Studies on the transport of enkephalin-like oligopeptides in rat intestinal mucosa.

Transport of [D-Ala2, D-Leu5]enkephalin (DADLE(], Tyr-D-Ala-Gly-Phe (TDAGP) and tyrosine into rat jejunum mucosal cells was investigated in vitro. Active transport of either the pentapeptide (DADLE) or the tetrapeptide (TDAGP) into jejunal villi was not detected. Because substantial degradation of these peptides occurred during incubation, the proteolytic enzyme inhibitors, bestatin (30 microM) or D-phenylalanine (20 mM), were added during uptake studies of DADLE or TDAGP, respectively. The presence of these inhibitors significantly reduced degradation of the oligopeptides; however, no accumulation of peptides occurred in the mucosal tissue. Tyrosine was actively transported by the jejunum mucosal cells demonstrating the viability of the transport mechanisms of this in vitro preparation. The results suggest that there are no active transport systems for enkephalin-like oligopeptides.

Enkephalin degradation in the guinea-pig ileum: effect of aminopeptidase inhibitors, puromycin and bestatin.

Degradation of enkephalin by aminopeptidases has been established as an important functional mechanism that terminates the pharmacological action of enkephalins in the guinea-pig ileum. Aminopeptidases are a family of enzymes and little is known regarding the specificity of individual enzymes with respect to the degradation of enkephalins. Puromycin is a general inhibitor of aminopeptidases and bestatin is a more selective inhibitor of Leu-aminopeptidases and aminopeptidase B. Both agents are capable of inhibiting enkephalin degradation in broken cell preparations from brain. However, only bestatin enhanced the pharmacological response to enkephalin in the guinea-pig ileum and ileal longitudinal muscle. Bestatin enhanced the response to enkephalin in a concentration-dependent fashion. Furthermore, bestatin also decreased the formation of [3H]Tyr and increased [3H]Leu-enkephalin content after incubation of the guinea-pig ileum with [3H]Leu-enkephalin. In contrast, puromycin did not shift the concentration-response curve to Met-enkephalin in either the intact guinea-pig ileum or the ileal longitudinal muscle and, likewise, no alteration in the degradation of [3H]Leu- or Met-enkephalin occurred with puromycin. A small enhancing effect of puromycin on the duration of the inhibitory effect of enkephalin was observed only in the guinea-pig longitudinal muscle. This enhancement cannot be explained by an effect on enkephalin degradation, but may be related to some other action of puromycin. These data support the importance of aminopeptidase activity to the degradation of enkephalin and indicate that enzymes which have properties in common with Leu-aminopeptidases rather than arylamidases may be the primary aminopeptidases responsible for terminating the pharmacological actions of enkephalins in intact guinea-pig ileal preparations.

Actin filaments in human skin fibroblasts are similar in normal persons and patients with Huntington's disease.

Actin filaments in skin fibroblasts from patients with Huntington's disease (HD) were examined using immunofluorescent methods. Actin filaments were seen along the axis of cell elongation (stress or sheath filaments) as well as in areas of membrane ruffling (lattice filaments). In some cases, filaments appeared to radiate from foci within the cell. Bundles of these filaments radiated in various directions at different depths within a cell. These structures are similar, in cells from both normal individuals and HD patients, to actin filaments observed in other cell types. The higher-than-normal confluent densities achieved in culture by fibroblasts from patients with Huntington's chorea do not involve alterations in the ultrastructure of actin filaments.