PubMed Health⌕ Search

Biomedical subjects

H Saunders

Publications and source records attributed to H Saunders.

At least 19 recordsLinked to original sources
PubMed1997

Protein phosphorylation and calcium uptake into rat forebrain synaptosomes: modulation by the sigma ligand, 1,3-ditolylguanidine.

The sigma ligand 1,3-di-O-tolylguanidine (DTG) increased basal dynamin and decreased depolarization-stimulated phosphorylation of the synaptosomal protein synapsin Ib without having direct effects on protein kinases or protein phosphatases. DTG dose-dependently decreased the basal cytosolic free Ca2+ concentration ([Ca2+]i) and blocked the depolarization-dependent increases in [Ca2+]i. These effects were inhibited by the sigma antagonists rimcazole and BMY14802. The nitric oxide donors sodium nitroprusside (SNP) and 8-(p-chlorophenylthio)guanosine-3',5'-cyclic monophosphorothioate decreased basal [Ca2+]i and the KCI-evoked rise in [Ca2+]i to an extent similar to DTG. SNP, but not DTG, produced a rise in cyclic GMP levels, suggesting that the effect of DTG on [Ca2+]i was not mediated via downstream regulation of cyclic GMP levels. DTG increased 45Ca2+ uptake and efflux under basal conditions and inhibited the 45Ca2+ uptake induced by depolarization with KCI. The KCI-evoked rise in [Ca2+]i was inhibited by omega-conotoxin (omega-CgTx)-GVIA and -MVIIC but not nifedipine and omega-agatoxin-IVA. The effect of DTG on decreasing the KCI-evoked rise in [Ca2+]i was additive with omega-CgTx-MVIIC but not with omega-CgTx-GVIA. These data suggest that DTG was producing some of its effects on synapsin I and dynamin phosphorylation and intrasynaptosomal Ca2+ levels via inhibition of N-type Ca2+ channels.

Animals↗
PubMed1996

Intrasynaptosomal free calcium levels in rat forebrain synaptosomes: modulation by sigma (sigma) receptor ligands.

The sigma receptor ligands (+) and (-)pentazocine and BD1008 (1-100 microM) were added to rat forebrain synaptosomes. Their effects on intrasynaptosomal free calcium ([Ca2+(+)]i) levels under basal conditions and after depolarisation with high potassium buffer (45 mM KCl), veratridine (25 microM) and 4-aminopyridine (4-AP, 1 mM) were determined. The sigma ligands elicited significant, concentration-dependent decreases in basal [Ca2+]i levels with an order of potency (-)pentazocine > (+)pentazocine = BD1008. The sigma ligands (at the maximum effective concentrations) also significantly inhibited the rise in [Ca2+]i levels produced by depolarisation with KCl, veratridine and 4-AP. The effect of (+) and (-)pentazocine (100 microM) to inhibit the depolarisation-dependent increase in [Ca2+]i levels was greater when veratridine and 4-aminopyridine were used to depolarise the synaptosomes than with KCl, whereas the effect of BD1008 (100 microM) was approximately equipotent using all three depolarising agents. However, BD1008 was more potent to inhibit the KCl-induced rise in [Ca2+]i compared to (+) and (-)pentazocine. The data demonstrate for the first time that sigma ligands decrease [Ca2+]i levels in rat forebrain synaptosomes and this suggests a possible mechanism for the changes to neuronal protein phosphorylation and neurotransmitter release previously observed with sigma ligands.

Animals↗
PubMed1996

Interaction of insulin, glucocorticoids, and protein kinase C in the regulation of insulin-like growth factor-binding protein-1 production by H4IIE rat hepatoma cells.

A sensitive RIA was used to examine regulation of IGFBP-1 in H4IIE rat hepatoma cells. IGFBP-1 was stimulated up to tenfold by dexamethasone and corticosterone, and this stimulation was abolished by RU486. The effect of dexamethasone increased with time in culture. Phorbol 12-myristate 13-acetate (PMA) stimulated IGFBP-1 up to fourfold with a maximal effect in short-term culture. Dexamethasone and PMA were additive in stimulating IGFBP-1. Under basal conditions IGFBP-1 production was linearly related to cell density: however, stimulation by dexamethasone was greatest in confluent cells, and PMA had a greater effect in sparse cultures. Insulin inhibited IGFBP-1 up to 80%, and this effect diminished with time in culture but was unaffected by cell density. Dexamethasone was stimulatory in the presence of a maximal inhibitory concentration of insulin, and insulin was inhibitory in the presence of maximal dexamethasone from 3-48 h in culture, regardless of cell density. PMA abolished the inhibitory action of insulin on IGFBP-1 secretion and mRNA expression during incubation periods of less than 4 h and not during longer incubations. PMA did not influence the stability of IGFBP-1 mRNA. We conclude that, in rat H4IIE cells, dexamethasone and PMA stimulate IGFBP-1 by independent mechanisms and speculate that when protein kinase C is activated the inhibitory action of insulin is blocked.

Animals↗
PubMed1994

Complex formation by human insulin-like growth factor-binding protein-3 and human acid-labile subunit in growth hormone-deficient rats.

Insulin-like growth factor-binding protein-3 (IGFBP-3), after first associating with IGF-I or IGF-II, is able to associate with the acid-labile subunit (ALS) and form a 140-kDa complex. To investigate the factors regulating ternary complex formation in vivo, human (h) IGFBP-3, hIGF-I, and hALS were administered in various combinations to GH-deficient (dw/dw) rats. hIGFBP-3 had a complex pattern of disappearance from the rat circulation, with an initial phase lasting minutes and a prolonged phase(s) lasting hours. If coinjected with hIGF-I, significantly more hIGFBP-3 was retained over 2 h. The molecular distribution of hIGFBP-3 was determined after size-separation chromatography. After an iv bolus of hIGFBP-3, 36.1 +/- 5.0% was in the 140-kilodalton complex at 5 min; this increased to 55.1 +/- 7.1% if hIGF-I was coinjected (P < 0.05). The 140-kDa complex disappeared slowly over hours, whereas 50- and 30-kDa forms of hIGFBP-3 cleared rapidly, with half-lives of minutes. To determine the importance of ALS in regulating the molecular distribution of hIGFBP-3, hALS was coinjected. Immunoreactive hALS disappeared slowly from the circulation and was shown to retain functional activity after 2 h in vivo. Coadministration of hALS did not influence the pattern of ternary complex formation, consistent with the presence of excess endogenous rat ALS. We conclude that ALS circulates in excess even in GH deficiency, is retained in the circulation for hours, and determines the stability of the 140-kDa complex, whereas IGF-I is a limiting factor in ternary complex formation by hIGFBP-3.

Animals↗
PubMed1994

Regulation of insulin-like growth factor-binding protein-1 in rat serum.

Previous studies support a role for insulin-like growth factor-binding protein-1 (IGFBP-1) in modulating insulin-like growth factor (IGF) availability for glucose homeostasis. We have developed a radioimmunoassay (RIA) for rat IGFBP-1 (rIGFBP-1) and have examined the regulation of circulating levels by nutritional and hormonal status. Rabbit antisera were raised against pure rIGFBP-1, and an assay was established with a sensitivity of 50 pg. In the rat, serum IGFBP-1 concentrations decrease with increasing developmental age. They were highest in fetal rat serum, exceeding 4 mg/L, and decreased to < 0.1 mg/L in adult animals. Serum rIGFBP-1 levels increased during fasting, 6-fold after 24 h and 18-fold after 48 h, and were suppressed to levels identical to ad libitum-fed control rats within 2 h of refeeding. Fasting levels were > 2-fold higher in female than male animals. IGFBP-1 concentrations were suppressed by > 50% in two rat models of insulin resistance. Levels increased in STZ-induced (streptozotocin) diabetes and were suppressed to normal with insulin treatment. Exercise stimulated rIGFBP-1 concentrations in fasting animals. On immunoblotting after SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis), rIGFBP-1 in serum appeared as a doublet with molecular masses at 31 and 33 kD. The components of this doublet did not vary across the range of experimental conditions. These observations indicate that the pattern of regulation of rIGFBP-1 is similar to that seen in previous studies of human IGFBP-1, with age, sex, and nutritional status being important regulators.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1993

Bioavailability of insulin-like growth factors (IGFs) in rats determined by the molecular distribution of human IGF-binding protein-3.

Insulin-like growth factor-binding protein-3 (IGFBP-3) forms a 140-kilodalton (kDa) complex with an acid-labile glycoprotein after complexing with IGF-I or IGF-II. To investigate the bioavailability of circulating IGFs in the rat, we determined the molecular distribution and disappearance of an iv bolus of human IGFBP-3 (130 micrograms/kg). Serum fractions were assayed after size-separation chromatography for human (h) and rat (r) IGFBP-3 with specific RIAs. Within 2 min of injection, 52.9 +/- 1.6% of the hIGFBP-3 appeared in a 140-kDa complex. This form remained in the circulation for hours, whereas hIGFBP-3 in 50- and 30-kDa forms disappeared within 30-60 min. The rapid complexing of hIGFBP-3 to the 140-kDa form did not occur in vitro. Measurement of endogenous rIGFBP-2 indicated that there was minimal exchange of hIGFBP-3 with rIGFBP-3 in the 140-kDa complex within the 60 min of the in vivo study. To determine the importance of IGF-I in regulating the molecular distribution of hIGFBP-3 in serum, the experiment was repeated in streptozotocin-diabetic rats, with total IGF-I levels 50% lower than control values. In these animals, 40.1 +/- 5.2% of the hIGFBP-3 appeared in the 140-kDa complex 2 min after injection, significantly less than that in controls (P < 0.05), and hIGFBP-3 disappeared more quickly from the circulation than in controls (P < 0.05). After coinjection of recombinant human IGF-I, the retention of hIGFBP-3 in the circulation was prolonged in both control and diabetic animals. Because IGFBP-3 must bind IGF before it can associate with the acid-labile subunit, these findings indicate a much greater availability of IGFs to the circulation than previously estimated.

Animals↗
PubMed1993

Effect of human insulin-like growth factor-binding protein-1 on the half-life and action of administered insulin-like growth factor-I in rats.

We have determined the effect of human insulin-like growth factor-binding protein-1 (hIGFBP-1) on the circulating half-life (t1/2) of human insulin-like growth factor-I (hIGF-I) and on hIGF-I-stimulated 2-deoxyglucose uptake in tissues of the cannulated conscious rat. The levels of hIGF-I in rat serum were measured by radioimmunoassay. The assay was carried out in the presence of partially purified rat IGF to remove interference from any IGFBPs not removed by acid-ethanol extraction. An intravenous bolus of 12.5 micrograms hIGF-I, given to 12-h fasted rats, disappeared from the circulation in a double exponential fashion with an initial t1/2 of 1.2 +/- 0.2 min (n = 8), which increased to 5.3 +/- 0.9 min when 100 micrograms hIGFBP-1 was co-administered (n = 5; P < 0.001). The second phase of disappearance of hIGF-I indicated an apparent t1/2 of 35.7 +/- 5.6 min which was not significantly altered by the co-infusion of hIGFBP-1. Circulating hIGFBP-1, measured with a primate-specific radioimmunoassay, disappeared in a single exponential fashion with a t1/2 of 8.8 +/- 0.7 min. A tracer amount of 2-deoxy-[1-3H]glucose was administered intravenously at the same time as the peptide(s) and the rate of tissue uptake and phosphorylation of 2-deoxy-[1-3H]glucose determined. Compared with a control group (n = 4), hIGF-I significantly stimulated hexose uptake into heart, soleus and red quadriceps muscles and hIGFBP-1 partially reversed this effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Regulation of rat insulin-like growth factor-binding protein-1: the effect of insulin-induced hypoglycemia.

Rat insulin-like growth factor-binding protein-1 (rIGFBP-1) was purified from H4IIE rat hepatoma cells by IGF-I affinity chromatography and reverse-phase HPLC. A rabbit antiserum (B2) was raised to rIGFBP-1 and a RIA established. Immunoreactive IGFBP-1 was present in rat amniotic fluid and in the medium conditioned by isolated rat hepatocytes and HTC rat hepatoma cells. To study the effect of hypoglycemia, fasting female Wistar rats were anesthetized and cannulated for multiple venous sampling after the administration of insulin or saline. Serum IGFBP-1 rose in adrenal intact rats from < 0.1 micrograms/ml to a maximum of 1.41 +/- 0.23 micrograms/ml approximately 120 min after insulin administration. Compared to adrenal-intact rats, adrenalectomized animals demonstrated a delayed rIGFBP-1 response to hypoglycemia and did not appear to have reached a maximum at 180 min. A slow rise in rIGFBP-1 levels throughout the sampling period was seen after saline injection in both adrenal-intact and adrenalectomized animals. Glucose, corticosterone, rat insulin, and human insulin levels were measured and none, alone, appeared responsible for the observed rIGFBP-1 responses. We conclude that 1) rIGFBP-1 is stimulated in response to hypoglycemia in a similar manner to glucose counterregulatory hormones, 2) an adrenal factor is required for an early rIGFBP-1 response to hypoglycemia, and 3) neither circulating glucose nor insulin levels, alone, are responsible for the observed patterns of response.

Adrenalectomy↗
PubMed1992

Radioimmunoassay of insulin-like growth factor-binding protein-6 in human serum and other body fluids.

A radioimmunoassay has been established for the insulin-like growth factor-binding protein, IGFBP-6, isolated from a human transformed fibroblast cell-line. The binding proteins IGFBP-I and IGFBP-3 did not cross-react, but both IGF-I and IGF-II markedly inhibited IGFBP-6 tracer binding to antiserum. This inhibition, greater for IGF-II than for IGF-I, was fully reversed by the addition of IGFBP-3 to sequester the IGFs. After fractionation of human serum and follicular fluid samples by gel chromatography, interference in the radioimmunoassay by fractions corresponding to the 150 kDa IGF-IGFBP complex could be eliminated by IGFBP-3. The equivalent fractions from cerebrospinal fluid and amniotic fluid fractionation did not interfere in the assay. The mean IGFBP-6 level in adult human serum was 0.221 +/- 0.110 mg/l, with values significantly higher in men than women, and slightly decreased in pregnancy. Similar values were seen in umbilical cord serum and in amniotic and follicular fluid samples, while the mean level in cerebrospinal fluid was slightly lower, 0.152 +/- 0.049 mg/l. This assay will facilitate studies on the regulation of IGFBP-6 production, and its role as an IGF carrier.

Amniotic Fluid↗
PubMed1990

Dual mechanisms of inhibition of the immune response by enterocytes isolated from the rat small intestine.

Antigen presentation by enterocytes isolated from the rat small bowel was studied by using T cell proliferation, and immunoregulatory function in an antigen-driven culture system, as indicator systems. Lymph node T cells obtained from rats immunized with ovalbumin (OA) failed to divide when cultured for 4 days in the presence of freshly isolated Ia+ enterocytes and OA. However, cell division was noted when enterocytes were removed after 18 h by Percoll gradient centrifugation, followed by culture of T cells for a further 4 days in the absence of antigen. The failure to divide in the primary culture was due to the secretion by enterocytes of a dialysable non-specific inhibitor. Antigen presentation by enterocytes was specific and was inhibited by monoclonal mouse anti-rat Ia antibody, OX6. An epithelial cell line (REC-2) was established from normal rat small intestine. These cells expressed Ia molecules following incubation with Concanavalin-A stimulated spleen cell supernatant, and were capable of both presenting antigen, and inducing interleukin-2 (IL-2) production, when cultured with primed T cells. Furthermore, Ia+ REC-2 cells functioned as stimulators in a primary mixed lymphocyte reaction (MLR). Both OA-primed T cells activated by enterocytes and antigen, and allogeneic MLR-activated T cells, mediated suppression which was not specific for the initiating antigen. These experiments indicated two mechanisms mediate suppression of cell division in gut mucosa. The contribution of these mechanisms to the control of inflammation at mucosal sites requires investigation.

Animals↗
PubMed1988

Changes in the axis of astigmatism: a longitudinal study.

Changes in the axis of astigmatism have been followed up in the same individuals over several decades. Only a proportion of subjects with direct astigmatism in their youth change to inverse astigmatism by way of oblique astigmatism.

Adolescent↗
PubMed1987

A longitudinal study of the age dependence of human ocular refraction--III. The mediation of changes from direct to inverse astigmatism examined by means of matrices of transition probabilities.

This study enquires into the manner in which the axis of astigmatism changes in the course of individual refractive histories. Specifically, two related problems are addressed: (1) how is the change from direct to inverse astigmatism mediated, and (2) what is the range of relative proportions of each of four variables (spherical ametropia, direct, inverse and oblique astigmatism) that occur in a sample population so that it can be considered randomly sampled and well distributed? Solutions to both problems are obtained by calculation of the probabilities with which transitions between such variables occur. A moderately sized longitudinal sample is used to demonstrate the new method. One of the conclusions is that the biological strategy for the mutation of the astigmatic axis is multi-faceted and that there is unlikely to be a single cause which can explain the process by which inverse astigmatism is achieved.

Adult↗
PubMed1986

A longitudinal study of the age-dependence of human ocular refraction--I. Age-dependent changes in the equivalent sphere.

Following on from a cross-sectional analysis of refraction data (Saunders, 1981), the present paper attempts the evaluation of serial recordings of a new sample of refractive corrections using longitudinal methods. This study compares the results of the cross-sectional and longitudinal methods, investigates whether or not the latter supports the conclusions of the former, examines to what accuracy this is achieved and, where the results differ, seeks a reason for this. It is demonstrated that in spite of such differences the two methods coincide in their conclusions.

Adolescent↗
PubMed1986

A longitudinal study of the age dependence of human ocular refraction--II. Prediction of future trends in medium and high myopia by means of cluster analysis.

A sample population of myopes with an initial correction of 2 DS or more is extracted from the longitudinal sample of ametropes reported by Saunders (1986). The myopes are partitioned by means of cluster analysis and, as a result, three distinct groups of myopes are identified. The time/regression equations which best describe the groups are stated. It is concluded that meaningful long-term prognosis of medium and high myopes is unlikely and that reasonable prediction of short-term trends requires at least two consecutive refraction data to determine the group allocation of a myope.

Age Factors↗