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Biomedical subjects

I C Green

Publications and source records attributed to I C Green.

At least 55 records · Page 3Linked to original sources
PubMed1990

Induction of lactogenic receptors in liver of hypophysectomized rats treated with bovine growth hormone-monoclonal antibody complexes.

Male hypophysectomized rats treated with bovine (b)GH-monoclonal antibody complexes showed enhanced weight gain compared with animals treated with bGH alone over a 12-day treatment period. Liver microsomes prepared from animals showing enhanced weight gain exhibited increased specific binding of human (h)GH. Studies on the specificity of these binding sites showed that they were lactogenic, 125I-labelled hGH being displaced by ovine prolactin, but not by non-mammalian growth hormones. In this respect they were similar to lactogenic binding sites in the liver of pregnant rats. Monoclonal antibodies to hGH blocked binding to lactogenic receptors to different extents. The pattern of such inhibition was similar, but not identical, for the receptors induced in hypophysectomized rats and those from pregnant rat liver. The evidence available suggests that the lactogenic receptors induced by bGH-monoclonal antibody complexes are not directly involved in the enhancement of growth.

Animals↗
PubMed1990

Immunological and insulin secretory studies on isolated porcine islets of Langerhans.

Since porcine islets are considered a likely tissue source for islet transplantation we have studied the insulin secretory responses to stimuli and some of the cell surface antigen characteristics of porcine islet cells. In a static incubation system, the threshold level of glucose required for the stimulation of insulin secretion from freshly isolated porcine islets was found to be between 2.8 and 4.2 mmol glucose/l. Arginine (5 mmol/l) and 3-isobutyl-l-methylxanthine (1 mmol/l) potentiated insulin release induced by 8.3 mmol glucose/l. Leucine (5 mmol/l) initiated release in the presence of 2 mmol glucose/l. Neither beta-hydroxybutyrate (10 mmol/l) nor octanoate (5 mmol/l) potentiated insulin release induced by 8.3 mmol glucose/l, but beta-hydroxybutyrate initiated release in the presence of 2 mmol glucose/l while octanoate did not. A 125I-labelled protein A binding assay and an enzyme-linked immunosorbent assay system were used to detect antibody binding to islet and non-islet cells. Monoclonal antibodies raised against intact rat islets were shown to bind to both porcine and rat islet cells but not to rat hepatoma tissue culture cells or rat insulinoma cells. The serum from recently diagnosed type I diabetics was shown to bind to rat islet cells in a 125I-labelled protein A binding assay, while serum from control subjects showed little, if any, binding. Porcine islet cells were unable to distinguish between the sera of recently diagnosed type I diabetics and controls in a similar assay. In conclusion, porcine islets respond to many of the major insulin secretagogues to which human islets are sensitive.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Methyl-3-isobutylxanthine↗
PubMed1990

Increased sensitivity to insulin-releasing and glucoregulatory effects of dynorphin A1-13 and U 50488h in ob/ob versus lean mice.

The effects of two kappa-opiate agonists, U 50488h and dynorphin A1-13, on plasma insulin and glucose concentrations in vivo and insulin release in vitro were tested in fasted genetically obese (ob/ob) and lean (+/+) mice at 12-15 wk of age. Fasting plasma insulin concentrations in ob/ob and lean mice were 1.22 +/- 0.10 and 0.23 +/- 0.05 nM, and plasma glucose levels were 6.90 +/- 0.84 and 4.70 +/- 0.29 mM, respectively. Administration of U 50488h (1 mg/kg body wt i.p.) to ob/ob mice dramatically raised plasma insulin by 670 and 790 pM at 15 and 30 min. Plasma glucose was raised from 5 min onward to a maximum increment of 4.2 mM above baseline. These effects were blocked by simultaneous administration of naloxone (10 mg/kg). A higher dose of U 50488h (10 mg/kg body wt i.p.) was required to produce significant increases in lean mouse plasma insulin (81 pM at 15 min) and glucose (0.7, 1.1, and 1.7 mM at 5, 15, and 30 min, respectively). Dynorphin (1 mg/kg body wt i.p.) raised plasma insulin in ob/ob mice by 380 and 410 pM at 15 and 30 min and raised plasma glucose by 1.6 mM at 15 min. In lean mice, the same dose of dynorphin had no effect on plasma insulin concentrations but induced a small rise in glucose. In ob/ob mice, the agonist-induced rise in glucose did not cause the insulin response, because insulin levels were not elevated by a glucose challenge.(ABSTRACT TRUNCATED AT 250 WORDS)

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1989

Central mu, delta, and kappa opioid binding sites, and brain and pituitary beta-endorphin and met-enkephalin in genetically obese (ob/ob) and lean mice.

The equilibrium dissociation constants and maximal binding capacities of 3H-dihydromorphine (DHM), 3H-D-Ala2-D-leu3-enkephalin (DADL), and 3H-dynorphin A(1-8) for their respective mu, delta, and kappa opiate binding sites were studied in brain membrane preparations from lean and genetically obese-hyperglycaemic (Aston ob/ob) mice. The concentration of kappa binding sites was 2.7 fold higher in obese compared with lean mouse brain (231 +/- 44.6 versus 83.8 +/- 10.3 fmoles 3H-dynorphin/mg protein respectively, mean +/- SEM). The concentration of delta binding sites in obese was 1.6 fold that in lean mouse brain (94.5 +/- 8.6 versus 59.5 +/- 6.5 fmoles 3H-DADL/mg protein). In contrast, the concentration of brain mu receptors was 40% lower in obese compared with lean mice (20.8 +/- 2.19 and 34.8 +/- 3.1 fmoles 3H-DHM/mg protein respectively). Binding affinities of delta and kappa sites for their respective ligands were not significantly different in lean v. obese mice. However, for mu sites, lean mouse binding data showed two affinities, one was not significantly different from obese (0.35 nM) the second was lower (1.18 nM) for DHM. Increases of approximately 5 fold and 3 fold in the brain content of beta-endorphin and met-enkephalin respectively, and no differences in brain dynorphin levels, were demonstrated in obese mice compared with lean controls. In obese mice, pituitary beta-endorphin content was 9 fold higher, met-enkephalin 4 fold higher and dynorphin 12 fold higher than in lean mice. The striking differences in opioid binding-site characteristics and in endogenous opioid peptide levels in obese compared with lean mice may contribute to the hyperphagia and, directly or indirectly, to the development of hyperglycaemia and hyperinsulinaemia in obese mice.

Animals↗
PubMed1989

Porcine islet isolation, cellular composition and secretory response.

Porcine islets were isolated by infusion of a warm collagenase solution into whole pancreata followed by static incubation at 37 degrees C for 15 minutes. The pancreata were then chopped into small pieces and the free islets purified by filtration and centrifugation over a ficoll gradient. The insulin:amylase ratio of the islets compared to that in the intact pancreas was determined in 19 pancreata and indicates that the isolated islets were of a high degree of purity. The distribution of insulin, glucagon, somatostatin and pancreatic polypeptide containing cells in pig pancreas sections was compared with that in rat. Porcine islets were much smaller and less well defined than rat islets with infiltration of acinar material even into the islet core. The levels of insulin, glucagon and somatostatin in porcine pancreas and isolated porcine islets were measured using conventional radioimmunoassay techniques. The ratio of these hormones in the pancreas was 105.1:5.8:1 respectively, and in the islets 105.1:0.68:0.087 respectively. Fragmentation of the islets during the isolation may have led to the loss of glucagon and somatostatin-containing cells. Islets cultured overnight and tested with a range of glucose concentrations for one hour did not show a significant stimulation of insulin secretion in the presence of 8.3 mM or 16.7 mM glucose compared to that in 2.8 mM glucose. However freshly isolated islets challenged with 8.3 mM, 13.9 mM and 22.2 mM glucose showed a 1.8 fold, 2.0 fold and 2.3 fold response respectively, over that in 2.8 mM glucose.(ABSTRACT TRUNCATED AT 250 WORDS)

Amylases↗
PubMed1988

Opiate-prostaglandin interactions in the regulation of insulin secretion from rat islets of Langerhans in vitro.

The inadequate insulin secretory response to glucose stimulation in non-insulin dependent diabetes has been attributed to many factors including high PGE2 levels blunting the secretory response, and to the existence of inhibitory opiate activity in vivo. The purpose of the present work was to see if there was a connection between these two independent theories. Radioimmunoassayable PGE2 in islets of Langerhans was found to be proportional to islet number and protein content and was typically 4 to 5pg/micrograms islet protein. Indomethacin (2.8 X 10(-5) M), sodium salicylate (1.25 X 10(-3) M) and chlorpropamide (7.2 X 10(-5) M) all lowered islet PGE2 levels and stimulated insulin release in vitro. Dynorphin (1-13), stimulated insulin release at a concentration of 6 X 10(-9) M, while lowering islet PGE2. Conversely, at a higher concentration, (6 X 10(-7) M), dynorphin had no stimulatory effect on insulin secretion and did not lower PGE2 levels in islets or in the incubation media. The stimulatory effects of dynorphin and sodium salicylate on insulin secretion were blocked by exogenous PGE2 (10(-5) M). PGE2 at a lower concentration (10(-9) M) did not exert any inhibitory effect on dynorphin- or sodium salicylate-induced insulin release. This concentration of exogenous PGE2 stimulated insulin release in the presence of 6mM glucose. Results from these experiments suggest that since an opioid peptide can lower endogenous PGE2 production in islets and since the stimulatory effects of the opioid peptide are reversed by exogenous PGE2 there may be interactions between these two modulators of insulin secretion.

Animals↗
PubMed1987

Heterogeneity of growth-hormone receptors detected with monoclonal antibodies to human growth hormone.

The specificity of hormone-receptor interactions has been examined with the aid of monoclonal antibodies (MABs) (EB1, EB2, QA68 and NA71) defining four non-overlapping antigenic determinants on human growth hormone (hGH). The results indicate that growth-hormone receptors in liver obtained from different sources differ with regard to their affinities and relative numbers; they may also differ with respect to the region of the growth-hormone molecule to which they bind. Antibody NA71 effectively inhibited hormone binding to all receptor preparations tested, although with various degrees of potency. Monoclonal antibody EB1 demonstrated a graded inhibition with respect to its ability to block 125I-hGH binding to receptors from various sources, the maximum inhibition being seen in receptor preparations from mouse and ovine liver and the minimum in rat liver. MABs EB2 and QA68 also showed various abilities to inhibit hormone-receptor interaction, depending on the origin of the receptor preparation. Furthermore, the receptor-binding characteristics of hormone-antibody complexes were dependent on whether the binding-site preparation was derived from pregnant, lactating or 'normal' animals. A particularly striking difference between the ability of hormone-MAB complexes to bind to receptors from different sources was seen for microsomes (microsomal fractions) derived from livers of animals of the 'Little' mouse strain. These animals become progressively obese, and it was shown that MABs were considerably more effective in inhibiting 125I-labelled hGH binding to microsomes from phenotypically obese mice than to those derived from their non-obese littermates. The results can be explained by the presence of multiple receptor types for GH, the relative proportions of which vary according to the physiological state of the animal, and possibly between species.

Animals↗
PubMed1983

The stimulation of glycogenolysis and gluconeogenesis in isolated hepatocytes by opioid peptides.

The opioid agonists [leucine]enkephalin, [D-Ala2,D-Leu5]enkephalin and dynorphin-(1-13)-peptide, but not morphine, stimulated the conversion of [2-14C]pyruvate into glucose and glycogenolysis when added directly to isolated hepatocytes. Naloxone produced a small but significant inhibition of both the basal and stimulated rate of incorporation of label into glucose but had no effect on the total glucose output by the cells. The effects of the opioid peptides were mediated by a cyclic AMP-independent mechanism.

Animals↗
PubMed1983

Opioid peptide effects on insulin release and c-AMP in islets of Langerhans.

The time course and specificity of the effect of opioid peptides on c-AMP production in the islets of Langerhans was examined. An enkephalin analogue, d-Ala2Me Phe4 Met(O)-ol enkephalin (DAMME, Sandoz) produced a significant stimulation of basal c-AMP levels, with a peak of stimulation at 5 minutes and a decline thereafter. These changes in intracellular c-AMP levels were of the same order of magnitude as those induced by other secretagogues, but did not coincide in time with the more rapid peak of enkephalin-induced insulin release. The rise in islet c-AMP and insulin secretion induced by DAMME and alpha-endorphin but not leu enkephalin was antagonised by naloxone. The effects of high and low concentrations of a variety of opioid peptides and naloxone on insulin release and islet c-AMP levels were determined, alpha-endorphin, dynorphin, leu enkephalin and met enkephalin all stimulated insulin secretion significantly, though not to the same extent. Higher concentrations of alpha-endorphin, dynorphin and met enkephalin inhibited insulin release relative to effects at low opiate concentrations. However, higher concentrations of leu enkephalin stimulated insulin release further. We conclude from these results that the mode of action of opioid peptides in stimulating insulin release is not via increased islet c-AMP exclusively. Furthermore, the results obtained with different classes of opioid suggest the presence of distinctive types of opiate receptor in islets of Langerhans.

Animals↗
PubMed1983

Effect of dynorphin on insulin and somatostatin secretion, calcium uptake, and c-AMP levels in isolated rat islets of Langerhans.

Dynorphin-[1-13], at concentrations of 5.8 X 10(-12) to 5.8 X 10(-9) M, stimulated insulin secretion from isolated islets of Langerhans of the rat, in medium containing 6 mM glucose. Higher concentrations of dynorphin had no significant effect on secretion. Dynorphin (5.8 X 10(-9) M) was unable to initiate insulin release from islets in the presence of 2 mM glucose, or to increase insulin secretion further in the presence of 20 mM glucose or 6 and 12 mM glyceraldehyde. Dynorphin-induced insulin secretion from islets was blocked by verapamil (5 microM) or by chlorpropamide (72 microM), but not by a mu opiate receptor antagonist, naloxone (0.11 microM), or by ICI 154129, a specific antagonist for the delta receptor (0.25 microM). Dynorphin had no effect on islet somatostatin secretion, under conditions in which insulin secretion was greatly stimulated. Glucose (20 mM) and glyceraldehyde (6 and 12 mM) significantly increased both insulin and somatostatin secretion. Dynorphin (5.8 X 10(-9) M) increased 45Ca2+ uptake into islets, and also increased intracellular islet c-AMP levels. These changes persisted when higher concentrations of dynorphin were used. These results suggest that (1) dynorphin is a very potent stimulus for insulin secretion; (2) dynorphin does not affect somatostatin secretion in static incubations of islets, in the same way as does glucose and glyceraldehyde; (3) dynorphin's effects may involve increased calcium ion movement and can be blocked by verapamil; (4) dynorphin can also increase islet c-AMP, and could thereby modulate the responsiveness of other secretagogues; (5) the actions of dynorphin on insulin secretion are not mediated by delta or mu opiate receptors in islets.

Animals↗
PubMed1981

Cell replication in the islets of langerhans of adult rats: effects of pregnancy, ovariectomy and treatment with steroid hormones.

It was possible to vary the replication rate of cells in the islets of Langerhans of adult rats. The rate of incorporation of [3H]thymidine into islet DNA was increased at 12 days of pregnancy to 2.3-fold and at 19 days of pregnancy to 1.3-fold that in control rats. Ovariectomy, which leads to lowered plasma levels of ovarian steroids, induced a significant and unexpected increase in the rate of thymidine incorporation into islets; treatment of ovariectomized rats with 2 micrograms oestradiol/rat per day for 3 days reversed this upward trend. When islets from normal rats were cultured with certain combinations of steroid hormones including progesterone and oestradiol or with insulin secretagogues, with the exception of glucose, a decreased rate of DNA synthesis was usually found compared with that in control rats. Since treatment with steroid hormones inhibited incorporation of [3H]thymidine into islets from ovariectomized rats and directly reduced incorporation into tissue-cultured islets from normal rats in vitro, it was concluded that increased levels of steroid hormones were not responsible for the higher rate of regeneration of islet cells in pregnant rats. However, a striking correlation between levels of blood glucose in vivo and DNA synthesis in islets in vitro has been observed.

Animals↗
PubMed1981

Insulin release and steroid-hormone binding in isolated islets of langerhans in the rat: effects of ovariectomy.

Ovariectomized rats showed a 30% increase in body weight and food intake over a 9 day period after operation. When pair-fed with normal controls, they had comparatively higher fasting serum levels of glucose and lower levels of insulin and progesterone than the normal rats. Treatment with oestradiol reversed these results. Insulin release from islets isolated from ovariectomized rats was significantly lower than from those of normal controls; the secretory responses were improved after administration of oestradiol to ovariectomized rats. Cytosol receptors for progesterone and oestradiol were measured in a 105 000 g supernatant fraction of islets from normal, ovariectomized and oestrogen-treated ovariectomized rats. Progesterone-receptor binding was dramatically reduced after ovariectomy but was restored to normal levels by oestradiol treatment of the rats. Oestradiol-receptor binding was not significantly affected by ovariectomy but was increased several fold by oestrogen treatment of ovariectomized rats. These results suggest that islets of Langerhans contain receptors for both progesterone and oestradiol, and that this receptor population is subject to change. Progesterone--but not oestradiol--receptor measurements could be correlated with alterations in the rates of secretion of insulin from islets. Oestrogen administration in vivo had profound effects on subsequent insulin release from islets, though this may have been mediated by way of an increase in the quantity of the progesterone receptor.

Animals↗
PubMed1980

Effect of enkephalins and morphine on insulin secretion from isolated rat islets.

The direct effects of an enkephalin analogue, (D-Ala2/MePhe4/Met/(O)-o1) enkephalin (DAMME), on insulin release from isolated islets of Langerhans of the rat have been investigated. DAMME had a dose-dependent effect on insulin secretion: low concentrations (10(-10) to 10(-8) mol/l) were stimulatory while high concentrations (10(-5) mol/l) were inhibitory in the presence of 8 mmol/l glucose. Similar effects were found with met-enkephalin, and with the longer acting alanine substituted met-enkephalin. Morphine sulphate (5 X 10(-7) mol/l) also stimulated insulin release. The effects of enkephalin and morphine were blocked by the specific opiate antagonist naloxone hydrochloride (1.2 X 10(-6) mol/l). The insulin secretory response of perifused islets to enkephalins and morphine was rapid, corresponding to the first phase of glucose induced insulin release. These observations suggest that there may be opiate receptors in islets, and that opioid peptides could modulate insulin release.

Animals↗
PubMed1980

The location of VIP in the pancreas of man and rat.

VIP has powerful stimulatory effects on both endocrine and exocrine pancreas but its localisation within the gland has not been established. In this study, human pancreas was obtained fresh at surgery (eleven) or within four hours of death (seven). The pancreas was also removed from rats (twenty-two). Immunocytochemical staining showed VIP to be present in fine nerve fibres in all areas of the pancreas. Many fibres were seen in the exocrine pancreas, running between the acini, and around ducts and blood vessels. In addition, dense networks of fibres were observed forming meshes around islets and occasional ganglia were found containing immunoreactive cell bodies. In general, there were fewer VIP fibres in the rat pancreas than in the human, but overall distribution was identical. The mean VIP content of whole human pancreatic tissue was 42 +/- 10 pmol/g wet weight (38 +/- 9 pmol/g in head, 49 +/- 6 pmol/g in body and 42 +/- 11 pmol/g in tail). Whole rat pancreatic tissue contained 28 +/- 7 pmol/g wet weight while preparations of isolated islets were found to contain 374 +/- 30 pmol/g. It is possible that the heavy VIP innervation of the islets described here indicates a role in the regulation of islet hormone release.

Animals↗
PubMed1979

Preservation of the effects of pregnancy on rat islets of Langerhans in tissue culture.

Islets of Langerhans, isolated from normal or 19-day pregnant rats, were cultured for 20 h at 37 degrees C in tissue culture medium 199. When islets were cultured in medium containing low glucose (5.5 mM), the higher adenylate cyclase activity and insulin secretory responses characteristic of islets from pregnant rats were maintained during the test period of 29 h. Islets from normal and pregnant rats were also cultured for 20 h in medium containing a very high glucose concentration (83.3 mM) in order to load the B cells with glycogen. It was found, after glycogen loading, that, while adenylate cyclase activity increased to a greater extent in islets from pregnant rats than controls, this activity was not increased in proportion to the striking changes in insulin release rate observed in pregnant rat islets. The results show that the difference in insulin secretory response between islets from normal and pregnant rats may be preserved when the islets are cultured for 20 h, and that these differences are enhanced for a variety of reasons after culture of islets in 83.3 mM glucose.

Adenylyl Cyclases↗