Responses of Beijing black hogs to porcine somatotropin

Somatotropin treatment of U.S-breed finishing hogs improves feed efficiency, growth rate and carcass lean-to-fat ratio. Because Chinese-bred hogs have poorer feed efficiency, growth rate and lean-to-fat ratio than U.S. bred hogs, the characteristics affected by porcine somatotropin (PST) may respond differently to treatment. In the present experiment, Beijing Black finishing hogs (a composite of a local Chinese, Berkshire and Yorkshire breeds) were treated with PST for 28 d from average initial to final weights of 67.8 to 96.6 kg. In hogs individually fed as much as they would eat four times a day (n = 12/treatment group, six gilts and six barrows), feed efficiency was improved by 22.4 and 29.9% by 2 and 4 mg/d PST, respectively (P less than .01), primarily due to increased growth rate (22.1 and 32.6% greater than control, respectively, P less than .01); feed intake was not affected. Performance of group-housed and group-fed hogs (six/pen, four pens/treatment) administered 2 mg/d PST for 28 d (average initial and final weights of 66.5 +/- 1.7 and 94.0 +/- 2.4 kg, respectively) was similar (22.7% improved feed efficiency, P less than .01; 25% increased growth rate, P less than .01). At slaughter, last rib backfat thickness was decreased an average of 19.2% for hogs treated with 2 and 4 mg/d PST (P less than .01). Percentage of total muscle, obtained by physical separation of the half-carcass, was increased an average of 13.5% (P less than .01), whereas percentage of total fat was decreased 21.8% (P less than .01) in PST-treated hogs. The pH, water-holding capacity and meat color scores of longissimus muscle from PST-treated hogs did not differ from those of control hogs. Growth rate, feed efficiency and muscle weight responses to PST treatment were at least as large as those for U.S. breeds.

Soybean metal-binding proteins: calmodulin purification by hydrophobic interaction with polymer 3520

Polymer 3520, a non-polar styrene divinylbenzene polymer, provides a simple way to purify calmodulin (CAM) from soybeans. This polymer, which selectively adsorbs CAM by hydrophobic interaction within the polymer matrix, contains no exchangeable groups; thus, interaction with CAM requires no Ca++ ions, and elution is achieved with 50% ethanol. Purification by this form of reversed-phase liquid chromatography is a substantial improvement over the conventional method, which requires high salt in elution buffers. CAM in soybean meal is first extracted with 80% ethanol in the presence of EGTA at room temperature and then chromatographed directly on a polymer 3520 column to yield pure CAM. Addition of non-ionic detergent (Nonidet P-40) to the ethanolic extract helps to separate extraneous proteins, lipids, sugars, and isoflavones. Such isolated CAM migrates as a single band during polyacrylamide gel electrophoresis and reversed-phase HPLC, and it retains activity stimulatory to phosphodiesterase.

Mechanisms underlying the supra-maximal thermogenesis elicited by aminophylline in rats

Previous studies showed that acute treatment with aminophylline (AMPY) significantly elevated maximum thermogenesis and improved cold tolerance in rats and man in severe cold. However, the exact mechanism by which AMPY enhances thermogenesis was unknown. Rats receiving enprofylline (ENPRO) (1.5 and 15 mg/kg, i.p.), a selective phosphodiesterase inhibitor, failed to show enhanced thermogenesis. In contrast, treatment with a selective adenosine receptor antagonist, 8-phenyltheophylline(8-PT; 2.5 to 10 mg/kg, i.p.), significantly increased (p less than 0.05) thermogenesis and cold tolerance. However, the maximal thermogenic effect by optimal dose of 8-PT (5 mg/kg) was significantly lower than that with optimal dose of AMPY (18.7 mg/kg, i.p.); the deficit could be eradicated by combining optimal 8-PT dose with a low dose of AMPY (1.25 mg/kg), but not with ENPRO. These results indicate that the thermogenic effect of AMPY is not by inhibition of phosphodiesterase but at least partially by antagonism of adenosine receptors. It is also apparent that older mechanisms in addition to adenosine antagonism are also involved in AMPY's thermogenic action.

Brown fat thermogenesis during hibernation and arousal in Richardson's ground squirrel

The thermogenic activity [mitochondrial guanosine 5'-diphosphate (GDP) binding] and capacity (uncoupling protein concentration, cytochrome oxidase activity) of brown adipose tissue have been investigated at different phases of the seasonally linked hibernation cycle in Richardson's ground squirrel. The amount of axillary brown adipose tissue and the total mitochondrial content of the tissue were substantially greater in hibernating squirrels than in squirrels caught posthibernation in April or May; cold acclimation induced qualitatively similar differences. The specific mitochondrial concentration of uncoupling protein was high under all conditions (compared with other species), differing little between hibernating, posthibernating, and cold-acclimated squirrels. The thermogenic capacity of brown adipose tissue in Richardson's ground squirrels is therefore modulated almost exclusively by changes in the mitochondrial content of the tissue. Mitochondrial GDP binding was increased on cold acclimation, but similar binding levels were observed in hibernating and posthibernation (May) animals. GDP binding and the GDP-sensitive component of acetate-induced mitochondrial swelling were increased during the early stages of arousal from hibernation. These changes, which indicate an activation of the thermogenic proton conductance pathway in arousal, occurred without an alteration in the specific mitochondrial concentration of uncoupling protein. Increased GDP binding during arousal is clearly due to the unmasking of binding sites, reflecting an acute activation of preexisting uncoupling protein.

Concomitant infection of HTLV-I and HIV-1: prevalence of IgG and IgM antibodies in Washington, D.C. area

Serum samples collected from four groups of individuals in the Washington, D.C. area were examined for the presence of IgG and IgM classes of antibody reacting against HTLV-I and HIV-1. These four groups were: (1) healthy adults with negative premarital VDRL test for syphilis (n = 113), (2) miscellaneous common disease patients (n = 155), (3) drug abusers (n = 130), and (4) homosexual men (n = 187). The former two groups are considered to be low-risk groups, and the latter two, high-risk groups. The prevalence of IgG antibody on ELISA/Western blot tests for these groups were respectively: (1) 5.3%/1.8%, (2) 5.2%/1.9%, (3) 13.9%/4.6%, and (4) 4.3%/1.6% for HTLV-I, and (1) 2.7%/0.9%, (2) 4.5%/0%, (3) 12.3%/5.4%, and (4) 8.0%/5.9% for HIV-1. Instances of possible concomitant infection as shown by the presence of antibodies against both HTLV-I and HIV-1 were found only in the latter two high-risk groups, i.e. two (1.5%) in group (3), and three (1.6%) in group (4) as confirmed by both Western blot and immunofluorescence tests. Out of 97 sera collected from drug abusers in 1985-86 which had IgG antibody by Western blot test against HIV-1, 23 (23.7%) were HTLV-I antibody positive by ELISA test (Group 5), and 8 of these were confirmed by Western blot test. Among these 8 persons, IgM antibody against HTLV-I was found in 2, while that against HIV-1 was positive in 7 persons.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin secretion and substrate homeostasis in prolonged hypothermia in rats

In hypothermia, impairment of metabolic substrate mobilization and utilization may be a factor limiting survival. By use of a newly developed technique, substrate profiles and their regulation by insulin were examined in hypothermic rats (body temperature 19 degrees C) over 24 h. Plasma glucose concentrations increased to approximately 300 mg/dl during cooling and remained high throughout the period of hypothermia. Free fatty acid (FFA) concentration was not altered during cooling or during the first 10 h of hypothermia (approximately 700 mu eq/l) but progressively decreased thereafter, reaching 420 mu eq/l by 20 h. Plasma insulin decreased dramatically during cooling and remained very low (9 +/- 2 microU/ml) during the whole period of hypothermia, reflecting the suppression of insulin secretion by isolated islets at low temperatures. To test he hypothesis that suppression of endogenous insulin secretion may hamper glucose utilization and thus limit survival in hypothermia, exogenous insulin was administered. At doses of 0.1, 0.5, and 1 U/kg intravenously, insulin slowly decreased plasma glucose and FFA. However, at 0.1 and 1 U/kg intraperitoneally, insulin resulted in a dose-dependent decrease in survival time in the hypothermic rat. It is possible that the antilipolytic effect of insulin may have outweighed any beneficial effect of improving glucose utilization in hypothermia.

The role of v-mos in transformation, oncogenicity, and metastatic potential of mink lung cells

A cloned line of S + L- mink lung cells (A clone), which exhibited a flat morphology, was superinfected with a novel dual-tropic virus (E1BX-MuLV) showing a broad host range and a B-tropism. These cells gave rise to transformed cells with two phenotypes: those which were still anchorage-dependent (AD), and those which readily detached spontaneously from the substratum and grew in suspension. A clone of these AD cells (B clone) was isolated and compared with a clone of the anchorage-independent suspension-cultured (AISC) cells (C clone). While the C clone exhibited a high oncogenicity and ability to metastasize in nude mice, the A and B clones were not tumorigenic. The integrated v-mos was greatly amplified in the C clone, and moderately increased in the B clone as compared with the A clone. The amounts of v-mos mRNA expressed by B and C clones paralleled those of v-mos sequence in their chromosomal DNA, whereas there was no detectable v-mos mRNA in the A clone. Thus, conversion of S + L- mink cells from an AD growth to an AISC phenotype accompanied by manifestation of oncogenicity and metastatic potential in nude mice is associated with amplification of integrated v-mos gene and its enhanced expression. Furthermore, a revertant (D clone) showing AD phenotype was derived from the C clone by selective growth in ouabain. This revertant exhibited a markedly decreased oncogenicity in nude mice, although the copy numbers of integrated v-mos gene and its mRNA did not differ from those of the parent C clone. While more p37mos protein was found in the C than in the D clone, it was not detectable in the A and B clone. The amounts of helper virus-related mRNA and infectious E1BX-MuLV were markedly higher in the B than in the C and D clones. It is concluded that v-mos gene amplification and overexpression is necessary for these cells to exhibit oncogenicity, but other factors associated with ouabain-resistance can modify or suppress its oncogenicity despite the v-mos amplification and mRNA overexpression.

The "hibernation induction trigger": specificity and validity of bioassay using the 13-lined ground squirrel

Even though the existence of the blood-borne "hibernation induction trigger" has been reported in the 13-lined ground squirrel, transfusion of plasma from hibernating rodents with other hibernating species as the recipients failed to induce the occurrence of summer hibernation. In order to verify whether the response to the "trigger" substance is species specific, the present study was carried out to compare the effect of plasma from hibernating Richardson's ground squirrels on the incidence of summer hibernation in both juvenile Richardson's and adult 13-lined ground squirrels. In two series of experiments, 13-lined ground squirrels entered hibernation quite readily independent of the treatment. The rate of occurrence of hibernation ranged from 78% after sham injection to 86% after warm saline, fresh summer active plasma, and fresh hibernating plasma, respectively. There were no differences in the number of hibernation bouts and the number of days in hibernation after each treatment. In contrast, none of the juvenile Richardson's ground squirrels entered hibernation after any of the treatments up to the end of the 8-week observation period. These results not only argue against the existence of blood-borne "trigger" substance, at least in the Richardson's ground squirrel, but also caution against the use of the 13-lined ground squirrel as a standard test animal for the bioassay of the "trigger" substance.

Calorimetric and spectroscopic studies of lipid thermotropic phase behavior in liver inner mitochondrial membranes from a mammalian hibernator

Arrhenius plots of various enzyme and transport systems associated with the liver mitochondrial inner membranes of ground squirrels exhibit changes in slope at temperatures of 20-25 degrees C in nonhibernating but not in hibernating animals. It has been proposed that the Arrhenius breaks observed in nonhibernating animals are the result of a gel to liquid-crystalline phase transition of the mitochondrial membrane lipids, which also occurs at 20-25 degrees C, and that the absence of such breaks in hibernating animals is due to a major depression of this lipid phase transition to temperatures below 4 degrees C. In order to test this hypothesis, we have examined the thermotropic phase behavior of liver inner mitochondrial membranes from hibernating and nonhibernating Richardson's ground squirrels, Spermophilus richardsonii, by differential scanning calorimetry and by 19F nuclear magnetic resonance and fluorescence polarization spectroscopy. Each of these techniques indicates that no lipid phase transition occurs in the membranes of either hibernating or nonhibernating ground squirrels within the physiological temperature range of this animal (4-37 degrees C). Moreover, differential scanning calorimetric measurements indicate that only a small depression of the lipid gel to liquid-crystalline phase transition, which is centered at about -5 degrees C in nonhibernating animals and at about -9 degrees C in hibernators, occurs. We thus conclude that the Arrhenius plot breaks observed in some membrane-associated enzymatic and transport activities of nonhibernating animals are not the result of a lipid phase transition and that a major shift in the gel to liquid-crystalline lipid phase transition temperature is not responsible for seasonal changes in the thermal behavior of these inner mitochondrial membrane proteins.

Variants of amphotropic type-C retrovirus isolated from cultures of Moloney- and Rauscher-MuLV-induced tumors

We isolated and characterized 2 strains of type-C retrovirus, R5NX and YACNX, from established lymphoid cell cultures derived from Rauscher-MuLV-induced lymphoma (RBL-5) in a C57BL/6 mouse, and Moloney-MuLV-induced lymphoma (YAC) in an A-strain mouse, respectively. The R5NX and YACNX viruses were compared with the prototype 4070A strain of amphotropic virus isolated from feral mice in California, and were found to belong to the same amphotropic virus class on the basis of viral interference, neutralization tests, and other biological properties. However, they were not quite identical with respect to viral neutralization antigens and restriction enzyme cleavage patterns of the proviral DNA. The possibility that these viruses may have been present in the original tumor together with the R-MuLV or M-MuLV as "exogenous" viruses rather than as contaminants of cell cultures by the 4070A virus is discussed. Although these 2 isolates were not pathogenic when inoculated into newborn C3H/HE mice, they could establish persistent infections in these mice.

Amplification and enhanced expression of the c-Ki-ras2 protooncogene in human embryonal carcinomas

Two cell lines of human embryonal carcinoma, Tera-1 and Tera-2, have been found to exhibit a 4- to 6-fold amplification of protooncogene c-Ki-ras2. The polyadenylic acid selected RNA also showed 8-fold or greater enhancement, showing marked elevation in the level of two major mRNAs, 5.7 and 4.0 kilobases, and two additional minor mRNAs, 2.3 and 1.2 kilobases, as compared with those of a normal human embryonic fibroblast cell line, MRC-5. More than one-half of the number of tumor samples obtained from metastatic human embryonal carcinomas also showed c-Ki-ras2 gene amplification and enhanced mRNA expression. However, the c-Ki-ras2 gene amplification did not always lead to enhanced mRNA expression, and some embryonal carcinomas showed mRNA overexpression without apparent c-Ki-ras2 gene amplification. These results suggest that human embryonal carcinomas may have c-Ki-ras2 amplification and/or overexpression before in vitro culture. Among various chromosomal changes observed in Tera-1 and Tera-2 cells, there were anomalies in chromosome 12 in which c-Ki-ras2 is located although these karyological changes alone could not account for the amplification observed. It is suggested that the genomic instability and active DNA replication during the early developmental period may give rise to changes involving c-Ki-ras2 which may contribute to oncogenic processes.

Metabolic and hormonal responses in theophylline-increased cold resistance in males

The effects of theophylline (a phosphodiesterase inhibitor-adenosine receptor antagonist) and substrate feeding (Ensure, 250 kcal/235 ml) on cold resistance were studied in seminude males undertaking submaximal (50% maximum O2 consumption), intermittent (34% of total time) exercise in the cold (-5 to 15 degrees C, individually adjusted) for 3 h. Each subject (n = 7) served as his own control and was tested on a weekly schedule. Under control treatment, rectal temperature (Tre) decreased by 0.9 degrees C to approximately 36.2 degrees C after cold exposure, whereas under theophylline and Ensure, the decrease of Tre was only 0.4 degrees C, indicating a significant increase (P less than 0.05) in cold resistance (50% better than control). The plasma concentration of theophylline was 4.8-5.9 micrograms/ml and was positively correlated with plasma concentration of free fatty acids. Plasma norepinephrine (NE) increased significantly during cold exposure; the absolute concentration was significantly higher after theophylline pretreatment. The plasma concentrations of glucose, epinephrine, cortisol, and adenosine 3',5'-cyclic monophosphate did not change and the changes of free thyroxine and triiodothyronine were minor. Together, the effectiveness of theophylline + Ensure in acutely increasing cold resistance may be due to increased substrate availability for thermogenesis, part of which, through theophylline's potentiation of both sympathetic release of NE and NE-stimulated lipolysis and part of which, through supplementary feeding of Ensure.

First report of an epidemic of diarrhoea in human neonates involving the new rotavirus and biological characteristics of the epidemic virus strain (KMB/R85)

An outbreak of diarrhoea in neonates occurred at the nurseries of the Department of Obstetrics of Zhao Tong Regional Hospital, Yunnan Province, from the middle of August to the end of November, 1985. Fifty-one percent of children were affected 2-8 days after birth. The clinical symptoms were mild; patients mainly had diarrhoea and did not vomit. Rotaviruses were detected in 66.7% by RNA PAGE and in 72.7% by EM. The virus strain designated as KMB/R85 had a typical morphology, which was indistinguishable from that of infantile rotaviruses by EM. The viral RNA genome was composed of 11 segments. The buoyant density in CsCl was 1.377 g/cm3. The KMB/R85 strain possessed a hemagglutinin for rhesus monkey erythrocytes. By ELISA, IEM, and HAI, it was found that KMB/R85 strain did not possess the common group antigen shared by group A rotaviruses and was antigenically similar to the Chinese adult diarrhoea rotavirus (serogroup B).

Enhancement of cold-stimulated thermogenesis in the corpulent rat (LA/N cp) by aminophylline

Previous studies on obese strains of rats (e.g., Zucker and LA/N cp) have shown that they are deficient in nonshivering thermogenesis and poor in cold tolerance. Our earlier studies have established that aminophylline (AMPY; 85% theophylline-15% ethylenediamine) is effective in significantly improving cold tolerance in the lean Sprague-Dawley rat regardless of age or thermogenic capacity. The present study tested whether AMPY may be also effective in improving cold tolerance in both young (12-18 wk) and older (36-42 wk) lean and corpulent LA/N cp rats. Contrary to previous reports, however, the norepinephrine (NE)-stimulated nonshivering thermogenesis was not only present but also equal in magnitude in the corpulent rats to that of their lean controls. Further, no difference in cold tolerance was observed between the two groups regardless of age. Similarly, AMPY (18.7 mg/kg ip) significantly improved thermogenesis and cold tolerance in both lean and corpulent rats, again without any age-related difference in response. These results indicate that, despite the existence of obesity, no difference in thermogenic capacity to either NE or cold stimulation is evident in the LA/N cp rats. Thus the ontogeny of obesity in this strain may be caused by factors other than deficiency in NE- or cold-stimulated thermogenesis at the end-organ level.

Seasonal difference in thermoregulatory responses to opiates in a mammalian hibernator

Accumulated evidence suggests that increased endogenous opioid activities may facilitate the onset of hibernation. The present study investigated the change in thermoregulatory responses following ICV infusion of morphine or [D-Ala2]-Met enkephalinamide (EK) in unanesthetized, unrestrained Columbian ground squirrels (Spermophilus columbianus) during its annual hibernation cycle. In the nonhibernating phase, low doses of either morphine (less than 160 micrograms) or EK (less than 400 micrograms) elicited a dose-related hyperthermia and an increase in heat production, whereas a higher dose of opiates caused hypothermia and a decrease in metabolic rate. Naloxone (5 mg/kg, SC) pretreatment reduced or reversed both the hyper- and hypothermic responses to opiates. Lower ambient temperature (5 degrees C) enhanced the hypothermic response and attenuated the hyperthermic response. In the hibernating phase, euthermic ground squirrels exhibited a reduced responsiveness to exogenous opiates: the hyperthermic response to low dose of morphine (10 micrograms) was significantly reduced and hyperthermia, rather than hypothermia was observed at the highest dose of morphine (160 micrograms). The reduced responsiveness to opiates observed during the hibernating phase seems to suggest a reduction in opiate receptor efficacy which is in agreement with the contention that an increase in endogenous opioid activities may be incumbent with the commencement of hibernation.

A simple purification of calmodulin by reversed phase chromatography with hydrophobic polymer 3520

A new adsorption chromatography procedure for the purification of calmodulin from bovine brain was developed using polymeric adsorbent 3520. Calmodulin was first isolated by DEAE-Cellulose column chromatography and further purified to apparent homogeneity following elution with 50% ethanol from the adsorbent column. Polyacrylamide gel electrophoresis showed one band either in the presence of Ca2+ or EGTA. The polymeric adsorbent 3520 is a non-polar polymer lacking exchangeable groups. The selective adsorption of calmodulin is based on hydrophobic interaction within the matrix, and is Ca2+ independent. Neither high salt (0.5 M NaC1) nor EGTA (5 mM) was able to elute the CaM from the adsorption column whereas ethanol (50%) eluted it completely. This method is simple to use and it provides highly purified calmodulin with high yield.

Structure and expression of two porcine genomic clones encoding class I MHC antigens

Two nonallelic porcine class I MHC (SLA) genes have been isolated and characterized. Both genes are expressed in mouse L cells, directing the synthesis of class I SLA molecules that carry common monomorphic determinants but are serologically distinct. The corresponding DNA sequences have been determined. The organization of both of these genes is similar to that of other class I genes: a leader exon, three exons encoding extracellular domains, a transmembrane exon, and three intracytoplasmic exons. The two genes are highly homologous in both exon and intron segments, with average homologies of 88% and 80%, respectively. Nucleotide changes in exon 2 are clustered, whereas those in the other exons are dispersed throughout. Comparison of the swine DNA sequences with class I genes from other species reveals a generally high conservation of exons 2, 3, 4, and 6 with lower homology in the remaining protein-encoding domains. Introns are markedly less well conserved, although moderate homology is found between swine and human class I MHC genes in both introns and 3' flanking regions. Taken together with comparisons of the deduced protein sequences, these data indicate an order of swine greater than human greater than rabbit greater than mouse in the relationship of class I genes.

Structure and expression of two porcine genomic clones encoding class I MHC antigens

Two nonallelic porcine class I MHC (SLA) genes have been isolated and characterized. Both genes are expressed in mouse L cells, directing the synthesis of class I SLA molecules that carry common monomorphic determinants but are serologically distinct. The corresponding DNA sequences have been determined. The organization of both of these genes is similar to that of other class I genes: a leader exon, three exons encoding extracellular domains, a transmembrane exon, and three intracytoplasmic exons. The two genes are highly homologous in both exon and intron segments, with average homologies of 88% and 80%, respectively. Nucleotide changes in exon 2 are clustered, whereas those in the other exons are dispersed throughout. Comparison of the swine DNA sequences with class I genes from other species reveals a generally high conservation of exons 2, 3, 4, and 6 with lower homology in the remaining protein-encoding domains. Introns are markedly less well conserved, although moderate homology is found between swine and human class I MHC genes in both introns and 3' flanking regions. Taken together with comparisons of the deduced protein sequences, these data indicate an order of swine greater than human greater than rabbit greater than mouse in the relationship of class I genes.

Substrate preference in aminophylline-stimulated thermogenesis

The present study investigated the suitability of different substrates on aminophylline (AMPY)-induced thermogenesis in rats during cold exposure. Feeding of distilled water 60 min prior to cold exposure in two-day fasted rats resulted in the lowest total heat production and final body temperature in both saline- and AMPY-treated groups. Feeding of 5 ml Intralipid (2 Kcal/ml), a triglyceride mixture, did not improve thermogenesis beyond the control levels. However, feeding of isocaloric substitutes of sucrose elevated significantly the total thermogenesis by 7.9% and 7.4% and final body temperature by 2.23 and 1.61 degrees C, respectively, in saline- and AMPY-treated groups. The increase in thermogenesis by sucrose is not due to its thermic effect. It is concluded that sucrose, in combination with AMPY, may be of value in improving resistance to cold.

Improving cold tolerance in elderly rats by aminophylline

During severe cold exposure, old rats (23-26 months) were less capable in maintaining normal body temperature as compared to young rats (6-9 months) due to lower rate of heat production (HP). Single injection of optimal doses of aminophylline (AMPY; 10 and 18.7 mg/kg, i.p.), a phosphodiesterase inhibitor which enhances the intracellular cyclic AMP concentration, significantly increased the rate of HP in old rats to levels beyond the control values observed in young rats. Consequently, cold tolerance of the old rats was significantly improved. This AMPY-improved cold tolerance is apparently not due to increased non-shivering thermogenesis (NST) since AMPY failed to enhance norepinephrine-stimulated NST in the old rats. It is likely that AMPY increased substrate mobilization and/or conversion, thereby circumventing the limiting role of substrate availability for shivering thermogenesis. Thus, the age-dependent decrease in cold tolerance may be due to a reduced capacity for substrate mobilization when challenged by cold.

Effects of fasting and aminophylline on norepinephrine-stimulated non-shivering thermogenesis

In an attempt to further elucidate the mechanisms of fasting-depressed maximum thermogenesis and cold tolerance, norepinephrine (NE)-stimulated non-shivering thermogenesis (NST) in cold-acclimated rats was used as a functional index of possible alterations in adrenergic efficacy after fasting. Fasting decreased the magnitude of maximum NE-Stimulated NST by 18.2% [6.87 +/- 0.47 Kcal (Kg X 75 X min)-1 well-fed vs. 5.81 +/- 0.39 Kcal (Kg X 75 X min)-1 fasted], but the apparent adrenergic binding affinity was not affected [Ke = 0.43 micrograms NE min-1 well-fed vs. 0.55 micrograms NE min-1 fasted]. Pretreatment with aminophylline [15 mg Kg-1, i.p.], a phosphodiesterase inhibitor, restored the fasting-depressed NE-stimulated NST to the fed level. The results suggest that the depression of maximum thermogenesis after fasting is not due to changes in adrenergic binding characteristics but to alteration in cAMP production/degradation, resulting in decreased substrate mobilization for thermogenesis.

Noncovalently bonded subunits of 22 and 28 kd are rapidly internalized by T cells reacted with anti-Leu-4 antibody

Using immunofluorescence analysis in a FACS or cytofluorograph, we monitored the density of four different human T cell surface molecules (Leu-1/OKT1, Leu-2/OKT5,8, Leu-3/OKT4, and Leu-4/OKT3) at different intervals of incubation at 37 degrees C with monoclonal antibodies that react with these structures. Leu-1 and Leu-2 are probable human homologues of the murine Lyt-1 and Lyt-2,3 antigens, respectively. Leu-3 is a 55 kd antigen that is restricted to Leu-2- (helper) T cells. Leu-4 is expressed by all peripheral T cells and has at least two components of 22 and 28 kd that have an undefined structural relationship. The ultimate degree of modulation of each antigen varied considerably. Modulation of Leu-4 was particularly striking, because this antigen disappeared completely from the cell membrane within 7 hr of culture with saturating concentrations of alpha Leu-4. After modulation of surface 125I-labeled T cells, Leu-4 was found in the detergent-solubilized cell lysate, but not in the cellfree supernatant, indicating that it was internalized. Our results also indicated that the internalized antigen-antibody complex existed in at least two forms: a) as an antigen-antibody complex having only the lower m.w. (22 kd) component bound to antibody, or b) as free antigen having the 28 kd chain in noncovalent association with the 22 kd moiety. These studies indicate that the Leu-4 structure is composed of at least two distinct chains that are noncovalently associated. The rapid modulation and structural properties of the Leu-4 complex are discussed in the context of its possible functions in T cell immunity.

Noncovalently bonded subunits of 22 and 28 kd are rapidly internalized by T cells reacted with anti-Leu-4 antibody

Using immunofluorescence analysis in a FACS or cytofluorograph, we monitored the density of four different human T cell surface molecules (Leu-1/OKT1, Leu-2/OKT5,8, Leu-3/OKT4, and Leu-4/OKT3) at different intervals of incubation at 37 degrees C with monoclonal antibodies that react with these structures. Leu-1 and Leu-2 are probable human homologues of the murine Lyt-1 and Lyt-2,3 antigens, respectively. Leu-3 is a 55 kd antigen that is restricted to Leu-2- (helper) T cells. Leu-4 is expressed by all peripheral T cells and has at least two components of 22 and 28 kd that have an undefined structural relationship. The ultimate degree of modulation of each antigen varied considerably. Modulation of Leu-4 was particularly striking, because this antigen disappeared completely from the cell membrane within 7 hr of culture with saturating concentrations of alpha Leu-4. After modulation of surface 125I-labeled T cells, Leu-4 was found in the detergent-solubilized cell lysate, but not in the cellfree supernatant, indicating that it was internalized. Our results also indicated that the internalized antigen-antibody complex existed in at least two forms: a) as an antigen-antibody complex having only the lower m.w. (22 kd) component bound to antibody, or b) as free antigen having the 28 kd chain in noncovalent association with the 22 kd moiety. These studies indicate that the Leu-4 structure is composed of at least two distinct chains that are noncovalently associated. The rapid modulation and structural properties of the Leu-4 complex are discussed in the context of its possible functions in T cell immunity.

Elicitation of supramaximal thermogenesis by aminophylline in the rat

Previous studies in rats indicate that maximal thermogenesis during severe cold exposure is suppressed by overnight fasting. Since fasting depresses sympathetic activity and the activity of adrenergic receptors, both of which affect substrate mobilization in cold, the present study attempted to restore maximal thermogenesis in fasted rats by exogenous sympathomimetics and a hypoxanthine (aminophylline). In overnight-fasted rats, exogenous sympathomimetics had no effect in further enhancing maximal thermogenesis induced by exposure to severe cold (in He-O2 at -10 degrees C), indicating maximization of endogenous sympathetic discharge and saturation of adrenergic receptor binding during severe cold exposure. In contrast, aminophylline (1.25-37.5 mg/kg ip) elicited "supramaximal thermogenesis" beyond control maximums in both fasted (+19.4%) and fed +14.4%) conditions in a dose-dependent manner, resulting in improved cold tolerance and prevention of hypothermia. Since aminophylline acts distally to adrenergic receptors to increase intracellular adenosine 3',5'-cyclic monophosphate concentration, it is possible that such increases could enhance substrate mobilization to support supramaximal thermogenesis in severe cold.