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Both increased and decreased fatty acid (FA) availability contribute to control of food intake. For example, it is well documented that intestinal FA reduces feeding by triggering enterondocrine secretion of satietogenic peptides, such as cholecystokinin (CCK) and glucagon-like peptide-1 (GLP-1). In contrast, mechanisms by which decreased FA availability increase feeding are not well understood. Over the past three decades substantial research related to FA availability and increased feeding has involved use of the orexigenic compound mercaptoacetate (MA). Because MA reportedly inhibits FA oxidation, it has been assumed that reduced FA oxidation accounts for the orexigenic action of MA. Recently, however, we demonstrated that MA antagonizes G protein-coupled receptor 40 (GPR40), a membrane receptor for long and medium chain FA. We also demonstrated that, by antagonizing GPR40, MA inhibits GLP-1 secretion and attenuates vagal afferent activation by FA. Because both vagal afferent activation and GLP-1 inhibit food intake, we postulated that inhibition of GPR40 by MA might underlie the orexigenic action of MA. We tested this hypothesis using male and female GPR40 knockout (KO) and wild-type (WT) mice. Using several testing protocols, we found that MA increased feeding in WT, but not GPR40 KO mice, and that GPR40 KO mice gained more weight than WT on a high-fat diet. Metabolic monitoring after MA or saline injection in the absence of food did not reveal significant differences in respiratory quotient or energy expenditure between treatment groups or genotypes. These results support the hypothesis that MA stimulates food intake by blocking FA effects on GPR40.

Mercaptoacetate (MA) is an orexigenic agent reported to block fatty acid (FA) oxidation. Recently, however, we reported evidence from isolated nodose ganglion neurons that MA antagonizes the G protein-coupled long- and medium-chain FA receptor GPR40. GPR40 mediates FA-induced secretion of the satietogenic incretin peptide glucagon-like peptide 1 (GLP-1), by enteroendocrine L cells, as well as FA-induced enhancement of glucose-stimulated insulin secretion. Our results in cultured nodose neurons suggest that MA would also block GPR40 in enteroendocrine cells controlling GLP-1 secretion. If so, this would suggest an alternative mechanism by which MA increases food intake. We tested the hypothesis that MA blocks FA-induced GLP-1 secretion in vitro using cultured STC-1 cells (a murine enteroendocrine cell line) and in vivo in adult male rats. In vitro, MA blocked the increase in both cytosolic Ca(2+)and GLP-1 release stimulated by FAs and also reduced (but less effectively) the response of STC-1 cells to grifolic acid, a partial agonist of the GPR120 FA receptor. In vivo, MA reduced GLP-1 secretion following olive oil gavage while also increasing glucose and decreasing insulin levels. The carnitine palmatoyltransferase 1 antagonist etomoxir did not alter these responses. Results indicate that MA's actions, including its orexigenic effect, are mediated by GPR40 (and possibly GPR120) receptor antagonism and not by blockade of fat oxidation, as previously believed. Analysis of MA's interaction with GPR40 may facilitate understanding of the multiple functions of this receptor and the manner in which FAs participate in the control of hunger and satiety., (Copyright © 2016 the American Physiological Society.)

β-mercaptoacetate (MA) is a drug known to block mitochondrial oxidation of medium- and long-chain fatty acids (FAs) and to stimulate feeding. Because MA-induced feeding is vagally dependent, it has been assumed that the feeding response is mediated by MA's antimetabolic action at a peripheral, vagally innervated site. However, MA's site of action has not yet been identified. Therefore, we used fluorescent calcium measurements in isolated neurons from rat nodose ganglia to determine whether MA has direct effects on vagal sensory neurons. We found that MA alone did not alter cytosolic calcium concentrations in nodose neurons. However, MA (60 μM to 6 mM) significantly decreased calcium responses to both linoleic acid (LA; 10 μM) and caprylic acid (C8; 10 μM) in all neurons responsive to LA and C8. GW9508 (40 μM), an agonist of the FA receptor, G protein-coupled receptor 40 (GPR40), also increased calcium levels almost exclusively in FA-responsive neurons. MA significantly inhibited this response to GW9508. MA did not inhibit calcium responses to serotonin, high K(+), or capsaicin, which do not utilize GPRs, or to CCK, which acts on a different GPR. GPR40 was detected in nodose ganglia by RT-PCR. Results suggest that FAs directly activate vagal sensory neurons via GPR40 and that MA antagonizes this effect. Thus, we propose that MA's nonmetabolic actions on GPR40 membrane receptors, expressed by multiple peripheral tissues in addition to the vagus nerve, may contribute to or mediate MA-induced stimulation of feeding., (Copyright © 2014 the American Physiological Society.)

Targeted disruption of the Alox15 gene makes mice resistant to angiotensin II-, DOCA/salt-, and N(ω)-nitro-L-arginine methyl ester (L-NAME)-induced experimental hypertension. Macrophages, a primary source of Alox15, are facilitating this resistance, but the underlying mechanism is not known. Because Alox15 metabolites are peroxisome proliferator-activated receptor (PPAR)γ agonists, we hypothesized that activation of macrophage PPARγ is the key step in Alox15 mediation of hypertension. Thioglycollate, used for macrophage elicitation, selectively upregulated PPARγ and its target gene CD36 in peritoneal macrophages of both wild-type (WT) and Alox15(-/-) mice. Moreover, thioglycollate-injected Alox15(-/-) mice became hypertensive upon L-NAME treatment. A similar hypertensive effect was observed with adoptive transfer of thioglycollate-elicited Alox15(-/-) macrophages into Alox15(-/-) recipient mice. The role of PPARγ was further specified by using the selective PPARγ antagonist GW9662. WT mice treated with 50 μg/kg daily dose of GW9662 for 12 days became resistant to L-NAME-induced hypertension. The PPARγ antagonist treatment also prevented L-NAME-induced hypertension in thioglycollate-injected Alox15(-/-) mice, indicating a PPARγ-mediated effect in macrophage elicitation and the resultant hypertension. These results indicate a regulatory role for macrophage-localized PPARγ in L-NAME-induced experimental hypertension.

Various mechanisms detect the presence of dietary triacylglycerols (TAG) in the digestive tract and link TAG ingestion to the regulation of energy homeostasis. We here propose a novel sensing mechanism with the potential to encode dietary TAG-derived energy by translating enterocyte fatty acid oxidation (FAO) into vagal afferent signals controlling eating. Peripheral FAO has long been implicated in the control of eating (141). The prevailing view was that mercaptoacetate (MA) and other FAO inhibitors stimulate eating by modulating vagal afferent signaling from the liver. This concept has been challenged because hepatic parenchymal vagal afferent innervation is scarce and because experimentally induced changes in hepatic FAO often fail to affect eating. Nevertheless, intraperitoneally administered MA acts in the abdomen to stimulate eating because this effect was blocked by subdiaphragmatic vagal deafferentation (21), a surgical technique that eliminates all vagal afferents from the upper gut. These and other data support a role of the small intestine rather than the liver as a FAO sensor that can influence eating. After intrajejunal infusions, MA also stimulated eating in rats through vagal afferent signaling, and after infusion into the superior mesenteric artery, MA increased the activity of celiac vagal afferent fibers originating in the proximal small intestine. Also, pharmacological interference with TAG synthesis targeting the small intestine induced a metabolic profile indicative of increased FAO and inhibited eating in rats on a high-fat diet but not on chow. Finally, cell culture studies indicate that enterocytes oxidize fatty acids, which can be modified pharmacologically. Thus enterocytes may sense dietary TAG-derived fatty acids via FAO and influence eating through changes in intestinal vagal afferent activity. Further studies are necessary to identify the link between enterocyte FAO and vagal afferents and to examine the specificity and potential physiological relevance of such a mechanism.

We examined food intake in chronically maintained decerebrate rats in response to two antimetabolic drugs known to stimulate food intake, 2-mercaptoacetate (MA) and 2-deoxy-D-glucose (2DG). MA reduces fatty acid oxidation, and 2DG reduces glucose utilization. Because previous work has shown that insulin-induced hypoglycemia increases food intake in decerebrate rats, we predicted that 2DG would have this same effect. MA-induced feeding requires vagal sensory neurons that terminate in the hindbrain. Cholecystokinin-induced suppression of feeding, which likewise requires vagal sensory neurons, has been shown to suppress food intake in decerebrate rats. Therefore, we predicted that MA's effects on feeding would also persist in decerebrate rats. In our experiments, the test diet (40% milk, diluted with water) was infused intraorally through a chronic cheek fistula. We found that sham controls consumed 258% and 230% of their baseline milk intake in response to 2DG and MA, respectively. Decerebrates consumed 239% of their baseline milk intake in response to 2DG, but did not increase their intake in response to MA. Because decerebration separates the hindbrain from the forebrain, these results indicate that 2DG-induced glucoprivation is capable of acting within the hindbrain to activate fundamental reflex circuitry for consummatory feeding responses, as shown previously for hypoglycemia. In contrast, MA affects food consumption only after forebrain processing of MA-induced vagal afferent signals and in the presence of intact ascending and descending neural pathways.

We investigated the effect of beta-oxidation inhibition on the fat ingestive behavior of BALB/c mice. Intraperitoneal administration to mice of mercaptoacetate, an inhibitor of fatty acid oxidation, significantly suppressed intake of corn oil but not intake of sucrose solution or laboratory chow. To further examine the effect of mercaptoacetate on the acceptability of corn oil in the oral cavity, we examined short-term licking behavior. Mercaptoacetate significantly and specifically decreased the number of licks of corn oil within a 60-s period but did not affect those of a sucrose solution, a monosodium glutamate solution, or mineral oil. In contrast, the administration of 2-deoxyglucose, an inhibitor of glucose metabolism, did not affect the intake or short-term licking counts of any of the tasted solutions. These findings suggest that fat metabolism is involved in the mechanism underlying the oral acceptance of fat as an energy source.

This study tests the hypothesis that the metabolic and endocrine shift characterizing the phase II-phase III transition during prolonged fasting is related to a decrease in fatty acid (FA) oxidation. Changes in plasma concentrations of various metabolites and hormones and in lipolytic fluxes, as determined by continuous infusion of [2-(3)H]glycerol and [1-(14)C]palmitate, were examined in vivo in spontaneously fasting king penguins in the phase II status (large fat stores, protein sparing) before, during, and after treatment with mercaptoacetate (MA), an inhibitor of FA oxidation. MA induced a 7-fold decrease in plasma beta-hydroxybutyrate and a 2- to 2.5-fold increase in plasma nonesterified fatty acids (NEFA), glycerol, and triacylglycerols. MA also stimulated lipolytic fluxes, increasing the rate of appearance of NEFA and glycerol by 60-90%. This stimulation might be partly mediated by a doubling of circulating glucagon, with plasma insulin remaining unchanged. Plasma glucose level was unaffected by MA treatment. Plasma uric acid increased 4-fold, indicating a marked acceleration of body protein breakdown, possibly mediated by a 2.5-fold increase in circulating corticosterone. Strong similarities between these changes and those observed at the phase II-phase III transition in fasting penguins support the view that entrance into phase III, and especially the end of protein sparing, is related to decreased FA oxidation, rather than reduced NEFA availability. MA could be therefore a useful tool for understanding mechanisms underlying the phase II-phase III transition in spontaneously fasting birds and the associated stimulation of feeding behavior.

The effects of hypoxia/aglycemia on microvascular endothelial permeability were evaluated, and the second messenger systems and the cytoskeletal-junctional protein alterations in this response were also examined. Monolayers of human dermal microvascular endothelial cells on microcarrier beads were exposed to either thioglycolic acid (5 mM, an O(2) chelator), glucose-free medium, or both stresses together. Permeability measurements were performed over a 90-min time course. Although neither hypoxia alone nor aglycemia alone increased endothelial permeability significantly, the combination of both increased significantly as early as 15 min. Intracellular Ca(2+) measurements with fura 2-AM showed that hypoxia/aglycemia treatment increased Ca(2+) influx. To determine the second messengers involved in increased permeability, monolayers were incubated for 30 min with the cytosolic Ca(2+) scavenger 3,4, 5-trimethoxybenzoic acid 8-(diethylamino)octyl ester (TMB-8, 0.1 mM), a classical protein kinase C (PKC) blocker, Gö-6976 (10 nM), a cGMP-dependent protein kinase (PKG) antagonist, KT-5823 (0.5 microM), or the mitogen-activated protein (MAP) kinase inhibitor PD-98059 (20 microM). Hypoxia/aglycemia-mediated permeability changes were blocked by chelating cell Ca(2+), PKC blockade, PKG blockade, and by inhibiting p38 MAP kinase-1. Finally, changes in the binding of junctional proteins to the cytoskeleton under the same conditions were assessed. The concentrations of occludin and pan-reactive cadherin binding to the cytoskeleton were significantly decreased by only both stresses together. However, these effects were also blocked by pretreatment with TMB-8, Gö-6976, KT-5823 (not in occludin), and PD-98059. These data suggest that hypoxia/aglycemia-mediated endothelial permeability may occur through PKC, PKG, MAP kinase, and Ca(2+) related to dissociation of cadherin-actin and occludin-actin junctional bonds.

In former work, intraperitoneal injection of 2-mercaptoacetate (MA), an inhibitor of fatty acid oxidation, increased food intake in rats, which was attenuated by hepatic branch vagotomy, and intraportal injection of MA increased the discharge rate in hepatic vagal afferents. In the present study, we investigated, whether intraperitoneal injection or intraportal infusion of MA affects the hepatic membrane potential in rats in vivo. The liver cell membrane potential was measured in anesthetized Sprague-Dawley rats with the microelectrode technique. Intraperitoneal injection of MA at a dose of 800 micromol/kg body wt significantly decreased the hepatocyte membrane potential by 3.8 mV, whereas at a dose of 400 micromol/kg, the depolarization (1.5 mV) of the membrane was not significant. In another strain of Sprague-Dawley rats, however, MA (400 micromol/kg) produced a significant depolarization of the hepatocyte membrane 50 min (2.6 mV) and 2 h (2.9 mV) after intraperitoneal injection. Intraportal infusion of MA (400 micromol/kg) significantly depolarized the membrane 20 and 50 min after infusion by 3.3 and 4.1 mV, respectively. MA at a dose of 800 micromol/kg also depolarized the membrane (4.8 mV after 50 min). These findings in principle are consistent with the "potentiostatic" hypothesis, postulating a link between the hepatic membrane potential, afferent vagal activity, and the control of food intake.

Nitric oxide (NO) is known to be an important endogenous modulator of leukocyte-endothelial cell interactions within the microcirculation. We examined leukocyte rolling and adhesion under baseline conditions and following thrombin (0.25 U/ml) superfusion in the mesentery of wild-type, inducible NOS (iNOS)-deficient (-/-), neuronal NOS (nNOS) -/-, and endothelial cell NOS (ecNOS) -/- mice to further our understanding of NO and leukocyte function. Baseline leukocyte rolling (cells/min) was significantly elevated in both the nNOS -/- (30.0 +/- 4.0) and ecNOS -/- mice (67.0 +/- 12.0) compared with wild-type mice (11.0 +/- 1.4). In addition, baseline leukocyte adherence (cells/100 micrometers of vessel) was also significantly elevated in the nNOS -/- (5.2 +/- 1.0) and ecNOS -/- (13.0 +/- 1.3) compared with wild-type animals (1.3 +/- 0.5). Deficiency of iNOS had no effect on baseline leukocyte rolling or adhesion in the mesentery. Baseline surface expression of P-selectin was observed in 68.0 +/- 9.0% of intestinal venules in ecNOS -/- mice compared with 10.0 +/- 2.0% in wild-type mice. Additional studies demonstrated that administration of an anti-P-selectin monoclonal antibody (RB40. 34) or the soluble P-selectin ligand, PSGL-1, completely inhibited the increased rolling and firm adhesion response in nNOS -/- and ecNOS -/- mice. Transmigration of neutrophils into the peritoneum following thioglycollate injection was also significantly augmented in nNOS -/- and ecNOS -/- mice. These studies clearly indicate the NO derived from both nNOS and ecNOS is critical in the regulation of leukocyte-endothelial cell interactions.

The present studies examined the development of ingestive responsiveness to blockade of fatty acid oxidation in rat pups using 2-mercaptoacetate (MA), an inhibitor of mitochondrial acyl-coenzyme A dehydrogenases, or methyl palmoxirate (MP), an inhibitor of carnitine palmitoyltransferase I (CPT-I). Rat pups aged 6, 9, 12, or 15 days of age received an intraperitoneal injection of 0, 100, 200, 400, or 800 mumol/kg MA, and intake of a commercial half-and-half or 15% glucose diet from the floor of test containers was assessed in a 30-min test beginning 1 h after administration of MA. The results demonstrate that, although no dose of MA affected intake of either diet in pups 9 days or younger, low doses of MA increased intake and the highest dose suppressed intake of both diets in pups 12 days of age or older. Physiological measurements indicated that levels of beta-hydroxybutyrate were significantly lower following doses of 400 or 800 mumol/kg MA in 9-, 12-, and 15-day-old pups and that gastric emptying was inhibited in 12 and 15 day olds by 800 mumol/kg MA. Intake of a commercial half-and-half diet from the floor of test containers was also assessed in 12- to 18-day-old rat pups 6.5 h after they received a gavage load of 0, 1.25, 2.5, 5, or 10 mg/kg MP. Unlike MA, MP did not increase intake of a commercial half-and-half diet in rat pups 12 or 15-18 days of age; instead, the highest dose of MP suppressed intake in 15- to 18-day-old pups. The failure of MP to enhance intake in pups at the ages tested is likely related to composition of dam's milk; rat milk is high in medium-chain fatty acids that do not require CPT-I for entry into mitochondria. Thus it is likely that MP does not significantly block fatty acid oxidation in pups at the ages tested. On the other hand, blockade of fatty acid oxidation produced by MA significantly affects intake by 12 days of age, suggesting it may be the first metabolic signal that influences intake in rat pups.

Because dissection of the common hepatic vagus branch attenuated the feeding response to intraperitoneal injection of mercaptoacetate (MA), an inhibitor of fatty acid oxidation, in rats fed a fat-enriched diet (18% fat), the effect of MA on the discharge rate in afferents of the common hepatic vagus branch was investigated. Intraportal infusion of the Na salt of MA (200, 400, and 800 mumol/kg) in rats adapted to the 18% fat diet dose dependently increased the discharge rate in afferents of the common hepatic vagus branch, whereas NaCl and the Na salt of the structurally related compound 2-mercaptopropionate had no effect. The lowest dose of MA yielding a significant increase in the discharge rate was 400 mumol/kg. This agrees with the dose dependence of the feeding response to MA. These findings are consistent with the notion that hepatic fatty acid oxidation controls food intake by modulating the discharge rate of vagal afferents.

Because it is commonly assumed that the major role of visceral afferents in food intake control is to terminate meals by carrying negative-feedback signals to the brain, we hypothesized that overconsumption should occur in rats with chemically lesioned visceral afferents if they were presented with an unfamiliar diet. Adult male Sprague-Dawley (SD) rats were treated with multiple doses of capsaicin or vehicle as a control. Five weeks later, a series of 3-h feeding tests after 24-h deprivation was carried out, first with chow and then with either a solid (vegetable shortening) or liquid (Ensure) unfamiliar high-fat diet. Both groups consumed similar amounts of their powdered chow maintenance diet, but capsaicin-treated rats consumed at least 50% more of either high-fat diet than vehicle controls (P < 0.01) at the beginning of the first trial. During second and third trials with the now-familiar high-fat diet, intake was no longer significantly different between the two groups, suggesting rapid engagement of redundant control mechanisms. These results support a role of capsaicin-sensitive visceral afferents in providing negative feedback for early meal termination during the ingestion of unfamiliar diets.

Siberian hamsters kept in long photoperiods (16 h light/day) at 10 degrees C do not display torpor when provided with food ad libitum but do reduce their body temperatures (Tb) from 37 degrees C to as low as 15 degrees C for several hours each day in response to food restriction. Female hamsters maintained in a long photoperiod and fed ad libitum were injected with 2-deoxy-D-glucose (2-DG), a glucose analogue that reduces cellular glucose oxidation, or mercaptoacetate (MA), a drug that disrupts fatty acid oxidation. Dosages of 2-DG in excess of 1,500 mg/kg body mass reliably induced torpor with latencies of approximately 50 min from time of injection to a decrease in Tb below 30 degrees C; 79% of females displayed torpor at a dosage of 2,500 mg/kg. MA was uniformly ineffective in inducing torpor and did not increase incidence of torpor when combined with 2-DG treatment or food restriction. Decreased availability of glucose may be the major metabolic signal for inducing torpor in Siberian hamsters; availability of fatty acids appears to play little if any role in regulating this behavior.

Food intake is reduced during parenteral nutrition (PN) proportionally to the amount of calories or composition of the solution infused. The relative importance of infused glucose and lipid, 50 and 30% of PN kilocalories, respectively, in reducing food intake during PN was examined. Glycolysis, fatty acid oxidation, or both were acutely disrupted with 2-deoxy-D-glucose (2-DG) and mercaptoacetate (MA). Rats receiving intravenous infusions of saline or a PN solution providing 100% of total daily calories (PN-100) received a single intraperitoneal injection of saline, 2-DG, and/or MA during the early light phase. 2-DG (1.4 or 2.2 mmol/kg) did not initiate feeding in PN-100 rats, although hyperglycemia was evident in all rats 1 h after 2-DG. Food intake of PN-100 rats after MA (0.4 mmol/kg) was approximately 50% that of control rats. When 2-DG (1.4 mmol/kg) and MA (0.4 mmol/kg) were administered concomitantly, PN-100 and control rats consumed the same amount of food. During PN-100, rats appeared to be more sensitive to losing metabolic energy derived from lipid than from glucose.

During parenteral nutrition (PN) glucoprivic-induced feeding appeared to be neutralized by the oxidation of infused fatty acids. With the use of a latin-square design, the feeding response to 2-deoxy-D-glucose (2-DG) and/or 2-mercaptoacetate (MA) was evaluated in male Sprague-Dawley rats with hepatic branch vagotomy (HV) or sham operations (SO). Rats received continuous infusions of 0.9% saline or PN providing 100% of daily caloric needs (PN-100) for four consecutive days. During PN-100, food intake was stimulated by 2-DG in HV rats and when fatty acid oxidation was simultaneously inhibited by MA. 2-DG-induced hyperglycemia was apparent under all conditions. Lipoprivic-induced feeding and increased plasma free fatty acid concentrations were absent in HV rats, whether MA was administered alone or with 2-DG. The feeding response to glucoprivic challenges is influenced by the relative availability of alternate energy sources. The lack of feeding response to 2-DG during PN-100 is mediated by vagal input of hepatic fatty acid oxidation status.

Lesions of the area postrema/nucleus of the solitary tract (AP/NTS) region abolish feeding induced by mercaptoacetate (MA) and 2-deoxy-D-glucose (2DG), metabolic inhibitors that selectively impair fatty acid and glucose utilization, respectively. Because the AP/NTS region is important for both MA- and 2DG-induced feeding, the present experiment investigated the involvement of the lateral parabrachial nucleus (1PBN), which is innervated by AP/NTS neurons, in these feeding responses. Electrolytic and ibotenic acid lesions were directed at the entire parabrachial nucleus or at specific lateral parabrachial subnuclei. Rats with electrolytic lesions were tested for feeding in response to 0.9% NaCl (subcutaneous or intraperitoneal), MA (400, 600, and 800 mumol/kg ip), and 2DG (100 and 200 mg/kg sc). Ibotenate-lesioned rats were tested with NaCl and MA only. Lesions were verified either by cresyl violet staining or by glial fibrillary acidic protein immunohistochemistry. Bilateral destruction of the 1PBN severely impaired or abolished MA-induced feeding. Cell bodies important for MA-induced feeding appear to be localized in the dorsal-central 1PBN subnuclear area, because both electrolytic and cytotoxin microlesions centered in this area abolished feeding in response to MA. Fibers of passage important for MA-induced feeding appear to pass through the external and superior 1PBN because electrolytic but not cytotoxin lesions of these subnuclei disrupted the feeding response. In contrast, 2DG-induced feeding did not differ significantly from sham-lesioned controls in any of the 1PBN lesion groups. These results indicate that 2DG and MA stimulate feeding by activating separate central neural pathways and, perhaps, distinct metabolic controls of food intake.

We examined the possibility that brain glucose or ketone availability may control suckling or precocious feeding in the preweanling rat. Brain glucoprivation induced by 5-thio-D-glucose injection into the 4th ventricle did not increase feeding on orally infused milk until 30 days of age, although hyperglycemia was evoked as early as 9 days by the same treatment. Plasma ketone levels varied with suckling status, but pharmacological blockade of hepatic free fatty acid oxidation, which restricts ketone availability (ketoprivation), failed to increase suckling. Because the suckling rat can switch energy substrates under nutritional duress, we combined glucoprivation and ketoprivation. Feeding was suppressed, and suckling was not affected. Finally, we injected ketones into the 3rd brain ventricle and found that they increased feeding. Thus, in contrast to the adult rat, reduced glucose or ketone utilization by the brain does not increase food intake in the preweanling, but increased circulating and brain ketone concentrations may arouse feeding.

Lyophilized bovine, porcine, and human choroid plexuses contain .02-.09 U of antidiuretic activity per milligram. The antidiuretic factor in bovine choroid plexus was concentrated 100 times by extraction with acetic acid, fractional precipitation with acetone and ethyl ether, gel filtration, and paper chromatography. Resulting choroid plexus fraction IIgammaB2 was eluted from Sephadex G-25 in position corresponding to molecular weight between 750 and 3,500; its antidiuretic activity was destroyed by trypsin, performic acid, and thioglycollic acid, but was not affected by leucine aminopeptidase, carboxypeptidase A or B, or cyanogen bromide. HgammaB2 possesses antidiuretic, pressor, and oxytocic potencies (measured in anesthetized-hydrated rat, anesthetized rat, and isolated rat uterus, respectively) of 1.9, 0.5, and 0.1 U/mg, respectively.

To assess the contribution of visceral sensory neurons to feeding induced by blockade of glucose and fatty acid metabolism, adult rats were anesthetized and treated systemically with capsaicin, a toxin that destroys fine-diameter unmyelinated primary sensory neurons, including many visceral sensory neurons. Rats were maintained on a fat-supplemented diet throughout experimentation. For feeding tests, intake of this diet was measured hourly for 6 h after systemic blockade of fatty acid or glucose utilization with mercaptoacetate (MA) or 2-deoxy-D-glucose (2-DG), respectively, after simultaneous administration of MA and 2-DG and after saline injection. 2-DG stimulated a dose-related feeding response that was similar in magnitude in both capsaicin and vehicle-treated rats. MA also stimulated a dose-related feeding response in vehicle-treated rats. However, capsaicin-treated rats did not eat in response to MA. In addition, 2-DG and MA were additive in their stimulation of feeding in vehicle-treated controls, but capsaicin-treated rats ate the same amount after 2-DG plus MA as they did in response to 2-DG alone. Thus glucoprivation and lipoprivation activate anatomically and chemically distinct receptors for the metabolic control of feeding.

The role of fatty acid oxidation in the control of food intake was studied using mercaptoacetate (MA), an inhibitor of fatty acid oxidation. Food intake, plasma free fatty acids (FFA) and ketone bodies, and blood glucose were measured. Rats were fed either a low-fat (LF, 3.33% fat) or a medium-fat (MF, 18% fat) diet. At the onset of the dark phase of the lighting cycle, MA did not affect food intake in LF rats but increased it 74% in MF rats in comparison to control. Four hours after the injection the effect of MA on food intake disappeared. In the middle of the bright phase of the lighting cycle, MA increased food intake in MF rats approximately 120% up to 6 h postinjection. After MA, plasma FFA concentration was elevated, and plasma 3-hydroxybutyrate concentration was lowered, indicating that fatty acid oxidation had been successfully reduced. MA did not affect blood glucose. These results indicate fatty acid oxidation is involved in the control of food intake, at least when the dietary fat level is relatively high.