Megakaryocytopoiesis in the Rat

Labeling of rat megakaryocytes was observed after a single intravenousinjection of tritiated thymidine, and the following conclusions were made.

1. Morphologic appearance of megakaryocytes corresponded to their stageof maturation.

2. Only the youngest recognizable megakaryocytes (stage I) appeared tohave a DNA synthetic period.

3. Megakaryocytes did not undergo permanent cellular division.

4. There was probably some degree of ineffective megakaryocytopoiesis.

5. The average total maturation time of rat megakaryocytes was estimatedto be 43-75 hours wih 8-14 hours in stage I, 11-19 hours in stage II, and24-42 hours in stage III.

6. There was continuous influx into the megakaryocyte compartment froma precursor compartment. The immediate precursor cell was morphologicallyunrecognizable, but it appeared to have a generation time of 16 hours, aDNA synthesis period of 10 hours and a post-synthetic maturation timeof 2 hours.

7. Reutilization of tritium probably accounted for maintenance of a highdegree of labeling of megakaryocytes for a period of 1.5-4 days.

Submitted on August 7, 1964 Accepted on November 22, 1964     

Urinary nicotine concentrations in cigarette and pipe smokers

Urinary concentrations of nicotine were studied in men who did not smoke (27) and in men who smoked cigarettes only (145) or pipes only (48). The median urinary nicotine concentrations were less than 50 ng/ml (the detection limit of the assay for urine tests) in the non-smokers, 1393 ng/ml in the cigarette smokers, and 1048 ng/ml in the pipe smokers. These values were standardised for urinary pH and creatinine concentration to allow for the fact that nicotine excretion is influenced by the acidity of the urine and by urinary flow rate. The high urinary nicotine concentrations in the pipe and cigarette smokers indicated that both types of smoker have relatively high systemic nicotine concentrations. This observation, together with the fact that large prospective studies have shown that pipe smokers have no material excess risk of coronary heart disease whereas cigarette smokers do, provides evidence that nicotine is unlikely to be the major cause of the excess deaths from coronary heart disease in cigarette smokers. This conclusion is consistent with earlier observations based on serum cotinine concentrations in smokers and non-smokers.     

Relationship of Hunger and Food Insecurity to Food Availability and Consumption

Objective To describe the relationship of new measures of hunger and food insecurity to household food supplies and individual food and nutrient intake.Design and Setting A questionnaire containing the Radimer/Cornell hunger and food insecurity items and questions on eating patterns and the frequency of fruit and vegetable consumption was administered to subjects during a personal interview in their homes. A 24-hour diet recall and a household food inventory were conducted at the initial interview and at a follow-up visit.Subjects Participants were 193 women drawn from a random sample of 308 women who had completed a previous health census in a rural New York State county. Subjects’ ages ranged from 15 to 40 years. All had children living at home and less than 16 years of education.Statistical analyses Regression analysis was used to test for linear trends across food insecurity groups for the household food inventory scores and for the frequency of consumption of fruits and vegetables, t Tests were used to assess differences between the food secure and food insecure groups for nutrient and food group means. A χ² test for trend was used to examine differences in the distribution of nutrient and fruit and vegetable intake between the food secure and food insecure groups.Results A significant decrease in the frequency of consumption of fruits and vegetables and the amount of food in the household and a significant increase in scores indicative of disordered eating patterns were associated with a worsening of food insecurity status. Potassium and fiber intake and fruit consumption differed significantly between the food secure and food insecure groups. The percentage of respondents consuming less than the Recommended Dietary Allowance for vitamin C and fewer than five fruits and vegetables per day was significantly greater among food insecure respondents than food secure respondents.Applications/conclusions The quantity of food available in households and consumption of fruits and vegetables decreased with increasingly severe problems with food insecurity and hunger. In this rural population, the Radimer/Cornell measures were useful in identifying households experiencing food insecurity and providing information about the nature of the food supply and the dietary intake problems experienced by food insecure households and persons, suggesting that these measures may be useful on community surveys designed to examine food insecurity issues. J Am Diet Assoc. 1996; 96:1019-1024.     

Combination of bright light and caffeine as a countermeasure for impaired alertness and performance during extended sleep deprivation

Effects of four conditions (Dim Light-Placebo, Dim Light-Caffeine, Bright Light-Placebo and Bright Light-Caffeine) on alertness, and performance were studied during the night-time hours across 45.5 h of sleep deprivation. Caffeine (200 mg) was administered at 20.00 and 02.00 hours and bright-light exposure (>2000 lux) was from 20.00 to 08.00 hours each night. The three treatment conditions, compared to the Dim Light-Placebo condition, enhanced night-time performance. Further, the combined treatment of caffeine and all-night bright light (Bright Light-Caffeine) enhanced performance to a larger degree than either the Dim Light-Caffeine or the Bright Light-Placebo condition. Beneficial effects of the treatments on performance were largest during the early morning hours (e.g. after 02.00 hours) when performance in the Dim Light-Placebo group was at its worst. Notably, the Bright Light-Caffeine condition was able to overcome the circadian drop in performance for most tasks measured. Both caffeine conditions improved objective alertness on the Maintenance of Wakefulness Test. Taken together, the above results suggest that the combined treatment of bright light and caffeine provides an effective intervention for enhancing alertness and performance during sleep loss.