Physiological measurement of luminal stirring in perfused rat jejunum

Poor stirring of intestinal contents yields a preepithelial diffusion barrier that is thought to be the rate-limiting step in absorption of many compounds. In many previous studies, the resistance of this barrier is equal to an unstirred water layer of 300-800 micron. Using three probes, CO, glucose, and [14C]warfarin, we measured the preepithelial resistance in a 30-cm segment in rats that were 1) conscious, 2) anesthetized with pentobarbital sodium, or 3) anesthetized and laparotomized. Measurements with each of the probes showed that the maximal preepithelial resistance in conscious rats was equivalent to an unstirred layer of only approximately 100 micron. Anesthesia roughly doubled this resistance, and anesthesia and laparotomy caused a sixfold increase (unstirred layer of approximately 600 micron). We conclude that the luminal stirring is much more efficient than previously has been appreciated. The very thick jejunal unstirred layers reported previously (300-800 micron) reflect the results of studies performed under nonphysiological conditions or studies employing inappropriate techniques to measure luminal stirring.

Behavioral effects of corticotropin-releasing factor: localization and characterization of central effects

Corticotropin-releasing factor (CRF) has potent behavioral effects when administered intracerebroventricularly to rats. CRF and its receptors are found in an uneven distribution in the brain. In an effort to localize the site of the anorectic effect of CRF, exogenous CRF or saline was injected into cannulas directed toward the paraventricular hypothalamic nucleus (PVN), lateral hypothalamus, ventromedial hypothalamus, globus pallidus, or striatum of rats. CRF decreased food intake only when injected into the PVN. In subsequent experiments PVN injections of CRF were shown to (1) increase grooming and movement; (2) not induce a conditioned taste aversion to saccharin in a single bottle test; and (3) inhibit the increase in feeding induced by injections of norepinephrine into the PVN. These results suggest that CRF induces not only anorexia, but also increased movement and grooming by action in the PVN.

Effect of bombesin and gastrin-releasing peptide on canine sphincter of Oddi

This study reports the effects of bombesin and gastrin-releasing peptide (GRP) on the canine sphincter of Oddi using a method that allows repeated cannulation of the biliary sphincter in the unanesthetized animal through a Thomas cannula placed opposite the biliary papilla. Immediately after intravenous administration of bombesin or GRP, phasic sphincter contractions disappeared, basal sphincter pressures fell, and common bile duct pressures rose. Because bombesin releases cholecystokinin (CCK) and CCK resulted in a similar pattern to that of bombesin, the bombesin effect on the sphincter of Oddi may have been secondary to CCK's effect on the sphincter. To test if the bombesin effect on the sphincter of Oddi was due to the release of CCK, we blocked CCK release by administration of somatostatin, having first established that somatostatin blocked endogenous CCK release in our animal model by use of an intraduodenal infusion of lipid. Exogenous administration of bombesin failed to alter sphincter of Oddi or common bile duct pressures in dogs treated with somatostatin. Somatostatin did not, however, block CCK's effect on gallbladder contraction, since exogenous administration of CCK after somatostatin injection resulted in the pressure changes in the biliary tree typical of CCK-induced gallbladder contraction. Thus bombesin administration appears to result in sphincter relaxation and gallbladder contraction by the release of endogenous CCK rather than by a direct effect. The increase in common bile duct pressures was due to gallbladder contraction, since this rise in pressure was abolished by cholecystectomy. The peptide effect on sphincter contraction and basal sphincter pressure were unaffected by cholecystectomy.

Effect of morphine and nalmefene on energy balance in diabetic and non-diabetic rats

Male rats made diabetic by intravenous injection of streptozotocin were used to evaluate the effect of the diabetic state on morphine- and nalmefene-induced changes in food intake and body weight. Morphine increased 4 hour food intake in non-diabetic rats after an initial injection, but increased intake in diabetic rats only after repeated injections. Unlike short term measurements, morphine decreased food intake when measured over 24 or more hours in both groups. Chronic injection of morphine decreased body weight only in non-diabetic rats. Feed efficiency data suggest that morphine had a more potent effect on energy balance in the non-diabetic rats. The opioid antagonist, nalmefene, did not alter body weight in either group and only altered food intake in the diabetic animals. These data are in concert with other reports indicating that the diabetic state renders animals less responsive to the effects of morphine on nociception and smooth muscle contraction.

Mutational specificity of benzo[a]pyrene diolepoxide in monkey cells

Benzo[a]pyrene diolepoxide (BPDE) is thought to be the major mutagenic and carcinogenic intermediate in benzo[a]pyrene metabolism in mammalian cells. In order to test the mutagenic specificity of this compound in mammalian cells, we have used the pZ189 shuttle vector system to identify and analyze point mutations induced when DNA treated in vitro with BPDE is replicated in monkey cells. We find that point mutations occur almost exclusively at G.C base pairs; G.C----T.A and G.C----C.G transversions and single base pair deletions occur most frequently. This pattern is consistent with the known preferential covalent binding of BPDE to G residues.

Effects of dietary fish oil on lung phospholipid fatty acid composition and intrinsic pulmonary vascular reactivity

A fish oil diet has been shown to lower systemic blood pressure in man and alter vascular reactivity to exogenous noradrenaline in man and rats. The effects of a fish oil diet on the vascular reactivity of the pulmonary circulation have not been assessed. The effect of dietary lipid composition on pulmonary artery pressure and vascular reactivity of 30 adult male Sprague-Dawley rats (250-300 g) was assessed in vivo (n = 9) and in the isolated perfused lung (n = 21). Isocaloric diets containing 20% lipid (% by weight) as fish oil, corn oil, or lard were given in unlimited quantities to the rats. After one month of the diet, pulmonary vascular reactivity to angiotensin II (0.15 micrograms) and hypoxia (fractional inspired oxygen 0.025) were assessed in the isolated perfused rat lung. The haemodynamic effects of the diet on resting normoxic pulmonary artery pressure (in vivo) were assessed in chloralose anaesthetised rats. The fish oil diet appreciably increased the content of eicosapentaenoic acid (C20:5) and docosahexaenoic acid (C22:6) in lung phospholipids but had no effect on pulmonary vascular reactivity. The arachidonic acid (C20:4) content of the lung was considerably decreased. Platelet counts were lower in the rats fed fish oil. The study indicates that a fish oil diet does not alter acute intrinsic pulmonary vascular reactivity despite pronounced changes in lung phospholipid fatty acid profile.

Mitogenic and antimitogenic transforming growth factors secreted by adenovirus 2- and simian virus 40-transformed hamster cells: possible roles in promoting tumorigenesis

Adenovirus 2 (Ad2)- and simian virus 40 (SV40)-transformed hamster embryo cells differ markedly in a number of phenotypic properties including their potential for inducing tumors in hamsters. Both Ad2- and SV40-transformed cells are immortalized and readily induce tumors in immunoincompetent newborn syngeneic hamsters, but only SV40-transformed cells are highly oncogenic in both adult syngeneic and allogeneic immunocompetent hamsters. The reasons for the difference in the oncogenic potential of the Ad2- and SV40-transformed phenotypes remain elusive. However, recent studies with transforming growth factors (TGFs) indicate that these factors play an important role in determining many phenotypic characteristics of transformed cells. To determine whether TGFs secreted by Ad2- and SV40-transformed hamster embryo cells differ, we have examined the ability of media conditioned by these two transformed cell phenotypes to modulate thymidine uptake in quiescent, untransformed cells. We found that both transformed phenotypes secrete very similar TGF alpha-like mitogenic factors which inhibit binding of 125I-labeled epidermal growth factor to its receptor. Our results also show that SV40-transformed cells, but not Ad2-transformed cells, secrete a powerful mitogenic inhibitor (MI). The MI secreted by SV40-transformed cells is inhibitory for several transformed and untransformed cell types and exerts a cytostatic, not cytolytic, action on untransformed primary hamster embryo cells. MI elutes from size exclusion high-performance liquid chromatography columns with a molecular weight of 24,000. Although MI has about the same molecular weight as TGF beta, it differs from TGF beta in two important respects: it is heat labile and it has a different target specificity for antimitogenic activity. The MI secreted by SV40-transformed cells also inhibits thymidine uptake by concanavalin A-stimulated spleen lymphocytes. This finding suggests that MI might contribute to the extreme oncogenicity of SV40-transformed cells by inhibiting mobilization of immune effector cells at the site of tumor cell proliferation.

Test of models for the sequence specificity of UV-induced mutations in mammalian cells

We have used mathematical modeling and statistical analysis to examine the correlation between UV-induced DNA damage and resulting base-substitution mutations in mammalian cells. The frequency and site specificity of UV-induced photoproducts in the supF gene of the pZ189 shuttle vector plasmid were compared with the frequency and site specificity of base-substitution mutations induced upon passage of the UV-irradiated vector in monkey cells. The hypothesis that the observed mutational spectrum is due to a preferential insertion of adenosine opposite UV photoproducts in the DNA template was found to best explain the mutational data. Models in which it was postulated that only (6-4) photoproducts, and not cyclobutane dimers, are mutagenic, or that the relative frequency of photoproduct formation does not influence mutation frequencies, fit the data much less well. This analysis demonstrates that molecular mechanisms of mutagenesis in mammalian cells can be deduced from mutational data obtained with a shuttle vector system.

Attenuation of the plasma prolactin response to restraint stress after acute and chronic administration of nicotine to rats

We have previously shown that a single dose of nicotine elevates plasma adrenocorticotropin (ACTH) levels in rats and has a biphasic effect on plasma prolactin (PRL). The stimulatory effect of nicotine on these stress responsive hormones desensitizes after a single injection of nicotine. Continuous exposure to nicotine also induces tolerance to its locomotor depressive and hypothermic effects, which have been associated with an increase of central [3H]nicotine binding. Thus, the acute and chronic administration of nicotine might induce changes in central nicotinic cholinergic circuits that affect the ACTH and PRL responses to stress. In the present study, a single dose of nicotine (0.75-3.0 mg/kg b.wt.) significantly inhibited the elevation of plasma PRL due to restraint stress initiated 60 min afterward. Five injections of nicotine during 1 day produced a similar attenuation of the PRL response to restraint stress but neither of these paradigms affected ACTH. In contrast, intermittent delivery of nicotine for 7 days failed to affect the PRL response to restraint stress; however, after withholding nicotine for 14 hr, high dose nicotine attenuated the PRL response to stress, whereas low dose nicotine remained ineffective. On the other hand, administration of the same schedule of low dose nicotine did significantly diminish the expected release of PRL in response to a final injection of nicotine (0.5-2.0 mg/kg b.wt.) in unstressed animals. In summary, a single dose or 5 doses of nicotine in 1 day attenuated the PRL response to restraint stress, whereas, after chronic administration, this effect was lost.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of kappa opiate agonists, cholecystokinin and bombesin on intake of diets varying in carbohydrate-to-fat ratio in rats

Effects of the dietary carbohydrate-to-fat ratio on opiate-stimulated eating and on naloxone-, cholecystokinin- and bombesin-suppressed eating were examined. Rats were fed either a high carbohydrate (cornstarch) diet (68% of energy from carbohydrate and 12% from fat), an intermediate diet (40% carbohydrate and 40% fat) or a high fat (corn oil and lard) diet (3% carbohydrate and 77% fat). Other rats self-selected from the high carbohydrate and high fat diets. Subcutaneous administration of naloxone, an opiate antagonist, generally suppressed intake of the high fat diet to a greater extent than intake of the high carbohydrate diet. Neither cholecystokinin octapeptide nor bombesin (administered intraperitoneally) exerted preferential suppression of fat intake. The opiate agonists ketocyclazocine and butorphanol tartrate administered subcutaneously at 1000 h preferentially, although not exclusively, stimulated intake of the high fat diet in a dose-dependent manner during the 6-h feeding trial. Repeated daily subcutaneous injections of butorphanol tartrate caused rats to consume more than 50% of their daily intake during the 6-h period postinjection; intake during the normal night feeding period was suppressed to maintain total daily intake equal to that of vehicle-injected rats. We conclude that stimulation of the opioid feeding system contributes to the overeating often associated with consumption of a high fat diet.

Effects of beta-chlornaltrexamine on food intake, body weight and opioid-induced feeding

beta-Chlornaltrexamine (beta-CNA) is a non-equilibrium opioid receptor antagonist which alkylates and inactivates opioid receptors. Because opioid peptides are thought to contribute to the regulation of food intake, we examined the effects of intracerebroventricular (icv) injections of beta-CNA on the food intake and body weight of male rats. We also tested the ability of beta-CNA to block food intake stimulated by selective agonists of kappa, mu and delta opioid receptors: dynorphin A2 (DYN), Tyr-D-Ala-Gly-(Me)Phe-Gly-ol (DAGO), and [(D-Ser2,Leu5]-enkephalin-Thr6 (DSLET). Treatment with beta-CNA caused a long-term (2-4 days) reduction in daily food intake and a concomitant reduction in body weight. An additional experiment indicated that the weight loss after beta-CNA treatment could be completely accounted for by the reduction in intake. beta-CNA treatment also abolished or greatly attenuated the feeding effects of DAGO, DSLET and DYN, even when these peptides were tested 26 hours after beta-CNA administration. The long duration of the effects of beta-CNA suggests that this compound will be a useful pharmacological tool in further study of the opioid feeding system.

Effects of xylitol on gastric emptying and food intake

We studied the effects of xylitol, the pentose-sugar alcohol, on gastric emptying of the solid-food component of a complex meal. Gastric emptying was measured in human volunteers by utilizing a standardized radiolabeled scrambled-egg meal. After ingestion of 25 g xylitol, gastric emptying was markedly prolonged (T-1/2 58 +/- 5 min control vs 91 +/- 7 min after xylitol [p less than 0.01]). Since delayed gastric emptying may affect food intake, we evaluated the effects of xylitol on calorie intake. Food intake after oral preloading with water resulted in intake of 920 +/- 60 kcal vs 690 +/- 45 kcal after 25 g of xylitol. In contrast, a preload of glucose, fructose, or sucrose failed to suppress food intake. Although xylitol decreased food intake and also delayed gastric emptying, these effects may be unrelated. Our data suggest a role for xylitol as a potentially important agent in dietary control.

Deletion mutations in the small t antigen gene alter the tissue specificity of tumors induced by simian virus 40

Subcutaneous injection of wild-type simian virus 40 into Syrian hamsters normally induces fibrosarcomas at the injection site. We showed that subcutaneous injection of three different small t deletion mutants (dl884, dl883, and dl890) led to the formation of abdominal reticulum cell sarcomas (lymphomas) in about 15% of the animals bearing tumors. The remainder of the tumors were fibrosarcomas occurring with prolonged latencies at the site of injection. We postulated that, in the absence of an active small t protein, which is thought to have cell growth-promoting properties, the mutant virus preferentially transforms rapidly proliferating lymphoid cells.

Effect of neuropeptide Y on ingestive behaviors in the rat

Neuropeptide Y (NPY) is a potent stimulator of food and water intake in rats. NPY still increases food intake even after a 2-h delay in access to food after central injection. When two injections of NPY are given 2 h apart, the second injection produced a substantial increase in food intake. This suggests that tolerance to the NPY effect does not develop after a single injection of NPY. NPY increases moving and exploration in the absence of food when rats are in their home environment but not when tested in a novel environment. Following administration of NPY, rats preferred a high-carbohydrate diet over a high-fat or high-protein diet. Microinjections of NPY showed that active sites included the anterior ventromedial nucleus, paraventricular nucleus of the hypothalamus, and the posterior lateral hypothalamus. NPY was neither additive nor synergistic when coadministered with norepinephrine. Whereas norepinephrine-induced feeding was inhibited by adrenalectomy and vagotomy, these maneuvers had no effect on NPY-induced food intake. This provides further evidence that NPY does not exert its effects on food intake through an alpha-adrenergic mechanism. The effects of NPY on food intake were attenuated by peripherally administered bombesin and centrally administered corticotropin-releasing factor and calcitonin. Cholecystokinin failed to inhibit NPY-induced feeding. NPY did not alter circulating glucose levels. These studies provide further insights into the role of NPY as a stimulator of ingestive behaviors.

H2 excretion after ingestion of complex carbohydrates

Malabsorption of fermentable material in a variety of foods was assessed by measurement of breath H2 excretion. Breath H2 increased well above that observed in fasting subjects after ingestion of 100 g of carbohydrate in oats, whole wheat, potatoes, corn, and baked beans. Rice caused only a minimal increase in H2 excretion and hamburger was associated with no increase. We estimated the malabsorption of fermentable material by comparing the H2 excretion for 9 h after ingestion of various complex carbohydrates with that after 10 g of lactulose. The mean malabsorption of fermented material after 100-g carbohydrate meals was 20 g for baked beans; 7-10 g for wheat, oats, potatoes, and corn; and 0.9 g for rice. Whole oats or whole wheat resulted in 2-5 times more H2 than did the refined flours. As purified fiber appeared to be a poor substrate for H2 production by fecal homogenates, we conclude that most complex carbohydrates, with the exception of rice, contain a good deal of fermentable material that escapes small bowel absorption and it seems likely that this fermentable material is malabsorbed starch.

Glucagon stimulation of brown adipose tissue growth and thermogenesis

Despite long-standing observations of a whole-body thermogenic effect of glucagon, the role of glucagon in activating thermogenesis in brown adipose tissue has not often been studied. We investigated the ability of administered glucagon to produce alterations in brown adipose tissue similar to changes produced by accepted stimuli of brown fat activity: cold, norepinephrine, and overfeeding. Eighteen days of glucagon injections (1 mg/kg) to male Sprague-Dawley rats produced, relative to saline-injected controls, decreases in feed efficiency and increases in brown adipose tissue weight, protein content, DNA content, and mitochondrial mass as reflected in cytochrome oxidase activity. The observed changes were similar, though of lesser magnitude, to changes produced in these same parameters induced by administration of norepinephrine (250 micrograms/kg) for a positive control group. Four days of glucagon administration (1 mg/kg) produced increases in specific activity of cytochrome oxidase and lipoprotein lipase. After 8 days of glucagon administration, changes in whole-pad activity similar to those seen with 18 days of administration were present. Glucagon also increased whole-pad lipoprotein lipase activity after 4 and 8 days. Surgically denervated interscapular brown adipose tissue retained its ability to respond to exogenous glucagon, though the magnitude of the response was diminished. Guanosine 5'-diphosphate (GDP) binding to brown adipose tissue mitochondria was measured as an assessment of functional state after 5 days of glucagon (1 mg/kg). There was an increase in GDP binding relative to controls whether expressed as picomoles per milligram mitochondrial protein or nanomoles per pad.(ABSTRACT TRUNCATED AT 250 WORDS)

High-dose naltrexone therapy and dietary counseling for obesity

There is considerable evidence that antagonism of the endogenous opioids will suppress food intake in a variety of animal species. The authors report a double-blind, placebo-controlled trial of the long-acting, orally active narcotic antagonist naltrexone in the promotion of weight loss in obese male subjects who were also undergoing dietary counseling for weight reduction. Subjects received medication (naltrexone, 300 mg/day or placebo) for 8 weeks following an initial 2-week single-blind placebo phase. The results failed to demonstrate an advantage for the active drug. However, the naltrexone was associated with hepatotoxicity when used at this dosage in this population.

Unique pattern of point mutations arising after gene transfer into mammalian cells

We have used a simian virus 40 (SV40)-based shuttle vector, pZ189, to analyze the sequence specificity of spontaneous point mutations that arise after transfection of this vector into monkey cells. The majority of the mutants which we studied had multiple base substitutions (mostly G-C----A-T transitions and G-C----T-A transversions) within the 160-bp region sequenced. Almost all of the mutations occurred in the right-hand G-C bp of one of the two following sequences, 5'-TC-3':3'-AG-5' or 5'-CC-3':3'-GG-5'. We postulate that these mutations result from DNA replication infidelity occurring during repair of the transfected DNA which has been damaged by cellular nucleases. The sequence specificity of the mutations suggests an effect of the following nucleotide on misincorporation wherein A (or less frequently T) is preferentially misincorporated opposite C when the next nucleotide inserted is A (or less frequently G). Our results support the utility of the shuttle vector as a model in studies on gene transfer and document the extreme plasticity of DNA transfected into mammalian cells.

The effect of naloxone on nocturnal food intake in female and male rats

Previous studies have shown that estradiol and progesterone can alter the response of female rats to naloxone. For example, ovariectomized rats receiving estradiol were found to be less sensitive to the anorexic effect of naloxone than ovariectomized rats receiving oil (vehicle) or progesterone. In the present paper, we evaluated the effect of naloxone on nocturnal food intake in female rats during each stage of the estrous cycle to determine whether changing levels of gonadal hormones in intact female rats would affect their response to naloxone. To evaluate the role testosterone might play in modulating the male rat's feeding response to naloxone we studied the effect of peripherally administered naloxone (0.1, 1.0 and 10 mg/kg) on nocturnal food intake of intact, castrate and castrate + testosterone propionate male rats. During late metestrus, diestrus and proestrus, female rats decreased nocturnal food intake following the administration of naloxone (1.0 and 10 mg/kg) SC (p less than 0.05). During estrus, female rats failed to decrease food intake following any of the doses of naloxone administered. The male rat's response to naloxone does not appear to be altered by the presence or absence of testosterone. Thus, the level of estradiol and progesterone at different stages of the estrous cycle may affect the female rat's response to the satiety effect of naloxone.

The effect of cholecystokinin on food intake in gonadectomized and intact rats: the influence of sex hormones

Cholecystokinin (CCK) suppresses food intake in a number of animal models, but appears to be less effective in females [5,23]. We studied the effect of CCK on food intake in female rats on each day of the estrous cycle. In addition, we evaluated the effect of sex hormones on food intake in intact and castrate male rats which had been injected daily with oil or testosterone propionate + oil and ovariectomized female rats injected daily with oil, estradiol, progesterone or estradiol + progesterone. Food intake in intact, castrate and castrate + testosterone replaced male rats was decreased by CCK (5, 10 and 20 micrograms/kg) IP (p less than 0.05). Food intake was decreased by CCK (20 micrograms/kg) only during diestrous and metestrus in cycling female rats. During metestrus, a period of low estradiol in the presence of progesterone, food intake was also suppressed by CCK (5 and 10 micrograms/kg). CCK failed to decrease food intake in ovariectomized females receiving oil, estradiol and estradiol + progesterone. However, animals receiving progesterone alone responded to the high dose of CCK (20 micrograms/kg). Our data suggest that the effect of CCK on food intake in female rats may be dependent on the presence of progesterone. The lack of sensitivity to CCK during proestrus and estrus suggests that estradiol may be modulating the "permissive" action of progesterone on CCK's satiety effect.

Naloxone but not CCK-8 may attenuate binge-eating behavior in patients with the bulimia syndrome

We undertook a study to see if putative anorectic agents could attenuate binge eating episodes in bulimic patients. Bolus intravenous administration, followed by continuous intravenous infusion of naloxone, resulted in a significant decrease in the amount of food consumed during binge-eating episodes, whereas bolus followed by continuous intravenous infusion of CCK-8 failed to significantly suppress binge eating behavior. These results suggest that the endogenous opioid system is involved in the maintenance of binge eating behavior in patients with bulimia.

Tumorigenicity of hamster and mouse cells transformed by adenovirus types 2 and 5 is not influenced by the level of class I major histocompatibility antigens expressed on the cells

Inbred hamster and mouse cells transformed by the nononcogenic adenovirus (Ad) serotypes, Ad2 and Ad5, are nontumorigenic in syngeneic adult animals, while cells from these species transformed by the highly oncogenic Ad12 are tumorigenic in such rodents. By immunoprecipitation and flow cytometry, cells from four of six Ad2- and Ad5-transformed hamster and mouse lines expressed high levels of cell-surface class I major histocompatibility complex (MHC) antigens, while cells from two of these six lines expressed low levels of cell-surface class I MHC antigens. The levels of class I MHC proteins expressed by cells from these latter two lines were comparable to the levels of cell-surface class I MHC proteins expressed by cells from Ad12-transformed hamster and mouse lines. Moreover, an Ad2-transformed line that had become highly oncogenic after in vivo adaptation showed the same high level of MHC expression as the nononcogenic parent. The amounts of class I mRNA, analyzed by RNA blotting, were, in general, consistent with the levels of class I antigens expressed on the surfaces of these cells. These results indicate that there is no correlation between the tumorigenicity in immunocompetent syngeneic adult rodents of Ad2- and Ad5-transformed hamster and mouse cells and the level of class I MHC antigens expressed on the surfaces of these cells. Thus, the expression of different levels of class I MHC proteins does not seem to explain the differences in the oncogenicity between nononcogenic and highly oncogenic human Ad serotypes.

Insulin and metabolic efficiency in rats. I. Effects of sucrose feeding and BAT axotomy

The role of insulin and brown adipose tissue (BAT) thermogenesis in metabolic efficiency (ME, the efficiency of body wt gain) was examined in rats with varied basal insulin status. Long-lasting insulin was administered using a protocol that did not alter food intake, yet increased ME in both groups. Half the rats were fed sucrose to stimulate BAT growth and thermogenesis. Insulin overrode the exaggerated decrease in ME in sucrose-fed diabetics, with only partial attenuation in controls. Interscapular BAT (IBAT) lipoprotein lipase activity was decreased in diabetic rats, restored by insulin treatment, and not affected in controls. Sucrose-fed diabetics and controls had their IBAT sham or bilaterally surgically denervated. Insulin decreased the thermogenic potential of BAT [cytochrome oxidase activity (COA)] in intact controls and diabetics; in the latter, insulin restored COA independent of BAT innervation. We conclude that insulin can increase ME without an associated increase in energy intake, regardless of basal insulin status, both insulin deficiency and excess decrease BAT thermogenic potential (COA), and hyperinsulinemia-induced increases in ME may result from decreased BAT mitochondrial proliferation.

Insulin and metabolic efficiency in rats. II. Effects of NE and cold exposure

The role of insulin in metabolic efficiency (ME, i.e., efficiency of body wt gain) was examined under conditions of maximal energy expenditure in control and diabetic rats. Long-lasting insulin was administered using a protocol that did not affect food intake and increased ME in both groups. Half the animals were injected chronically with norepinephrine (NE). NE alone in controls decreased body weight and ME and increased brown adipose tissue (BAT) growth, thermogenic potential [cytochrome c oxidase activity (COA)], and lipoprotein lipases (LPL) activity; however, in diabetics, body weight, ME, and food intake all decreased and only BAT LPL activity and DNA content increased. The combination of NE and insulin increased BAT protein and COA in diabetics; in controls, all BAT measures were further increased and ME was intermediate to that of either treatment alone. Cold exposure decreased body weight and ME, increased food intake and qualitatively produced similar increases in BAT growth, COA, and LPL activity in both controls and diabetics. In diabetics, combined cold exposure and insulin did not affect the increase in BAT growth or LPL activity resulting from either treatment alone, but in controls this combination decreased BAT growth and COA. It is concluded that, even under conditions of maximal energy expenditure, both extremes of basal insulin status result in decreased BAT growth and thermogenic potential, but have opposite effects on ME.

Neuropeptides as regulators of consummatory behaviors

The control of ingestive behavior involves a variety of neurotransmitters, including monoamines, peptides and amino acids. For the past decade many investigators have focused their research on the role that regulatory peptides play in eating behavior. Many peptides, including cholecystokinin, bombesin, calcitonin, corticotropin-releasing factor, neurotensin and somatostatin, have been reported to decrease the amount of food ingested by laboratory animals. In contrast, a relatively small number of peptides increase food intake. The present review describes the effects of these peptides on consummatory behaviors in various species and their sites of action.