PubMed Health⌕ Search

Biomedical subjects

D J Flint

Publications and source records attributed to D J Flint.

At least 73 records · Page 4Linked to original sources
PubMed1992

Growth-hormone-prolactin interactions in the regulation of mammary and adipose-tissue acetyl-CoA carboxylase activity and gene expression in lactating rats.

The factors and mechanisms responsible for the reciprocal changes in lipogenesis in rat mammary gland and adipose tissue during the lactation cycle have been investigated. Lactation decreased the activation status and mRNA concentration of acetyl-CoA carboxylase in adipose tissue. Litter removal decreased the mRNA concentration of acetyl-CoA carboxylase in the mammary gland and increased the enzyme's mRNA concentration and activation status in adipose tissue. Lowering serum prolactin concentration in lactating rats decreased the amount of mammary acetyl-CoA carboxylase mRNA and increased that of adipose tissue, and increased the activation status of the enzyme in adipose tissue. Decreasing serum growth hormone (GH) alone had little effect on acetyl-CoA carboxylase in lactating rats, although it did lower pup growth rate and serum concentration of insulin-like growth factor-I. Lowering serum GH concentration exacerbated the effects of decreasing serum prolactin on mammary-gland (but not adipose-tissue) acetyl-CoA carboxylase mRNA and further increased the rise in activation status of the adipose-tissue enzyme induced by decreasing serum prolactin. Changes in acetyl-CoA carboxylase mRNA in both mammary and adipose tissue were paralleled by changes in total enzyme activity except after litter removal, when there was a disproportionately large decrease in total enzyme activity of the mammary gland. Thus prolactin has a major and GH a minor role in the regulation of acetyl-CoA carboxylase activity during lactation. Changes in mammary activity in response to prolactin and GH are primarily due to alterations in gene transcription, whereas adaptation in adipose tissue involves both changes in gene transcription and activation status.

Acetyl-CoA Carboxylase↗
PubMed1992

Critical evaluation of a theory of molecular recognition using human insulin-like-growth-factor-I fragment 21-40 and its complementary peptide.

Using solid-phase methods we have synthesized human insulin-like-growth-factor-I (IGF-I) fragment 21-40 (IGF-I 21-40) and the peptide derived from the 5'----3' translation of the complementary nucleic acid of this peptide, 'I-FGI 20-40' (the complementary peptide). According to a recently proposed theory of molecular recognition, these two peptides should bind specifically to each other. We have tested this theory by using both solid- and solution-phase direct-binding assays for this complementary-peptide pair. We have also investigated the ability of I-FGI 20-40 to interfere with native IGF-I binding during radioimmunoassay (r.i.a.), radio-receptor (r.r.a.) assay and ligand-blot analysis of IGF-binding proteins. We have obtained no evidence of any interaction between IGF-I 21-40 and I-FGI 20-40 in either solid- or solution-phase assays. In addition, I-FGI 20-40 does not interfere in the assays used to detect IGF-I binding antibodies (r.i.a.), receptors (r.r.a.) or binding proteins (ligand blots). Our data therefore question the universality of this particular theory of molecular recognition.

Amino Acid Sequence↗
PubMed1992

Immunological manipulation of adiposity.

Although hormonal regulators of adiposity are available they as yet have not been licensed for use. Withdrawal periods and delivery systems are still potential problems in maximizing their effectiveness. Immunization techniques, on the other hand, suffer none of the problems of withdrawal periods or requirement for frequent injection/implantation. As such they are clearly perceived as safe, economic and should have a positive animal welfare image. They are, however, not without their problems. Active immunization in particular involves an autoimmune response and this is typically difficult to evoke and virtually impossible to regulate. In addition, the fact that antibodies may have immunoneutralizing and immunoenhancing properties may explain the apparently contradictory results obtained in various studies as, for example, in the case of immunization against somatostatin. As our knowledge of immune responsiveness and its control increases, however, the possibilities for immune intervention should increase considerably. We may then be faced with ethical rather than practical limitations as to how far we should manipulate growth and body composition.

Adipose Tissue↗
PubMed1992

Changes in the plasma concentration of gastric inhibitory polypeptide and other metabolites in response to feeding in sheep.

Plasma concentrations of gastric inhibitory polypeptide (GIP)-like activity were determined in sheep before and after refeeding following a 48-h fast. Plasma concentrations increased significantly after feeding, from about 250 pg/ml to about 550 pg/ml. Other metabolites in plasma also increased at this time, reflecting the absorption of nutrients from the gastrointestinal tract. Significant increases were observed in the plasma concentrations of acetate, beta-hydroxybutyrate and triacylglycerol. By comparing the time-courses of the changes in concentration of GIP and other metabolites in plasma, possible sites of secretion and secretagogues of GIP in ruminant animals are proposed. The results demonstrate that GIP is secreted in response to nutrient absorption in adult ruminants and that, as in simple-stomached animals, the absorption of long-chain free fatty acids plays an important role in this secretion.

3-Hydroxybutyric Acid↗
PubMed1992

Investigation of the mechanism of action of growth hormone in stimulating lactation in the rat.

The role of GH was examined using an antiserum to rat GH (anti-rGH). When administered to lactating rats on day 2 of lactation it was without effect, whereas bromocriptine markedly suppressed milk production, with no additional effect of combined treatment. On day 6 of lactation, treatment with anti-rGH was also without effect, whilst bromocriptine again suppressed milk production. Combined treatment, however, suppressed milk synthesis completely, suggesting that GH was capable of maintaining about 50% of normal milk yield in the absence of prolactin at day 6 of lactation. By day 14 of lactation, anti-rGH treatment alone was capable of decreasing milk yield by about 20%, and again milk secretion only stopped completely when GH and prolactin were suppressed. These data suggest that the role of GH in supporting lactation increases as lactation progresses. The effects of GH in stimulating growth and in increasing milk yield in ruminants have been proposed to be mediated via insulin-like growth factor-I (IGF-I). In rats treated with anti-rGH, both IGF-I and IGF-II were decreased in serum. The concentration of the major IGF-binding protein (IGFBP-3) was not, however, affected by inhibition of GH or prolactin individually, but was decreased in animals treated with bromocriptine and anti-rGH. In animals given both bromocriptine and anti-rGH, concurrent treatment with recombinant bovine GH maintained milk yield at 50% of control values and normalized serum IGF-I, IGF-II and IGFBP-3 concentrations. By contrast, concurrent treatment with IGF-I or IGF-II, despite normalizing their respective concentrations in serum, failed to affect milk yield.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

The role of growth hormone, prolactin and insulin-like growth factors in the regulation of rat mammary gland and adipose tissue metabolism during lactation.

Inhibition of prolactin secretion with bromocriptine and neutralization of GH action with a specific antiserum to rat GH (rGH) were used to explore the modes of action of GH and prolactin in maintaining lactation in the rat. Treatment of dams with anti-rGH caused a small reduction in litter weight gain whilst bromocriptine reduced litter weight gain by 50%. When both treatments were combined, however, milk yield ceased completely and this was accompanied by a wide variety of effects on mammary lipid metabolism including decreases in the mRNA concentrations of acetyl CoA carboxylase, fatty acid synthase, malic enzyme and lipoprotein lipase. Activities of acetyl CoA carboxylase and lipoprotein lipase were also significantly reduced. Reciprocal changes were evident in adipose tissue with increases in acetyl CoA carboxylase and lipoprotein lipase activities. In conjunction with a decreased lipolytic response to noradrenaline in adipose tissue of animals given the combined treatment of bromocriptine and anti-rGH, this represented a co-ordinated series of changes to reduce lipid synthesis in the mammary gland and enhance lipogenesis and triglyceride storage in adipose tissue as milk production ceased. All of these effects could be prevented in part by concurrent treatment with GH, but insulin-like growth factor-I (IGF-I) and IGF-II failed to affect any of the parameters measured.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1992

Mechanism of action of cytotoxic antibodies to adipocytes on adipose tissue, liver and food intake in the rat.

The aim of this study was to characterize in greater detail the effects of anti-(rat adipocyte plasma membrane) antisera (A/S 83 and A/S 164) that had previously been shown to cause large reductions in total body fat. Both antisera produced lymphocytic infiltration of adipose tissue and reduction of adipocyte numbers seven days after treatment as well as a reduction in food intake and body weight on the first day of treatment. In addition A/S 164 produced a sedative effect for 2-4 h after treatment and induced gross abnormalities of the liver after seven days. Antibody-mediated complement activation was shown to be a critical requirement for all of these effects since animals treated with cobra venom factor (CVF) to deplete serum complement levels showed none of the described effects. Further evidence in support of a role for complement was the large decrease in serum complement levels 12 h after antiserum treatment. The effects of A/S 164 on liver morphology could be successfully dissociated from those on adipose tissue by adsorption of the antiserum with liver membranes. The adsorbed antiserum, which retained in vitro reactivity with adipose tissue but not with liver, induced a significant reduction in adipose tissue mass in vivo whilst the effect on liver morphology was almost completely abolished. Serum free fatty acid and triglyceride levels increased 6-24 h after treatment but then returned to normal, suggesting a very transient release of adipose tissue triglycerides. These results indicate that complement activation is a common pathway for all of the effects produced.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1991

Insulin binding to skeletal muscle microsomes in lactating and dry sheep.

Microsomes were prepared from skeletal muscles taken from lactating and non lactating ewes. Insulin binding to these microsomes was not affected by reproductive status. There were significant differences in the ability of individual muscles to bind insulin. These differences correlated with the function of the muscle, as defined by the predominant muscle fibre type.

5'-Nucleotidase↗
PubMed1991

Long-term effect of a sheep antiserum to rat growth hormone in vivo in rats is explained by the rat anti-sheep immunoglobulin response.

A specific antiserum to rat GH (anti-rGH) raised in sheep was used in young male and lactating rats. In both models a group of rats was found which appeared to generate a low response (low responders) to the injected sheep immunoglobulin, and was characterized by the ability of the antiserum to cause inhibition of growth for more than 21 days in the male rats, and to abolish milk yield when prolactin concentrations were lowered in the females. In the groups which generated a high response to the anti-rGH (high responders), growth was retarded for only 2-3 days in male rats, with a moderate milk yield maintained in lactating animals. The low-response animals were found to have a significantly longer half-life for circulating anti-rGH, when compared with the high-response animals. After 21 days, in the age-matched male rats, levels of anti-rGH were undetectable in the high-responders, whereas the low-response animals, which were nearly 160 g lighter, still had approximately 4.5 ml anti-rGH/l in their circulation. This anti-rGH was still capable of neutralizing GH, as concentrations of insulin-like growth factor-I (IGF-I) were 13.6 +/- 3.5 (mean +/- S.E.M.) and 76.9 +/- 2.0 nmol/l in the low-response and high-response groups respectively. The reason for these differences would appear to be that the immune response mounted by these low-response animals to the exogenous sheep immunoglobulin (i.e. rat anti-sheep) 7 days after treatment was less than 10% of that seen in the high-response group.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Identification and characterization of glucose transport proteins in plasma membrane- and Golgi vesicle-enriched fractions prepared from lactating rat mammary gland.

Plasma membrane- and Golgi vesicle-enriched membrane fractions were prepared from day-10 lactating rat mammary glands. Each fraction was found to contain a single set of D-glucose-inhibitable cytochalasin B-binding sites: plasma membranes and Golgi vesicles bound 20 +/- 2 and 53 +/- 4 pmol of cytochalasin/mg of membrane protein (means +/- S.E.M.), with dissociation constants of 259 +/- 47 and 520 +/- 47 nM respectively. Anti-peptide antibodies against the C-terminal region (residues 477-492) of the rat brain/human erythrocyte glucose transporter labelled a sharp band of apparent Mr 50,000 on Western blots of both fractions. Treatment with endoglycosidase F before blotting decreased the apparent Mr of this band to 38,000, indicating that it corresponded to a glycoprotein. Confirmation that this immunologically cross-reactive band was a glucose transporter was provided by the demonstration that it could be photoaffinity-labelled, in a D-glucose-sensitive fashion, with cytochalasin B. Quantitative Western blotting studies yielded values of 28 +/- 5 and 23 +/- 3 pmol of immunologically cross-reactive glucose transporters/mg of membrane protein in the plasma membrane and Golgi vesicle fractions respectively. From comparison with the concentration of cytochalasin B-binding sites, it is concluded that a protein homologous to the rat brain glucose transporter constitutes the major glucose transport species in the plasma membranes of mammary gland epithelial cells. Glucose transporters are also found in the Golgi membranes of these cells, at least half of them being similar, if not identical, to the transporters of the plasma membrane. However, their function in this location remains unclear.

Animals↗
PubMed1990

Insulin resistance of hind-limb tissues in vivo in lactating sheep.

1. The effects of varying the plasma insulin concentration by infusion while maintaining euglycaemia by infusion of glucose on nutrient arterio-venous differences across the hind-limb and mammary gland in lactating and non-lactating sheep were investigated. 2. Insulin infusion increased the glucose arterio-venous difference across the hind-limb; this effect of insulin was decreased by lactation, suggesting that lactation induces insulin resistance in skeletal muscle. 3. Lactation increased but insulin infusion decreased the plasma concentrations of acetate, beta-hydroxybutyrate and non-esterified fatty acids. 4. Insulin infusion decreased the arterio-venous differences of acetate and hydroxybutyrate across the hind-limb; this effect of insulin is probably indirect, resulting from the decrease in plasma concentrations of these metabolites. 5. Infusion of insulin had no effect on the glucose arterio-venous difference across the mammary gland, but did decrease the oxygen arterio-venous difference. 6. The results suggest that lactation results in insulin resistance in skeletal muscle, at least with respect to glucose utilization; this should facilitate the preferential utilization of glucose by the mammary gland.

Acetates↗
PubMed1990

Teladorsagia circumcincta egg output at the onset of natural and induced lactation in ewes.

Nineteen ewes maintained under 'worm-free' conditions received anthelmintic and 1 week later were dosed on 5 days each week with 500 Teladorsagia circumcincta larvae for between 10 and 12.5 weeks. Faecal egg counts were determined twice weekly. There were three groups: pregnant (P) ewes (n = 6) which each reared twin lambs, hormone-treated (H) ewes (n = 7) which were not pregnant and were given exogenous hormones (dexamethasone, oestradiol-17 beta, progesterone) for 37 days to induce udder development and milk production, and untreated barren (B) ewes (n = 6). The plasma concentrations of oestradiol-17 beta, prolactin and progesterone were measured. Starting 10-15 days before birth in Group P, there was a biphasic periparturient rise in egg count and the onset of the first peak in egg count preceded the parturient peak in plasma prolactin concentration by several days. Most Group H (5/7) and all Group B ewes remained highly resistant to Teladorsagia infection throughout, despite an induced rise in prolactin concentrations in Group H ewes. It was concluded that factors other than prolactin initiate the periparturient rise but that prolactin is one factor which maintains the response once lactation commences.

Animals↗