Hypoxanthine Uptake in Isolated Rat Renal Cortical Tubule Fragments

Isolated renal tubule fragments prepared from adult Sprague-Dawley rats were used to study the cellular uptake of hypoxanthine. This uptake was rapid, reaching a steady state after 30 min of incubation. Analysis of the intracellular pool during the initial uptake and at the steady state revealed a concentration gradient of hypoxanthine consistent with active transport, although only one-third of the transported hypoxanthine remained unmetabolized. The remainder of the transported hypoxanthine was converted to inosine and inosinic acid, but detectable conversion to uric acid was not noted. A kinetic analysis of uptake revealed that two systems for cellular entry of hypoxanthine existed with K(m1) = 0.005 and K(m2) = 0.80 mM. Hypoxanthine uptake at physiologic concentrations was oxygen, sodium, and temperature dependent, but the addition of metabolic fuels and alteration of the medium pH over the range of from 6.1 to 7.4 had no effect. Adenine, guanine, and inosine inhibited the uptake of hypoxanthine via the low-K(m) system which mediates the majority of uptake at physiologic levels. Xanthine, uric acid, and probenecid inhibited uptake via the high-K(m) system, but did not affect uptake via the low-K(m) system. The data indicate that hypoxanthine at physiologic levels is transported into the renal tubule cell via a system different from that for other oxypurines.     

Hair cadmium content: Is it a biological indicator of the body burden of cadmium for the occupationally exposed worker?

The primary objective of this study was to evaluate the cadmium (Cd) levels measured in scalp hair as a potential predictive index of the body burden of Cd. In vivo measurements of kidney and liver Cd along with hair, blood, and urine Cd levels were obtained in 29 industrially-exposed workers and ten control subjects. The relationship of hair Cd levels to the Cd values for the kidney, liver, blood, and urine were tested using nonparametric analyses. In the control group no statistically significant correlations were found. In the Cd-exposed workers with more than one year of employment there were weak correlations (p ≤ 0.05); however, the relationships were not sufficiently quantitative for predicting the status of an individual worker. Furthermore, when workers with less than one year of exposure were included in the analysis, no significant correlations were obtained. Although this latter group of workers had low body burdens of Cd, exceptionally high Cd concentrations were found in their hair - an observation that was unexpected. It was concluded that hair Cd levels are not a good index of body burden of Cd in the industrially-exposed individual.     

Skeletal turnover and total body elemental composition during extended calcitonin treatment of Paget's disease

Twenty patients with generalized symptomatic Paget's disease had serial measurements of radiocalcium turnover and/or total body elemental composition by in vivo neutron activation analysis during long-term calcitonin therapy. Despite maintained clinical improvement, seven of 15 patients showed partial or total loss of the initial decelerating effect of calcitonin on skeletal turnover, whereas the remaining eight patients maintained the calcitonin-induced deceleration. The changes in skeletal turnover were roughly proportional to the induced changes in serum alkaline phosphatase and urinary hydroxyproline. However, disparities in the magnitude of the changes among the three parameters were not uncommon. Total body calcium was increased by a mean of 22% above predicted prior to calcitonin and decreased significantly by 4% during long-term calcitonin treatment. Total body phosphorus, nitrogen, and sodium also decreased. The phosphorus and sodium losses appeared to be mostly from the skeleton. These data confirm histologic evidence of the disappearance of pagetic bone, resumption of normal lamellar bone formation, and radiographic evidence of a decrease in bone volume during calcitonin treatment and indicate the relative magnitude of this effect. The action of calcitonin in this regard possibly represents a specific effect on Paget's disease beyond its general skeletal effect to reduce cellular activity.     

A simple method for measuring a picogram of acetylcholine using the clam (Mya arenaria) heart

1. A simple and reliable method is described for assaying 1 pg or less of acetylcholine (ACh) using a strip of clam (Mya arenaria) heart.2. Clam heart preparations generally are extremely selective for ACh. The preparation described is at least 10(5) times less sensitive to the following: acetyl coenzyme A, adrenaline, choline, dopamine, gamma-aminobutyric acid, glutamic acid, histamine, 5-hydroxytryptamine and noradrenaline.3. Because this preparation is one of the most sensitive known for detecting ACh, it should prove useful for assaying particularly low levels of this substance in biological extracts.     

Collision behavior of young drivers. Impact of the change in the age of majority.

A comparison of the number of collisions experienced by young male drivers in London, Ontario, before and after the reduction in the legal age for drinking and purchasing alcoholic beverages from 21 to 18, indicated that the change in the law led to an increase in the collision involvement of young drivers.