Localization of plutonium retention in the small intestine of the neonatal rat, guinea pig, baboon and macaca after Pu-citrate ingestion.

The retention of Pu-citrate in the gastrointestinal wall was compared at similar post ingestion times after ingestion at 2 days of age by rats and guinea pigs and at 1 to 34 days by neonatal primates. The small intestine was the main site of the Pu retention in all species. In rats and primates, most of the Pu was retained in the distal ileum, whereas in guinea pigs it was more homogeneously distributed. In the rats, Pu was retained in the epithelial cells on villi, but in the guinea pigs and primates it was confined to the macrophages under the epithelial cells in the lacteal region.

Effects of the chemical forms and valency states of neptunium on its jejunal transfer in the rat.

The transfer of various Np(IV) and Np(V) chemical forms across the small intestine of rats was measured in instilled and perfused jejunum. Instillation of Np(V) nitrate together with citrate or DTPA resulted in the same absorption of Np as after instillation of Np(V) nitrate alone (3 per cent per hour). Perfusion of Np(V) nitrate with bicarbonate or DTPA resulted in a similar transfer (2 per cent) but added citrate or ascorbate resulted in reduced transfer (0.8 per cent). Addition of phytate reduced Np transfer in both instilled and perfused jejunum (0.4 per cent). Np(IV) transfer was usually the same as, or less than that of, the corresponding Np(V) forms. Np(IV) transfer was similar in perfused and instilled jejunum, increasing from 0.2 per cent in the presence of citrate and phytate, to 1 per cent with EDTA and DTPA. Except for phytate, all the forms of Np(V) tested behaved like Np(V) nitrate after transfer from the intestine or after intravenous injection. By contrast, the behaviour of Np(IV) varied for all the forms tested and, for a given form, varied as a function of the experimental procedure used, i.e. jejunal instillation, perfusion, or intravenous injection. These findings suggest that the intestinal transfer of Np might occur via the intercellular pathway, and that it is controlled by both the molecular weight of the Np compound and its stability constant.

Acute lesions induced by alpha-irradiation of intestine after plutonium gavage of neonatal rats.

After gavage of two-day-old rats with 238Pu(IV)-citrate at 17.4 MBq/kg (122 kBq per animal), 45 per cent of the animals died during the second week following ingestion. Histological analysis showed that death was due to acute intestinal lesions caused by alpha-radiation that resulted in denudation of the ileum. Under these experimental conditions, the total alpha-dose delivered to the ileal wall and its contents was estimated at 150 Gy. No acute lesions were observed after gavage of two-day-old rats with Pu-citrate at 5.3 MBq/kg.

Hypophysectomy and the sympatho-adrenal system in cold acclimation.

Hypophysectomy does not impair the increase in weight of brown adipose tissue and adrenals following cold acclimation of the rat. In brown fat, the cold-induced increases in NE and 5 HT contents are not modified by hypophysectomy. In adrenals, hypophysectomy does not change the NE content, but a fall in epinephrine content was observed.

Transfer of Np(V) nitrate from gastrointestinal segments of the adult rat.

The transfer of soluble Np(V) nitrate was measured in gastrointestinal segments from adult rats by two procedures: instillation, in segments in which the physico-chemical form of Np might be modified by gastrointestinal factors; and perfusion, in segments in which the luminal state of Np remains constant. These assays allowed accurate measurement of the Np(V) transferred from the intestine to the whole body. The amount measured was proportional to segment length and to the duration of the experiments, which lasted for periods of 0.25 to 2 h. Under these experimental conditions, hourly transfer values were about 2 percent, both per millilitre of Np(V) solution instilled and per 10 cm of jejunum perfused. This flux is very much greater than that which may be deduced from studies in which Np was gavaged into intact rats. Intestinal transfer of Np was constant for Np concentrations ranging from 5 X 10(-12) M to 1 X 10-4) M. Raising the concentration of Np(V) to more than 1 X 10(-4) M reduced its intestinal transfer. Addition of Fe(II) also reduced it. The small intestine was the main site of Np(V) absorption, since the transfer from instilled jejunum was about 20 times that observed from the stomach, and no difference was noted between jejunal and duodenal transfer.

Post-natal development of brown adipose tissue in the rat bred at 23 degrees C or 28 degrees C.

In view to study the effects of thermal environment on the development and the thermogenic activity of interscapular brown adipose tissue (BAT), young rats born at 23 degrees C or 28 degrees C were sacrificed at 1, 3, 7, 11, 14 or 21 days after birth. The rate of increase in animal weight was quite the same at both temperatures up to the 14th day. The development of BAT and its contents in lipids, in water and in noradrenaline indicate that the energetic activity of the tissue is greatly stimulated in rats kept at 23 degrees C up to the 11th day. It is concluded that in rats bred in the habitual thermal conditions (23 degrees C), the occurrence of non shivering thermogenesis (NST) is important during the period of ten days after birth; in the following period NST could be progressively replaced by other thermoregulatory processes.

[Effect of breeding temperature on the growth and composition of brown fat in the newborn rat]. / Effet de la température d'élevage sur le développement et la composition du tissu adipeux brun du rat nouveau-né.

The weight and the lipid, water and norepinephrine contents of the interscapular brown adipose tissue from 1, 3, 7, 11, 14 and 21 day aged rats were measured. The animals were maintained at an ambiant temperature of 16 degrees, 23 degrees or 28 degrees C from birth. It is concluded that nonshivering thermogenesis is not necessary after 3 days of age in animals kept at 28 degrees C and after 11 days of age in the ones kept at 23 degrees C. However that thermogenesis persists for all the suckling period in those kept at 16 degrees C.

Variations of rat brown adipose tissue composition during cold acclimatization.

The modifications in weight and composition (lipids, proteins, water) of rat interscapular brown adipose tissue (BAT) were studied along the six first weeks of cold exposure and acclimatization. The variations of noreponephrine content was also investigated. During the first day of cold exposure, the major part of tissue lipids was released. During the following two days there was a fall in lipid and norepinehprine contents and uptake of water. Then, until the end of the first week a rapid repletion occurred. At that moment the relative pass of the tissue and the amounts of its principal components reached values which are not changed during the following weeks. We can conclude that the adaptative changes in the levels of BAT essential components are carried out at the end of the first week of cold exposure, long time before the non shivering thermogenesis is entirely effective.

[Variations of triglycerides and of plasma free fatty acids in the rat as a function of the duration of cold maintenance]. / Variations des triglycérides et des acides gras libres plasmatiques chez le rat, en fonction de la durée de maintien au froid.

During the first day of rat exposure to cold (4 degrees C), there was a rapid and regular decrease in plasmatic triglyceride levels and an increase in the free fatty acid ones. These levels remained constant for one week then, untill the third week, they changed slowly and reached the typical levels found in cold acclimated animals. After six weeks of cold exposure, triglycerides were 2.5 fold lesser than in controls and free fatty acids were increased by 50%.