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.

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.

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.

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.

Measurements of the asphyxial oxygen level for Rhinomugil corsula, Tilapia mossambica, Puntius sarana and Carassius auratus at 30 and 35 ~ revealed that at 35 ~ the lethal oxygen level was higher for T. mossambica and P. sarana and lower for R. corsula, but it remained the same for C. auratus at 30 and 35 ~