Using E-mail as an interactive teaching tool.

The author describes using e-mail as a tool for teaching ethics to internal medicine residents. By sending residents a description of an ethics problem and asking them to respond prior to a scheduled conference, he was able to ensure an informed discussion and to identify learners' knowledge and skill deficits.

Route of access of secretin into rabbit duodenal lumen during acid perfusion.

The route of entry of immunoreactive secretin into the duodenal lumen during acid perfusion is unknown. Possible sites include paracellular diffusion from the extracellular space, transapical secretion from S cells, or leaching from cells damaged by the perfusate. Antisecretin in the extracellular space and interstitium should reduce access due to paracellular diffusion from the interstitium without significantly affecting secretion or leaching. We therefore studied the effect of intravenous antisecretin antibody on luminal secretin output. Two groups of rabbits received either intravenous normal rabbit serum (controls) or antisecretin antibody, before perfusing a closed segment of duodenum with hydrochloric acid. Preliminary experiments established that duodenal perfusion with HCl concentrations below 0.025N produced no apparent mucosal damage on electron microscopy. HCl concentrations above this significantly damaged the mucosa. In the control group, perfusion with 0.01N, 0.0125N, and 0.025N hydrochloric acid resulted in a dose-dependent increase in secretin in the perfusate. Secretin output was markedly reduced in the group injected with secretin antibody. Antisecretin antibody significantly reduced bile flow at all levels of HCl concentration in the duodenal perfusate. These data suggest that luminal secretin is probably derived from the interstitium and travels to the lumen across narrow paracellular channels.

Identification and characterization of intragenic sequences which repress human immunodeficiency virus structural gene expression.

Examination of the life cycle of the human immunodeficiency virus (HIV) has shown that multiple levels of regulation exist, including some which require the virus-encoded Rev protein. In the absence of Rev, mRNAs encoding the structural proteins remain untranslated, a phenomenon which appears, in part, to be caused by nuclear entrapment of these RNA species. To examine the basis for repression of structural gene mRNA expression, a heterologous assay system was utilized to determine whether regions present within gag and pol contain elements capable of suppressing gene expression when present in cis. Both genes were found to contain cis-acting repressor sequences (CRS) that block gene expression when present within the 3' untranslated portion of a heterologous gene transcript. The element within pol was found to have the strongest repressive effect. While Rev alone was unable to reverse the repression observed with the pol sequence, addition of the env Rev-responsive element (RRE) in cis and Rev in trans did cause reversal of inhibition. Deletion mutagenesis defined a 260-bp element within the 3' portion of pol that contains a potent CRS which functions when present in the sense orientation. The corresponding region in HIV-2 pol was found to contain a functionally similar CRS element. To examine the mechanism of repression, the effects of the CRS elements on both the abundance and subcellular distribution of the mRNAs were examined. Neither was dramatically altered when examined in the context of a heterologous reporter (chloramphenicol acetyltransferase) mRNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Mutational analysis of the HIV-1 Rev protein and its target sequence, the Rev responsive element.

The human immunodeficiency virus type 1 (HIV-1) Rev protein is a positive posttranscriptional regulator of viral structural gene expression and essential for virus replication. Rev mediates its effects through interaction with an RNA target sequence, the Rev responsive element (RRE), present within the env mRNA. Previous studies have shown that the basic stretch of amino acids are required for Rev's ability to bind RNA, whereas residues present near the carboxy terminus are essential for full biological activity. Deletion mutagenesis was used to define the minimal domain required for RNA binding and function. We found that amino acids 8 through 67 confer full binding activity, whereas full biological activity requires the presence of residues 8 through 83. The minimal RNA binding sequence of HIV-1 Rev also interacts and functions with the HIV-2 and SIV RRE elements, indicating that the same domain is responsible for the biological activity with different, but related viruses. Mutational analysis of the RRE was also carried out in an effort to further define elements crucial for its function. Our findings indicate that interaction with Rev involves a stretch of three G nucleotides present at the base of a stem loop structure previously shown to be critical for Rev binding. These results suggest that the high degree of secondary structure of the RRE RNA may serve as a guide to bring Rev in contact with a primary nucleotide sequence required for stable protein-RNA association.

Gastropathy and ketoconazole malabsorption in the acquired immunodeficiency syndrome (AIDS).

STUDY OBJECTIVE: To correlate oral ketoconazole absorption with gastric acid secretion in patients with the acquired immunodeficiency syndrome (AIDS). DESIGN: Prospective measurement of maximal acid output and oral ketoconazole absorption with and without 0.1-N hydrochloric acid. SETTING: Hospital in-patients in university medical center. PATIENTS: Ten consecutive male patients with AIDS. INTERVENTION: Maximal acid output was determined after pentagastrin stimulation in all patients. Serum ketoconazole levels were measured the day after ingestion of a 200-mg ketoconazole tablet in the fasted state. On the final day, ketoconazole was ingested with 200 mL of 0.1-N hydrochloric acid. MEASUREMENTS AND MAIN RESULTS: Maximal acid output was below 15 mEq/h in 7 of 10 patients. In all 7, the area under the serum ketoconazole concentration-time curve was below normal (1.4 +/- 0.9 mg/h.L; mean +/- SE), and absorption was normalized by hydrochloric acid (9.9 +/- mg/h.L). Two of three patients with maximal acid outputs above 15 mEq/h had normal ketoconazole absorption (15.1 +/- 6.7 mg/h.L). CONCLUSIONS: The bioavailability of oral ketoconazole is reduced in patients with AIDS, largely as a result of gastric hypochlorhydria. Ketoconazole tablets should therefore be given with acid in these patients.