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Biomedical subjects

E K Frandsen

Publications and source records attributed to E K Frandsen.

15 recordsLinked to original sources
PubMed1988

Receptor binding of pancreatic spasmolytic polypeptide in intestinal mucosal cells and membranes.

Rat intestinal mucosal cells contain receptors for pancreatic spasmolytic polypeptide (PSP). The binding of 125I-PSP was rapid, saturable, reversible and specific. PSP competed with 125I-PSP for binding to the receptors and 10(-7) M of PSP half-maximally inhibited 125I-PSP binding. The normalized PSP dose-response graphs in intact cells and crude membranes were superimposable. Scatchard plots of PSP binding to membranes were curvilinear, indicating multiple classes of binding sites, negative cooperative interaction between sites or a combination of both. PSP increased the rate of dissociation of the 125I-PSP-receptor complex compared to the rate observed by dilution only, thus giving evidence that negative cooperative interaction may occur between PSP binding sites. The half-life of the fast dissociating complex was about 1.5 min and that of the slow dissociating complex 38 min. These values were independent of the receptor occupancy. The increased rate of dissociation at high receptor occupancy stemmed from a shift in the ratio of the pool sizes of fast and slow dissociating receptor complexes.

Animals↗
PubMed1988

Influence of timing in the fructosamine assay.

The fructosamine assay, based on the measurement of the reducing activity in serum at alkaline pH, provides an index of protein glycation. The reducing activity is expressed in equivalents of 1-deoxy-1-morpholinofructose (DMF) by direct comparison with the activity either of this synthetic compound or with a secondary protein standard calibrated against DMF. This study reports the influence of assay timing on the apparent serum fructosamine concentration. The kinetics of alkaline reducing activity in serum differed from that in both DMF and a secondary protein standard. When compared with DMF, activity in serum increased but decreased relative to the protein standard as the pre-incubation interval of the assay was shortened. The use of secondary protein standards results in underestimation of serum fructosamine concentrations when the pre-incubation phase of the assay is shorter than that used for the calibration of the secondary standard. Ascorbate exerted an inhibitory effect in fructosamine assays with pre-incubation times exceeding 5 min. The inhibition increased with both the concentration of ascorbate and the duration of the pre-incubation.

Ascorbic Acid↗
PubMed1988

Serum fructosamine in diabetic pregnancy.

Serum fructosamine was measured in 275 blood donors, in 559 subjects with a normal pregnancy, in 32 gestational diabetics being treated with insulin and 69 being treated by diet only, and in 53 pregnant subjects with established diabetes. In none of the pregnant subgroups did the mean fructosamine concentration exceed that of the donor group. The concentration in normal pregnant subjects showed a modest but significant decrease with gestational age and an increase with maternal age. Hyperglycemic non-pregnant subjects (n = 24) had significantly increased serum fructosamine concentrations, and 96% of these subjects exceeded the upper 95% confidence limit for fructosamine in the donor group. A highly significant correlation was demonstrated between serum fructosamine and preprandial plasma glucose in the hyperglycemic subjects. A weak, but significant, correlation was shown for the entire population sample of antenatal patients, while this was non-significant within each of the sub-groups comprising established diabetics and gestational diabetics, respectively.

Adult↗
PubMed1987

Glucagon receptor binding, dissociation and degradation in rat liver plasma membranes studied by a microperifusion method.

The association process of glucagon receptor binding in purified rat liver plasma membranes and prolonged incubation of the hormone-receptor complex at 30 degrees C did not result in degradation of bound labelled glucagon. In contrast, up to 95% of the non-membrane-bound labelled glucagon was degraded. The rate of spontaneous dissociation of the glucagon-receptor complex was slow, and amounted to about 0.1% per min of that bound. GTP greatly enhanced the rate of dissociation. Half the maximal dissociation of the complex was effected by 10(-5) mol/l of GTP under equilibrium binding conditions. At maximally effective concentrations of GTP, 80% of the glucagon-receptor complex was dissociated within 2 min. A microperifusion system for the perifusion of isolated plasma membranes was devised and used for the separation of labelled glucagon from the plasma membranes subsequent to a GTP-induced dissociation of the hormone-receptor complex. Rebinding of the dissociated peptide to fresh membranes showed that maximum binding ability was retained. The glucagon molecule was protected against degradation while bound to the receptor, indicating that the glucagon effector system is completely separate from the inactivating system(s) in isolated plasma membranes. Thus, the hormonal effect of glucagon could be exerted through the sequential interaction of each glucagon molecule with several receptors.

Animals↗
PubMed1987

New, simple insulin-receptor assay with universal application to solubilized insulin receptors and receptors in broken and intact cells.

A new, simple insulin-receptor-binding assay has been devised. The assay is based on the separation of free and receptor-bound 125I-labeled insulin in 80% ethanol. It was found that the insulin-receptor complex was fully stable at this ethanol concentration, regardless of the source of the receptor employed. The assay has been evaluated with solubilized insulin receptors and membrane-bound receptors from human placenta and porcine liver as well as intact cells with the IM-9 cell line. The assay is simple, rapid, and has large capacity. Comparisons of the ethanol-based assay to the conventionally employed assays with polyethylene glycol or microfuge centrifugation for the separation of free and bound 125I-insulin revealed large discrepancies between the assays. The ethanol-based assay always appeared to provide a better separation. Microfuge centrifugation of placental membranes precipitated approximately 3% of the ethanol-precipitable insulin-receptor complex, while polyethylene glycol precipitation of solubilized insulin receptors varied between 40 and 80% of the ethanol precipitability, depending on the receptor concentration employed.

Cell Membrane↗
PubMed1986

Receptor binding of pancreatic spasmolytic polypeptide (PSP) in rat intestinal mucosal cell membranes inhibits the adenylate cyclase activity.

The recently isolated pancreatic spasmolytic polypeptide, PSP, interacted with specific binding sites in the gastrointestinal tract and inhibited the adenylate cyclase activity in rat intestinal mucosal cell membranes. The binding sites appeared to be heterogeneous and Scatchard analysis of the binding data indicated the presence of at least two classes of sites. The high-affinity low-capacity binding sites and the low-affinity high-capacity binding sites had apparent dissociation constants of 1.3 X 10(-7) mol/l and 4.2 X 10(-6) mol/l, respectively. The PSP induced inhibition of the adenylate cyclase activity was independent of the stimulatory state of the enzyme. The basal activity as well as that stimulated by VIP and secretin was half maximally inhibited at approximately 3 X 10(-5) mol/l of PSP. The inhibitory effect of PSP was independent of the agonist concentration employed. PSP did not affect the receptor binding of VIP nor did VIP affect the receptor binding of PSP.

Adenylyl Cyclase Inhibitors↗
PubMed1985

Structure-function relationships in glucagon. Re-evaluation of glucagon-(1-21).

Glucagon-(1-21) was prepared fully synthetically as well as by carboxypeptidase A digestion of natural porcine glucagon. Neither of the two preparations had glucagon agonistic effects with regard to receptor binding or adenylate cyclase activation in purified rat liver plasma membranes. Nor did these preparations contain lipolytic activity in isolated free fat cells. A preliminary batch of glucagon-(1-21) prepared by carboxypeptidase A digestion did, however, contain 1-2% glucagon bioactivity. This activity was separated from glucagon-(1-21) by high-performance liquid chromatography and quantitatively recovered in four minor hind peaks which eluted close to but not in a position identical to the elution position of native glucagon.

Adenylyl Cyclases↗
PubMed1985

Reduction of diabetes incidence of BB Wistar rats by early prophylactic insulin treatment of diabetes-prone animals.

A group of 36 diabetes-prone BB Wistar rats were given prophylactic insulin treatment with heat-treated bovine ultralente insulin (15 IU X kg-1 X day-1) from 50 to 142 days of age. The incidence of Type 1 (insulin-dependent) diabetes at the end of the treatment period was compared to that of 36 control animals given insulin only from the first day of glycosuria. At withdrawal of the prophylactic insulin treatment, 6 of 36 treated animals were insulin-dependent, while 15 of 36 control animals had developed diabetes (p less than 0.02). One control animal (day 153) and 2 insulin-treated animals (day 172 and 186) subsequently developed diabetes, yielding an overall diabetes incidence of 16 of 36 controls against 8 of 36 insulin treated (p less than 0.05). The finding that prophylactic insulin treatment of diabetes-prone BB Wistar rats reduced the incidence of diabetes suggests a relationship of the immune destruction of B cells to the endogenous insulin production/secretion rate.

Animals↗
PubMed1976

Action of cholecystokinin, cholinergic agents, and A-23187 on accumulation of guanosine 3':5'-monophosphate in dispersed guinea pig pancreatic acinar cells.

The COOH-terminal octapeptide of cholecystokinin (CCK-OP) and carbamylcholine each increased calcium outflux, cellular cyclic GMP and amylase secretion in dispersed guinea pig pancreatic acinar cells. Following addition of CCK-OP or carbamylcholine, cellular cyclic GMP increased as early as 15 s, became maximal after 1 to 2 min, and then decreased steadily during the subsequent incubation. For both CCK-OP and carbamylcholine there was close agreement between the dose-response curve for stimulation of calcium outflux and that for increase of cellular cyclic GMP. With CCK-OP an effect on both functions could be detected at 10(-10) M and maximal stimulation occurred at 3 X 10(-8) M. With carbamylcholine an effect on both functions could be detected at 10(-5) M and maximal stimulation occurred at 3 X 10(-3) M. Atropine inhibited stimulation of both cyclic GMP and calcium outflux by carbamylcholine but not by CCK-OP. Stimulation of calcium outflux or cellular cyclic GMP by CCK-OP or carbamylcholine did not require extracellular calcium since stimulation occurred in a calcium-free, ethylene glycol bis(beta, beta-aminoethyl ether) N,N'-tetraacetic acid (EGTA)-containing solution. The divalent cation ionophore A-23187 increased bidirectional fluxes of calcium, cellular cyclic GMP and secretion of amylase from dispersed pancreatic acinar cells. Like CCK-OP and carbamylcholine, the ionophore stimulated calcium outflux and cellular cyclic GMP in a calcium-free, EGTA-containing solution. These results suggest that in pancreatic acinar cells the initial step in the sequence of events mediating the action of ionophore as well as that of CCK-OP and carbamylcholine is stimulation of calcium outflux, and that this stimulation then increases cellular cyclic GMP.

Animals↗
PubMed1976

Structure-function relationship: immunologic.

It is suggested that the antigenic site of glucagon for the specific sera is located within the 24-29 section of the molecule and within the 2-23 section for the fully cross-reacting sera. Biologically inactivated glucagon may retain immunoreactivity in spite of the loss of receptor-binding activity.

Animals↗