Psychoneuroendocrine effects of methadone maintenance

A variety of neuroendocrine and psychiatric dysfunctions have been demonstrated in humans maintained on opiates, but both have not previously been examined in the same population. We performed a series of neuroendocrine challenge tests in men participating in a methadone maintenance clinic and in normal controls. Psychiatric diagnoses were made with DSM-III Criteria, using the Diagnostic Interview Schedule, and subjects also completed the Symptom Checklist. Our results in the methadone group suggest (a) near-maximal stimulation of prolactin secretion, with a blunted prolactin response to insulin hypoglycemia, (b) mild suppression of cortisol levels, but an exaggerated cortisol response to stimulation, (c) a delayed and inhibited insulin response to food ingestion with resulting mild hyperglycemia, (d) low body weight, but elevated calorie ingestion, and (e) inability to concentrate urine when dehydrated, which was partially corrected by administration of arginine vasopressin. Phobic disorder was associated with a lower prolactin response to both inhibitory and stimulatory challenges. Depression did not appear to be related to the increased cortisol response to stimulation. These results suggest several potentially fruitful areas for future investigation, including the prolactin system and anxiety disorders, nutrient ingestion and metabolism, and posterior pituitary function.

Effects of streptozotocin-induced diabetes on feeding stimulated by centrally administered opioid agonists

The potencies of several opioid agonists are reduced in diabetic animals and in animals made hyperglycemic via injections of glucose. In this report we examined the effects of streptozotocin-induced diabetes on the feeding responses to centrally administered opioid agonists with differing receptor selectivities. The selective mu receptor agonist Tyr-D-Ala-Gly-(Me)Phe-Gly-ol (DAGO) caused a larger increase in intake in diabetic rats than in controls. In both groups feeding responses were greater on the fourth day of daily injections than on the first day. The delta receptor agonist [D-Ser2,Leu5]-enkephalin-Thr6 (DSLET) stimulated intake in controls but not in diabetics. However, the elevated baseline and large variability in intake of the diabetics in this experiment prevent drawing a conclusion on diabetes-induced changes in the potency of this peptide. No differences between controls and diabetics were apparent in the feeding responses to U50, 488H, a selective kappa receptor agonist. These data suggest that diabetes may differentially affect the classes of opioid receptors or the binding of ligands to these receptors.

Opiate antagonist nalmefene inhibits ethanol-induced flushing in Asians: a preliminary study

Ethanol-induced flushing (EIF) occurs in up to 80% of Asians and is characterized by facial flushing, tachycardia, and increased cardiac output. Since endogenous opiates and prostaglandins may be mediators of flushing syndromes, we attempted to block EIF in four Asian flushers with single doses of either the opiate antagonist nalmefene, or the prostaglandin synthesis inhibitor indomethacin. Nonflushers (2 Caucasian, 2 Asian) and four Asian flushers were given on separate days water, ethanol (0.4 g/kg p.o.), ethanol plus nalmefene (2 mg i.v.), or ethanol plus indomethacin (50 mg p.o.). Ethanol concentrations of flushers and nonflushers were similar. Mean (+/- SEM) plasma acetaldehyde concentrations of flushers (28.2 +/- 11.8 microM) were significantly greater than nonflushers (1.4 +/- 0.5 microM) following ethanol ingestion (p less than 0.001). Ethanol alone always induced a significant rise in facial skin temperature [mean area under the curve (AUC) = 5142 +/- 648 % delta T x min, p less than 0.01] and of pulse (mean AUC = 1622 +/- 120 bpm x min, p less than 0.001) in flushers compared to water ingestion. A single dose of nalmefene (2 mg i.v.) but not indomethacin (50 mg p.o.), reduced the mean (+/- SEM) ethanol-induced rise in facial skin temperature of flushers by 58 +/- 14% (p less than 0.05) without changing plasma acetaldehyde concentrations. These data are preliminary evidence that the opiate antagonist, nalmefene, blocks some of the vascular manifestations of EIF without altering the elevated plasma concentrations of acetaldehyde.

Use of a simian virus 40-based shuttle vector to analyze enhanced mutagenesis in mitomycin C-treated monkey cells

When monkey cells were treated with mitomycin C 24 h before transfection with UV-irradiated pZ189 (a simian virus 40-based shuttle vector), there was a twofold increase in the frequency of mutations in the supF gene of the vector. These results suggest the existence of an enhancible mutagenesis pathway in mammalian cells. However, DNA sequence analysis of the SupF- mutants suggested no dramatic changes in the mechanisms of mutagenesis due to mitomycin C treatment of the cells.

Fidelity of DNA synthesis in a mammalian in vitro replication system

We have used the simian virus 40 (SV40)-based shuttle vector pZ189 in a forward-mutation assay to determine the fidelity of DNA replication in the in vitro DNA replication system developed by J.J. Li and T.J. Kelly (Proc. Natl. Acad. Sci. USA 81:6973-6977, 1984). We find that very few base substitution errors (approximately 1/180,000 bases incorporated) are made during in vitro replication of the pZ189 vector in a system derived from CV-1 monkey cells. This replication is completely dependent on added SV40 T antigen and presumably reflects synthesis that is initiated at the SV40 replication origin. The observed level of fidelity is far greater than that reported for in vitro replication of DNA by conventionally purified eucaryotic DNA polymerases alpha and beta. Thus, there must be additional cellular factors in the crude in vitro system that serve to enhance the fidelity of DNA replication.

Viral gene inhibition of class I major histocompatibility antigen expression: not a general mechanism governing the tumorigenicity of adenovirus type 2-, adenovirus type 12-, and simian virus 40-transformed Syrian hamster cells

The association between the level of class I major histocompatibility (MHC) antigen expression and the tumorigenic phenotype was determined for cells from a series of 15 lines of adenovirus type 2 (Ad2)-, Ad12-, and simian virus 40 (SV40)-transformed hamster cells and 16 lines of cells established from hamster tumors induced by SV40 mutants. These cells range from nontumorigenic to highly tumorigenic in both syngeneic and allogeneic adult hamsters. The Ad2-transformed cells--cells that were nontumorigenic in syngeneic adult hamsters--expressed either high levels or low levels of class I MHC antigens. The SV40-transformed cells--cells transformed in vitro that produced tumors with equal efficiency in both syngeneic and allogeneic adult hamsters--or cells derived from SV40-induced tumors expressed very high levels of class I MHC antigens. The Ad12-transformed cells uniformly expressed low levels of class I MHC antigens; these cells produced tumors 200- to 1,000-fold less efficiently in allogeneic adult hamsters than in syngeneic adult hamsters and produced tumors with about the same efficiency in immunoimmature newborns and immunocompetent syngeneic adult hamsters. We conclude that the expression of either high levels or low levels of class I MHC antigens is, at most, a minor factor in the differences observed among these adenovirus- and SV40-transformed cells in their tumor-inducing capacity in naive, immunocompetent hamsters.

Enhancement of DNA repair capacity of mammalian cells by carcinogen treatment

To determine whether DNA excision repair is enhanced in mammalian cells in response to DNA damage, as it is in bacteria as part of the SOS response, we used an expression vector-host cell reactivation assay to measure cellular DNA repair capacity. When UV-damaged chloramphenicol acetyltransferase (CAT) vector DNA was introduced into monkey cells (CV-1), the level of CAT activity was inversely related to the UV fluence due to inhibition of CAT gene expression by UV photoproducts. When CV-1 cells were treated with either UV radiation or mitomycin C, 24-48 h before transfection, CAT expression from the UV-irradiated plasmid was increased. This increase also occurred in a line of normal human cells, but not in repair-deficient human xeroderma pigmentosum cells. We confirmed that this increase in CAT expression was due to repair, and not to production of damage-free templates by recombination; the frequency of generation of supF+ recombinants after transfection with UV-irradiated pZ189 vectors carrying different point mutations in the supF gene did not significantly increase in carcinogen-treated CV-1 cells. From these results we conclude that carcinogen treatment enhances the excision-repair capacity of normal mammalian cells.

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.