Regulation of taurine transport by Escherichia coli heat-stable enterotoxin and guanylin in human intestinal cell lines.

The human colon carcinoma cell lines Caco-2 and HT-29 take up taurine actively. Treatment of Caco-2 cells with Escherichia coli heat-stable enterotoxin (STa) or with guanylin inhibited taurine uptake by approximately 40%. In contrast, neither STa nor guanylin changed the uptake of taurine in HT-29 cells. The inhibition in Caco-2 cells was associated with a decrease in the maximal velocity as well as in the affinity of the transporter. STa caused a 21-fold increase in guanosine 3',5'-cyclic monophosphate (cGMP) levels in Caco-2 cells with no change in cAMP levels. Neither cGMP nor cAMP levels were affected by STa treatment in HT-29 cells. Experiments with protein kinase inhibitors suggested that protein kinase A may mediate the observed effects of STa on taurine uptake. In accordance with this suggestion, treatment of Caco-2 cells with cholera toxin, which elevated intracellular cAMP levels, was found to inhibit taurine uptake. The steady state levels of the taurine transporter mRNA transcripts were not altered as a result of STa treatment. Studies with Caco-2 cells grown on permeable filters revealed that STa acts from the apical side. The taurine uptake from the apical side was inhibited by STa, but the taurine uptake from the basolateral side remained unaffected. It is suggested that the activity of the intestinal taurine transporter may be regulated by protein kinase A at a posttranslational level and that the intestinal absorption of taurine may be impaired during infection with enterotoxigenic strains of E. coli.

Cryopreservation of murine ovarian tissue.

To determine the feasibility of ovarian transplantation using cryopreserved tissue, ovaries were removed from anesthetized 12- to 20-week-old female mice. The controls consisted of a sham-operated group and an oophorectomized group, and the experimental groups were autologous transplants with and without cryopreservation. Ovaries for cryopreservation were suspended in 1.4 M dimethyl sulfoxide Tyrode's solution, at 22 degrees C for 5 min and cooled at a controlled rate (0.5 degrees C/min) to -55 degrees C. The ovaries were stored in liquid nitrogen for 1 to 30 days and then thawed at room temperature. Thawed ovarian tissue was washed free of dimethyl sulfoxide and transplanted. Subsequent daily examination of vaginal cytology indicated ovarian endocrine activity in all groups except those oophorectomized without transplants. Animals receiving ovarian tissue, fresh and cryopreserved, were euthanized at diestrus I, 6 weeks postoperatively, for ovarian histology; both groups demonstrated folliculogenesis. The histology and endocrine function of autotransplanted cryopreserved ovaries were similar to those of nonfrozen transplanted ovaries and of ovaries in sham-operated groups.

Properties of taurine transport in a human retinal pigment epithelial cell line.

The characteristics of taurine transport were studied in a human retinal pigment epithelial cell line (HRPE). Uptake of taurine into monolayer cultures of the HRPE cells was markedly stimulated by the presence of NaCl in the uptake medium whereas the uptake was negligible in its absence. This NaCl-dependent uptake was an active process as the cells were able to accumulate taurine against a concentration gradient. The uptake rate of taurine was found to be many-fold greater than that of gamma-aminobutyric acid (GABA). Unlabeled taurine and GABA competed with radiolabeled taurine for the uptake process, the former being more effective than the latter. However, uptake of radiolabeled GABA was not affected by unlabeled taurine and GABA. Substrate specificity studies revealed strong interaction of beta-amino acids with the transport system responsible for taurine uptake. alpha-Amino acids failed to inhibit taurine uptake. A specific anion requirement was observed for optimal activity of the taurine transport system and Cl- was the most supportive among several anions tested. Kinetic analyses showed that multiple Na+ and one Cl- were involved in transfer of one taurine molecule. The transport process consisted of a single saturable system with a Michaelis-Menten constant of 2.0 +/- 0.1 microM. These results show that the HRPE cell line expresses a high-affinity taurine transport system. This is the first demonstration of the presence of the taurine transporter in the human retinal pigment epithelium and the HRPE cell line may provide a useful model system for future studies involving taurine transport in the retinal pigment epithelium.

The effects of burnishing NaF/kaolin/glycerin paste on dentin permeability.

The effects on dentin permeability of burnishing NaF, kaolin, or glycerin, alone and in various combinations, were determined using an in vitro system. The results indicate that the important variable was not any of the constituents of the paste but the burnishing process itself. Burnishing dentin creates a partial smear layer on the dentin surface, thereby occluding the orifices of dentinal tubules sufficiently to reduce fluid movement across dentin 50 to 80%.

Decision analysis in evaluation of hypergastrinemia.

Hypergastrinemia and gastric acid hypersecretion are the principal laboratory features of Zollinger-Ellison syndrome. Decision and cost-effectiveness analyses were employed in the present study to compare and contrast the diagnostic strategies of initial gastric analysis followed by secretin infusion test versus secretin infusion test alone in the evaluation of hypergastrinemia in patients suspected of having gastrinoma. The results of this study showed that 59 percent of patients with elevated serum gastrin values were either hypochlorhydric or achlorhydric. Application of decision analysis to either diagnostic strategy demonstrated that gastric analysis followed by secretin infusion test, if indicated, was superior in expected value than secretin infusion test alone. Likewise, in this group of patients, performance of gastric analysis in the outpatient setting prior to secretin infusion testing was financially more advantageous than performance of secretin infusion testing alone. These results also demonstrate the importance of performing gastric analysis prior to anticipated hospitalization for evaluation of suspected gastrinoma. Such testing would obviate unnecessary hospitalization and medical costs.

Immune disorders of the gastrointestinal tract and liver.

Immune disorders of the gastrointestinal tract and hepatobiliary systems comprise a diverse group of illnesses which share in common certain overlapping and yet distinctive expressions of cellular and humoral immunity. As is evident from material contained in this article, controversy and disparate results frequently characterize the study of immune mechanisms in a given disease process. Nonetheless, advances in quantitation of specific immunocyte function and phenotypic expression have greatly facilitated the depth of understanding of the immune process related to these disorders. Challenges for future clinical investigation of these disorders are to characterize cell-specific target antigens to which immunologic attack is directed and to unravel the immunogenetic mechanisms that trigger and direct immune-mediated injury to host tissues. It is anticipated that continued investigation of immune disorders of the gastrointestinal tract and liver will clarify pathogenetic mechanisms and thus permit formulation of rational and effective therapies.

Clinically significant vitamin B12 deficiency secondary to malabsorption of protein-bound vitamin B12.

Protein- (chicken serum) bound [57Co]cyanocobalamin absorption was evaluated in five hypochlorhydric patients who had developed B12 deficiency despite having normal absorption of unbound crystalline vitamin B12. All five patients had decreased urinary excretion of protein-bound B12 (0.06--0.34%) as compared to twelve normal controls (0.61--5.6%), P less than .001. Improvement in protein-bound B12 absorption in four of the five patients occurred with the exogenous administration of hydrochloric acid, pepsin, gastric intrinsic factor, or a combination thereof. Vitamin B12 deficiency developing in the setting of hypochlorhydria may result from deficiency of acid-peptic digestion of B12 bound to protein and/or a relative deficiency of intrinsic factor. This digestive defect is not detected with tests which measure the absorption of unbound crystalline B12 but is detected by a simple test which employs B12 bound to chicken serum as the form of protein-bound B12.

Immunity to colon cancer assessed by antigen-induced inhibition of mixed mononuclear cell migration.

A purified preparation of mixed human peripheral blood lymphocytes and monocytes was used in an inhibition-of-migration assay for cell-mediated immunity to cancer of the colon. This preparation was reproducibly antigen-responsive and migrated with greater reliability than did a more complex cell mixture. Of 27 patients with this disease, cells from 24 showed inhibited migratio in response to colon carcinoma antigen. Uninhibited migration patterns were found in each of the 52 cancer-free controls, including eight patients with nonmalignant disease initially diagnosed as cancer of the colon, and in nine patients with surgically cured adenocarcinoma of the colon.