Some effects of continuous low-dose congenital exposure to methylmercury on organ growth in the rat fetus

Congenital low-dose exposure of rat fetuses to methylmercury produced smaller offspring without anatomical abnormalities. The present study explored the mechanisms of the smallness of fetuses. The pregnant rats were given methylmercury water (25 ppm) from day 1 of pregnancy continuously until day 20 of gestation. There was a negative correlation of fetal weight and maternal and fetal mercury burden. The whole organ DNA and protein content of the livers and kidneys in the experiments were significantly lower than the control (P less than 0.05) indicating that there were fewer cells per organ in the mercury exposed fetuses. When the data were compared on a per gram of tissue basis, there was no significanct difference, indicating that the number and size of the cells of each were not diminished. The incorporation of 3H-thymidine into fetal tissue DNA was also substantially lower in the experimental group indicating decreased proliferative activity. We conclude from this study that, at least for some major organs, the decreased size in the mercury exposed fetuses is due to fewer cells in the organs due to decreased proliferative activity.

Effects of guar gum and wheat bran on lipid metabolism of rats

The effects of guar gum and wheat bran on blood and liver lipid levels of rats were measured. In experiment 1, rats were fed ad libitum a 55% sucrose diet containing 0, 15 or 25% wheat bran for 3 weeks. Postprandial plasma triglyceride, liver triglyceride and liver cholesterol values in rats fed the sucrose diet with wheat bran were significantly lower than values for rats fed the diet without wheat bran. Neither fasting plasma triglyceride nor cholesterol values were altered by wheat bran. In experiment 2, rats were meal-fed one of four experimental diets for 3 weeks: sucrose, sucrose-cholesterol, sucrose-cholesterol-bran or sucrose-cholesterol-guar gum. Rats fed sucrose-cholesterol-guar gum diet had significantly lower fasting plasma total cholesterol, liver triglyceride and liver cholesterol values, but higher plasma high density lipoprotein (HDL) cholesterol values than those fed sucrose-cholesterol diet. These values were similar for the sucrose-cholesterol and sucrose-cholesterol-bran groups. Fasting plasma triglyceride levels were not altered by wheat bran or guar gum. These studies indicate that while guar gum lowers fasting plasma total cholesterol and raises HDL cholesterol, wheat bran does not.

Plant fiber. Carbohydrate and lipid metabolism

Plant fibers are the portions of plant foods that are not digested in the human small intestine. During this century, remarkable advances have been made in defining the characteristics and importance of most nutrients such as carbohydrate, proteins, fats, vitamins, and minerals. Plant fibers have largely been neglected because they considered to have no nutritive values. In the last decade, however, considerable attention has been focused on the various plant fibers because of their influence on gastrointestinal physiology. Evidence is emerging that plant fibers have profound influences on human nutrition because they alter the absorption and metabolism of many nutrients. We will review the evidence that plant fibers greatly influence the absorption and subsequent metabolism of carbohydrates and fats.

Aluminum induced pulmonary granulomatosis

The association of aluminum dusts and pulmonary fibrosis with emphysema in workers in the aluminum processing and manufacturing industries is well established. The early and minimal reactions of the lungs to the aluminum dusts are not known. This report presents the first case of pulmonary granulomatosis associated with aluminum inhalation. The occupational history of this patient was thoroughly examined, and the aluminum was identified by electron probe microanalysis of the lung biopsy specimen. The granulomatous response in this patient was similar to that observed in rabbits following aluminum dust inhalation. Hypersensitivity or individual idiosyncrasy may play a role in the development of the pulmonary granulomas following exposure to aluminum.

Malignant mesothelioma with minimal asbestos exposure

The association of malignant mesothelioma and asbestos fibers is well established. The minimal exposure that may produce the tumor is not known. The present report documents the minimal exposure by thorough examination of occupational history and personal hobbies, and counting of the number of asbestos fibers in the lungs. The evidence for the elemental composition of asbestos fibers by electron probe (EDAX) is also presented.

Small-signal analysis of response of mammalian muscle spindles with fusimotor stimulation and a comparison with large-signal responses

1. Response dynamics of primary and secondary muscle spindle endings to small-amplitude sinusoidal stretches were found to be unaltered by tonic repetitive stimulation of fusistatic or fusidynamic fibers. 2. Overall sensitivity of these receptors is decreased by fusistatic stimulation and either unchanged, increased, or decreased by fusidynamic stimulation at rates of 75/s or greater. 3. In the case of primary endings, the results obtained with small-amplitude sinusoidal stretches are not compatible with the response of these receptors to large-amplitude ramp stretches. The difference is explained by dependence of receptor dynamics on stretch amplitude. Fusistatic stimulation tends to prevent those changes in dynamics, whereas fusidynamic stimulation tends to enhance them. 4. In the case of secondary endings, the results obtained with small- and large-amplitude stretches appear to be compatible with a linear model for this receptor (i.e., one with dynamics independent of input parameters). 5. By modulating the frequency of stimulation applied to fusimotor fibers and comparing the resulting afferent response to the receptor response to stretch dynamic characteristics of intrafusal muscle contraction can be deduced. The results suggest that the dynamics of fusiastatic and fusidynamic contraction are the same and, furthermore, that they are the same as those of extrafusal muscle. We note that the result is incompatible with measurements of the time course of twitch and tetanus development and suggest, therefore, that muscle dynamics are a function of contractile state.

Carbon tetrachloride-induced changes in mixed function oxidases and microsomal cytochromes in the rat lung

The effects of a single exposure, by gastric intubation or inhalation, to carbon tetrachloride (CCL4) on rat lungs were assessed. By 1 to 7 days, focal areas of alveolar collapse, septal edema, and modification of type II pneumonocytes were observed. By 24 hours after exposure to the toxin, there were no identifiable changes in surfactant levels or distribution. Microsomes obtained from the lungs and prepared for analysis revealed marked decreases in cytochrome P-450 content and P-450-related N-demethylation of dimethylaniline. Only a transient reduction of cytochrome b5 occurred, with a rebound exceeding control values during the period of pulmonary healing. Whether the lung acted as an excretory route (following intubation) or as an absorption path (after inhalation) made little difference. Carbon tetrachloride had no effect on in vitro microsome composition and function unless supplemented with a reduced form of nicotinamide adenine dinucleotide phosphate (NADPH) generating system. Under these circumstances, there was a reduction in both cytochromes b5 and P-450. Our data indicate that a considerable chemical modification of the pulmonary tissues had taken place, with no accompanying easily recognized changes in cellular structure. Furthermore, evidence for the in vitro destruction of pulmonary microsomal cytochromes P-450 and b5, unrelated to peroxidation, is indicated by these findings.

Argininemia

The clinical features of argininemia in two cousins included hyperactivity, spasticity, ataxia, retardation, and repeated attacks of hyperammonemia. Study of a large kindred suggests that arginase-deficiency is transmitted as a Mendelian recessive. Treatment with an essential amino acid mixture with the total nitrogen intake limited to the requirement, controlled the hyperammonemia, reduced the plasma arginine level, and permitted a marked clinical improvement. There has been a significant increase in intelligence levels; the previously retarded children are now approaching the normal range of function.