induced by aorta constriction (AC) between the renal arteries in 6-month-old male Goto-Kakizaki (GK) type 2 diabetic and control Wistar rats. Fasting plasma glucose averaged 162±11 and 87±2 mg/dL in GK and Wistar rats, respectively. AC produced hypertension in the right kidney (above AC) and near normal blood pressure in the left kidney (below AC), with both kidneys exposed to the same levels of glucose, circulating hormones, and neural influences. After 8 weeks of AC, blood pressure above the AC (and in the right kidney) increased from 109±1 to 152±5 mm Hg in GK rats and from 106±4 to 141±5 mm Hg in Wistar rats. The diabetic-hypertensive right kidneys in GK-AC rats had much greater increases in albumin excretion and histological injury compared with left kidneys (diabetes mellitus only) of GK rats or right kidneys (hypertension only) of Wistar-AC rats. Marked increases in ER stress and oxidative stress indicators were observed in diabetic-hypertensive kidneys of GK-AC rats. Inhibition of ER stress with tauroursodeoxycholic acid for 6 weeks reduced blood pressure (135±4 versus 151±4 mm Hg), albumin excretion, ER and oxidative stress, and glomerular injury, while increasing glomerular filtration rate in hypertensive-diabetic kidneys. These results suggest that diabetes mellitus and hypertension interact synergistically to promote kidney dysfunction and injury via ER stress., (© 2017 American Heart Association, Inc.)

Insulin receptor substrate 2 (IRS2) is one of the 3 major leptin receptor signaling pathways, but its role in mediating the chronic effects of leptin on blood pressure, food intake, and glucose regulation is unclear. We tested whether genetic inactivation of IRS2 in the entire brain (IRS2/Nestin-cre mice) or specifically in proopiomelanocortin (POMC) neurons (IRS2/POMC-cre mice) attenuates the chronic cardiovascular, metabolic, and antidiabetic effects of leptin. Mice were instrumented with telemetry probes for measurement of blood pressure and heart rate and with venous catheters for intravenous infusions. After a 5-day control period, mice received leptin infusion (2 μg/kg per minute) for 7 days. Compared with control IRS2(flox/flox) mice, IRS2/POMC-cre mice had similar body weight and food intake (33±1 versus 35±1 g and 3.6±0.5 versus 3.8±0.2 g per day) but higher mean arterial pressure (MAP) and heart rate (110±2 versus 102±2 mm Hg and 641±9 versus 616±5 bpm). IRS2/Nestin-cre mice were heavier (38±2 g), slightly hyperphagic (4.5±1.0 g per day), and had higher MAP and heart rate (108±2 mm Hg and 659±9 bpm) compared with control mice. Leptin infusion gradually increased MAP despite decreasing food intake by 31% in IRS2(flox/flox) and in Nestin-cre control mice. In contrast, leptin infusion did not change MAP in IRS2/Nestin-cre or IRS2/POMC-cre mice. The anorexic and antidiabetic effects of leptin, however, were similar in all 3 groups. These results indicate that IRS2 signaling in the central nervous system, and particularly in POMC neurons, is essential for the chronic actions of leptin to raise MAP but not for its anorexic or antidiabetic effects., (© 2015 American Heart Association, Inc.)

We examined whether central melanocortin 3 and 4 receptor (MC3/4R) blockade attenuates the blood pressure (BP) responses to chronic L-NAME or angiotensin II (Ang II) infusion in Sprague-Dawley rats implanted with telemetry transmitters, venous catheters, and intracerebroventricular cannula into the lateral ventricle. After 5 days of control measurements, L-NAME (10 μg/kg/min IV, groups 1 and 2) or Ang II (10 ng/kg/min IV, groups 3 and 4) were infused for 24 days, and starting on day 7 of L-NAME or Ang II infusion, the MC3/4R antagonist SHU-9119 (24 nmol/d, n=6/group; groups 1 and 3) or vehicle (saline 0.5 μL/h, n=6/group; groups 2 and 4) was infused intracerebroventricularly for 10 days. A control normotensive group also received SHU-9119 for 10 days (n=5). L-NAME and Ang II increased BP by 40±3 and 56±5 mm Hg, respectively, although heart rate was slightly reduced. MC3/4R blockade doubled food intake and reduced heart rate (≈40 to ≈50 bpm) in all groups. MC3/4R blockade caused only a small reduction in BP in normotensive group (4 mm Hg) and no change in rats receiving Ang II, although markedly reducing BP by 21±4 mm Hg in L-NAME-treated rats. After SHU-9119 infusion was stopped, food intake, heart rate, and BP gradually returned to values observed before SHU-9119 infusion was started. Ganglionic blockade at the end of L-NAME or Ang II infusion caused similar BP reduction in both groups. These results suggest that the brain MC3/4R contributes, at least in part, to the hypertension induced by chronic L-NAME infusion but not by Ang II., (© 2014 American Heart Association, Inc.)

Although signal transducer and activator of transcription 3 (Stat3) is a key second messenger by which leptin regulates appetite and body weight, its role in specific neuronal populations in metabolic regulation and in mediating the chronic effects of leptin on blood pressure is unknown. The current study tested the hypothesis that Stat3 signaling in proopiomelanocortin (POMC) neurons mediates the chronic effects of leptin on mean arterial pressure (MAP), as well as on glucose regulation, energy expenditure, and food intake. Stat3(flox/flox) mice were crossed with POMC-Cre mice to generate mice with Stat3 deletion specifically in POMC neurons (Stat3(flox/flox)/POMC-Cre). Oxygen consumption (Vo2), carbon dioxide respiration (Vco2), motor activity, heat production, food intake, and MAP were measured 24 hours/d. After baseline measurements, leptin was infused (4 μg/kg per min, IP) for 7 days. Stat3(flox/flox)/POMC-Cre mice were hyperphagic, heavier, and had increased respiratory quotients compared with control Stat3(flox/flox) mice. Baseline MAP was not different between the groups, and chronic leptin infusion reduced food intake similarly in both groups (27 versus 29%). Vo2, Vco2, and heat production responses to leptin were not significantly different in control and Stat3(flox/flox)/POMC-Cre mice. However, leptin-mediated increases in MAP were completely abolished, and blood pressure responses to acute air-jet stress were attenuated in male Stat3(flox/flox)/POMC-Cre mice. These results indicate that Stat3 signaling in POMC neurons is essential for leptin-mediated increases in MAP, but not for anorexic or thermogenic effects of leptin.

Although the central nervous system melanocortin system is an important regulator of energy balance, the role of proopiomelanocortin (POMC) neurons in mediating the chronic effects of leptin on appetite, blood pressure, and glucose regulation is unknown. Using Cre/loxP technology we tested whether leptin receptor deletion in POMC neurons (LepR(flox/flox)/POMC-Cre mice) attenuates the chronic effects of leptin to increase mean arterial pressure (MAP), enhance glucose use and oxygen consumption, and reduce appetite. LepR(flox/flox)/POMC-Cre, wild-type, LepR(flox/flox), and POMC-Cre mice were instrumented for MAP and heart rate measurement by telemetry and venous catheters for infusions. LepR(flox/flox)/POMC-Cre mice were heavier, hyperglycemic, hyperinsulinemic, and hyperleptinemic compared with wild-type, LepR(flox/flox), and POMC-Cre mice. Despite exhibiting features of metabolic syndrome, LepR(flox/flox)/POMC-Cre mice had normal MAP and heart rate compared with LepR(flox/flox) but lower MAP and heart rate compared with wild-type mice. After a 5-day control period, leptin was infused (2 μg/kg per minute, IV) for 7 days. In control mice, leptin increased MAP by ≈5 mm Hg despite decreasing food intake by ≈35%. In contrast, leptin infusion in LepR(flox/flox)/POMC-Cre mice reduced MAP by ≈3 mm Hg and food intake by ≈28%. Leptin significantly decreased insulin and glucose levels in control mice but not in LepR(flox/flox)/POMC-Cre mice. Leptin increased oxygen consumption in LepR(flox/flox)/POMC-Cre and wild-type mice. Activation of POMC neurons is necessary for the chronic effects of leptin to raise MAP and reduce insulin and glucose levels, whereas leptin receptors in other areas of the brain other than POMC neurons appear to play a key role in mediating the chronic effects of leptin on appetite and oxygen consumption.

We examined whether systemic or central nervous system (CNS) inhibition of nitric oxide synthase exacerbates the cardiovascular responses of chronic CNS melanocortin 3/4 receptor activation. Sprague-Dawley rats implanted with telemetry probes, venous catheters, and intracerebroventricular (ICV) cannulae were divided in 3 groups. After control measurements, the NO synthase inhibitor L-NAME was infused (10 μg/kg/min intravenous) for 17 days and, starting on day 7 of L-NAME infusion, the melanocortin 3/4 receptor agonist melanotan II (MTII; 10 ng/hr; group 1) or saline vehicle (group 2) was infused ICV for 10 days. A third group not treated with L-NAME also received MTII ICV. Melanocortin 3/4 receptor activation caused a greater increase in mean arterial pressure (MAP) and heart rate in rats treated with intravenous L-NAME (35 ± 6 mm Hg and 56 ± 8 bpm) than L-NAME plus vehicle or MTII alone (22 ± 5 and 9 ± 2 mm Hg, and 26 ± 14 and 27 ± 5 bpm), despite a 58% and 50% reduction in food intake during the first 6 days of MTII infusion. To test if the amplified pressor response to MTII after L-NAME was attributable to a reduction in nitric oxide availability in the brain, we also infused L-NAME directly into the CNS alone or in combination with MTII. ICV infusion of L-NAME plus MTII caused only ≈ 10 mm Hg increase in MAP with no change in heart rate, similar to the effects of ICV infusion of MTII alone, whereas ICV infusion of L-NAME alone had no effect on MAP. These results suggest that reduction in peripheral, but not CNS, nitric oxide production augments MAP sensitivity to CNS melanocortin 3/4 receptor activation.

Previous studies suggest that activation of the CNS melanocortin system reduces appetite while increasing sympathetic activity and arterial pressure. The present study tested whether endogenous activity of the CNS melanocortin 3/4 receptors (MC3/4-R) contributes to elevated arterial pressure in the spontaneously hypertensive rat (SHR), a model of hypertension with increased sympathetic activity. A cannula was placed in the lateral ventricle of male SHR and Wistar (WKY) rats for chronic intracerebroventricular (ICV) infusions (0.5 muL/h). Mean arterial pressure (MAP) and heart rate (HR) were recorded 24 hour/d using telemetry. After 5-day control period, rats were infused with MC3/4-R antagonist (SHU-9119, 1 nmol/h-ICV) for 12 days, followed by 5-day posttreatment period. MC3/4-R antagonism increased food intake in SHR by 90% and in WKY by 125%, resulting in marked weight gain, insulin resistance, and hyperleptinemia in SHR and WKY. Despite weight gain, MC3/4-R antagonism reduced HR in SHR and WKY ( approximately 40 bpm), while lowering MAP to a greater extent in SHR (-22+/-4 mm Hg) than WKY (-4+/-3 mm Hg). SHU9119 treatment failed to cause further reductions in MAP during chronic adrenergic blockade with propranolol and terazosin. These results suggest that endogenous activity of the CNS melanocortin system contributes to the maintenance of adrenergic tone and elevated arterial pressure in SHR even though mRNA levels for POMC and MC4R in the mediobasal hypothalamus were not increased compared to WKY. These results also support the hypothesis that weight gain does not raise arterial pressure in the absence of a functional MC3/4-R.

This study tested whether the melanocortin 4-receptor (MC4R) is essential for the chronic cardiovascular and metabolic actions of leptin. Twenty- to 22-week-old male wild-type (WT) C57BL/6J and obese MC4R (-/-) mice (N=5 to 6 per group) were implanted with radiotelemetric transmitters and catheters for measuring mean arterial pressure (MAP) and heart rate 24 hours per day and intravenous infusions. After a 3-day stable control period, leptin was infused (2 microg/kg per minute IV) for 7 days in WT, obese ad libitum-fed MC4R (-/-), and nonobese pair-fed MC4R (-/-) mice. WT mice receiving vehicle for 7 days served as controls. MC4 (-/-) mice were 30% heavier and had 4- and 11-fold increases in plasma insulin and leptin levels, respectively, compared with WT mice. Despite obesity, MAP and heart rate tended to be lower in MC4R (-/-) mice compared with WT mice. Chronic leptin infusion in the different groups increased plasma leptin levels to 45 to 65 ng/mL. Seven-day leptin infusion in WT mice increased MAP by 12+/-3 mm Hg despite a 35% reduction in food intake and an 8% reduction in body weight. Leptin did not alter plasma glucose but reduced plasma insulin in WT mice (5.9+/-1.0 versus 3.0+/-0.5 microU/mL). These cardiovascular and metabolic actions of leptin were abolished in obese and nonobese MC4R (-/-) mice. These data suggest that MC4R deficiency, and not obesity-induced leptin resistance, abolished the cardiovascular and metabolic actions of leptin in obese MC4R (-/-) mice. Thus, a functional MC4R is essential for the chronic cardiovascular and metabolic actions of leptin.

Previous studies suggest that blockade of melanocortin 3 and 4 receptors (MC3/4-R) markedly attenuates the chronic hypertensive effects of leptin. Although obesity has been reported to be associated with leptin "resistance," it is unclear whether obesity alters the cardiovascular and metabolic effects of chronic MC3/4-R activation. Therefore, we tested whether the cardiovascular and metabolic actions of MC3/4-R activation are attenuated in Sprague-Dawley rats fed a high-fat diet (HF, n=6) compared with rats fed a standard chow (NF, n=6) for 12 months. A 21G steel cannula was placed in the lateral ventricle for ICV infusion, and arterial and venous catheters were implanted for measurement of mean arterial pressure (MAP) 24 hours/day and IV infusions. After a 5-day control period, rats were infused with MC3/4-R agonist melanotan II (10 ng/h, ICV), for 10 days followed by a 5-day recovery period. HF rats were heavier (558+/-21 versus 485+/-13 g) with 140% more visceral fat than NF rats, hyperleptinemic (8.9+/-0.5 versus 2.7+/-0.5 ng/mL), and insulin resistant. HF rats also had higher MAP (109+/-3 versus 100+/-1 mm Hg). Chronic melanotan II infusion significantly increased MAP in HF and NF (7+/-2 and 6+/-1 mm Hg), decreased caloric intake (-32+/-2 and -25 +/-2 kcal/day), and reduced insulin levels in both groups by approximately 50%. Thus, the metabolic and cardiovascular actions of chronic MC3/4-R activation are preserved in diet-induced obesity, supporting a potential role for the hypothalamic melanocortin system in obesity hypertension.

The purpose of this study was to test whether the melanocortin-4 receptor (MC4R) is critical in the development of hypertension associated with obesity and its metabolic disorders. MC4R-deficient homozygous (-/-) and heterozygous (+/-) and wild-type (WT) C57BL/6J mice 17 to 19 weeks old (n=5 to 7 per group) were implanted with telemetry devices for monitoring 24-hour mean arterial pressure (MAP) and heart rate (HR). After 3-day stable control measurements on normal-salt diet (NSD; 0.4% NaCl), mice received a high-salt diet (HSD; 4% NaCl) for 7 days, followed by 3-day recovery on NSD. MC4R (-/-) mice were severely obese compared with MC4R (+/-) and WT mice (body weight 48+/-1.5 versus 31+/-0.6 and 30+/-0.5 g respectively). On NSD, MAP was similar in all groups of mice (MC4R (-/-) 110+/-3 mm Hg; MC4R (+/-) 109+/-2 mm Hg; WT 114+/-2 mm Hg), and HR in MC4R (-/-) was lower than in WT (604+/-5 versus 645+/-9 bpm; P<0.05) but not different from MC4R (+/-) (625+/-13 bpm) mice. HSD did not significantly alter MAP or HR in any of the groups. Epididymal and retroperitoneal fat weights and plasma leptin levels were several-fold greater in MC4R (-/-) compared with MC4R (+/-) and WT mice. Plasma insulin and glucose levels were also significantly greater in MC4R (-/-) than in MC4R (+/-) and WT mice. These data suggest that despite obesity, visceral adiposity, hyperleptinemia, and hyperinsulinemia, MC4R (-/-) mice are neither hypertensive nor salt sensitive, indicating that a functional MC4R may be necessary for the development of hypertension associated with obesity and its metabolic abnormalities.

Although excess hypothalamic agouti-related peptide (AGRP), an endogenous antagonist of the melanocortin 3/4 receptor, causes hyperphagia and obesity, its role in regulating cardiovascular function is unclear. This study examined control of mean arterial pressure (MAP), heart rate (HR), and metabolism during chronic central administration of AGRP in rats. A cannula was placed in the lateral ventricle for intracerebroventricular infusion, and arterial and venous catheters were implanted for monitoring MAP and HR 24 hours per day, as well as intravenous infusions. After a 5-day control period, rats received AGRP (n=6; 0.02 nmol per hour ICV) or artificial cerebrospinal fluid (aCSF; n=9; 0.02 nmol per hour ICV) for 12 days, followed by a 5-day recovery period. A third group was infused intracerebroventricularly with AGRP and pair-fed to match food intake of control rats (n=7). AGRP produced a peak decrease in MAP and HR of -7+/-2 mm Hg and -68+/-7 bpm, respectively, despite increased food intake (from 23+/-0.5 to 36+/-3 g per day) and weight gain (from 350+/-8 to 454+/-5 g). AGRP also increased glomerular filtration rate, plasma insulin, glucose, and leptin. AGRP infusion in pair-fed rats produced a peak decrease in HR of -70+/-8 bpm but did not alter MAP or other variables. The metabolic effects of AGRP may be secondary to hyperphagia because they were abolished in pair-fed rats. aCSF infusion did not change any of the variables studied. These results demonstrate that increased central nervous system AGRP levels produce chronic reductions in MAP and HR despite marked increases in food intake and weight gain that normally tend to raise arterial pressure.

The present study examined whether blockade of melanocortin receptors subtypes 3 and 4 (MC3/4-R) inhibits chronic cardiovascular and dietary responses to leptin infusion. A cannula was placed in the lateral ventricle of male Sprague-Dawley rats for chronic intracerebroventricular (ICV) infusion via osmotic minipump, and arterial and venous catheters were implanted for measurement of mean arterial pressure (MAP) and heart rate (HR) 24 h/d and IV infusions. After a 5-day control period, rats received (1) 0.9% saline vehicle ICV for 12 days plus leptin (1 microg/kg per minute IV, n=5) during the final 7 days; (2) MC3/4-R antagonist SHU-9119 (1 nmol/h ICV) for 12 days plus leptin (1 microg/kg per minute IV, n=6) during the final 7 days; and (3) SHU-9119 (1 nmol/h ICV, n=8) for 12 days. Leptin infusion in vehicle-treated rats caused a small increase in MAP (5+/-1 mm Hg) despite reduced food intake (23+/-1 to 10+/-1 g/d) and decreased body weight (-6%+/-1%). SHU-9119 infusion completely prevented the cardiovascular and dietary actions of leptin, leading to increased food intake (23+/-1 to 49+/-4 g/d) and body weight (+30%+/-2%), markedly decreased HR (-77+/-9 bpm), and caused a decrease in MAP (-6+/-1 mm Hg). Similar results were observed when SHU-9119 was infused alone in vehicle-treated rats. Leptin decreased plasma insulin to 30% of control values, an effect that was also abolished by SHU-9119 treatment, which caused a 5-fold increase in plasma insulin concentration. Thus, MC3/4-R antagonism completely blocked the chronic cardiovascular, satiety, and metabolic effects of leptin, suggesting that the hypothalamic melanocortin system plays an important role in mediating these actions of leptin.

Endothelial dysfunction has been suggested to play an important role in the development of obesity-induced hypertension. Because endothelin release increases in response to endothelial damage, we examined whether endothelin-1 contributes to increased arterial pressure in a model of visceral obesity produced by feeding Sprague-Dawley rats a high-fat (HF) diet (40% fat w/w, n=6) for 12 months. Arterial and venous catheters were implanted for measurement of mean arterial pressure (MAP) and heart rate (HR) 24 hours per day and intravenous infusions. After a 5-day control period, rats were infused with the selective endothelin-1 type A receptor (ET-A) blocker ABT-627 (2.5 mg/kg per day, IV) for 9 days, followed by a recovery period. Rats fed a standard chow (normal fat, or NF, group: n=6) for 12 months were also infused with ET-A blocker and were used as controls. Compared with NF rats, HF rats had higher MAP (113+/-4 versus 98+/-2 mm Hg), increased visceral fat (18.7+/-2.0 versus 10.8+/-1.4 g), and 3.2-fold increase in plasma leptin despite similar total body weight gain. Long-term ET-A blockade markedly reduced MAP in HF (-14+/-3 mm Hg) and NF (-14+/-2 mm Hg), but it had no effect on HR, GFR, or PRA. These results indicate that a long-term HF diet may cause visceral obesity and increased MAP, even in the absence of major changes in total body weight. Endothelin-1 appears to play an important role in the maintenance of arterial pressure in rats fed HF and NF diets, but it does not appear to contribute to increased MAP in this model of diet-induced hypertension.

Acute studies have shown that MC3/4-R stimulation increases sympathetic activity, but the role of adrenergic activation in mediating the cardiovascular and renal responses to chronic melanocortin 3- and 4-receptor (MC3/4-R) activation is unknown. The present study tested whether chronic MC3/4-R activation raises blood pressure and whether these changes are attenuated by alpha1+beta-adrenergic blockade. Rats were instrumented with an intracerebroventricular (ICV) cannula and arterial and venous catheters for measurements of mean arterial pressure (MAP) and heart rate (HR) 24 hours per day, and intravenous infusions. After control measurements, rats were intravenously infused with either saline vehicle (n=7) or alpha1+ beta-adrenergic antagonists (n=6, terazosin+propranolol, 10 mg/kg per day each) for 21 days. Five days after starting the vehicle or adrenergic blockade, the MC3/4-R agonist, MTII (10 ng/h), was infused ICV for 11 days followed by a 5-day recovery period. Another group of rats was infused with the adrenergic antagonists for 21 days but received the saline vehicle ICV for 11 days (n=7). MC3/4-R activation decreased food intake from 21+/-1 to 8+/-2 g/d by day 3 of MC3/4-R activation, and increased MAP and HR by an average of 8+/-2 mm Hg and 9+/-5 bpm, respectively. Adrenergic blockade did not alter the MC3/4-R-mediated decrease in food intake but abolished the increases in MAP and HR (1+/-2 mm Hg and -12+/-5 bpm, respectively, compared with control). ICV vehicle infusion during adrenergic blockade did not alter food intake or MAP. Glomerular filtration rate was unchanged in both the vehicle-infused and adrenergic blocked rats during MC3/4-R activation. These results indicate that the chronic actions of MC3/4-R activation on MAP and HR are mediated by adrenergic activation.

This study examined the importance of aldosterone (ALDO) in mediating changes in renal function and increased mean arterial pressure (MAP) during the development of dietary-induced obesity in chronically instrumented dogs. Mean arterial pressure, heart rate (HR), and cardiac output (CO) were recorded 24 hours per day in lean dogs (n=7) before and after administration of an ALDO antagonist, eplerenone (EP) (10 mg/kg twice daily), for 10 days. After 10 days of EP treatment, the dogs (n=7) were given a supplement of cooked beef fat for 5 weeks while EP was continued. An untreated group (n=6) was fed a high fat diet for 5 weeks and used as control (C). In lean dogs, EP decreased MAP from 89+/-4 to 84+/-4 mm Hg and glomerular filtration rate from 67.4+/-6.8 to 53.2+/-4.9 mL/min while inducing a small negative Na+ balance (-42+/-12 mEq). Plasma renin activity increased from 0.4+/-0.1 to 2.7+/-0.7 ng AI/mL per hour and plasma K+ increased from 4.8+/-0.1 to 6.1+/-0.3 mEq/L. After 5 weeks of a high fat diet, body weight increased 45% to 53% in EP and C obese dogs. In C dogs, MAP increased by 16+/-3 mm Hg, compared with only 7+/-1 mm Hg in EPLE dogs. Compared with untreated dogs, the EP dogs had smaller increases in CO (18+/-4.6% versus 43+/-1.5%), HR (33+/-5% versus 60+/-3%), glomerular filtration rate (19+/-5% versus 38+/-6%), and cumulative Na+ balance (138+/-35 mEq versus 472+/-110 mEq) after 5 weeks of a high fat diet. Thus, EP markedly attenuated glomerular hyperfiltration, sodium retention, and hypertension associated with chronic dietary-induced obesity. These observations indicate that ALDO plays an important role in the pathogenesis of obesity hypertension.

This study examined control of cardiovascular and renal function during chronic melanocortin-3/4 receptor (MC3/4-R) activation or inhibition. Arterial and venous catheters were implanted in Sprague-Dawley rats for measurements of mean arterial pressure (MAP) and heart rate (HR) 24 h/d and for intravenous infusions, and the lateral ventricle was cannulated for chronic intracerebroventricular (ICV) infusions. In experiment 1, after a 5-day control period, rats were administered the MC3/4-R agonist MTII (n=7, 10 ng/h ICV) or 0.9% saline (n=6, ICV) for 14 days, followed by a 5-day recovery period. In experiment 2, after a 5-day control period, rats were administered the MC3/4-R antagonist SHU-9119 (n=7, 1 nmol/h ICV) or 0.9% saline vehicle (n=7, ICV), or pair-fed during SHU-9119 infusion (n=5, 1 nmol/h ICV) for 12 days, followed by a 5-day recovery period. MC4-R activation transiently decreased food intake from 23+/-1 to 10+/-2 g/d. Despite the hypophagia, MC3/4-R activation increased MAP by 7+/-1 mm Hg. MC3/4-R inhibition for 12 days increased food intake from 21+/-1 to 35+/-4 g/d, decreased HR by 53+/-11 bpm, and caused no change in MAP despite the marked weight gain. In rats that were pair-fed to prevent increased food intake, MC3/4-R inhibition further decreased HR (-87+/-9 bpm), whereas MAP was unchanged. Thus, chronic hypothalamic MC3/4-R activation raises arterial pressure despite decreased food intake, whereas MC3/4-R inhibition causes marked weight gain without raising arterial pressure. These observations are consistent with the hypothesis that an intact hypothalamic MC3/4-R may be necessary for excess weight gain to raise arterial pressure.