In vitro, release of cholecystokinin from hypothalamus and frontal cortex of Sprague-Dawley, Zucker lean (Fa/-) and obese (fa/fa) rats

Cholecystokinin (CCK) has been suggested as a putative satiety factor, whose site of action is in the hypothalamus. The genetically obese (fa/fa) Zucker rat has been proposed as a model of human obesity. Though hypothalamic tissue levels of CCK did not vary between the fa/fa rat and age-matched lean littermates (25.5 +/- 5.7 vs. 27.6 +/- 5.2 pmoles/g tissue) we sought to determine if the releasability of hypothalamic and cortical CCK was the same in lean and obese rats. The in vitro superfusion paradigm was used to study the release of CCK and substance P (sP) from hypothalamus, and CCK and vasoactive intestinal polypeptide (VIP) from frontal cortex. The potassium stimulated release of CCK from obese rat hypothalamic tissue was significantly higher than from lean rat hypothalamus (3.62 +/- 0.3 vs. 1.91 +/- 0.3 fmole equivalents CCK-8/mg tissue/10 min). Similarly, sP release was exaggerated in obese rats in a parallel fashion (5.56 +/- 0.44 vs. 2.761 +/- 0.46 fmoles/mg tissue/10 min). However, the potassium stimulated release of CCK and VIP from cortical tissue was the same in all three groups of rats. The obese Zucker rat thus, may have an anomalous release of CCK and sP from the hypothalamus, but not from the frontal cortex, an area not presumably associated with satiety.     

Leptin-like effects of MTII are augmented in MSG-obese rats

To evaluate whether MTII, a melanocortin receptor 3/4 agonist, is working in hypophagic and hypothermogenic obese model, we measured food intake, body weight, oxygen consumption, and fat mass following intracerebroventricular (i.c.v.) infusion of MTII in monosodium glutamate (MSG)-induced obese rats. MTII, or artificial cerebrospinal fluid (aCSF), was infused into i.c.v. with an osmotic minipump for 1 week. MSG-obese rats were induced by neonatal injection of MSG. Five-month-old MSG rats were characterized by hypophagia, lower oxygen consumption, hyperleptinemia, and obesity compared to age-matched control rats. The infusion of MTII decreased their food intake, visceral fat, and body weight in MSG-obese rats compared with aCSF-infused rats. The oxygen consumption was increased by MTII treatment in MSG-obese rats compared with aCSF as well as pair fed (PF) rats. Interestingly, these leptin-like effects of MTII were greater in MSG-obese rats than in controls, which might be related to the increased expression of melanocortin receptor 4 (MC4R) in the hypothalamus of MSG-obese rats. Our results suggested that both anorexic and thermogenic mechanisms were activated by MTII in the MSG-obese rats and contributed to the decrease in body weight and fat mass. Moreover, there was a sensitization to MTII caused by upregulation of the melanocortin receptor in the MSG-obese rats.     

The influence of dehydroepiandrosterone and 8-OH-DPAT on the caloric intake and hypothalamic neurotransmitters of lean and obese Zucker rats

The 5 HT(1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)-tetraline (8-OH-DPAT) increases the food intake of satiated Zucker rats, both lean and obese. Associated with this increased intake are changes in the hypothalamic content of serotonin and its metabolite, 5-HIAA (5-hydroxyindole-3-acetic acid); serotonin is increased while the level of 5-HIAA is decreased. Analysis of individual 5-HIAA/5-hydroxytryptamine (5-HT) ratios, a measure of serotonin turnover indicate that 8-OH DPAT affected serotonin turnover equally and dramatically in both phenotypes. This would be an expected physiological action of an autofeedback mechanism by a 5-HT(1A) receptor agonist. Dehydroepiandrosterone (DHEA) at doses as low as 10 mg/kg blocks the 8-OH-DPAT-induced increase in food intake but does not alter food intake of control satiated Zucker rats. The mechanism of DHEA's action was investigated by monitoring the steroid's effect on hypothalamic neurotransmitters in this satiated model. DHEA by itself induced some change in 5-HIAA in the obese satiated model but not the lean. 8-OH-DPAT, by itself, dramatically decreased serotonin turnover in either lean or obese rats, and DHEA combined with 8-OH-DPAT did not further change serotonin turnover, suggesting DHEA may work through mechanisms other than monoamines to cause its inhibition of 8-OH-DPAT-induced behavioral effects at such low doses.     

Expression of dopaminergic receptors in the hypothalamus of lean and obese Zucker rats and food intake

As revealed by previous microdialysis studies, basal and food intake-accompanied dopamine release significantly differs in the hypothalamus of obese vs. lean Zucker rats. In the present study, we determined whether dopaminergic receptors are also compromised in obesity. Dopaminergic D(1) and D(2) receptor mRNA expression was studied in the ventromedial hypothalamus (VMH), lateral hypothalamic area (LHA), and the adenohypophysis (AH) of obese and lean Zucker rats using RT-PCR technique. In obese Zucker rats, we found an upregulation of D(1) receptor mRNA in the VMH and AH and a downregulation in the LHA, whereas D(2) receptor mRNA was downregulated in both the VMH and LHA, but not changed in the AH, compared with lean rats. Also, an increase of D(1) receptor staining was seen in the paraventricular nucleus of obese rats by immunohistochemistry. We selected the VMH to test if the observed changes in the dopamine receptor expression of obese rats induce behavioral sensitization to dopamine as expressed by hyperphagia. The overnight food-deprived rats received a single VMH injection (10 nmol) of sulpiride (D(2) receptor antagonist) or saline as control, then food was provided and 1-h food intake was measured. Food intake after sulpiride vs. saline injection was greater in obese rats but was not different in lean rats. Our data suggest that downregulation of D(2) receptor in the hypothalamus at least in the VMH induces behavior sensitization for having large meals. Low D(2) receptor expression may be causal for an exaggerated dopamine release observed in obese rats during food ingestion and for reduced satiety feedback effect of dopamine. High level of D(1) receptor expression in the VMH and low in the LHA may also contribute to the specific feeding pattern in obese rats represented by large meal size and low meal number.     

Decreased plasma leptin levels in lean and obese Zucker rats after treatment with the serotonin reuptake inhibitor fluoxetine.

Leptin inhibits feeding, stimulates thermogenesis and decreases body weight. Serotonin reduces food intake when injected into the hypothalamus and may interact with other neurotransmitters in the control of appetite. We therefore investigated the effects of the serotonergic drug fluoxetine, which inhibits serotonin reuptake, on food intake and plasma leptin levels in lean and obese Zucker rats. Fluoxetine significantly reduced food intake in lean and obese rats, both acutely after a single injection (10 mg/kg) and during continuous subcutaneous infusion (10 mg/kg/day for 7 days). Plasma leptin levels were reduced after both 4 hours and 7 days of fluoxetine administration in lean and after 7 days in fatty rats (all p<0.01). We have previously suggested that serotonin may decrease food intake by inhibiting neuropeptide Y neurones, and we further suggest that it also inhibits leptin, possibly by an effect on white adipose tissue.     

Cardiovascular and metabolic responses to fasting and thermoneutrality are conserved in obese Zucker rats

The primary purpose of the study was to test the hypothesis that reduced leptin signaling is necessary to elicit the cardiovascular and metabolic responses to fasting. Lean (Fa/?; normal leptin receptor; n = 7) and obese (fa/fa; mutated leptin receptor; n = 8) Zucker rats were instrumented with telemetry transmitters and housed in metabolic chambers at 23 degrees C (12:12-h light-dark cycle) for continuous (24 h) measurement of metabolic and cardiovascular variables. Before fasting, mean arterial pressure (MAP) was higher (MAP: obese = 103 +/- 3; lean = 94 +/- 1 mmHg), whereas oxygen consumption (VO(2): obese = 16.5 +/- 0.3; lean = 18.6 +/- 0.2 ml. min(-1). kg(-0.75)) was lower in obese Zucker rats compared with their lean controls. Two days of fasting had no effect on MAP in either lean or obese Zucker rats, whereas VO(2) (obese = -3.1 +/- 0.3; lean = -2.9 +/- 0.1 ml. min(-1). kg(-0.75)) and heart rate (HR: obese = -56 +/- 4; lean = -42 +/- 4 beats/min) were decreased markedly in both groups. Fasting increased HR variability both in lean (+1.8 +/- 0.4 ms) and obese (+2.6 +/- 0.3 ms) Zucker rats. After a 6-day period of ad libitum refeeding, when all parameters had returned to near baseline levels, the cardiovascular and metabolic responses to 2 days of thermoneutrality (ambient temperature 29 degrees C) were determined. Thermoneutrality reduced VO(2) (obese = -2.4 +/- 0.2; lean = -3.3 +/- 0.2 ml. min(-1). kg(-0.75)), HR (obese = -46 +/- 5; lean = -55 +/- 4 beats/min), and MAP (obese = -13 +/- 6; lean = -10 +/- 1 mmHg) similarly in lean and obese Zucker rats. The results indicate that the cardiovascular and metabolic responses to fasting and thermoneutrality are conserved in Zucker rats and suggest that intact leptin signaling may not be requisite for the metabolic and cardiovascular responses to reduced energy intake.     

Unexpected regulation of hypothalamic neuropeptide Y by food deprivation and refeeding in the Zucker rat.

Neuropeptide Y strongly stimulates food intake when it is injected in the hypothalamic paraventricular (PVN) and ventromedian (VMN) nuclei. In Sprague-Dawley (SD) rats, NPY synthesis in the arcuate nucleus (ARC) is increased by food deprivation and is normalized by refeeding. We have previously shown that the obese hyperphagic Zucker rat is characterized by higher NPY concentrations in this nucleus. NPY might therefore play an important role in the development of hyperphagia. The aim of the present study was to determine if the regulation by the feeding state works in the obese Zucker rat. For this purpose, 10 weeks-old male lean (n = 30) and obese (n = 30) Zucker rats were either fed ad libitum, either food-deprived (FD) for 48 hours or food-deprived for 48 h and refed (RF) for 6 hours. NPY was measured in several microdissected brain areas involved in the regulation of feeding behavior. NPY concentrations in the ARC was about 50% greater in obese rats than in lean rats (p less than 0.02) whatever the feeding state. In the VMN, NPY concentrations were higher in the lean FD rats than in the obese FD rat (p less than 0.001). Food deprivation or refeeding did not modify NPY in the ARC, in the VMN or in the dorsomedian nucleus whatever the genotype considered. On the other hand, food deprivation induced a significant decrease in NPY concentrations in the PVN of lean rats. This decrease was localized in the parvocellular part of this nucleus (43.0 +/- 1.9 (FD) vs 54.2 +/- 2.1 (Ad lib) ng/mg protein; p less than 0.005). Ad lib levels were restored by 6 hours of refeeding. These variations were not observed in the obese rat. The regulation of NPY by the feeding state in the Zucker rat was therefore very different from that described in the SD rats. Strain or age of the animals used might explain these differences. High NPY levels and absence of regulation in obese Zucker rats could contribute to the abnormal feeding behavior of these rats.     

GABAergic modulation of ventilation and peak oxygen consumption in obese Zucker rats.

Obesity is often associated with a reduced ventilatory response and a decreased maximal exercise capacity. GABA is a major inhibitory neurotransmitter in the mammalian central nervous system. Altered GABAergic mechanisms have been detected in obese Zucker rats and implicated in their hyperphagic response. Whether altered GABAergic mechanisms also contribute to regulate ventilation and influence exercise capacity in obese Zucker rats is unknown and formed the basis of the present study. Eight lean [317 +/- 18 (SD) g] and eight obese (450 +/- 27 g) Zucker rats were studied at 12 wk of age. Ventilation at rest and ventilation during hypoxic (10% O(2)) and hypercapnic (4% CO(2)) challenges were measured by the barometric method. Peak O(2) consumption (VO(2 peak)) in response to a progressive treadmill test to exhaustion was measured in a metabolic treadmill. Ventilation and VO(2 peak) were assessed after administration of equal volumes of DMSO (vehicle) and the GABA(A) receptor antagonist bicuculline (1 mg/kg). In lean animals, bicuculline administration had no effect on ventilation and VO(2 peak). In obese rats, bicuculline administration significantly (P < 0.05) increased resting ventilation (465 +/- 53 and 542 +/- 72 ml. kg(-1). min(-1) for control and bicuculline, respectively), ventilation during exposure to hypoxia (899 +/- 148 and 1,038 +/- 83 ml. kg(-1). min(-1) for control and bicuculline, respectively), and VO(2 peak) (62 +/- 3.7 and 67 +/- 3.5 ml. kg(-0.75). min(-1) for control and bicuculline, respectively). However, in obese Zucker rats, ventilation in response to hypercapnia did not change after bicuculline administration (608 +/- 96 vs. 580 +/- 69 ml. kg(-1). min(-1)). Our findings indicate that endogenous GABA depresses ventilation and limits exercise performance in obese Zucker rats.     

Effect of adrenalectomy on the activity of small intestine enzymes in monosodium glutamate obese rats

It is well known that adrenalectomy (ADX) reverses the eating and energy balance disturbances in a variety of models of obesity associated with elevated food intake. We have previously demonstrated enhanced functional activity in the small intestine of neonatally monosodium glutamate-treated (MSG) obese rats despite the absence of overeating and we concluded that these changes might also contribute to the development of MSG obesity. The objective of the present experiments was to investigate whether ADX would affect the small intestinal functions and whether their changes would counteract attenuation or prevention of obesity development in MSG rats. Therefore the investigation was carried out in MSG-obese Wistar male rats and untreated intact rats adrenalectomized on day 40, as well as in lean littermates of MSG rats and intact rats subjected to Sham-ADX surgery. All animals had free access to a standard pellet diet after weaning. At the age of 80 days, body mass, body fat content and food consumption as well as changes of the brush-border-bound duodenal and jejunal alkaline phosphatase (AP), the dipeptidyl(amino)peptidase IV (DPP IV) and maltase activity were measured. During the postoperative period, ADX resulted in a significant decrease of mass gain in both MSG and control rats (P<0.05). ADX fully prevented the development of obesity in MSG rats (significantly decreased epididymal+retroperitoneal fat pad mass, P<0.05) and increased mean daily food intake (P<0.001). These effects were only minimal in the ADX controls suggesting that enhanced adrenal secretion is involved in the expression of MSG obesity and its complications. The AP activity in obese MSG rats was increased by about 21 % (P<0.01) in both intestinal segments when compared to the lean controls, whereas no parallel variations in the activities of DPP IV and maltase were observed in the intestinal parts mentioned. In MSG rats, ADX significantly reduced the AP activity in the duodenum and jejunum (P<0.01). A similar tendency was also seen in the DPP IV activity of adrenalectomized MSG rats as well as in lean control rats. Nevertheless, no significant effect of adrenal withdrawal on maltase activity was found. These results indicate that the decrease of enzyme activities in the small intestine and the different effectiveness of nutrient absorption might be a significant factor preventing the development of excess adiposity in glutamate-treated rats. This information contributes to a better understanding of the importance of small intestinal function for the development of obesity and its maintenance in later life.     

Starvation increases gastrointestinal somatostatin in normal and obese Zucker rats: a possible regulatory mechanism

Normal, male Sprague-Dawley (S-D) rats and female, lean and obese Zucker rats were studied in the fed state and after 48 hours of food deprivation. Somatostatin-like immunoreactivity (SLI) was measured from acetic acid extracts of oesophagus-cardia, stomach, small and large intestine, pancreas, hypothalamus, pituitary and cerebellum. Within the CNS, the highest levels of SLI were found in the hypothalamus, while in the gut, these levels were highest in the stomach and pancreas. All Zucker rats displayed higher hypothalamic levels of SLI than did S-D rats. Obese Zucker rats in the fed state differed from their lean littermates in that SLI levels were lower in oesophagus-cardia, stomach and hypothalamus, while being higher in pancreas and pituitary. The response to starvation in both obese and lean Zucker rats was qualitatively similar, and included significant increases in stomach and oesophagus-cardia SLI, but with a significant fall hypothalamic SLI. We have concluded that the increase in gastrointestinal SLI with starvation in Zucker as well as in S-D rats may represent a significant regulatory mechanism in nutrient homeostasis. We postulate that gastric SLI may decrease the availability of intestinal insulin secretagogues in the fasting state. This adaptive mechanism appears to be intact in the obese Zucker rat.     

Activation of the central melanocortin system contributes to the increased arterial pressure in obese Zucker rats

We have previously demonstrated that leptin-mediated activation of the central nervous system (CNS) melanocortin system reduces appetite and increases sympathetic activity and blood pressure (BP). In the present study we examined whether endogenous melanocortin system activation, independent of leptin's actions, contributes to the regulation of BP and metabolic functions in obese Zucker rats, which have mutated leptin receptors. The long-term cardiovascular and metabolic effects of central melanocortin-3/4 receptor (MC3/4R) antagonism with SHU-9119 were assessed in lean (n = 6) and obese (n = 8) Zucker rats. BP and heart rate (HR) were measured 24-h/day by telemetry and an intracerebroventricular cannula was placed in the brain lateral ventricle. After stable control measurements, SHU-9119 was infused intracerebroventricularlly (1 nmol/h) for 10 days followed by a 10-day recovery period. Chronic CNS MC3/4R antagonism significantly increased food intake and body weight in lean (20 ± 1 to 45 ± 2 g and 373 ± 11 to 432 ± 14 g) and obese (25 ± 2 to 35 ± 2 g and 547 ± 10 to 604 ± 11 g) rats. No significant changes were observed in plasma glucose levels in lean or obese rats, whereas plasma leptin and insulin levels markedly increased in lean Zucker rats during CNS MC3/4R antagonism. Chronic SHU-9119 infusion in obese Zucker rats reduced mean arterial pressure (MAP) and HR by 6 ± 1 mmHg and 24 ± 5 beats/min, whereas in lean rats SHU-9119 infusion reduced HR by 31 ± 9 beats/min while causing only a transient decrease in MAP. These results suggest that in obese Zucker rats the CNS melanocortin system contributes to elevated BP independent of leptin receptor activation.     

Regional Fat Pad Growth and Cellularity in Obese Zucker Rats: Modulation by Caloric Restriction

Objective : To investigate, in young obese male Zucker rats, the effects of chronic food restriction and subsequent refeeding on: 1) parameters of nonadipose and adipose growth, 2) regional adipose depot cellularity [fat cell volume (FCV) and number], and 3) circulating leptin levels. Research Methods and Procedures : Obese (fa/fa) and lean (Fa/?) male Zucker rats were studied from age 5 to 19 weeks. After baseline food intake monitoring, 10 obese rats were subjected to 58 days of marked caloric restriction from ad libitum levels [obese‐restricted (OR)], followed by a return to ad libitum feeding for 22 days. Ten lean control rats and 10 obese control rats were fed ad libitum for the entire experiment. All rats were fed using a computer‐driven automated feeding system designed to mimic natural eating patterns. Results : After food restriction, OR rats weighed significantly less than did lean and obese rats and showed a significant diminution in body and adipose growth as compared with obese rats. Relative adiposity was not different between obese and OR rats and was significantly higher than that of lean rats. The limitation in growth of the adipose tissue mass in OR rats was due mostly to suppression of fat cell proliferation because the mean FCV in each of the four depots was not affected. Serum leptin levels of OR and obese rats were not different from each other but were significantly higher than those of lean rats. Discussion : Marked caloric restriction affects obese male Zucker rats in a manner different from that of nongenetic rodent models (i.e., Wistar rats). In comparison with the response to caloric deprivation of Wistar rats, these calorically restricted obese male Zucker rats appeared to defend their relative adiposity and mean FCV at the expense of fat cell number. These findings indicate that genetic and/or tissue‐specific controls override the general consequences of food restriction in this genetic model of obesity.     

Impaired responsiveness of renal sensory nerves in streptozotocin-treated rats and obese Zucker diabetic fatty rats: role of angiotensin

Increasing afferent renal nerve activity decreases efferent renal nerve activity and increases urinary sodium excretion. Activation of renal pelvic mechanosensory nerves is impaired in streptozotocin (STZ)-treated rats (model of type 1 diabetes). Decreased activation of renal sensory nerves would lead to increased efferent renal nerve activity, sodium retention, and hypertension. We examined whether the reduced activation of renal sensory nerves in STZ rats was due to increased renal angiotensin activity and whether activation of the renal sensory nerves was impaired in obese Zucker diabetic fatty (ZDF) rats (model of type 2 diabetes). In an isolated renal pelvic wall preparation from rats treated with STZ for 2 wk, PGE2 failed to increase the release of substance P, from 5 +/- 1 to 6 +/- 1 pg/min. In pelvises from sham STZ rats, PGE2 increased substance P release from 6 +/- 1 to 13 +/- 2 pg/min. Adding losartan to the incubation bath increased PGE2-mediated release of substance P in STZ rats, from 5 +/- 1 to 10 +/- 2 pg/min, but had no effect in sham STZ rats. In pelvises from obese ZDF rats (22-46 wk old), PGE2 increased substance P release from 12.0 +/- 1.2 to 18.3 +/- 1.2 pg/min, which was less than that from lean ZDF rats (10.3 +/- 1.6 to 22.5 +/- 2.4 pg/min). Losartan had no effect on the PGE2-mediated substance P release in obese or lean ZDF rats. We conclude that the mechanisms involved in the decreased responsiveness of the renal sensory nerves in STZ rats involve activation of the renin angiotensin system in STZ but not in obese ZDF rats.     

Feeding response to ghrelin agonist and antagonist in lean and obese Zucker rats

Ghrelin is a new orexigenic and adipogenic peptide primarily produced by the stomach and the hypothalamus. In the present experiment, we determined the circulating ghrelin levels in 60-week old fa/fa Zucker rats with a well-established obesity (n = 12) and in their lean (FA/FA) counterparts (n = 12). We also tested the feeding response of both groups to intra-peritoneal (I.P.) injection of ghrelin agonist and antagonist. Obese rats ate significantly more than the lean rats (21.7 +/- 1.1 vs. 18.3 +/- 0.3 g/day; p < 0.01). Their plasma ghrelin concentration was 35% higher than that in the lean homozygous rats (p < 0.025). GHRP-6 (1 mg/kg I.P, a GHS-R agonist) stimulated food intake in lean but not in obese rats (p < 0.01), whereas [D-Lys)]-GHRP-6 (12 mg/kg I.P., a GHS-R antagonist) decreased food intake in both groups (p < 0.0001). These results indicate that the obese Zucker rat is characterized by an increase in plasma ghrelin concentrations and by an attenuated response to a GHS-R agonist. They support a role for ghrelin in the development of obesity in the absence of leptin signaling.     

Effects of leptin on hypothalamic arcuate neurons in Wistar and Zucker rats: an in vitro study

Leptin, a product of the ob gene, decreases food intake and body weight in both Wistar and Zucker obese rats when administered centrally or peripherally. To examine whether these leptin effects might be mediated through a neuropeptide Y (NPY) signaling pathway in the medial part of the arcuate nucleus of the hypothalamus (vmARC), the effects of leptin on vmARC neurons in Wistar and Zucker obese rats were examined electrophysiologically using brain slice preparations. Bath application of leptin inhibited about 60% of the vmARC neurons recorded in slices from Wistar rats. Similar inhibitory effects of leptin on vmARC neurons were also observed under low-Ca2+, high-Mg2+ Ringer's solution. However, inhibitory effects were almost absent under Ringer's solution containing a protein kinase C inhibitor, chelerythrine chloride. In slices from Zucker obese rats, leptin inhibited only about 25% of the vmARC neurons recorded, and the proportion of neurons inhibited was significantly smaller for these rats than for Wistar rats. These results suggest that reductions in food intake and body weight induced by leptin in both Wistar and Zucker obese rats are partly mediated via inhibition of an NPY signaling pathway in the vmARC.     

Impaired nitric oxide synthase-dependent dilatation of cerebral arterioles in type II diabetic rats

The goals of this study were to determine the effects of type II diabetes mellitus on nitric oxide synthase-dependent responses of cerebral arterioles and on endothelial nitric oxide synthase (eNOS) protein in cerebral arterioles. We examined dilatation of cerebral (pial) arterioles in 13-15 week old male lean and diabetic obese Zucker rats in response to nitric oxide synthase-dependent agonists (acetylcholine and adenosine diphosphate (ADP)) and a nitric oxide synthase-independent agonist (nitroglycerin). We found that acetylcholine (10 microM) increased cerebral arteriolar diameter by 10 +/- 3% (mean +/- SE) in lean Zucker rats, but by only 2 +/- 2% in diabetic obese Zucker rats (p<0.05). In addition, ADP (100 microM) increased cerebral arteriolar diameter by 20 +/- 2% in lean Zucker rats, but by only 8 +/- 2% in diabetic obese Zucker rats (p<0.05). In contrast, nitroglycerin produced similar vasodilatation in lean and diabetic obese Zucker rats. Thus, impaired dilatation of cerebral arterioles in diabetic obese Zucker rats is not related to non-specific impairment of vasodilatation. Following these functional studies, we harvested cerebral microvessels for Western blot analysis of eNOS protein. We found that eNOS protein was significantly higher in diabetic obese Zucker rats than in lean Zucker rats (p<0.05). Thus, type II diabetes mellitus impairs nitric oxide synthase-dependent responses of cerebral arterioles. In addition, eNOS protein from cerebral blood vessels is increased in diabetic obese Zucker rats.     

LY226936 Administered Orally and Centrally to Obese Zucker Rats Suppresses Food Intake and Body Weight Gain

LY226936, methylcarbamothoic acid-S-(4,5-dihydro-2-thiazolyl) ester, is a new compound that, when administered to obese Zucker rats, caused reduced food intake. LY226936 reduced the food consumption after a single oral dose of 50 and 100 mg/kg. On chronic oral administration to meal-fed obese (5 to 35 mg/kg. once daily) and to fed obese and lean (15 mg/kg. twice daily) Zucker rats, LY226936 reduced food intake and body weight gain for periods ranging from 40 to 48 days. The effect on both parameters was statistically significant. There is no evidence in our studies that tolerance to the actions of LY226936 developed. LY226936 decreased the consumption of both high carbohydrate and high fat diets. Food consumption of meal-fed obese Zucker rats was reduced significantly each time a single dose of 10 ugm LY226936 per rat was infused intracerebroventricularly. None of the receptors studied (mu and kappa opioid, CCK, serotonin, neuropeptide Y, galinin, N-methyl-D-aspartic acid) appeared to bind LY226936 and therefore, appear not to be involved in the depression of food intake by the obese Zucker rat.     

Plasma B-cell tropin (ACTH22-39) concentration in lean and obese (ob/ob) mice and lean and obese (fa/fa) Zucker rats

A method has been developed for the measurement of plasma concentrations of Beta-cell tropin (BCT), which is a potent insulinotropic and lipogenic peptide secreted by the pituitary. The method was employed to compare plasma Beta-cell tropin concentrations between lean and genetically obese (ob/ob) mice and between lean and genetically obese (fa/fa) Zucker rats. The plasma concentration in lean mice was 0.17 +/- 0.02 (5)nmole/l (mean +/- SEM, n = 5), while that in obese (ob/ob) mice was significantly higher, being 2.88 +/- 1.13 (5)nmole/l. The plasma BCT concentration in Zucker rats was 0.14 +/- 0.02 (15)nmole/l, while that in obese Zucker (fa/fa) rats was significantly higher, being 1.69 +/- 0.72 (16)nmole/l. These results explain previously observed differences in the Beta-cell tropin-like biological activity in plasma from lean and obese animals, and support the hypothesis that the peptide has a role in the development of hyperinsulinaemia and obesity.