Late functional and circulatory changes in rats after local irradiation

[Evaluation of late radiation-induced changes in superficial microcirculation after acute beta-irradiation. II. Prognostic importance of cutaneous Doppler laser]

OBJECTIVE

The changes that occur in the tissular microcirculation after accidental acute irradiation account for some of the early effects of such irradiation, especially at the cutaneous level. The prognostic importance of the cutaneous laser doppler was tested in an experimental model of acute beta-irradiation.

METHODS

Ten pigs were given beta-irradiation with a high single localized dose of 90Sr/90Y (32 or 64 Gy, 7 mg/cm2) delivered to the flank, and were evaluated 2, 7, 14, 21 and 28 days thereafter. Each individual was its own control. The local microcirculation was measured in the resting state and during thermal stimulation at 42 degrees C, using a Periflux cutaneous Doppler laser with p413 probes. Three periods of six minutes each were continuously recorded: period 1 (P1) represented basal resting cutaneous perfusion, with the slope p corresponding to the increase in perfusion when two minutes of thermal stimulation at 42 degrees C began; P2 to plateau perfusion during this stimulation; and P3 to perfusion on the return to equilibrium.

RESULTS

After acute beta-irradiation in the pig, all the cutaneous microcirculation parameters measured (P1, p, P2 and P3) had risen at day 2 in the irradiated area by a factor of 2 to 4, depending on the dose (p < 0.001), compared to the adjacent control area. On the other hand, as from day 7, the resting and the stimulated microcirculation varied little, except for a reduction of the slope p by a factor of 2 (p < 0.05) after the strongest radiation dose.

CONCLUSION

After acute irradiation, the increase in the resting cutaneous microcirculation may correspond to immediate but transitory capillary vasodilatation that accompanies the initial erythema in accidental irradiation. The absence of vascular response to thermal stimulation seems to be a good means of reaching an early diagnosis of delayed cutaneous radiation necrosis.

Complications of combined intraoperative radiation (IORT) and external radiation (ERT) of the upper abdomen: an experimental model

An experimental model in the rabbit is presented which is suitable for analysis of clinically relevant, early side-effects of combined upper abdominal IORT and ERT. Fractionated ERT alone given through an upper abdominal a.-p. field including the entire stomach caused gastric ulcerations within < or = 58 days. Latent times decreased with increasing dose and the ED50 for occurrence of ulcers was 39 +/- 3.3 Gy. Single doses of IORT of 20-40 Gy alone administered through a 2-cm diameter field localized on the coeliac axis and carefully excluding any intestinal mucosa caused neither gastric ulcerations nor other clinical symptoms. When ERT with 40 Gy was preceded by IORT with 20-40 Gy or by sham IORT, 13 out of 15 animals developed ulcers after latent times which in a life-table analysis were shown to be significantly shorter than after ERT alone. However, a statistically significant IORT dose-dependence of latent time or incidence of ulcers could not be demonstrated in the present experiment. The most significant histological changes were observed in the areas of gastric ulcers. Already during ERT, the mucosal epithelium was depleted and regenerative activity was evident in spite of ongoing fractionated irradiation. However, profound irregularities in glandular structure and distribution, as well as number of proliferating epithelial cells were still present in healed ulcers at 80 days. In summary, IORT to the coeliac artery did precipitate the development of gastric ulcers induced by subsequent ERT. On the one hand, the data indicate that the surgical procedure of IORT did contribute to this effect. On the other hand, IORT to the coeliac artery could cause transient, functional alterations in blood supply to the depending organs, i.e. the stomach, and could thus precipitate the development of radiation-induced ulcers.

Conditioned medium from irradiated bovine pulmonary artery endothelial cells stimulates increased protein synthesis by irradiated bovine lung fibroblasts in vitro

Pulmonary fibrosis, a potentially fatal consequence of radiation exposure, occurs by unknown mechanisms. The hypothesis that endothelial cells, injured by radiation, could alter the biochemical function of lung fibroblasts, was tested by exposing cultures of bovine pulmonary artery endothelial cells to 0 or 5 Gy radiation and then incubating them in fresh medium for 48 h. This endothelial cell conditioned medium (ECCM) was then applied to irradiated or nonirradiated cultures of bovine lung fibroblasts. Forty-eight hours later the fibroblasts were analyzed for their ability to synthesize DNA and protein. The ECCM from injured cells stimulated fibroblast protein synthesis twofold to threefold in irradiated fibroblasts without increasing DNA synthesis. It also stimulated a significant but less marked increase in protein synthesis in nonirradiated fibroblasts. Two-dimensional gel electrophoresis revealed this increased synthesis to be expressed in less than 10% of the 1100 separable fibroblast proteins. This study shows that endothelial cells injured by radiation produce factors that stimulate injured fibroblasts to markedly increase their synthesis of certain intracellular proteins, while not stimulating fibroblast replication.

Effects of single doses of gamma-radiation on pig lung

Using a 133Xe wash-out technique changes in the gas exchange capacity of the pig lung have been studied after irradiation with a range of single doses of 60Co gamma-rays. Lung function was assessed for periods up to 104 weeks after irradiation. It was found that the gas exchange capacity of the lung was impaired as early as 4 weeks after irradiation. After a dose of 9 Gy the initial impairment in lung function was resolved within 13 weeks, while after 14.7 Gy damage persisted. The degree of impairment in lung function during the relatively early pneumonitic and late fibrotic phases was indistinguishable and suggested that the late functional impairment was a continuation of the earlier damage. The results of the lung function tests were converted into quantal data and ED50 values of 9.68 +/- 0.3 Gy for early (4-26 weeks) and 9.73 +/- 0.34 Gy for late (39-104 weeks) damage were obtained. The ED50 value for fibrosis and focal scarring based on the histological assessment, 104 weeks after irradiation, was 11.12 +/- 0.9 Gy. The differences in ED50 values were not significant.

Dose-dependent and time-dependent changes in the choroid plexus of the irradiated rat brain

A histological assessment has been made of both time- and dose-related changes in the choroid plexus after the local irradiation of the rat brain with single doses of 17.5-25 Gy of X rays. These investigations involved the serial killing of animals 1-52 weeks after irradiation and the quantitative and semiquantitative evaluation of histological sections. Counts of the relative number of cells in the choroid plexus of the lateral ventricles showed an atrophy of the epithelial layer after 13 weeks. However, this was not as marked as the reduction in the number of endothelial cells in the wall of blood vessels. Moreover, the epithelium had recovered by 39 weeks after irradiation, while the dose-related depletion in endothelial cells tended to be progressive. A highly correlated group of changes in the vascular-connective tissue was used to produce a numerical "factor". This represented a combined score of radiation damage which was both time- and dose-related. These data suggest that, as an expression of late radiation damage to the choroid plexus, the effect on the endothelium was more important than that to the epithelial cells.

Lung damage after hemithoracic irradiation: dependence on mouse strain

A comparative study was performed on CBA, C57Bl mice and their F1 hybrid cross (CBBF1) after right hemithorax irradiation using doses ranging from 15 to 35 Gy. A dose-dependent increase in breathing rate was observed, corresponding to the expression of radiation pneumonitis in the irradiated lung. The use of hemithoracic irradiation enabled this to be observed without any lethality. Results obtained from X-ray computerized tomography (CT), lung weight and histology complemented the breathing rate studies. CBA mice showed a peak response at 16 weeks followed by a decline in breathing rate coincident with a compensatory hypertrophy of the shielded left lung. The manifestation of radiation pneumonitis in C57Bl mice was considerably delayed, supporting previous findings on whole-thorax irradiated animals. The latent period in CBBF1 hybrid mice was intermediate between the parent strains.

Revascularization of autogenous skin grafts placed on irradiated tissue

Vascular changes in rat skin after irradiation were examined microangiographically. Revascularization of the skin transplanted during the chronic stage after irradiation was also studied. The results obtained through these examinations revealed higher vascular densities at the acute and the subacute stages, and low values at the chronic stages compared with those of the control. Furthermore, when the skin grafts were transplanted to the irradiated beds in the chronic stage, primary revascularization was scant, and the inhibited capillary proliferation in the recipient sites prevented new vessel penetration. This explains to why grafts transplanted to previously irradiated beds fail to survive.

Late vascular effects of whole brain X-irradiation in the mouse

The whole brains of mice were irradiated with 250 kVp X-rays at 120 rads min-1 (1.6 mm Cu HVL, TSD 50 cm), and a histological study was carried out. The dose range of X-irradiation was from 1,300 to 2,500 rads, i.e., 1,300, 1,500, 1,750, 2,000, and 2,500 rads. Eighty-six mice were used for histological examination. For microscopic examination, the mice were killed at regular postirradiation intervals between 15 and 20, 31 and 40, 41 and 50, 51 and 60, 61 and 70, 71 and 80, 81 and 90, 139 and 177 weeks. The brains were removed immediately thereafter, fixed in Bouin's solution, and embedded in paraffin. A histological examination was performed by a morphometric estimation of vascular lesions, in which the degree of the damage to the arterial system was scored in whole serial brain sections. Necrosis (encephalomalacia), atrophy, cell infiltration, and telangiectatic vascular change of the brain, caused as a result of the fibrinoid necrosis of the large arteries, were observed. Dose-dependent incidence of the fibrinoid necrosis increased between 41 and 87 weeks after irradiation. Mean score of fibrinoid necrosis increased dose dependently approximately 60 weeks after irradiation. It is suggested that scores of large vessel damage do relate to dose at 41 to 87 weeks, and can be used to quantify the vessel injury, and that fibrinoid necrosis of the large vessels may relate to the incidence of radionecrosis.

Late functional changes in the vasculature of the rat brain after local X-irradiation

The brains of young adult rats were irradiated with doses of 500-4000 rad. At intervals of 3-15 months after irradiation regional changes in the functional vasculature were investigated using the iodoantipyrine extraction technique. Modifications in vascular function were restricted to animals locally irradiated with doses of 2000 and 3000 rad. The first change was observed three months after irradiation and was characterized by a reduction in antipyrine extraction in the mid-brain and brain stem of animals irradiated with 2000 rad. At six and nine months after exposure to both 2000 and 3000 rad significant increases in antipyrine extraction were found in the four brain regions examined, although the effect was greatest in the mid-brain. These results are compared and contrasted with functional changes reported in other normal tissues; the link between these functional changes in the brain vasculature and the appearance of gross vascular lesions after a latent period of one year is discussed. It is suggested that the increase in iodoantipyrine extraction represents a regulatory reaction by the vasculature of the brain to tissue hypoxia and that focal vascular lesions in the brain occur as a consequence of the failure of this reaction to hypoxia.

Blood flow clearance changes in pig skin after single doses of X rays

Early and late changes in the functional vascularity of pig skin have been evaluated after X-irradiation. These changes were assessed using a quantitative isotopic clearance technique. Two waves of radiation-induced changes in isotopic clearance were demonstrated. The first wave, observed after an interval of three weeks, was characterized by the faster clearance of the tracer from areas of irradiated skin. The second wave, which reached a peak after 12 weeks, was denoted by a slowing of the clearance rate relative to normal skin. The modification in vascular function observed at 12 weeks was transient, function returning to normal as late radiation damage developed. The changes observed in the pig have many similarities with those recorded in man but are markedly different from those found in rodents. These differences are discussed with respect to the vascular structure of the skin of the animal species investigated.

Biochemistry of late effects in rat lung after hemithoracic irradiation

The right hemithorax of rats was exposed to 1 kR of roentgen rays, the animals were killed at different times, and various physiologic and biochemic parameters (DNA, protein, collagen, sialic acid, lysosomal enzymes, fibrinolytic activity, peroxides and blood flow ratio between irradiated and non irradiated lung) were determined from 1 day until 11 months after irradiation. A decrease in relative blood flow was observed from 2 weeks until 11 months, a decrease in phospholipids from one to 3 months and a decrease in fibrinolytic activity from 1 day to 11 months after irradiation. At several times a decrease in sialic acid and cathepsin D was also noted. The changes are discussed with respect to the pathogenetic mechanisms of late lung damage.