D. Cremonini

Irradiation at Different Times of the Day Morphology and Kinetics of the Small Intestine

Rats were irradiated at different time of the day with sublethal doses on the abdomen only, and qualitative and quantitative morphologic modifications were determined. The experiments seemed to be demonstrate that in the groups irradiated at night and at the end of the light period early injury is not severe whereas in the group irradiated at the end of the dark period repair of the injury seems to be more effective.

Behaviour of the Proliferative Compartment of the Small Intestine at Different Times of the Day

The modifications of mitotic and labelling indices in animals killed at different hours of the day were analysed. The invertase activity was also assayed. This brush border enzyme, synthetized by the differentiating cells, showed a clear circadian rhythm with a maximum in the night and a minimum near the end of the light period. Mitotic and labelling indices showed the highest activity in the night and at noon. The positions of mitotic and labelled epithelial cells in the crypt were also determined. The frequency of labelled cells in the different positions of the crypt evidenced a shift of these cells towards the crypt-villus junction in the late afternoon with a consequent reduction of the differentiating compartment.

S-Phase Cell Distribution in the Small Intestine Irradiated at Different Times of the Day I. Acute Irradiation Injury

The S-phase cell distribution has been analysed to evaluate the behaviour of proliferative cells in the intestinal epithelium after irradiation at different times of the day. A marked reduction of S cell frequency was observed at early intervals after abdominal irradiation; this reduction was particularly evident in the lower half of the crypts. At subsequent intervals a progressive extension of the proliferative compartment, with labelled cells also at the top of the crypt, was present. The irradiated groups generally showed a homogeneous behaviour even if a more marked reduction in S-phase cells was observed in group C. The invertase activity, a brush border enzyme synthetized during the differentiation process, presented a different behaviour at the early intervals in the irradiated groups. When the extension of the proliferative compartment occurred the invertase activity reached values close to zero. The modifications in brush border enzymes and in S-phase cell distribution, at early killing times, led to the hypothesis of an early differentiation.

Modifications of S-Phase Cell Distribution in the Intestinal Crypts after Multiple Daily Fractionation

The effects obtained by multiple daily fractionation (3 Gy X 2 or 3 Gy X 2 X 2) on the distribution of S-phase cells along the crypt of the small intestine were investigated. The frequency of labelled cell distribution was reduced at early intervals; then the proliferating compartment gradually extended to the villus junctions. During recovery labelled cell frequency in the lower half of the crypts returned to control levels, while labelled cells were present in the differentiating area. With lower total dose modifications were milder and, as early as 72 h before exposure, distribution was already similar to controls. Invertase activity showed an initial increase and a higher reduction during acute damage when fractionation with higher doses was used. A lack of return to normal activity was present even 11 days after exposure when, however, the characteristic circadian pattern was observed.

S-Phase Cell Distribution In The Small Intestine Irradiated at Different Times Of The Day: II. Recovery Phase

Modifications occurring during recovery in the small intestine of animals exposed to the same radiation dose given at different times of the day were evaluated. S-phase cell distribution along the crypts and invertase activity were evaluated to ascertain the functional capacity of epithelial cells. In animals killed between 5 and 6 days after exposure, S-phase cell distribution and functional conditions tended towards normality although recovery was not complete. Labelled cells occurred also at villus junctions, demonstrating limitation in size of the differentiating compartment. This was confirmed by reduced activity of the brush border enzymes. Animals irradiated at the end of the dark period recovered more quickly and efficiently. In this group, labelled cell distribution was almost the same as in the controls starting from 120 h, and invertase activity was also closer to the controls than in any other group.

Modifications of Small Intestine Lysosomal Enzymes after Irradiation at Different Times of the Day

The modification of lysosomal enzyme activities in animals irradiated with the same sublethal dose at 4 different times of the day is reported. The results confirmed the absence of circadian fluctuations in all the lysosomal enzymes and in protein content. A difference in behaviour between acid beta-galactosidase and beta-glucuronidase on the one hand and between acid phosphatase and cathepsin D on the other was evident in irradiated animals. The results showed that acid beta-galactosidase and beta-glucuronidase increase from the early intervals after irradiation and reach the highest activity between 36 and 48 h. At these intervals autolysis phenomena, heavy cellular alterations and numerous phlogosis cells are present in the epithelium. Only beta-glucuronidase and acid beta-galactosidase indicate the level of radiation injury.

14C Leucine Uptake in Rat Tissues at Different Times after Irradiation

The uptake of 14C leucine administered at different intervals after irradiation, but always 4 and 8 h before the animals were killed, has been evaluated in tissues with different proliferative activity and protein synthesis. The results have demonstrated an increased uptake and a more rapid elimination of the tracer after irradiation. In the small intestine a lower amount of TCA insoluble fraction was observed when the morphologic injury was evident, while protein synthesis significantly increased during the initial phase of appearance of the injury and mainly during the recovery phase of epithelial cells. Kidney and plasma had levels higher than controls at all intervals.

Circadian activity of rat kidney enzymes

Alkaline phosphatase, LAP, β-glucuronidase and cathepsin D activities and protein content of the kidney homogenate did not show any circadian rhythm in animals sacrificed at different hours of the day. The fluctuations of maltase appear modest and not dependent on a light/dark cycle.