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Biomedical subjects

S Bloom

Publications and source records attributed to S Bloom.

At least 145 records · Page 8Linked to original sources
PubMedDate not supplied

Probability of monozygotic twinning as a reflection of the genetic control of cell development.

The stability of the incidence of monozygotic twinning (MZT) suggests that its origin is genetically, rather than environmentally, controlled. Available data, though scant, supports our hypothesis that the MZT probability is (1/2)K, where K is a species-specific integer parameter. For humans MZT occurs in about four of 1000 births, which is close to one occurrence in 2(8) births, i.e. K = 8. The environmental factors are not the cause of MZT, but may influence its expression. When this influence is in effect under some extreme experimental conditions the above form of MZT probability is observed. Binary structure of the MZT probability provides insight into genetic control mechanism of cell division.

Cell Division↗
PubMedDate not supplied

Enhancement of cardiotoxic effects of beta-adrenergic bronchodilators by aminophylline in experimental animals.

To examine the cardiotoxic interaction between beta-adrenergic bronchodilators and theophylline, we tested the effects of isoproterenol or bitolterol alone and in combinations with aminophylline in experimental animals, both electrocardiographically and histologically. The sc LD50 values for isoproterenol in 4- to 5-month-old, 500-600 g (heavy) and 1.5- to 2-month-old, 150-200 g (small) male Sprague-Dawley rats were 0.6 mg/kg and 1300 mg/kg, respectively, and values for bitolterol were 4 mg/kg and greater than 1800 mg/kg, respectively. Results of the electrocardiographic studies in heavy rats, using the calculated LD20 dosage of isoproterenol with or without pretreatment of aminophylline, demonstrated that both mortality and the arrhythmia-inducing effect of isoproterenol were significantly potentiated by aminophylline but only mortality was increased in small rats. Aminophylline also potentiated the electrocardiographic effects of 1/40 of the LD50 dosage of isoproterenol in heavy rats but did not enhance the effects of bitolterol at this dose level. Potentiation of the arrhythmogenic effect of isoproterenol was also observed in rabbits. The severity of the myocardial lesions produced by isoproterenol or bitolterol in heavy rats was significantly enhanced by aminophylline. The heavy rat appears to be a sensitive model for studying the interaction of these classes of drugs.

Adrenergic beta-Antagonists↗
PubMedDate not supplied

Lipolysis is an important determinant of isoproterenol-induced myocardial necrosis.

The cardiotoxic effect of isoproterenol (ISO) is associated with, and possibly due to, calcium overload. Prior work suggests that calcium entry into cardiac myocytes after ISO administration occurs in two phases: an early rapid phase, followed by a slow phase beginning about 1 hour after ISO injection, leading to a peak myocardial calcium level after about 4 hours. We have tested the relationship of these phases to myocardial necrosis (MN) by determining the time after ISO administration at which the commitment to MN occurs. This was done by administration of propranolol at various times before and after ISO. In addition, since ISO induces lipolysis, and lipids can be toxic, experiments were conducted to determine if adrenergically-activated lipolysis could play a significant role in ISO-MN. We found that propranolol protected the myocardium equally well when administered anytime within 2 hours of ISO injection, but had no effect when given 4 hours after ISO. This showed that metabolic events taking place more than two hours after ISO injection are required for ISO-MN. As expected from prior work, there was a small and consistent amount of propranolol-resistant ISO-MN. Lipolysis, assessed by measuring serum glycerol levels, increased to tenfold above base line at one hour after ISO administration and returned to near basal levels at 4 hours. Potentiation of lipolysis by intravenous injections of phospholipase A2 (PLA2) or lipoprotein lipase (LPL) to rats treated with ISO substantially augmented MN. Propranolol completely blocked the increase in necrosis produced by PLA2 when given with ISO. Lipases induced only minimal necrosis in the absence of ISO. Administration of adenosine (an anti-lipolytic agent), oxfenicine (an inhibitor of mitochondrial palmitoyl carnitine transferase), or vitamin C (an anti-oxidant) resulted in a 55-60% reduction in MN. These results suggest that critical necrosis-determining events occur between 2 and 4 hours after ISO administration and imply a relationship between ISO-induced lipolysis, calcium influx, and ISO-MN. We hypothesize that importance of lipolysis as a determinant of ISO-MN is related to the generation of free fatty acids, their oxidized/metabolic products, or direct damage to plasma membrane.

Adenosine↗
PubMedDate not supplied

Physician awareness of rehabilitation costs.

Containment of health care costs is a pressing national issue. In this study, we examined physician knowledge of rehabilitation hospital costs by quantifying their awareness of hospital charges. All physicians at a free-standing rehabilitation hospital were surveyed. Approximately one-half of the physicians responded, including 19 attending and 17 resident physicians. The survey addressed three issues: physicians' estimate of the billing fee (hospital charge to the patient) for various items; how confident they were of the charge; and how frequently they ordered each item. The survey listed 65 items including diagnostic testing, drugs, therapies, and equipment. The average error in the charge estimates was quite large. For example, it was 52, 48, and 108% for hematologic tests, imaging studies, and pharmaceuticals, respectively. Charges were underestimated twice as often as they were overestimated. Physicians' confidence in their knowledge of these fees was quite low. They indicated that they were guessing 80 to 90% of the time, had an idea of the cost for 10 to 20% of the items, and were confident in their knowledge for less than 1% of the items. There were no significant correlations between accuracy of the charge estimates and ordering frequency, actual charge of the item, or experience level of the physicians.

Awareness↗
PubMedDate not supplied

Paradoxical actions of quinidine in hyperpermeable heart cells.

The effect of quinidine on the inotropic state was examined using small fragments of hyperpermeable ventricular muscle in vitro. In concentrations of 10(-5) and 10(-4) M, quinidine had no effect on the force of spontaneously contracting fibers. At a concentration of 10(-3) M, contractile force increased by at least twofold. We conclude that the negative inotropic action of quinidine is not by a direct action on intracellular organelles of the heart.

Animals↗
PubMedDate not supplied

Sinoatrial automaticity and transmembrane potentials in hamsters on a magnesium-deficient diet.

We studied the effects of moderate Mg deficiency on sinus node automaticity and atrial muscle transmembrane potential in hamsters. The Mg-deficient hamsters (Mg-D) were fed a diet containing less than 2.0 mmol/kg Mg (0Mg) for 7 days. They were then fed 0Mg enriched with 10 mmol/kg Mg acetate for 12 days. Control animals (Mg-N) were fed a Mg-sufficient diet consisting of 0Mg supplemented with 100 mmol/kg Mg acetate. Sinoatrial preparations from Mg-N and Mg-D animals were superfused in vitro with Tyrode solution at 36 degrees C. Transmembrane potentials were recorded using intracellular microelectrodes. Preparations from Mg-D hamsters beat at a more rapid spontaneous rate than did those from Mg-N animals. A decrease in [Mg]0 enhanced the automaticity of Mg-N preparations, but not of Mg-D preparations. The negative chronotropic action of carbamycholine (CBL) was greater in the Mg-D than in the Mg-N preparations. When driven at a constant rate, the atrial muscle fibers of Mg-D hamsters repolarized more rapidly than did those of the Mg-N group. The resulting difference in the action potential duration (APD) was independent of membrane resting potential (MRP), amplitude of the action potential (AAP), and velocity of depolarization during phase 0 (Vmax), which were the same in both groups of preparations. The APD was shortened to a similar extent, proportionally, by 100 nM CBL in both preparations, while MRP, AAP, and Vmax remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMedDate not supplied

Helping employees stretch their retirement dollars.

Under a provision of the Deficit Reduction Act of 1984, employees who participate in qualified defined contribution pension programs can increase retirement income by spreading out the installments over an annually redetermined life expectancy. The provision also enables employees to withdraw more than the minimum required distribution during periods of inflation and to continue receiving payments beyond age 100. In most cases, the change in distribution will provide payments throughout the participant's lifetime and a small balance for the participant's estate--rather than a fixed number of mandatory withdrawals spread over a shorter period.

Actuarial Analysis↗