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Biomedical subjects

R J Rubin

Publications and source records attributed to R J Rubin.

At least 55 records · Page 3Linked to original sources
PubMed1990

Diffusion and redistribution of lipid-like molecules between membranes in virus-cell and cell-cell fusion systems.

The kinetics of redistribution of lipid-like molecules between the membranes of two fused spherical vesicles is studied by solving the time-dependent diffusion equation of the system. The effects on the probe redistribution rate of pore size at the fusion junction and the relative sizes of the vesicles are examined. It is found that the redistribution rate constant decreases significantly, but not drastically, as the relative size of the pore to that of the vesicles decreases (the bottleneck effect). In general, the time scale of the probe redistribution rate is determined by the size of the vesicles that is loaded with the probe before the activation of the fusion. For a pore size 50 A in diameter and a typical diffusion coefficient of 10(-8) cm2/s for lipids, the mixing half times for typical virus-cell and cell-cell fusion systems are less than 30 ms and above 200 s, respectively. Thus, although the redistribution of lipid-like probes by diffusion is not rate limiting in virus-cell fusion, redistribution by diffusion is close to rate limiting in spike-protein mediated cell-cell fusion.

Biophysical Phenomena↗
PubMed1989

Complications of colostomies.

One hundred twenty-six patients underwent 130 end colostomies, 44 for benign and 86 for malignant disease, and were followed for an average of 35 months. The left or sigmoid colon was used in 99 and the transverse colon in 31. Stomas were made electively in 98 patients and urgently in 32. Seventy-six stomas were brought out through the incision and 54 from separate sites. There were 69 complications in 55 patients (44 percent) including 11 strictures, 9 wound infections, 14 hernias, 9 small-bowel obstructions, 4 prolapses, 2 abscesses, 1 peristomal fistula, 17 skin erosions, and 2 poor stoma locations. Fifteen complications required reoperation. Five of these procedures included stoma revision. Total numbers of complications were not related to the stoma site, the disease process, the urgency of the procedure, or the segment of colon used. Wound infections, however, were increased in urgently made stomas. The incidence of hernia was equivalent in stomas brought out through the incision or at a separate site. Forty-one patients (30 percent) had 43 colostomies closed an average of 3.5 months after creation. Thirteen patients had 14 complications--5 wound infections, 6 hernias, 2 small-bowel obstructions, and 1 rectovaginal fistula. One patient died. Four patients required reoperation. There were no anastomotic leaks. Complications were equivalent in Hartmann closures and transverse colostomy closures. Complications were similar in stomas created for cancer and those created for diverticular disease.

Colonic Diseases↗
PubMed1988

The possible role of the ethanol-inducible isozyme of cytochrome P450 in the metabolism and distribution of carbon disulfide.

Acute treatment with ethanol and other alcohols has been shown to potentiate the hepatotoxicity of certain xenobiotics, in part via induction of the mixed-function oxidase (MFO) system. Carbon disulfide (CS2)-induced hepatotoxicity and inhibition of the MFO system have been shown to be a consequence of MFO metabolism. In the present study, the ability of several different alcohols to induce the hepatic MFO metabolism of CS2 and the effects of this induction on CS2 distribution and hepatotoxicity were examined in rats. Eighteen hours after alcohol administration (1/2 LD50 dose, po), CS2 microsomal MFO metabolism was significantly enhanced, in order of descending potency, by isopropanol, methanol, and ethanol pretreatments, but not by isobutanol pretreatment. The degree of enhancement of CS2 metabolism by different alcohols paralleled the enhancement of nitroanisole O-demethylation and aniline hydroxylation, MFO activities associated with the ethanol-inducible isozyme of cytochrome P450. CS2 (1 mg/kg, ip, 3 hr) inhibited only the cytochrome P450-mediated activities enhanced by alcohol pretreatment. These results suggest that CS2 metabolism is catalyzed by the ethanol-inducible isozyme. Alcohol-induced rats had significantly more 14CS2-derived radioactivity in the liver than control and isobutanol-pretreated rats 3 hr after dosing (1 mg/kg, ip). However, only methanol pretreatment resulted in an increased retention of 14CS2-derived radioactivity in plasma, brain, and kidney. Unlike other alcohol pretreatments, methanol decreased the total 14C expired during the 3-hr period after CS2 dosing and caused a significant (twofold) increase in plasma glutamic-pyruvic transaminase, measured 24 hr after CS2 exposure (625 mg/kg). These data indicate that alcohol induction of MFO-dependent CS2 metabolism per se is not sufficient to result in CS2-induced hepatic damage although it does lead to loss of specific cytochrome P450 function.

Alanine Transaminase↗
PubMed1988

Mean lifetime of microtubules attached to nucleating sites.

A simple two-phase (cap; no cap) macroscopic model describing the kinetic behavior at a labile tip of a microtubule has been proposed [Hill, T. L. (1984) Proc. Natl. Acad. Sci. USA 81, 6728-6732]. In the model, a microtubule exists either in a slowly growing phase (first-order rate constant, alpha) characterized by the existence of a GTP-tubulin cap at the growing tip; or the same microtubule exists in a rapidly shrinking phase (first-order rate constant, beta), which is entered if/when the GTP-tubulin cap is lost through a fluctuation, thus exposing GDP-tubulin subunits, which constitute the body of the microtubule. Transition between the two phases--i.e., loss of a cap (first-order rate constant, k) or formation of a new cap (first-order rate constant, k') occurs very infrequently and in a stochastic manner. In vitro experiments with centrosome-nucleated microtubules by Mitchison and Kirschner and Monte Carlo kinetic simulations, based on a realistic set of microscopic rate constants that apply to the end of a microtubule, suggest this alternation between two "quasimacroscopic" phases. In this paper, I outline the calculation of the mean lifetime of a microtubule nucleated on a centrosome by using Hill's model. For a microtubule M units long in the slowly growing phase, the mean lifetime for complete depolymerization is [M(k + k') + alpha + beta](beta k - alpha k')-1, provided that beta k greater than alpha k'. If the microtubule is in the rapidly shrinking phase, then the mean lifetime is M(k + k')(beta k - alpha k')-1, provided that beta k greater than alpha k'. In case beta k less than alpha k', the microtubule grows indefinitely, and the mean lifetime is infinite.

Adenine Nucleotides↗
PubMed1988

Electrocoagulation of selected carcinoma of the rectum.

Abdominoperineal resection for the treatment of carcinoma of the rectum has been the benchmark for all other forms of therapy since Miles described the procedure in 1908. During the past 25 years, 81 patients have had carcinoma of the rectum treated curatively by electrocoagulation and have been observed for five years or more. Treatment was selectively applied to those patients whose tumors were less than 7.5 centimeters from the anal verge with less than 50 per cent of the rectum involved. All of the tumors were freely movable. The over-all five year survival rate was 47 per cent. Thirty-one of the 81 patients underwent conversion to abdominoperineal resection because of recurrence. The survival rate for those treated by electrocoagulation alone was 58 per cent and for those converted to abdominoperineal resection, 29 per cent. The survival rate was 65 per cent for those with lesions less than 4 centimeters in diameter versus 30 per cent for those with lesions more than 4 centimeters. The morbidity rate was 21.0 per cent and the mortality rate was 2.7 per cent. There were an additional 33 patients treated for palliation with only one five year survivor. Electrocoagulation for the treatment of carcinoma of the distal part of the rectum is a reasonable alterative to abdominoperineal resection when selectively applied.

Adenocarcinoma↗
PubMed1988

Is preoperative colonoscopy necessary in carcinoma of the colon and rectum?

The incidence of synchronous polyps of the colon has been shown to be 25 to 40 per cent and the incidence of synchronous carcinomas to be two to eight per cent. Because of this, many surgical groups now advocate routine preoperative colonoscopy on all patients with colon carcinoma. The possibility of spreading and implanting tumor cells with the colonoscope has prompted the authors to purposely avoid preoperative colonoscopy and then clear the colon of any missed lesions with an early postoperative colonoscopy. This study is a retrospective review of 104 patients who have undergone a partial colectomy for colon and rectal carcinoma followed by a postoperative colonoscopy between June 1982 and June 1986. The purpose is to determine the adequacy of intraoperative palpation to detect synchronous neoplasms, and to further define the role of perioperative colonoscopy. The results of 34 per cent synchronous polyps and 5.8 per cent synchronous carcinomas parallels previous studies. The six patients with synchronous carcinomas were discovered by intraoperative palpation and the operation was modified in four of the six patients. Postoperative colonoscopy revealed polyps in 20 per cent of the patients, but all of these were amenable to snare polypectomy or electrocoagulation. No carcinomas were overlooked by palpation. It is our conclusion that intraoperative palpation is adequate for detection of synchronous carcinomas and therefore the risk and expense of preoperative colonoscopy can be avoided. Early postoperative colonoscopy, however, is imperative to clear the colon of small polyps which have the potential to progress to carcinoma.

Adult↗
PubMed1988

Value of subcutaneous and intraperitoneal antibiotics in reducing infection in clean contaminated operations of the colon.

A prospective study of 443 patients undergoing clean contaminated operations of the colon was undertaken to determine the efficacy of subcutaneous and intraperitoneal antibiotics in reducing infection. All of the patients received a mechanical intestinal preparation as well as preoperative antibiotics taken orally and preoperative and postoperative antibiotics administered intravenously. The over-all wound infection rate was 2 per cent. The routine additional use of subcutaneous or intraperitoneal antibiotics had no proved efficacy in this study.

Administration, Cutaneous↗
PubMed1987

Preoperative localization of intermittently bleeding small intestinal tumors using Tc-99m labeled red blood cell scanning. Report of two cases.

Frequent tagged red blood cell scans offer an important diagnostic adjunct to help define a site of intermittent bleeding. Success is based upon scanning at two-to-four-hour intervals. Two patients are presented who experienced intermittent episodes of melena and hematochezia over prolonged periods of time. In each case an extensive diagnostic work-up had been performed on multiple occasions and failed to demonstrate the source. Utilizing a Technetium-99 macroaggregated albumin (Tc-99m) tagged red blood cell scan, an intermittently bleeding lesion within the small bowel was identified in each instance. In order to detect an intermittently bleeding lesion within the small bowel, more frequent scanning intervals are recommended. Due to rapid clearing of tagged red blood cells into the colon from the small-bowel bleeding point, the source may be obscured by longer, routine scanning intervals.

Aged↗
PubMed1986

The role of nasointestinal intubation in elective colonic surgery.

One hundred thirty-eight consecutive patients undergoing elective colonic resections were treated prospectively and randomly with either a long intestinal (Cantor) tube preoperatively, a nasogastric tube placed intraoperatively, or no gastrointestinal tube at all. Patients were evaluated for length of hospital stay, duration of postoperative ileus, adequacy of intraoperative intestinal decompression, gastric dilatation, and operative complications. No significant difference could be seen in the tubed or no-tube group.

Adult↗
PubMed1985

Electrogalvanic stimulation in the treatment of levator syndrome.

The records of 102 patients with levator syndrome were reviewed. All had failed trials of conservative management prior to treatments with electrogalvanic stimulation. The symptoms of 12 patients were subsequently found not to be due to levator syndrome. Of 90 patients with correct diagnoses, 77 percent were relieved or improved after courses of electrogalvanic stimulation, a valuable adjunct to the management of this frustrating condition.

Electric Stimulation Therapy↗