Search PubMed⌕ Search

Biomedical subjects

K Borland

Publications and source records attributed to K Borland.

13 recordsLinked to original sources
PubMed1991

Successful treatment of diabetes with the biohybrid artificial pancreas in dogs.

We have investigated a new hybrid artificial pancreas device to transplant islet allografts without immunosuppression. The device consists of a chamber through which passes a copolymer membrane connected to standard vascular grafts. Islets are placed inside the chamber but are outside of the blood stream. Nominal molecular porosity of 80,000 daltons permits free diffusion of nutrients and insulin across the membrane but inhibits the entry of immunoglobulins and immunocytes from the blood stream into the chamber. Initial studies focused on the technical feasibility of implanting the unseeded (no islets) devices. In 12 normal mongrel dogs, the arterial limb of the device was anastomosed end-to-end to the common iliac artery and the venous limb end-to-side to the common iliac vein. Vascular patency was monitored by an audible bruit over the device. Two devices currently remain patent at 388 and 421 days. The remaining experiments failed due to thrombosis and membrane rupture, with 2 failing as late as 170 and 279 days. In a second series, both arterial and venous anastomoses were done end-to-side and dogs were placed on low-dose aspirin therapy. All 8 dogs are currently maintaining patent unseeded devices (96-226 days postimplantation). Subsequent studies determined the function of devices seeded with isolated canine pancreatic islet allografts in totally pancreatectomized, severely diabetic dogs. Diabetes was controlled by once-a-day insulin injection. After 2-3 weeks of diabetic control, a seeded device was implanted. Diabetic control was monitored by fasting blood levels and postprandial and intravenous glucose tolerance tests, and vascular patency by the loudness of the bruit. In the first series of 6 dogs given seeded devices without aspirin, no significant function was discernible, with failure attributable to thrombosis, poor islet viability, and surgical complications. In the second series of 13 dogs given aspirin, 8 dogs have required an appreciably lower dose of injected insulin to maintain fasting blood glucose at acceptable levels. Of note are 4 dogs that required virtually no exogenous insulin for at least 3 weeks. One dog lost function on day 74 and another still requires no insulin at 267 days postimplantation. However, despite normal fasting glucose levels, the glucose tolerance tests showed delayed return to normal levels. Weight lost following pancreatectomy was rapidly regained in the presence of a functioning seeded device. Histologic examination of the removed devices revealed no signs of rejection.

Animals↗
PubMed1987

Differential expression of opioid peptide genes by testicular germ cells and somatic cells.

Spermatogenic cells have been previously shown to be a major site of testicular proenkephalin gene expression. Using RNA gel-blot analysis of purified mouse and hamster germ cells and of testes from prepuberal and germ cell-deficient mutant mice, we now have demonstrated that, in addition to its previously described expression by somatic (Leydig) cells, the gene for a second opioid peptide precursor, pro-opiomelanocortin (POMC), is also expressed by spermatogenic cells. Of particular significance is the finding that the RNAs for proenkephalin and POMC are differentially regulated during spermatogenesis. Two forms of POMC RNA were detected in mouse testis, a larger component 675- to 750-nucleotides (nt) in size common to somatic and spermatogenic cells and a smaller 625-nt RNA found only in pachytene spermatocytes. Two distinct, cell-specific proenkephalin RNAs were also shown to be present in mouse testis: a 1700-nt transcript previously shown to be expressed by spermatogenic cells and a 1450-nt form associated with somatic cells. These data suggest that proenkephalin- and POMC-derived peptides are produced by both somatic cells and germ cells in the testis and in germ cells these two families of opioid peptides may function at different stages of spermatogenesis.

Animals↗
PubMed1986

Interaction of rat Sertoli cells with a collagen lattice in vitro.

Sertoli cells from rats aged 15, 20, and 25 d were subcultured onto collagen-coated, plastic dishes. If the collagen was released from the plastic surface by rimming, the floating rafts of collagen showed uniform shrinkage. If the collagen was allowed to remain attached to the plastic, holes appeared in the collagen with cells from rats aged 25 d but not with those of 15 d. Cells from rats aged 20 d caused fewer and smaller holes to appear. The holes were associated with the formation of clumps of spherical cells from which elongated Sertoli cells extended into the surrounding collagen to end near holes. Rhodamine-phalloidin revealed diffusely distributed actin in the spherical cells in contrast to well-developed microfilaments in the peripheral elongated cells. Addition of cytochalasin B (5 micrograms/ml) to the medium prevented contraction of the floating rafts and the development of holes in the attached collagen. In addition, cytochalasin B caused the peripheral cells to become spherical and to separate from the clumps. Moreover, rhodamine-phalloidin revealed that actin in the peripheral cells occurred as clumps without microfilaments when cytochalasin B was present. When Sertoli cells were subcultured onto silicone rubber films, the cells produced wrinkling of the rubber surface within 4 h of plating. These observations were interpreted to mean that Sertoli cells exert local tractional forces on various substrata. These forces require actin, presumably acting by a contractile mechanism. When the collagen is attached to plastic and the cells are organized into clumps with radiating elongated cells (cells from rats aged 25 d), the tractional forces in the elongated cells reorganize the collagen fibers to produce holes. When cells are uniformly distributed (cells from rats aged 15 d), holes are not formed. When the collagen is released from the plastic surface, tractional forces cause the floating rafts to shrink. These interactions of the cells with collagen are likely to be important in determining the shape of the Sertoli cell in vivo, the polarity of the cell, and its biochemical differentiation.

Age Factors↗
PubMed1986

Production of components of extracellular matrix by cultured rat Sertoli cells.

Sertoli cells from rats aged 15, 20, and 25 days were cultured in plastic dishes and extracted with Triton X-100 (0.1 percent w/v) or sodium deoxycholate (2 percent w/v). Residues left after extraction were found to contain three proteins characteristic of extracellular matrix (fibronectin, collagen IV, and laminin). These proteins were identified by four methods: indirect immunofluorescence, co-migration with standard proteins on electrophoresis in polyacrylamide gels, immunoblotting (Western blots), and immunoprecipitation after incubating the Sertoli cells with [35S]methionine. In addition, fibronectin was identified by immunoelectron microscopy with a second antibody conjugated to colloidal gold. In the same cell residues, heparan sulfate was tentatively identified by the first of these methods. The cells used in these studies were shown, by electron microscopy, to be essentially pure cultures of Sertoli cells (greater than 95% pure). Since 100 percent of the cells examined showed positive and specific immunofluorescent staining with well-characterized antibodies to the four components of the extracellular matrix, and since studies with colloidal gold revealed the presence of fibronectin closely associated with and inside cells identified by electron microscopy as Sertoli cells, it must be concluded that Sertoli cells synthesize these four proteins and presumably heparan sulfate. Evidently, cultured Sertoli cells can synthesize and secrete some of the components of an extracellular matrix.

Animals↗
PubMed1986

Occurrence of spectrin-like protein in Y-1 adrenal tumor cells.

With the aid of two monospecific antibodies raised in rabbits (antimouse erythrocyte spectrin and antimouse brain spectrin), the presence of a spectrin-like protein was demonstrated in mouse adrenal tumor (Y-1) cells. Y-1 cells contain two large polypeptides, with mol wt characteristic of nonerythroid spectrin alpha- and beta-subunits (240,000 and 235,000). When proteins from plasma membranes of Y-1 cells were electrophoretically transferred to a nitrocellulose membrane, two polypeptides with mol wt of 240,000 and 225,000 were specifically stained with antimouse erythrocyte (rbc) spectrin immunoglobulin G (IgG). The rbc spectrin antibody was used to immunoprecipitate Y-1 spectrin from a neutral detergent (physiological ionic strength) cell extract. The 240,000 (alpha)- and 235,000 (beta)-dalton polypeptides were immunoprecipitated in a 1:1 molar ratio, despite the fact that the antibody recognizes only the alpha-subunit. Two-dimensional chymotryptic peptide-mapping analysis indicated that the 240,000- and 235,000-dalton subunits of Y-1 adrenal tumor spectrin are structurally unique and share limited homology with mouse rbc spectrin alpha- and beta-subunits, but are nearly identical to the mouse brain spectrin 240,000-dalton alpha-subunit and 235,000-dalton beta-subunit. Indirect immunofluorescence with anti-rbc or antibrain spectrin IgG and goat antirabbit IgG conjugated with rhodamine demonstrated intense staining at the plasma membrane and throughout the cytoplasm of Y-1 cells, with little staining within the nucleus.

Adrenal Gland Neoplasms↗
PubMed1985

Identification of a spectrin-like protein in Sertoli cells.

Sertoli cells prepared from rats ages 15 and 25 days were shown to contain a spectrin-like protein. Indirect immunofluorescence with monospecific antimouse erythrocyte immunoglobulin G (IgG) and with monospecific antimouse brain spectrin IgG revealed specific staining in Sertoli cells. Both antibodies precipitated two spectrin-like peptides of 240,000 and 235,000 daltons from cells solubilized with octyl glucoside. Proteins from Sertoli cell membranes were separated by electrophoresis on polyacrylamide gels containing sodium dodecyl sulfate and electrophoretically transferred to nitrocellulose membrane. Incubation of nitrocellulose membrane with either of the two antibodies, followed by horseradish peroxidase conjugated to second antibody, revealed only the larger, or alpha, spectrin subunit (Western blots). Both antibodies were used to provide immunoautoradiographic identification of the spectrin-like protein. In this procedure, spectrin and Sertoli cell membranes were shown to compete with [125I]-labeled spectrin from mouse erythrocytes for binding to antimouse erythrocyte spectrin IgG. Finally, two-dimensional proteolytic mapping of the 240,000- and 235,000-dalton peptides demonstrated limited spot homology with rat erythrocyte spectrin. However, subcellular fractions from Sertoli cells all contained a spectrin-like protein showing high homology from fraction to fraction. It is concluded that Sertoli cells contain a spectrin-like protein that is seen in cell fractions prepared by centrifugation, i.e., mitochondria, microsomes, nuclei, cytoplasm, and plasma membranes. Although homology with spectrin from erythrocytes or brain is not seen in peptide maps, the alpha subunit shares antigenic determinants with spectrin from erythrocytes. The beta subunit is believed to be precipitated by antispectrin as the result of binding to the alpha subunit, since the beta subunit shows no detectable antigenic homology with that of spectrin.

Animals↗
PubMed1985

The influence of insulin and insulin-like growth factor-I on hexose transport by Sertoli cells.

Insulin stimulates the synthesis of lactate by cultured Sertoli cells prepared from rats aged 13 days, to a much greater extent if glucose is present in the incubation medium than when it is absent. Insulin also stimulates the transport of 3-O-methyl-D-[14 C]glucose into cultured Sertoli cells. This increased transport results from a decrease in the Michaelis-Menten constant (Km) of methylglucose for the transport system without change in maximum velocity (Vmax). Moreover, insulin stimulates influx of the glucose analog and is without effect on efflux. Insulin does not alter transport of methylglucose in peritubular fibroblasts or in mixed populations of germ cells. It was observed that whereas insulin stimulates transport of methylglucose at micromolar concentrations, insulin-like growth factor I (IGF I) exerts the same effect at nanomolar (physiological) concentrations. Moreover, the response to insulin plus IGF I is the same as the maximal responses to either hormone alone. In view of the effects of insulin and IGF I on glucose transport by Sertoli cells and in view of the importance of lactate as a substrate for germ cells, it is suggested that IGF I may be important for the development of normal germinal epithelium in rat testes.

3-O-Methylglucose↗
PubMedDate not supplied

Evaluation of the hybrid artificial pancreas in diabetic dogs.

Immunoisolation of nonsyngeneic tissue using a selectively permeable membrane is designed to facilitate transplantation without the use of immunosuppression. The authors' studies have evaluated a hybrid artificial pancreas device that is implanted as an arteriovenous vascular shunt. Devices containing allogeneic or xenogeneic islets were implanted in diabetic dogs who had undergone pancreatectomies, and the devices eliminated the requirement for exogenous insulin for control of fasting glycemia in 11 animals for periods ranging from 1 to 8 months. Furthermore, unseeded devices in normal dogs have been shown to remain patent for over 2 years with low doses of aspirin as the only anticoagulant. These results indicate that this approach has potential as a therapy for diabetes.

Animals↗