Structure and expression of novel spliced leader RNA genes in Caenorhabditis elegans.

Approximately 25% of Caenorhabditis elegans genes are organized as operons. Polycistronic transcripts are converted to monocistronic mRNAs by 3' cleavage/polyadenylation and 5' trans-splicing with untranslated, 5' termini of mRNAs encoded by downstream genes in operons are acceptors for > or = 7 recently discovered "novel" SLs and a classical SL (SL2). Diversity in SL exons is now partly explained by the discovery and characterization of five novel genes that encode C. elegans SL RNAs. These novel SL RNAs contain a 22- or 23-nucleotide SL followed by conserved splice donor and downstream sequences that are essential for catalysis of trans-splicing reactions. The SL3 alpha, SL4, and SL5 RNA genes are tightly clustered on chromosome III; their 114-nucleotide transcripts deliver three distinct SLs to mRNAs. The SL3 beta and SL3 gamma RNA genes are on chromosome I, but are not tightly linked. SL RNAs 3 alpha, 3 beta, and 3 gamma provide identical 5' leader exons, although their 3' sequences diverge. Transcription of SL 3-5 RNA genes appears to be driven by flanking DNA elements that are homologous with segments of promoters for the C. elegans SL2 RNA and small nuclear RNA genes. RNase protection assays demonstrated that novel SL RNAs are transcribed in vivo and accumulate in the poly(A-) RNA pool. SL3 exons are transferred to mRNAs as frequently as SL2 exons. In contrast, SL4 is appended to mRNAs 10% as frequently as SL3. The abundance of SL4 RNA increased 6-fold during postembryonic development, and the SL4 RNA gene promoter is active principally in hypodermal cells.

Outcome of carotid endarterectomy performed at a community medical center.

From 1990 to 1992 there was a 43% increase in the number of carotid endarterectomies (CEAs) performed at our institution. Not coincidentally the North American Symptomatic Carotid Endarterectomy Trial study was published in August 1991. To determine whether CEAs could be performed safely at community medical centers, records of 181 consecutive CEAs performed during a 30-month period at a suburban community medical center were reviewed. CEAs were performed by 14 surgeons: six vascular, three thoracic, and five general surgeons. Among all patients 87% had lesions with > or = 70% stenosis. Seventy percent of CEAs were performed on symptomatic patients, 84% of whom had stenoses > or = 70%. Among asymptomatic patients 96% had stenoses > or = 70%. There were five instances of neurologic complications in the perioperative period--two transient ischemic attacks, two reversible ischemic neurologic deficits, and one permanent neurologic deficit. One patient died. The mortality rate was 0.6%, the combined major stroke/mortality rate was 1.2%, and the any stroke/mortality rate was 2.2%. There were five patients with nonfatal major complications--one with myocardial infarction, one with pulmonary edema, one with congestive heart failure, and two with postoperative arrhythmia. Thirteen minor complications included eight cases of cranial nerve dysfunction. These data demonstrate that CEAs can be performed safely at community medical centers.

The effect of choline supplementation on hepatic steatosis in the parenterally fed rat.

Information regarding hepatic function during total parenteral nutrition in rats is often extrapolated to the clinical situation, but the steatosis observed in that species may simply reflect choline deficiency and be irrelevant to man. The effect of choline supplementation on hepatic lipid content and triglyceride secretion was examined in parenterally fed rats. Eighty to 90-day-old rats were randomized into three groups; group I received oral Purina Chow ad libitum, groups II and III received identical total parenteral nutrition regimens with the exception that group III received supplemental choline. After 7 days, peripheral triglyceride uptake was inhibited with Triton WR1339, the rate of secretion of 14C-labeled triglyceride measured after a bolus injection of 1-14C-palmitic acid, and total hepatic lipid content was measured. Total hepatic lipid content was elevated in group II (86.3 mg/g) and group III (83.3 mg/g), and both differed significantly from the control group I (35.2 mg/g, p less than 0.01), but the choline supplementation appeared to make no difference. Hepatic secretion of 14C-palmitic acid as 14C-triglyceride was reduced in group II (0.73%/ml plasma), and group III (0.72%/ml plasma) compared to group I (1.06%/ml plasma, p less than 0.05), and was unaffected by choline. The hepatic steatosis produced in the parenterally fed rat did not appear to be due to choline deficiency but to some other factors which may be important in man.

Pathogenesis of hepatic steatosis in the parenterally fed rat.

Hepatic steatosis frequently complicates total parenteral nutrition (TPN). Some of the mechanisms responsible were examined in rats receiving calories as dextrose (CHO-TPN) or dextrose plus lipid emulsion (Lipid-TPN). Hepatic triglyceride content increased approximately threefold after CHO-TPN and twofold after Lipid-TPN (P less than 0.02). Hepatic triglyceride fatty acid composition reflected endogenous synthesis. Hepatic acetyl-Coenzyme A carboxylase specific activity increased fourfold after CHO-TPN and twofold after Lipid-TPN, and it correlated positively with hepatic lipid content (r = 0.82). The activities of the microsomal enzymes of complex lipid synthesis were unchanged in the TPN groups. Both TPN regimens suppressed hepatic triglyceride secretion, measured by the rise in plasma triglyceride and the incorporation of [14C]palmitic acid into plasma triglyceride after intravenous Triton. Hepatic triglyceride secretion correlated negatively with total hepatic lipid content (r = -0.89). CHO-TPN increased the uptake of a radiolabeled triglyceride emulsion and increased hepatic lipase activity, whereas Lipid-TPN decreased both. Both adipose and cardiac lipase were higher for Lipid-TPN animals than for CHO-TPN or control animals. Hepatic 14C-triglyceride content was increased in both TPN groups as compared with controls after the injection of 1-[14C]-palmitic acid. This increment was proportional to the decreased hepatic secretion. Triglyceride fatty acid oxidation was significantly suppressed by CHO-TPN, less so by Lipid-TPN. Free fatty acid oxidation was suppressed only by CHO-TPN. The results suggest that the steatosis induced by TPN in rats was due to enhanced hepatic synthesis of fatty acid and reduced triglyceride secretion. Reduced hepatic triglyceride uptake, enhanced fatty acid oxidation, and enhanced peripheral tissue plasma triglyceride lipolysis when CHO-TPN is supplemented with lipid may modulate the accumulation of hepatic triglyceride and, along with reduced synthesis of fatty acid, lead to a lower hepatic triglyceride content.

A simple method of obtaining repeated venous blood samples from the conscious rat.

A method for repeated venous blood sampling from the conscious, unrestrained rat is described using a silastic femoral vein catheter buried within a scrotal pouch.