The effect of local hyperthermia on the small intestine of the mouse

Neurological Complications after 434 MHz Microwave Hyperthermia of the Rat Lumbar Region Including the Spinal Cord

Hyperthermia was applied in the region of the vertebral column from the second to the fifth lumbar vertebra using a ring-shaped 434 MHz microwave radiator. In all experiments temperatures were measured at a 'reference' thermocouple which was placed against the fourth lumbar vertebra. After 60 min of heat treatment at 'reference' temperatures of 43.0 degrees C, 44.0 degrees C and 45.0 degrees C (+/- 0.05 degrees C) the average maximal temperature inside the vertebral canal were 42.6 degrees C, 43.0 degrees C and 43.8 degrees C (+/- 0.3 degrees C), respectively. At all 'reference' temperatures the maximal core temperature of the animal did not exceed 40.5 +/- 0.3 degrees C after 60 min of heat treatment. Dorsal skin and muscle temperatures in the treatment area reached 'reference' temperature, and transient skin and muscle necrosis was observed after treatment for 1 h at 'reference' temperatures at 44 degrees C and 45 degrees C. Temperatures in the peritoneal cavity approximately 1 mm ventrally of the vertebral column rose to 41.8 degrees C after 60 min at reference 43.0 degrees C. Treatment at spinal cord temperature 42.6 degrees C for 60 min did not induce any significant neurological effects. Motoric dysfunction of the hind legs, such as difficulties with walking, was observed after 60 min treatment at spinal cord temperatures of 43.0 degrees C or 43.8 degrees C. In addition, 24 h after treatment at 43.8 degrees C for 60 min loss of tail tonus was observed, as well as loss of sensory function in the hind limbs. Recovery from the neurological disorders, except for the loss of tail tonus, occurred within 2 weeks after treatment. Histopathological examination revealed necrosis in the central areas of the spinal cord at 3 days and complete necrosis at 7 days after treatment at 43.8 degrees C for 60 min.

THERMAL DOSE REQUIREMENT FOR TISSUE EFFECT: EXPERIMENTAL AND CLINICAL FINDINGS

In this review we have summarized the basic principles that govern the relationships between thermal exposure (Temperature and time of exposure) and thermal damage, with an emphasis on normal tissue effects. We have also attempted to identify specific thermal dose information (for safety and injury) for a variety of tissues in a variety of species. We address the use, accuracy and difficulty of conversion of an individual time and temperature (thermal doses) to a standardized value (eg equivalent minutes at 43 degrees C) for comparison of thermal treatments. Although, the conversion algorithm appears to work well within a range of moderately elevated temperatures (2-15 deg C) above normal physiologic baseline (37-39 deg C) there is concern that conversion accuracy does not hold up for temperatures which are minimally or significantly above baseline. An extensive review of the literature suggests a comprehensive assessment of the "thermal does-to-tissue effect" has not previously been assembled for most individual tissues and never been viewed in a semi-comprehensive (tissues and species) manner. Finally, we have addressed the relationship of thermal does-to-effect vs. baseline temperature. This issues is important since much of the thermal dose-to-effect information has been accrued in animal models with baseline temperatures 1-2 deg higher than that of humans.

Changes in blood flow in locally heated intestine of rats

Male Fischer rats were surgically castrated through a lower midline incision and a 5-8 cm long segment of small intestine was fixed to the interior of the right scrotum. Two weeks after the surgery, the herniated intestine was heated by immersing the scrotum into a water bath at different temperatures and the blood flow in the intestine was measured with the radioactive microsphere method. The blood flow in the herniated intestine increased 1.5-2.0 times when the scrotum was heated with 42.5 and 43.5 degrees C water baths for 60-90 min, but began to decrease when heated longer, although the blood flow after heating for 120 min at these temperatures was still slightly larger than the blood flow before heating. Upon heating the scrotum with 44.5 degrees C water bath, the blood flow in the herniated intestine increased to 3-fold of control by 90 min and then rapidly recessed. Massive histological damage was observed 24 h after heating with 44.5 degrees C water bath for 60 min. The blood flow in the intestine measured 1 day after 60 min heating with 43.5 degrees C and 44.5 degrees C water bath was found to be only slightly decreased. Given the relatively small decrease in blood flow, the severe damage in the intestine 24 h after heating may be attributed to direct damage to parenchymal cells.

Continuous hyperthermic peritoneal perfusion for the prevention of peritoneal recurrence of gastric cancer: randomized controlled study

We performed continuous hyperthermic peritoneal perfusion (CHPP) or continuous normothermic peritoneal perfusion (CNPP) combined with cisplatin (CDDP) 300 mg/kg and mitomycin C (MMC) 30 mg/kg in an attempt to prevent peritoneal recurrence after surgery for gastric cancer. Twenty-two patients were treated with perfusion using about 10 liters of saline heated to 41 degrees to 42 degrees C (CNPP group); 18 patients were treated with saline heated to 37 degrees to 38 degrees C (CNPP group); and 18 patients underwent only gastric surgery without perfusion (control group) in a randomized control study. There were two deaths (9%) due to peritoneal recurrence in the CHPP group, four (22%) in the CNPP group, and four (22%) in the control group. The 1-, 2-, and 3-year survival rates were 95%, 89%, and 68%, in the CHPP group; 81%, 75%, and 51%, in the CNPP group; and 43%, 23%, and 23%, in the control group, respectively. There was a significant difference between the three survival curves by the log-rank test (p < 0.01). This difference showed that CNPP and CHPP are both effective procedures for preventing peritoneal recurrence. The maximum concentrations in the perfusate of total and free CDDP with 300 mg administration were 12.2 and 10.1 micrograms/ml, respectively, at the end of the perfusion, and the maximum concentrations of total and free CDDP in plasma were 2.1 and 1.0 micrograms/ml, respectively. The maximum concentrations of MMC in perfusate and plasma with 30 mg administration were 1.00 and 0.05 micrograms/ml, respectively, which are intraperitoneally cytotoxic but systemically safe concentrations.

Thermal enhancement of radiation-induced leg contracture

Early and late damage in the normal tissues of the legs of mice was compared following treatment with radiation alone or radiation followed immediately by hyperthermia. Hyperthermia was given by immersing the hind leg in a water bath at 43.0 degrees, 43.3 degrees, or 43.5 degrees C for 1 hr. Damage was assayed by measuring leg contracture at various intervals from 5 to 365 days after treatment. At 5 days after treatment, only hyperthermia-induced contracture was observed. At 10 and 20 days, contracture increased with radiation dose in heated legs, but little contracture had developed in mice treated with radiation alone. By 45 through 365 days, however, contracture correlated with radiation dose both in mice treated with radiation alone as well as in those treated with radiation and hyperthermia. The greatest differential in the slopes of the dose response curves, suggesting hyperthermic radiosensitization, was seen 20 days after treatment. Nevertheless, at 365 days, contracture was still significantly greater in the mice treated with radiation and hyperthermia (43.5 degrees bath) than in the irradiated controls. Thermal enhancement ratios (TERs) were calculated from LCD50 values (LCD50 = radiation dose that would give a stated level of leg contracture in 50% of the mice). For greater than or equal to 3 mm contracture, TERs were 4.1 to 7.9 at 30 days, depending on bath temperature, but only 1.1 to 1.5 at 365 days. For an isoeffect of greater than or equal to 7 mm contracture, TERs were 1.9 to 5.3 at 30 days, and 0.8 to 1.8 at 365 days. Thus, contracture was enhanced more at 20 to 30 days after treatment with radiation and hyperthermia than at 120 through 365 days. Radiation damage not only appeared earlier in mice treated with hyperthermia than in those treated with radiation alone, but after the highest temperature tested (43.5 degrees bath), contracture was greater from 5 through 365 days after treatment than in controls treated with radiation alone.

The effect of hyperthermia and radiation on small bowel permeability using 51Cr EDTA and 14C mannitol in man

A prospective study was conducted to study the effect of radiotherapy (RT) and regional pelvic hyperthermia (HT) on intestinal permeability in three groups of patients. Fifteen acted as cancer controls, receiving RT away from the peritoneal cavity, 21 patients received radical pelvic or abdominopelvic RT and 13 patients pelvic RT followed by pelvic HT using a BSD 1000 phased array applicator. Small bowel permeability was measured by oral administration of a mixture of [51Cr]EDTA, [14C]mannitol and lactulose before and after a course of treatment. The absorption of each marker was calculated by measuring the urinary excretion over 0-6 and 0-12 hours. The 6 hour collection gave results similar to the 12 hour collection, but had logistical advantages. The EDTA absorption rose and the mannitol absorption fell during a course of treatment, but the best index of permeability change was the EDTA/mannitol ratio (E/M). The E/M ratio rose by a factor of 2.4 (P less than 0.001) and 1.82 (P = 0.05) following RT and RT/HT respectively. There was no significant difference between the RT and RT/HT groups but the thermal dose to the RT/HT group was low (23 min./equiv 43 degrees C over three or four fractions in 4 weeks). There was no correlation between small bowel permeability and bowel frequency. The E/M permeability test is a useful simple functional assay for assessing small bowel damage after RT and RT/HT.

Morphological and functional recovery of rat small intestine following localized hyperthermia

Structural and functional changes in the rat small intestine following localized hyperthermia were examined. In anaesthetized male Sprague-Dawley rats a 10 cm segment of mid-small intestine was temporarily exteriorized, suspended in a cup containing Krebs-Ringer solution, and either heated at 43.5 degrees C or sham-heated at 38 degrees C for 45 min. The intestinal segments were studied 1, 4, 7, 21 and 42 days later by histopathological examination, determination of wet weight, dry weight and gross segment area, and by measuring absorption of 15 mM D(+)-glucose containing 14C-labelled D(+)-glucose as a tracer. Intestinal glucose transport was assessed by two different techniques: the everted sac method (in vitro) and luminal perfusion-recirculation (in vivo). After 1 day, heated intestinal segments exhibited marked mucosal damage, consisting of loss of epithelial cells and destruction of villi. Re-epithelialization had occurred by day 4, but mucosal architecture remained abnormal throughout the observation period. Hyperthermia caused significant thickening of the intestinal wall: at 4 days the thickening was due to oedema, whereas at 42 days tissue mass per cm2 in heated segments had increased by approximately 53 per cent compared with sham-heated control segments. At 1 day, net glucose transport in vitro in heated segments was reduced to 20 per cent and the serosal/mucosal concentration ratio to 57 per cent of that of control segments. In vivo, glucose transport in heated intestine at 4 days was 45 per cent of that of controls. From 4 days on, glucose transport improved gradually, and at 42 days there was no significant difference between heated and sham-heated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of exocrine pancreatic secretions on hyperthermic injury of rat small intestine

The influence of the exocrine pancreatic secretions on development of small intestinal injury following localized hyperthermia was studied. In male Holtzman rats the excretory pancreatic ducts were occluded with metal hemostatic clips. An intraperitoneal injection of [3H]thymidine was given 3 weeks later. Three or 48 h after the injection a 10 cm segment of small intestine was exteriorized through a midline abdominal incision and heated at 38.0 degrees C, 42.5 degrees C, or 43.5 degrees C for 45 min. Intestinal damage was assessed 24 h after hyperthermia. The following four endpoints were used: histopathological injury score, the number of villi per intestinal circumference, the number of labelled epithelial cells in fixed areas of autoradiographic specimens, and incorporation of [3H]thymidine as determined by liquid scintillation counting. The correlation of results among the four methods of assessment was highly significant. The autoradiography data showed better correlation with both morphological parameters than the results of liquid scintillation counting. There was significantly less damage in heated segments from pancreatic duct-occluded animals than in segments from sham-operated controls. When hyperthermic injury was assessed morphologically the protection conferred by pancreatic duct occlusion was equivalent to lowering the temperature of heating by 1 degree C. It is concluded that morphological criteria may be superior to endpoints based on [3H]thymidine incorporation for assessment of hyperthermic injury in rat small intestine. Reducing the intraluminal pancreatic secretions appears to confer significant protection from small bowel injury after localized hyperthermia.

1985 Douglas Lea memorial lecture. Hyperthermia in the treatment of cancer

There are sound biological reasons for using hyperthermia in the treatment of malignant disease. This review includes a discussion of this rationale and describes effects of hyperthermia either given alone or in combination with ionising radiation to cells in vitro, tumours or normal tissues. Topics discussed include thermotolerance, step-down sensitisation, fractionation, re-treatment of previously irradiated sites, thermal enhancement ratio and thermal dose. Problems of heat delivery and temperature measurement are considered and the current status of clinical studies is stated briefly.

The effect of step-down heating on mouse small intestinal mucosa

Step-down heating (SDH) was investigated in mouse small intestine by giving a primary (conditioning) treatment at or above 43 degrees C followed by a test treatment below 43 degrees C. Crypt dose-response curves following SDH were compared with those obtained using the test treatment alone; the SDH effect was characterized by a reduction in shoulder (an additive effect) and an increase in slope (thermosensitization). The thermosensitization ratio, defined as slope SDH-heated/slope single-heated, was independent of the conditioning temperature but increased to a maximum of approximately three as the duration of conditioning increased. Thermosensitization was eliminated when the conditioning treatment was itself sufficient to cause significant crypt loss and, also, when the interval between the two treatments was 0.5 h or longer. This period was less than that required for either recovery of the 'shoulder' on the crypt dose-response curve or the development of thermotolerance following the primary treatment. Thermotolerance which develops in intestine during prolonged hyperthermia (after approximately 100 min) was not affected by SDH and Arrhenius analysis indicated that the activation energy for temperatures below 43 degrees C was not significantly altered by SDH. In summary, the SDH effect on small intestine, assessed using the crypt loss endpoint, was similar to thermosensitization observed in vitro. However, the lower magnitude of the effect and its complex dependence on the primary heat treatment suggest either that crypt cells respond to SDH in a unique and characteristic manner or that the crypt assay in vivo and reproductive survival in vitro do not reflect the same endpoint.

Further studies on the response of intestinal crypt cells of different hierarchical status to eighteen different cytotoxic agents

Adult male mice were treated with one or two different doses of each of 18 different cytotoxic agents. They were sampled at various times (3-12h) thereafter, and the spatial distributions of cell death in the small intestinal crypts were studied. Dead or dying cells or cells carrying dead cell fragments were examined histologically, and all of these were recorded (for convenience as apoptotic fragments), relative to the cell position in the crypt. Thus, distributions of apoptotic fragments against cell position were determined. A regression analysis of the data obtained at different times after administration of each agent was undertaken and the position of the median of the spatial distribution of presumptive target cells was deduced for each cytotoxic agent. The accuracy of this median value was determined to be +/- 0.5 cell positions. From these median values, the different cytotoxic agents could be divided roughly into three groups: [3H]thymidine, isopropyl-methane-sulphonate, gamma-rays, bleomycin and adriamycin all have their median values (susceptible cells) at cell positions 4 to 6; bischlorethylnitrosourea, actinomycin D, cyclophosphamide and cycloheximide at cell positions 6-8; mechlorethamine, triethylenethiophosphoramide, vincristine, 5-fluorouracil, hydroxyurea and methotrexate at cell positions 8-11. The position of these medians was considered in relation to the killing of clonogenic cells. Preliminary studies on the distributions of dead cells after myleran, cis-platinum and heat (hyperthermia) were also reported. There is a general tendency for antibiotics and radiation to attack the lower cell positions in the crypt. Alkylating agents on the other hand have a somewhat broad spectrum of action. Antimetabolites and a microtubule dissociating agent act on higher cell positions. No difference could be detected between two different forms (sources) of actinomycin D. The changes in the yields of apoptotic and mitotic cells with time and the migration velocities of cells in the crypts carrying apoptotic fragments after exposure to cytotoxics are also presented.

Arrhenius analysis of the heat response in vivo and in vitro of human melanoma xenografts

The response to heat treatment in vivo (40.5-44.0 degrees C) and in vitro (40.5-45.5 degrees C) of five human melanoma xenografts was studied. Specific growth delay was used as a measure of response after treatment in vivo. Colony-forming ability was assayed in soft agar after treatment in vitro. Dose-response curves were established and subjected to Arrhenius analysis. The Arrhenius curves were found to have an inflection point at 42.0-43.0 degrees C in vivo and 41.5-42.5 degrees C in vitro. The activation energies were in the ranges 426-771 kJ/mol in vivo and 676-739 kJ/mol in vitro above the inflection point and 774-1661 kJ/mol in vivo and 1118-2190 kJ/mol in vitro below the inflection point. Above the inflection point the activation energies in vivo and in vitro were not significantly different for any of the melanomas, and furthermore were similar to those reported for rodent tumours, normal tissues and cells in culture in the same temperature range. Below the inflection point on the other hand the activation energies were lower in vivo than in vitro. This difference was probably a consequence of differences in the physiological conditions in vivo and in vitro. The activation energies in vitro in this temperature range were comparable to those reported for normal tissues and cells in culture.

Localized hyperthermia and X-irradiation of murine jejunum in situ: a new method

In C3H mice, preparative surgery apposed a 15 mm length of jejunum to the peritoneal surface of the ventral abdominal wall. After the mice healed, manipulation of the abdominal wall made possible selective hyperthermic treatment and X-irradiation of the immobilized jejunal segment (IJS) while it remained within the peritoneal cavity and in continuity with the rest of the intestines. For hyperthermia, the ventral abdominal wall and attached IJS was flattened between two aluminium plates immersed in a standard water bath. The temperature at the mesenteric attachment of the IJS was within 0.5 degrees C of a 44 degrees C bath 100 s after immersion and within 0.3 degrees C at steady-state. Xenon-133 washout studies showed that the treatment technique did not compromise blood flow to the IJS. The preparative surgery left the IJS normally responsive to X-irradiation as determined by crypt microcolony assay. Hyperthermia treatment by itself at 44 degrees C for up to 20 min caused no loss of crypts or villi; however, adjuvant 5-15 min 44 degrees C hyperthermia displaced the X-ray crypt-survival curves towards lower doses without changing their slopes. Nevertheless, formal statistical analyses admitted both additive and multiplicative interpretations of the effects of X-irradiation and adjuvant hyperthermia on intestinal crypt survival. After adjuvant hyperthermia, the surviving crypts were preferentially clustered near the mesenteric attachment to a greater extent than was expected from the asymmetry of the heat dose.

Reversible injury after mild hyperthermia

Skin contraction and leg contracture resulted from immersion of mice legs in a water bath at temperatures of 42.5 degrees to 43.7 degrees C for 45 to 90 minutes. The maximum contracture was observed between 5 and 15 days after treatment, but little damage remained after about 30 days. After healing of the early tissue damage, there was no progression of residual damage in skin up to 490 days after treatment. In contrast, radiation-induced contracture develops rapidly after 14 days, and may continue to progress for 100 days or more. In the present studies, leg contracture could be attributed primarily to injury in the skin, because skinning the legs before measuring eliminated most of the contracture. Temperature differences between subcutaneous tissue and deep muscle were not consistently observed or statistically significant, and probably made little or no contribution to the difference in thermal response of these tissues.

Effect of hyperthermia on the radiation response of Chinese hamster small intestine

The Chinese hamster small intestine was surgically exteriorised from the ligament of Trietz to the ileocaecal junction and heated for 8 min at 44.3 degrees C (a non-lethal dose) at various intervals before or after whole-body 60Co irradiation. Hyperthermia exposure immediately after irradiation reduced the LD50/7 from the control of 1,230 cGy to 798 cGy (thermal enhancement ratio, TER, of 1.5). At an interval between irradiation and hyperthermia of 2 h the LD50/7 was 935 cGy, and it remained at that value for intervals of 2-24 h. The increase in the LD50/7 by 2 hours after irradiation probably represents the repair of radiation damage that can interact with hyperthermia, and after two hours the two modalities interact independently. When the small intestine was exposed to 44.3 degrees C hyperthermia immediately prior to irradiation, the LD50/7 was reduced to 658 cGy (TER = 1.8). As hyperthermia and radiation treatments were separated the LD50/7 returned to the control value by 24 h and was unchanged over 24-72 h. This indicates that by 24 h, recovery from hyperthermia damage that could interact with radiation damage was complete. For the sequence hyperthermia----radiation, 33% of the hyperthermia damage was repaired by 1 h; whereas for radiation----hyperthermia, 85% of the radiation damage was repaired by 1 h. The sequence-dependent interaction of hyperthermia and radiation damage in normal tissues is complex, but the kinetics of interaction for the sequence radiation----hyperthermia seem to be predictable for several normal tissues in different species.

Time-temperature relationships for hyperthermal radiosensitisation in mouse intestine: influence of thermotolerance

Thermal enhancement of radiation injury to the crypt compartment of mouse small intestinal mucosa has been measured as a function of heating time for temperatures in the range 41.0-44.0 degrees C. All the hyperthermal treatments used were themselves subthreshold for gross tissue injury. With this limitation, thermoradiosensitisation increased linearly with duration of hyperthermia for temperatures in the range 42.3-44.0 degrees C. Using temperatures below 42.0 degrees C, there was a saturation in effect for treatments longer than approximately 40-90 min, possibly due to the development of thermotolerance. The thermoradiosensitisation isoeffect curve relating heating time with temperature was biphasic with the transition occurring between 41.8 and 42.0 degrees C. For temperatures above the transition, a 1 degree C change was equivalent to a factor of 2.6 in heating time; below the transition, a 1 degree C change was equivalent to a factor of 5.4. Time-temperature relationships for thermoradiosensitisation in other rodent tissues are reviewed and compared with the general relationships for direct thermal injury, previously derived from experimental studies. The results are discussed with relevance to the interpretation of in vivo thermal enhancement of radiation injury.

Hyperthermia for cancer: a practical perspective

A causal relationship between hyperpyrexia and tumor regression was first suggested in 1866, when Busch reported the cure of a histologically diagnosed sarcoma in a middle-aged woman, following a bout of erysipelas. Over the years, interest in the effect of heat on cancer has remained alive, but this interest has increased dramatically in recent years. The literature on this subject is broadly reviewed and the clinical results discussed. It is apparent from clinical studies thus far that it is a relatively simple undertaking to treat superficial neoplasms with hyperthermia. However, the major challenges in clinical thermotherapy pertain to patients with deeply situated tumors. The lack of safe and reliable methods of monitoring temperature in deep tissues is a major impediment to a thorough understanding of thermal dosimetry in clinical hyperthermia, and routine thermal dosimetry in clinical hyperthermia will have to await the development of reliable noninvasive thermometry. As responses have been reported with modest levels of hyperthermia, the need for thermometry is somewhat lessened, given that invasive monitoring is imperfect and somewhat risky when used in deeply seated tumours. The eventual place of thermotherapy in the treatment of malignant tumours in man is as yet unclear and must be rigourously and thoroughly assessed in well-designed, prospective, randomized patient trials.

Effect of hyperthermia on murine myeloid precursors

Murine bone marrow was exposed to hyperthermia temperatures of 41.5 to 45.5 degrees C. The proliferation capacity of myeloid progenitor and committed precursors was assayed in vivo utilizing spleen colony formation and diffusion chamber (DC) techniques. The survival of both pluripotential (CFU-S) and committed myeloid (CFU-DG) stem cells decreased exponentially with an increase in the heating period. Progression from CFU-S to CFU-DG significantly altered thermal sensitivity in the temperature range examined. Proliferation of mature granulocyte-monocytes (G-M) in DC is more thermostable than their stem cell precursors. Heat inactivation energies (enthalpies) of CFU-S and CFU-DG were derived from the slope of the heating time survival curves. Enthalpy of CFU-S is 300 kcal/mole below 43 degrees and 105 kcal/mole above 43 degrees. The enthalpy of CFU-DG is 250 and 145 kcal/mole below and above 43 degrees, respectively.

The effect of radiation alone and of radiation followed by hyperthermia on the vasculature of mouse intestine

The effect on the vasculature of mouse intestine was observed following: (a) irradiation alone; and (b) irradiation followed at intervals of 0-60 days by hyperthermia. Specimens of intestine were removed after sacrifice and the vasculature revealed by benzidine staining before clearing in resin. The mean visible venous tree (VVT) was used as a parameter for assessing damage. The same hyperthermal treatment was used throughout: 1 h at 41.0 degrees C with the gut externalised. Following irradiation by 9 Gy, the VVT was not significantly reduced in the first 15 days, but decreased steadily by 34% in the next 45 days. In addition two transient reversible reductions occurred: the first immediately following irradiation, not counteracted by hyperthermia and thought to result from spasm; the second after about 40 days, counteracted by heating and thought to be caused by partial occlusion of the arterioles, resulting from irradiation. Reduction in VVT 26 days after irradiation appeared to be independent of dose from 6 to 10 Gy. Sensitivity to hyperthermia was maximal 15 days after irradiation.

Production of systemic hyperthermia in the rat

The design of clinical trials employing whole-body hyperthermia in cancer therapy has been hampered due to lack of a suitable animal model. We describe a technique for reproducibly and efficiently inducing whole-body hyperthermia in Sprague-Dawley rats, using halothane and oxygen anesthesia and immersion in a hot water bath. Core body temperatures of between 41.5 and 43 degrees C were induced and maintained for periods of up to 200 min and survival curves were determined. The time of exposure at a given temperature that resulted in death in 50% of the animals within 24 hr after heating (LD50/24 hr) was calculated by linear logistic regression analysis. LD50 24 hr values of 115, 61, 57, 25 and 16 min were obtained for temperatures of 41.75, 42.0, 42.25, 42.5 and 42.75 degrees C respectively. This heating technique is compared to several more toxic methods for inducing whole-body hyperthermia with respect to possible pharmacological and physiological differences.

The development of thermotolerance in hyperthermal injury to the villus compartment of mouse small intestine

The development and decay of thermotolerance in the villus compartment of the intestinal mucosa of mouse was investigated by giving a primary treatment of 41.5 degrees C for 1 hour (subthreshold for thermal injury) at various intervals before a second, test treatment of 43.0 degrees C for 30 min. The test treatment was given 65 hours after an intraperitoneal injection of 3H-thymidine (i.e. at a time when the heavily labelled cells could be seen to have moved from the crypts on to the upper halves of the villi) and thermal damage assessed by loss of radioactive label. A transient tolerance to the second treatment was induced by the primary treatment. This 'thermotolerance' was maximal 3-13 hours after the first treatment and had decayed by 24 hours. Both the extent and time course of expression and decay of thermotolerance in this post-mitotic functional compartment were very similar to those previously reported for damage to the proliferative epithelium as assayed by crypt loss. This suggests either that the kinetics of thermotolerance are not dependent on the proliferative status of the tissue or that there is a common limiting factor in thermotolerance development, despite the apparent difference between the two mucosal compartments in their susceptibilities to thermal injury.

Effect of intestinal hyperthermia in the Chinese hamster

If hyperthermia is to become a useful cancer therapeutic modality, normal tissue response must be thoroughly understood. The hyperthermia response of Chinese hamster intestine was studied by immersion of the exteriorized small intestine in heated tissue culture medium. After heating, the small intestine was reinserted, the incision closed, and animals observed until death. Animals exposed to 42.5 degrees, 43.5 degrees, or 44.5 degrees C intestinal hyperthermia exhibited LD50/7 values (including 95% intervals) of 56 min (52.9-59.3), 29 min (26.4-31.8), or 14 min (13.2-14.6), respectively. An Arrhenius plot of LD50/7 vs 1/T degree K exhibited an inactivation energy of 139 kcal/mole, which corresponds well with values generally reported for cellular inactivation. Hamster intestine conditioned with a sublethal exposure of 8 min at 44.5 degrees C developed thermotolerance to subsequent 44.5 degrees C hyperthermia. Thermotolerance induction was maximal by 24 hr; the LD50/7 for the second dose of hyperthermia increased from 6 min at 44.5 degrees C at zero time to 21 min at 44.5 degrees C after a treatment interval of 24 hr (thermotolerance ratio of 3.5). The LD50/7 subsequently decreased from 21 min to 12 min at 44.5 degrees C (the control value) by 96 hr. The hyperthermia response of this tissue was predicated by previous results from the Chinese hamster ovary (CHO) fibroblast cell line in tissue culture, and is also similar to several mouse normal tissues.

The relationship between heating time and temperature: its relevance to clinical hyperthermia

It is well known that for a given level of damage to either cells in vitro or tissues in situ the relationship between temperature and time of application undergoes a transition in the range 42-43 degrees C and that above this temperature a change of 1 degree C is equivalent to a change in heating time by a factor of two. The present study has concentrated on establishing the relationship between time and temperature over a wide range. The investigation is in two parts, i.e. a review of the literature and an experimental study in which the endpoint used was necrosis in the tail of the baby rat. The aim is to provide information which might help solve a major clinical problem, namely the lack of a satisfactory means of relating treatments given with different temperatures for different lengths of time. The difficulty arises because there is no satisfactory definition of heat dose, in this context. The results confirm the relationship given above for temperatures above the transition. However, below the transition a change of 1 degree C is equivalent to a change in heating time by a factor of six. It is suggested that these relationships provide a means of monitoring a treatment in which the temperature does not remain constant and may vary within a heated volume. The method may also be used to compare treatments from different centres. An indication of the considerable uncertainties of the procedure is given.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of prolonged heating on the thermal enhancement ratio in X-irradiated murine intestine

When the jejunum in mice was heated for 20-180 min at temperatures between 40.3 and 42.3 degrees C, followed immediately by X-irradiation, the thermal enhancement ratio (TER) for crypt survival increased and then tended to decline with longer heating times. At the higher temperatures, the TER was higher and the peak value was reached with shorter heating times. The decline in TER with longer heating times may be due to the development of thermotolerance.

Thermal tolerance to whole body hyperthermia

Thermal tolerance, that is, a reduced sensitivity to a succeeding heat treatment, has been noted in vitro and following local hyperthermia in normal tissues and malignant tumors. However, information is sparse concerning thermal tolerance following systemic hyperthermia, thereby limiting our ability to design optimally fractionated systemic hyperthermia treatment protocols. A technique for reproducibly inducing systemic hyperthermia in the rat is described, and the survival curve for rats exposed at 42.5 degrees C for periods of up to 75 minutes is presented. Using this system, increased survival of rats to systemic hyperthermia at 42.5 degrees C was demonstrated 30 hours after an initial sublethal conditioning exposure (41.8 degrees C for 1 hour). The LD50 (the time of exposure lethal to 50% of the rats) at 42.5 degrees C was increased by a factor of approximately 2 in the animals exposed to the sublethal conditioning. This increase in LD50 demonstrates the development of thermal tolerance to killing by whole body hyperthermia.

Effect of prior hyperthermia on subsequent thermal enhancement of radiation damage in mouse intestine

Hyperthermia given in conjunction with X-rays results in a greater level of radiation injury than following X-rays alone, giving a thermal enhancement ratio (TER). The effect of prior hyperthermia ('priming') on TER was studied in the small intestine of mouse by giving 42 X 0 degrees C for 1 hour at various times before the combined heat and X-ray treatments. Radiation damage was assessed by measuring crypt survival 4 days after radiation. TER was reduced when 'priming' hyperthermia was given 24-48 hours before the combined treatments. The reduction in effectiveness of the second heat treatment corresponded to a reduction in hyperthermal temperature of approximately 0 X 5 degrees C, a value similar to that previously reported for induced resistance to heat given alone ('thermotolerance') (Hume and Marigold 1980). However, the time courses for development and decay of the TER response were much longer than those for 'thermotolerance', suggesting that different mechanisms are involved in thermal damage following heat alone and thermal enhancement of radiation damage.

Increased hyperthermal response of previously irradiated mouse intestine

The effect of prior irradiation (6-10 Gy of X rays) on the response of mouse jejunum to 43.0 degrees C hyperthermia was investigated. A dose of 6 Gy has no significant effect on the crypt loss measured after hyperthermia. However, intestine which had received 8-10 Gy showed increased susceptibility to subsequent thermal injury. Between approximately one and 2 weeks after 9 Gy, the thermal response of the intestine of CFLP mice increased such that, at maximal effect, heating pre-irradiated intestine at 43.0 degrees C was approximately equivalent to heating untreated intestine at 43.5 degrees C. The effect of prior irradiation was transient and appeared to have been "forgotten" after 2-3 months, a finding of particular relevance to the clinical situation. The results are discussed with reference to any radiation injury to intestine which might influence the expression of hyperthermal damage in situ.

A comparison of thermal enhancement ratios for fast neutron and x irradiation of two normal tissues in rodents

The effects of a hyperthermal treatment of one hour on radiation damage to baby rat cartilage and mouse intestine were compared for 250 kVp X irradiation and cyclotron-produced neutron irradiation (mean energy of about 7.5 MeV). Heat, in the range 41.0 degrees C-43.0 degrees C, caused no observable gross tissue injury when given alone. When heat was given immediately before radiation, the radiation damage was enhanced. There was no qualitative differences between response after fast neutrons and after X rays. Thermal enhancement ratios (TER) were similar for the two tissues and were not affected by the type of radiation used. Thus, the relative biological effectiveness (RBE) of fast neutrons compared with X rays was not markedly altered by combining radiation with hyperthermia.

The response of mouse intestine to combined hyperthermia and radiation: the contribution of direct thermal damage in assessment of the thermal enhancement ratio

The thermal enhancement of X-ray damage to mouse jejunum has been assessed when heating was achieved by immersion of an exteriorized loop of intestine in Krebs-Ringer solution. The results have been compared with those previously obtained following heating in situ. The primary effect of 1 hour of mild hyperthermia was to reduce the should of the crypt survival curve obtained following X-rays given alone. Thermal enhancement ratio (TER) values increased with increasing temperature, up to 42.3 degrees C, and were within the range reported for other normal tissues. However, when hyperthermia itself caused crypt loss and the contribution of hyperthermal killing to the overall tissue response was taken into account, there was little enhancement of radiation damage. There was no evidence of a large increase in TER at high temperatures, as is seen in some tumours and has been reported by Merino, Peters, Mason and Withers (1978) for intestine. It is possible that very high TER values which have previously been reported mainly reflect the heat-alone component of damage. Some of the implications of these results are discussed in relation to the combination of heat and radiation in therapy.

The relationship between heating time and temperature for inhibition of growth in baby rat cartilage by combined hyperthermia and X-rays

The relationship between the Thermal Enhancement Ratio (TER) for X-ray damage and time of heating has been investigated in epiphyseal rat cartilage. The TER at each temperature rises steeply with increasing heating time. Data obtained using various heat treatments with 8 Gy of X-rays have been analysed in terms of stunting "rate' as measured by the slope of the dose-effect curve obtained for each temperature. The "rate' of stunting per unit heating time, induced by thermally enhanced X-ray damage is compared with the "rate' of stunting induced by heat alone. The two are similar each having an activation energy of approximately 550kJ mole-1, as determined using the Arrhenius equation. Halving the heating time requires at 1 degrees C temperature increase to achieve the same degree of thermal enhancement of X-ray damage. Similar results have been reported previously for damage caused by heat alone. Over a range 42 degrees C-45 degrees C, the threshold heating time to cause direct thermal injury falls within the range of times used to enhance X-ray damage. It is suggested that a component of damage due to direct thermal injury, indistinguishable from radiation damage and thermally enhanced radiation damage, will contribute to TER assessments in some experimental systems.

Effects of hyperthermia on a neurogenic rat cell line (BT4C) in culture. Development of thermal tolerance during continuous heating

The malignant neurogenic rat cell line BT4C developed tolerance to further heat injury after continuous heating in culture at 41.0 and 42.0 degrees C for 8 and 2 hours, respectively. Survival was evaluated by colony forming ability. The proliferative capacity of the surviving cells was reduced after heating as shown by a decrease in size of the colonies.