Effects of in utero exposure to low dose ionizing radiation on development in the rat.

Most studies of in utero effects of ionizing irradiation involve high doses and examination at postnatal intervals. Little information is available on the effects of low levels of ionizing radiation on embryogenesis. The developmental effects of in utero exposure to 50 cGy gamma radiation on gestational day-9.5 was investigated using Sprague-Dawley rats. Irradiated rats and appropriate controls were killed at prenatal intervals of 4h, 48h and 10 days after exposure. Fetuses were examined for abnormalities and random samples of tissues were prepared for microscopic study. With the exception of the neuroepithelium, no histopathological changes were observed in embryos 4h after exposure to 50 cGy. In irradiated embryos, mitoses were reduced within the neuro-epithelium; pyknosis and some necrosis of cells were apparent at this gestational interval. Among the gross developmental abnormalities observed in embryos 48h after irradiation, excessive flexion of the embryo and abnormal flexion of the head were the only ones that appeared to be radiation-induced. The mean numerical score (42.3 +/- 0.2, controls; 42.4 +/- 0.1, irradiated) for 17 morphological parameters examined in fetuses at this gestational period compares favorably with other studies. Controls, however, showed greater variability in the extent of development of their forebrain, olfactory system, midbrain, hindbrain, and caudal neural tube. In all cases, there was evidence of slower development in these regions compared to their irradiated counterparts. At term, no significant differences in litter size or resorption rates were observed in irradiated animals compared to the controls, but there was a higher incidence of defective eye development, spinal curvature and visceral anomalies.(ABSTRACT TRUNCATED AT 250 WORDS)

Postnatal development of the rat CNS following in utero exposure to a low dose of ionizing radiation.

In utero exposure to ionizing radiation is of importance because of its potential health risks. The developing nervous system is particularly vulnerable and the consequences of exposure to low levels of radiation (< or = 1 Gy) are not well established. The developmental effects of maternal exposure to 50 cGy gamma-radiation on gestational days (GD) 9.5, 15, and 18 were investigated in Sprague Dawley rats. Rats exposed on GD-9.5 along with appropriate controls were killed at 4 h, 48 h, and 10 days post-irradiation while those irradiated on GD-15 and GD-18 were killed postnatally (PN) on days 7 and 26. All were examined for developmental anomalies and representative samples of brains were processed for microscopic study. No significant developmental differences were observed between irradiated and control embryos killed 48 h after irradiation on GD 9.5. However, in irradiated fetuses a larger number of developmental anomalies were observed at term. Defects of the eye and of spinal curvature were the most common malformations encountered. Mitoses were reduced within the neuroepithelium of embryos irradiated on GD-9.5 and evidence of pyknosis and necrosis was seen 4 h after irradiation. The capacity of surviving primitive neural cells for repair, however, was such that by 48 h after exposure the irradiated nervous system no longer differed from controls. Rats irradiated on GD-15 and GD-18 and examined on PN-26 exhibited clusters of small, dark, pyknotic neurons within the hippocampal and dentate gyri, often bilaterally.(ABSTRACT TRUNCATED AT 250 WORDS)

Smoking and caffeine and alcohol intake during pregnancy in a northern population: effect on fetal growth.

OBJECTIVES: To assess the prevalence of smoking and of caffeine and alcohol intake during pregnancy in a northern population and to determine the relation of these factors to birth weight, length and head circumference. DESIGN: Questionnaire survey and collection of maternal and newborn measurements. SETTING: Ten communities in the Inuvik Zone, NWT. PATIENTS: A total of 162 women (56 Inuit, 38 Indian, 37 white and 31 mixed race) who presented for prenatal care in their community and gave birth in Inuvik between September 1987 and January 1990 and their newborns. RESULTS: In all, 64% (101/159) of the women smoked, 57% (88/154) ingested more than 300 mg of caffeine daily, and 34% (50/145) drank alcohol during their pregnancy. Smoking, caffeine intake and binge drinking were most frequent among the Inuit and Indian mothers. Smoking was significantly associated with decreased birth weight (p less than 0.001) and length (p less than 0.05). Alcohol intake, especially binge drinking, was significantly associated with decreased head circumference (p less than 0.05). Caffeine was found not to be related to any of the outcome variables after smoking was controlled for through stepwise multiple regression. CONCLUSIONS: The marked prevalence of smoking and alcohol intake during pregnancy and their effects on the newborn are public health concerns in the Northwest Territories and warrant intensive countermeasures.

The sensitivity of the thoracolumbar spinal cord of the mouse to hyperthermia.

Twelve millimeters of the thoracolumbar spinal cord of mice has been treated with a radiofrequency heating system which has been shown previously to produce localized and controllable elevation of temperature. The severity of neurological damage was assessed by measuring the reduction in the reflex leg extension of the hind legs of the mice from video-recorded images and by scoring the performance of the mice by a negative geotaxis test. The response to treatment was rapid with maximum paralysis occurring within a few days after treatment. Only minor symptoms were observed in those animals which had not developed paralysis within 2 weeks. A 40% reduction in the reflex leg extension was chosen as an end point, and the percentage of mice having reached the end point for different thermal doses was determined in groups of nine mice. The ED50 for heating for 1 h was 43.1 degrees C and for heating at 45 degrees C was 10.8 min. An increase in temperature by 1 degree C required a decrease in time by a factor of 2.25 to produce the same effect. Thermotolerance was observed 24 h after preheating at 45 degrees C for 1.9 min with a thermotolerance ratio of 1.7. The rapid response and high sensitivity of the spinal cord will have to be taken into consideration in the clinical application of hyperthermia.

Thermal dosimetry of spinal cord heating in the mouse.

Three systems for the localized heating of the spinal cord of the mouse have been evaluated by measuring the temperatures in the spinal canal (Tsp); at a reference location dorsal to the spine (Tdo), and by numerically calculating temperature distributions throughout two-dimensional transverse cross-sections through the middle of the heated region. The systems assessed were water bath heating alone, water bath-rf combination and rf heating alone with oblique, dorsally located electrodes. It has been established that (1) for all systems delta T (where delta T = Tdo-Tsp) decreased throughout a 1 h heating period-this was attributed to changes in blood flow; (2) there existed a considerable variation in the experimental value of delta T, particularly for rf heating. The resulting error in the estimation of Tsp from a measured value of Tdo can be reduced by making use of the observed correlation between delta T and the slope of a temperature decay curve measured at the beginning of the heating period; (3) rf alone best spares adjacent visceral and superficial tissues from significant elevation of temperature.

The calculation of transmission through a photon beam attenuator using sector integration.

A calculational scheme is presented for the prediction of the transmitted fraction (TR) through an attenuator of known material and physical dimensions, at any point in a photon beam, for a beam of any shape or size. The method considers the total TR to be composed of scatter and primary components and computes the scatter component by sector integration. The input for the calculations consists of measured narrow- and broad-beam transmitted fractions through lead in air for various circular fields, thicknesses of the attenuator, and angles from the central axis, in a geometry approximating typical treatment conditions. The method has been tested for the case of a uniform half slab and a 45 degree wedge in a 4-MV photon beam. It was found that the use of TR values obtained by the above method reduced the maximum absorbed dose computation error from 8% computed with a commercially available algorithm to 3%, in a typical treatment setup. This method is generally applicable to any shaped attenuator such as a wedge or compensator covering whole or part of a radiation field.

Effect of rioprostil, an oral prostaglandin E1 analogue, on lower oesophageal sphincter pressure and on the motility of the distal oesophagus in healthy volunteers.

The influence of rioprostil on the resting pressure of the lower oesophageal sphincter (LESP) and on the bolus-stimulated contraction wave amplitude of primary peristalsis is investigated in 9 healthy male volunteers receiving placebo or 300 micrograms and 600 micrograms of rioprostil orally in a randomized, double-blind, threefold crossover study. Manometry is performed using the low-compliance pneumohydraulic infusion system. The results show that: rioprostil, 600 micrograms, slightly increases LESP (ns) and contraction wave amplitudes, measured 10 cm above the lower oesophageal sphincter (LES) (p = 0.0039); rioprostil in both doses does not change the contraction wave amplitudes of the distal oesophagus, 5 cm above the LES; the duration of the peristaltic contractions is not altered. We conclude that rioprostil, in doses which effectively inhibit gastric acid and pepsin secretion and heal peptic ulcers, has no inhibitory effects on oesophageal motility. Studies are warranted, therefore, to establish the efficacy of rioprostil in the treatment of reflux oesophagitis.

Effect of rioprostil, an oral prostaglandin E1 (PGE1) analogue, on lower esophageal sphincter pressure and on the motility of the distal esophagus in healthy volunteers.

The influence of rioprostil on the resting pressure of the lower esophageal sphincter (LESP) and on the bolus-stimulated contraction wave amplitude of primary peristalsis was investigated in 9 healthy male volunteers receiving placebo or 300 and 600 micrograms of rioprostil orally in a randomised, double-blind, threefold cross over study. Manometry was performed using the low-compliance pneumohydraulic infusion system. Rioprostil in a dose of 600 micrograms slightly increased LESP and contraction wave amplitudes measured 5 cm and 10 cm above LES. The duration of the peristaltic contractions was not altered. We conclude that rioprostil in doses which inhibit effectively gastric acid and pepsin secretion and heal peptic ulcers has no inhibitory effects on esophageal motility. Thus rioprostil may be a candidate to treat reflux esophagitis and studies are warranted to establish its efficacy.

Comparative seroepidemiology of cytomegalovirus infection in the Canadian Arctic and an urban center.

We conducted a seroepidemiologic study of cytomegalovirus (CMV) infection among 9,928 Inuit (Eskimo), Dene (Indian) and non-native inhabitants of the Northwest Territories (NWT) of Canada between April 1983 and March 1985. 4,184 inhabitants of Edmonton, a large predominantly white urban center served as controls. Sera were screened for antibody to CMV by enzyme-linked immunosorbent assay (ELISA). The prevalence rates of CMV antibody increased with age in all ethnic groups. By the age of two years 69.2 percent of Dene, 63.5 percent of Inuit, 33.3 percent of non-native and 22.9 percent of Edmonton children had CMV antibody. Over the age of five years Inuit children had higher rates of CMV antibody than Dene children (P less than .05) reflecting differences in infant adoption, breastfeeding practices and patterns of child care in the two native groups. By the age of 15 to 19 years 81.1 percent of Dene and 88.5 percent of Inuit women had CMV antibody compared to 48.8 percent of non-native and 50.9 percent of Edmonton women (P less than .05). Native children had higher prevalence rates than non-native children living in the NWT (P less than .05). Compared to similarly aged Edmonton residents, non-native children in the NWT 2 to 4 years and 5 to 9 years of age had a higher prevalence of CMV antibody (P less than .05). We observed a higher prevalence rate of CMV antibody among non-native children (10-14 years) and young women (15-19 years) living in predominantly native communities compared to those living in predominantly non-native communities in the NWT (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)