Guinea Pig Adipose Tissue Research Articles

Influence of fish oil on usage of [1-14С] palmitic acid in the synthesis of lipids in the tissues of guinea pigs under hypercholesterolemia in vitro

It’s studied in vitro the intensity of lipid synthesis of various classes (fatty acids, cholesterol, phospholipids and acylglycerols) in homogenates of liver, brain, small intestinal mucosa and adipose tissue after daily single injection of guinea pigs with cholesterol (300 mg/kg body weight) for 30 days. For this purpose, it’s determined the radioactivity of the lipid fractions of the referred above tissue homogenates of guinea pigs that was incubated with [1-14C] palmitic acid. It’s established the inhibitory effect of exogenous cholesterol, under increase its level in the diet of guinea pigs, on the diacylglycerol synthesis and on the free cholesterol in the small intestine mucosa and on the triacylglycerol synthesis in adipose tissue under usage as a precursor – [1-14C] palmitic acid. It’s determined a significant reduction in the intensity of total lipids and individual lipid classes by using as a precursor [1-14C] palmitic acid in in vitro conditions in the brain, liver, small intestinal mucosa and adipose tissue of guinea pigs with hypercholesterolemia when it’s given them fish oil as feed.

Cholesterol-induced inflammation and macrophage accumulation in adipose tissue is reduced by a low carbohydrate diet in guinea pigs.

BACKGROUND/OBJECTIVESThe main objective of this study was to evaluate the effects of a high cholesterol (HC) dietary challenge on cholesterol tissue accumulation, inflammation, adipocyte differentiation, and macrophage infiltration in guinea pigs. A second objective was to assess whether macronutrient manipulation would reverse these metabolic alterations.MATERIALS/METHODSMale Hartley guinea pigs (10/group) were assigned to either low cholesterol (LC) (0.04g/100g) or high cholesterol (HC) (0.25g/100g) diets for six weeks. For the second experiment, 20 guinea pigs were fed the HC diet for six weeks and then assigned to either a low carbohydrate (CHO) diet (L-CHO) (10% energy from CHO) or a high CHO diet (H-CHO) (54% CHO) for an additional six weeks.RESULTSHigher concentrations of total (P < 0.005) and free (P < 0.05) cholesterol were observed in both adipose tissue and aortas of guinea pigs fed the HC compared to those in the LC group. In addition, higher concentrations of pro-inflammatory cytokines in the adipose tissue (P < 0.005) and lower concentrations of anti-inflammatory interleukin (IL)-10 were observed in the HC group (P < 0.05) compared to the LC group. Of particular interest, adipocytes in the HC group were smaller in size (P < 0.05) and showed increased macrophage infiltration compared to the LC group. When compared to the H-CHO group, lower concentrations of cholesterol in both adipose and aortas as well as lower concentrations of inflammatory cytokines in adipose tissue were observed in the L-CHO group (P < 0.05). In addition, guinea pigs fed the L-CHO exhibited larger adipose cells and lower macrophage infiltration compared to the H-CHO group.CONCLUSIONSThe results of this study strongly suggest that HC induces metabolic dysregulation associated with inflammation in adipose tissue and that L-CHO is more effective than H-CHO in attenuating these detrimental effects.

The guinea pig as a model for metabolic programming of adiposity

The human infant accumulates body fat during intrauterine life. The guinea pig shares this characteristic and is born with similar adiposity; thus, it may be a relevant model to study obesity programming. The objective of this study was to evaluate guinea pig adipose tissue (AT) development and the effect of a maternal high-fat diet on the offspring's body composition. In experiment 1, adipogenesis dynamics were evaluated at 3, 10, 21, and 136 d in epididymal and retroperitoneal AT with the use of (2)H(2)O labeling. In experiment 2, dams received a control or high-fat diet from mating to 21 d after delivery. The offspring received a high-fat diet from 22 to 105 d; adiposity was measured at 2, 21, 54, and 97 d. The fractional proliferation rate (FPR) of cells in epididymal AT was 25.2% of cells synthesized in 5 d at 3 d of age and decreased over time (P < 0.001). Age had no effect on retroperitoneal FPR (P = 0.179). In both depots, the fractional synthesis rate (FSR) of palmitate decreased extensively from day 3 to day 10, increasing by day 21 and declining by day 136 (P < 0.001). The FSR of triglycerides decreased with age (P < 0.001). A maternal high-fat diet increased the offspring's adiposity at 2 d and 21 d (P < 0.05) but had no effect on body composition later in life. Adipogenesis in the guinea pig is very active during early life and was altered by a maternal high-fat diet; thus, it is an adequate model for intrauterine fat deposition. However, there were no effects of maternal diet later in life.

In vitro Differentiation of Adipose-Derived Stem Cells into Hair Cell-Like Cells in Guinea Pigs

ObjectiveAdipose-derived stem cells(ADSCs) are suggested to possess a highly plastic ability to differentiate into several specific cell types in addition to adipocyte lineages, including germ layer tissue-specific cell lineages such as chondrocyte, myocyte, neuronal, and osteoblast lineages. The aim of this study is to establish an in vitro culture technique for ADSCs in an adult guinea pig model that facilitate their differentiation into hair cell-like cells. Materials and MethodsCells from inguinal fat pads in adult guinea pigs were cultured with ß-mercaptoethanol, RA, Forskorin, Heregulin, bFGF, BDNF and EGF. Cellular differentiation was examined using immunocytochemistry techniques. ResultsThe ADSCs demonstrated hair cell immunophenotypes with expression of epitopes of the hair cell marker protein myosin VIIa. Conclusion ADSCs from adult guinea pig adipose tissue can differentiate into hair cell-like cells when cultured in vitro. ADSCs may serve as seed cells for tissue engineering.

Thyrotropin Receptors in Brown Adipose Tissue: Thyrotropin Stimulates Type II Iodothyronine Deiodinase and Uncoupling Protein-1 in Brown Adipocytes

It has been demonstrated that TSH receptors are expressed not only in thyroid gland but also in extrathyroidal tissues. Brown adipose tissue of guinea pig has been reported to express TSH receptor messenger RNA (mRNA), but the physiological roles of TSH receptors in brown adipose tissue have not been understood. We studied the expression and function of TSH receptors in rat brown adipose tissue and cultured rat brown adipocytes. Northern analysis demonstrated the expression of TSH receptor mRNA in rat brown adipose tissue and cultured rat brown adipocytes. TSH receptor mRNA in rat brown adipose tissue was decreased by cold exposure of the rat, and its mRNA in cultured rat brown adipocytes was also decreased by incubation with TSH or (Bu)2cAMP. TSH increased the intracellular cAMP concentration in cultured rat brown adipocytes in a dosedependent manner. Type II iodothyronine deiodinase mRNA, its activity, and uncoupling protein-1 mRNA in cultured rat brown adipocytes were significantly increased by incubation with TSH in a dose-dependent manner. These results suggest the expression of functional TSH receptors in brown adipose tissue, which may be involved in regulation of the expression of type II iodothyronine deiodinase and uncoupling protein-1.

Thyrotropin receptors in brown adipose tissue: thyrotropin stimulates type II iodothyronine deiodinase and uncoupling protein-1 in brown adipocytes.

It has been demonstrated that TSH receptors are expressed not only in thyroid gland but also in extrathyroidal tissues. Brown adipose tissue of guinea pig has been reported to express TSH receptor messenger RNA (mRNA), but the physiological roles of TSH receptors in brown adipose tissue have not been understood. We studied the expression and function of TSH receptors in rat brown adipose tissue and cultured rat brown adipocytes. Northern analysis demonstrated the expression of TSH receptor mRNA in rat brown adipose tissue and cultured rat brown adipocytes. TSH receptor mRNA in rat brown adipose tissue was decreased by cold exposure of the rat, and its mRNA in cultured rat brown adipocytes was also decreased by incubation with TSH or (Bu)(2)cAMP. TSH increased the intracellular cAMP concentration in cultured rat brown adipocytes in a dose dependent manner. Type II iodothyronine deiodinase mRNA, its activity, and uncoupling protein-1 mRNA in cultured rat brown adipocytes were significantly increased by incubation with TSH in a dose-dependent manner. These results suggest the expression of functional TSH receptors in brown adipose tissue, which may be involved in regulation of the expression of type II iodothyronine deiodinase and uncoupling protein-1.

Mechanisms of Gender-specific TCDD-induced Toxicity in Guinea Pig Adipose Tissue

After treatment with TCDD, the activities of cytosolic AhR-associated c-Src kinase, microsomal protein kinase C (nPKCϵ), microsomal c-Src kinase, nuclear p 44/42 MAPK, c-Jun N terminus kinase, and the amount of microsomal pan-Ras protein were different in males and females. TCDD did not decrease body or adipose tissue weights in transgenic src-deficient male mice as compared to their wild-type littermates, and the activity of AhR-associated c-Src kinase was not increased by TCDD in src-deficient male mice. Similar results were obtained when TCDD was given to male guinea pigs treated with the Src-kinase inhibitor, geldanamycin. Treatment with estradiol protected male guinea pigs from TCDD-induced wasting. TCDD induced similar changes in protein tyrosine kinase activity in adipose tissues of castrated male and intact female guinea pigs. The gender-specific mechanisms of TCDD-induced toxicity appear to involve c-Src kinase, nPKCϵ, and pan-Ras, as well as overlap in the cytosolic signal transduction pathways of TCDD and sex steroids.

Identification of c-Src as the integral component of the cytosolic Ah receptor complex, transducing the signal of 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) through the protein phosphorylation pathway

We have shown previously that 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) under cell-free conditions causes a significant rise in protein tyrosine kinase activity of cytosol from male guinea pig adipose tissue, and that such an effect of TCDD is Ah-receptor dependent. In the present study, we obtained evidence indicating that c-Src protein kinase is the protein kinase activated by TCDD and that this kinase is associated specifically with the Ah-receptor-complex proteins in cytosol from adipose tissue and liver of guinea pig and liver of C57B1/6] mouse, and in NIH 3T3 mouse fibroblast cells. Here, we present evidence that c-Src protein is functionally attached to the Ah-receptor (AhR) and is specifically activated upon ligand binding. This conclusion is based on several lines of evidence: (a) TCDD caused activation of protein tyrosine kinase activity when administered directly to purified Ah-receptor immunoprecipitate; (b) this stimulatory effect of TCDD was abolished when the cytosol was immunodepleted of c-Src protein or Ah-receptor protein by preincubating with anti-c-Src or anti-Ah-receptor antibody, followed by the addition of TCDD to the remaining portions of cytosol; (c) when Ah-receptor immunoprecipitate was incubated with TCDD, and the kinase(s) released to the super-natant was analyzed on autoradiography of two-dimensional (2D) electrophoresis, 32P-labeled c-Src protein was recognized; (d) the same 32P-labeled-phosphoprotein with M r = 60 kDa and pI = 6.1 was found in the immunoprecipitate with anti-c-Src antibody on 2D autoradiograms; (e) this same phosphoprotein disappeared when the supernatant of the Ah-receptor immunoprecipitate was immunodepleted of c-Src protein by anti-c-Src antibody; and (f) a structure-activity relationship study with TCDD and three dioxin-congeners revealed a rank order for their potency in activation of c-Src kinase activity to be identical to that of previously determined toxicity indices: i.e. TCDD>1,2,3,7,8-pentachlorodibenzo- p-dioxin (1,2,3,7,8-PCDD) > 1,2,4,7, 8-pentachlorodibenzo- p-dioxin (1,2,4,7,8-PCDD)>2,7-dichlorodibenzo- p-dioxin (2,7-DCDD). Consistent with these results, TCDD-induced c-Src kinase activity was abolished when c-Src immunoprecipitate's suspension was preincubated with 0.1 or 1 μM α-naphthoflavone (AhR blocker) for 10 min prior to the addition of TCDD. In addition, pretreatment of 3T3 fibroblast cells with 3-methylcholanthrene abolished TCDD-induced c-Src kinase activity in AhR-immunoprecipitate. We conclude that c-Src protein kinase is associated specifically with the AhR complex along with hsp90 in the cytosol of these cells and that upon ligand binding to the Ah-receptor subunit, c-Src is activated and released from the complex.

Protective action of dehydroascorbic acid on the Ah receptor-dependent and receptor-independent induction of lipid peroxidation in adipose tissue of male guinea pig caused by TCDD administration.

The effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on lipid peroxidation, 3H-Me-glucose (3H-Me-glu), and 14C-dehydroascorbic acid (14C-DHA) uptakes were studied in adipose tissue of male guinea pig. Under in vitro test conditions, using isolated adipose tissue in a culture medium (explant culture), TCDD reduced the uptake of 3H-Me-glu and 14C-DHA in a dose- and time-dependent fashion. The IC50 values of TCDD's action were 0.04 and 2 nM on 14C-DHA and 3H-Me-glu uptakes, respectively. TCDD (10 nM) also suppressed glucose transporting activity within 15 minutes in explant-cultured adipocytes. Cytochalasin B (CB) and nonlabeled D-glucose inhibited 14C-DHA uptake also in a dose-dependent manner. In addition, TCDD was found to induce lipid peroxidation in explant-cultured adipose tissue. This effect of TCDD was similar to that of a typical lipid peroxidation inducer, CCl4, and it was dose and time dependent. TCDD caused a statistically significant rise in lipid peroxidation at a concentration as low as 0.1 nM after 60 minutes of treatment in explant culture. Unexpectedly, the Ah receptor partial antagonists, 4,7-phenanthroline and alpha-naphthoflavone, did not fully antagonize TCDD-induced lipid peroxidation in explant-cultured adipocytes. In vivo treatment of TCDD also induced lipid peroxidation. Among seven organs of male guinea pig tested, the levels of lipid peroxidation in adipose tissue and in liver increased at 1 and 40 days following a single i.p. dose of TCDD (1 microgram/kg). The results of an in vivo time-course study indicated that such an effect of TCDD was most pronounced after 40 days of treatment. Finally, we have tested the protective role of some antioxidants on TCDD-induced lipid peroxidation under explant-culture conditions. The results indicated that DHA, but not ascorbic acid, could completely abolish TCDD-induced lipid peroxidation. The protective effect of DHA on TCDD-induced lipid peroxidation was stronger than that of alpha-tocopherol and uric acid, and this effect was blocked by CB. We conclude from these studies that TCDD acts in this guinea pig tissue through two different routes: one is the Ah receptor-dependent route causing the reduction of the level of glucose transporters and subsequent decrease of cellular uptake of DHA and the other, the Ah receptor-independent route causing the overall lipid peroxidation. Nevertheless, it appears likely that both events are antagonized by DHA.

Protective action of dehydroascorbic acid on the Ah receptor‐dependent and receptor‐independent induction of lipid peroxidation in adipose tissue of male guinea pig caused by TCDD administration

The effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on lipid peroxidation, 3H-Me-glucose (3H-Me-glu), and 14C-dehydroascorbic acid (14C-DHA) uptakes were studied in adipose tissue of male guinea pig. Under in vitro test conditions, using isolated adipose tissue in a culture medium (explant culture), TCDD reduced the uptake of 3H-Me-glu and 14C-DHA in a dose- and time-dependent fashion. The IC50 values of TCDD's action were 0.04 and 2 nM on 14C-DHA and 3H-Me-glu uptakes, respectively. TCDD (10 nM) also suppressed glucose transporting activity within 15 minutes in explant-cultured adipocytes. Cytochalasin B (CB) and nonlabeled D-glucose inhibited 14C-DHA uptake also in a dose-dependent manner. In addition, TCDD was found to induce lipid peroxidation in ex-plant-cultured adipose tissue. This effect of TCDD was similar to that of a typical lipid peroxidation inducer, CCl4, and it was dose and time dependent. TCDD caused a statistically significant rise in lipid peroxidation at a concentration as low as 0.1 nM after 60 minutes of treatment in explant culture. Unexpectedly, the Ah receptor partial antagonists, 4,7-phenanthroline and α-naphthoflavone, did not fully antagonize TCDD-induced lipid peroxidation in explant-cultured adipocytes. In vivo treatment of TCDD also induced lipid peroxidation. Among seven organs of male guinea pig tested, the levels of lipid peroxidation in adipose tissue and in liver increased at 1 and 40 days following a single i.p. dose of TCDD (1 μg/kg). The results of an in vivo time-course study indicated that such an effect of TCDD was most pronounced after 40 days of treatment. Finally, we have tested the protective role of some antioxidants on TCDD-induced lipid peroxidation under explant-culture conditions. The results indicated that DHA, but not ascorbic acid, could completely abolish TCDD-induced lipid peroxidation. The protective effect of DHA on TCDD-induced lipid peroxidation was stronger than that of α-tocopherol and uric acid, and this effect was blocked by CB. We conclude from these studies that TCDD acts in this guinea pig tissue through two different routes: one is the Ah receptor-dependent route causing the reduction of the level of glucose transporters and subsequent decrease of cellular uptake of DHA and the other, the Ah receptor-independent route causing the overall lipid peroxidation. Nevertheless, it appears likely that both events are antagonized by DHA. © 1997 John Wiley & Sons, Inc. J Biochem Toxicol 11: 269–278, 1997.

Regulation by 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) of the DNA binding activity of transcriptional factors via nuclear protein phosphorylation in guinea pig adipose tissue

2,3,7,8-Tetrachloro- p-dioxin (TCDD) induced a modest stimulation of nuclear protein phosphorylation in expiant tissue cultures in 10 min, followed by a substantial decrease in the level of total protein phosphorylation activity in the nucleus. Curiously, this TCDD-induced decline in nuclear protein phosphorylation was accompanied by an increase in cytosolic and extranuclear protein phosphorylation activity. One of the main causes for such a decrease in the protein phosphorylation activity in the nucleus appears to be related to some increase in protein phosphatase activities as judged by the counteractions of okadaic acid and Na 3VO 4 to the above effect. In addition, TCDD induced changes in nuclear protein kinase activities as well. Manganese-stimulated protein kinase was found to be the predominant type of nuclear protein phosphorylating activity affected by TCDD, with 60% of the total activity due to heparin-sensitive casein kinase II (CK II), a major nuclear protein kinase. The level of CK II activity in the nuclear protein preparation from adipose tissue of TCDD-treated guinea pigs (1 μg/kg) in the presence of 100 nM heparin was only 35% of the control value after 24 hr. In addition, TCDD was found to increase the protein kinase C and microtubule-associated protein 2 kinase activities as early as 15 min after treatment in isolated adipose tissues in culture. Under in situ incubation conditions with expiant tissues in culture, TCDD rapidly enhanced the DNA binding activity of the transcriptional factor AP-1, whereas the same treatment reduced c-Myc DNA binding activity. Genistein, a specific protein tyrosine kinase inhibitor, abolished the stimulatory effect of TCDD on AP-1 binding activity, but not on DNA binding activity of c-Myc. Phorbol ester (TPA) increased the binding activity of AP-1 and c-Myc, as expected. However, TCDD in combination with TPA caused a slight reduction in binding activity of both transcriptional factors. On the other hand, in the presence of forskolin, the stimulatory effect of TCDD on AP-1 binding activity and the inhibitory effect on c-Myc were still apparent. Okadaic acid almost abolished the binding activity of c-Myc, whereas in combination with TCDD a stimulatory effect was found. These observations are consistent with the idea that TCDD regulates the DNA binding activity of AP-1 and c-Myc mainly through modulating their states of phosphorylation by altering protein kinase and phosphatase activities.

Apparent lack of beta 3-adrenoceptors and of insulin regulation of glucose transport in brown adipose tissue of guinea pigs

Norepinephrine-induced thermogenesis was substantial in adipocytes from brown adipose tissue (BAT) of cold-acclimated guinea pigs but absent in adipocytes from BAT of warm-acclimated guinea pigs. There was no thermogenic response to any beta 3-adrenergic agonist (CL-316,243, ZD-7114, BRL-28410, CGP-12177). The receptor was characterized as a beta 1-adrenoceptor. Adrenergic agonists stimulated adenylate cyclase in membranes from BAT of both warm- and cold-acclimated guinea pigs also via a beta 1-adrenoceptor; beta 3-adrenergic agonists had no effect. Glucose transport by brown adipocytes from warm-acclimated guinea pigs was not stimulated by either norepinephrine or insulin. Cold acclimation induced the appearance of stimulation of glucose transport by norepinephrine in association with the appearance of a large capacity for thermogenesis, but there was little improvement in response to insulin. GLUT4 was present in membranes from BAT of both warm- and cold-acclimated guinea pigs. Insulin is known to have an antilipolytic effect on both BAT and white adipose tissue of guinea pigs. Thus there is a selective lack of insulin-regulated glucose transport that is not improved by cold acclimation. Guinea pigs may have a mutated component of the translocation mechanism for GLUT4. beta 3-Adrenoceptors appear to be absent in brown adipocytes of adult guinea pigs, as in white adipocytes of guinea pigs, yet are known to be present in the gut. Tissue-specific expression of beta 3-adrenergic receptors in guinea pigs may differ from that in rats, in which receptors are expressed in the adipose tissues and gut.

Evidence for a second pathway in the action mechanism of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Significance of Ah-receptor mediated activation of protein kinase under cell-free conditions.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) when administered directly to a nuclear-free subcellular homogenate of guinea pig adipose tissue, caused a significant rise in protein kinase activities within 1-10 min. Such a rapid response was not expected, based on the classic transcriptional mechanism of action for TCDD, i.e. TCDD first binds with its cytosolic Ah-receptor, translocates into the nucleus, dimerizes with "arnt" (a nuclear transcription factor), and activates genes containing "xenobiotic-responsive element" (XRE). The above actions of TCDD on protein kinases were clearly blocked by two specific Ah-receptor blockers, even under cell- and nucleus-free conditions. TCDD-induced increases in protein phosphorylation occurred mainly in cytosolic preparations (i.e. 100,000 g supernatant) devoid of nucleus, microsomes and plasma membranes and were still observed in the presence of inhibitors of protein phosphatases. Furthermore, TCDD caused a rise in protein tyrosine kinase activity in a purified Ah-receptor preparation, as well as in an isolated heat shock protein 90 complex preparation containing the Ah-receptor. This activation took place in the presence of actinomycin D and cycloheximide, indicating a portion of TCDD's action that is unrelated to de novo protein synthesis in this process. We have also obtained evidence indicating that this action of TCDD triggers the protein kinase mediated growth factor signal transduction pathway, such as stimulation of mitogen activated protein kinase 2 and tyrosine kinase activity. These results clearly support the view that the basic action pathway for such a TCDD-induced activation of protein kinases is distinctly different from its conventional action pathway involving changes in gene transcription in the nucleus.

2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD)‐induced changes in glucose transporting activity in guinea pigs, mice, and rats in vivo and in vitro

The toxic action of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on glucose uptake was studied on different species, sexes, and strains of animals by using a nonmetabolizable glucose analog, 3-0-methyl D [1-3H] glucose (3H-Me-glc). We have found a drastic reduction in glucose uptake in different organs from male guinea pigs in vivo as well as in vitro. Female guinea pigs were less responsive to this effect of TCDD compared to males. Highly TCDD-responsive mice strains responded in the same way as the male guinea pigs, while less TCDD-responsive mice strains did not. A reduction in glucose uptake was found in explant adipose tissue cultures (in vitro) of male mice (highly TCDD-responsive) after a 4 hour incubation with 10(-8) M TCDD. In less responsive mice strains, stimulation was observed using the same model (in vitro). In the case of male rats, as well as male guinea pigs, glucose uptake was highly reduced by 10(-8) M TCDD using an in vitro system of explant adipose tissue. The Ah-receptor blocker, 4,7-phenanthroline, abolished the effect of TCDD on inhibition of glucose uptake in adipose tissue of male guinea pigs both in vivo and in vitro. Transcription and translation inhibitors (actinomycin D and cycloheximide, respectively) were tested separately or in combination with TCDD using the guinea pig adipose tissue culture model. It was found that actinomycin D could block the effect of TCDD on glucose uptake throughout the experiment time (360 min) while cycloheximide blocked TCDD action for about 60 minutes. Protein kinase inhibitors (e.g., genistein, neomycin) did not change the effect of TCDD on glucose uptake in male guinea pig adipose tissue. Based on these observations, we conclude that TCDD inhibits Me-glc uptake in various organs in guinea pigs, mice, and rats, and this response is mediated by the Ah-receptor.

Site-specific differences in the responses of guinea-pig adipose tissue to changes in the fatty acid composition of the diet

Young adult guinea-pigs were fed on diets differing mainly in triacylglycerol content of 18:2 (n-6), 18:3 (n-3) and 18:1 (n-9) fatty acids for six to twelve weeks. All animals gained weight normally. The fatty acid compositions of triacylglycerols in nine adipose depots (3 superficial, 3 intra-abdominal, 2 intermuscular and the plantar paw pad) were analyzed using capillary gas chromatography. Each site demonstrated a specific pattern of fatty acid compositional changes: some fatty acids changed more rapidly than others, and within each class of sites (e.g. the superficial sites) some depots showed faster compositonal change than other depots. The results suggest that some adipose depots readily exchange circulating fatty acids, or modify existing fatty acids, while others have a lower rate of fatty acid turnover.

2,3,7,8‐tetrachlorodibenzo‐P‐dioxin induced alterations in protein phosphorylation in guinea pig adipose tissue

An in situ (explant tissue culture) model has been developed to study the effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), hormones, and growth factors either alone or in combination. In our model system, the effect of TCDD on protein phosphorylation was greatly affected by the presence or the absence of externally added D-glucose. In the presence of a physiologically relevant level of glucose (13.3 mM), TCDD clearly stimulated protein phosphorylation as in the case of in vivo data. However, in the absence of D-glucose, TCDD clearly inhibited protein phosphorylation. On the other hand, TCDD reduced the glucose uptake activity in isolated adipose tissue either in the presence or absence of D-glucose (13.3 mM). Therefore, the TCDD-induced reduction of glucose transport does not appear to be related directly to the simultaneous rise in protein phosphorylation. For comparison, several agents which are known to affect protein phosphorylation were tested. These hormonal agents generally affected the TCDD-untreated adipose tissues in the manner expected from their known actions, indicating that this in situ model is an adequate system to study their independent actions. The TCDD-treated adipose tissue samples showed only mild or insignificant response to these hormonal stimuli. In terms of the changes in the pattern of protein phosphorylation activities, the action of TCDD appeared to resemble that of EGF and T3. Since under in situ conditions no agents such as EGF or T3 can be expected to be present, the observed TCDD-induced changes are suggestive of the basic intracellular changes in cellular activities. The types of TCDD-induced protein kinases appear to be protein tyrosine kinases and protein kinase C.

2,3,7,8-Tetrachlorodibenzo-p-dioxin causes reduction of glucose transporting activities in the plasma membranes of adipose tissue and pancreas from the guinea pig.

Toxicity from 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure results in severe metabolic imbalances leading to a loss of fat stores in many animal species, a phenomenon known as the wasting syndrome. In this paper, we report that TCDD treatment at very low doses (0.03-1 micrograms/kg, single intraperitoneal injection) causes a profound reduction of glucose uptake by guinea pig adipose tissue, pancreas and brain. This effect of TCDD is dose-dependent, with a dose as small as 0.03 micrograms/kg resulting in a significant decrease. In adipose tissue, the decrease begins within 6 h of treatment and persists at least 28 days. The Vmax of glucose transport was decreased by TCDD treatment, whereas the Km was unchanged. Liver behaves oppositely to adipose tissue. At early stages of treatment (6-12 h) glucose uptake was depressed, while at later stages (24-96 h) it was increased. In situ (explant tissue culture) treatment with TCDD yields similar trends as in vivo studies for glucose uptake in all three tissues. In adipose tissue culture TCDD starts reducing glucose uptake after 30 minutes. The inhibitory potencies of three dioxin congeners on adipose glucose transporting activities follows the same order of their toxicities in vivo. TCDD's effect on glucose transport is sensitive to cytochalasin B, a specific inhibitor of glucose transporter proteins. Based on these observations and the importance of glucose transporters to cellular energy maintenance, we conclude that at least in guinea pigs the reduction of glucose transporters in various tissues is one of the major causes for TCDD-induced wasting syndrome, which is so prominent in this species.

TCDD (2,3,7,8-tetrachlorodibenzo-P-dioxin) causes reduction in glucose uptake through glucose transporters on the plasma membrane of the guinea pig adipocyte.

A single dose of 2,3,7,8-TCDD (1 micrograms/kg, i.p. injection) resulted in a significant decrease in cellular 3-O-methyl-[3H]-glucose uptake by guinea pig adipose tissue and pancreas after 24 hours. An in situ tissue culture study in which pieces of adipose tissue were incubated with 10(-8)M TCDD showed a time-dependent decrease in glucose uptake. Reconstitution of adipocyte plasma membrane from tested or control animals into artificial liposomes also resulted in this difference in glucose uptake. Binding of [3H]-cytochalasin B, a specific inhibitor of glucose transporter proteins, was significantly lower in acetone-ether powder preparations of TCDD-treated adipose tissue than from controls, suggesting that the total titer of these proteins is decreased by TCDD. Finally, the relevance of these results to glucose or lipid metabolism was tested. Lipoprotein lipase (LPL) activity of guinea pig adipose tissue was decreased after 8 hours of in situ incubation with TCDD indicating that glucose uptake was depressed at an earlier time point. These findings may contribute to a better understanding of dioxin-induced "wasting syndrome".

Expression and translation of the growth hormone-receptor gene in the guinea-pig.

The refractoriness of guinea-pigs to the growth-promoting actions of exogenous GH has been suggested to be due to a deficiency or defect in tissue GH receptors or in GH-receptor gene expression. GH-receptor mRNA was, however, demonstrated by Northern blot analysis and by the polymerase chain reaction in extracts of guinea-pig liver, adipose tissue, brain, hypothalamus and pituitary gland. High-affinity, low-capacity binding sites for radio-labelled ovine GH were also demonstrated on the plasma membranes of guinea-pig liver and were similar to those in rat liver. These results demonstrate that the unresponsiveness of guinea-pigs to exogenous GH is not due to the absence of GH receptors.

The effect of exercise and in vivo treatment with ACTH and norepinephrine on the lipolytic responsiveness of guinea pig (Cavia porcellus) adipose tissue

1. In adipose slices of the guinea pig (Cavia porcellus), adrenocorticotrophic hormone (ACTH) produced a significantly higher lipolytic response (increased Vmax and decreased Km) as compared to norepinephrine (NE), thus indicating a marked difference with human adipose tissue. 2. Exercise-training caused a significant increase in the affinity of the lipolytic response in adipose tissue towards both ACTH and NE, but had no significant effect on Vmax. 3. Prolonged in vivo treatment with both ACTH and NE significantly decreased the responsiveness (affinity and capacity) of adipose slices towards ACTH. Responsiveness towards NE was much less affected.