An iron requirement for the synchronous progression of colonic cells following fasting and refeeding.

Evidence is presented to show dietary iron to be a major co-factor in the colonic hyperplasia observed following fasting and refeeding. The iron component serves to remove a fasting induced colonic G1 cycle block and produce the resultant synchronous progression of cells through the cycle. Deleting iron from the refed diet results in no colonic hyperplasia and/or synchronous progression of cells. The results are discussed from the viewpoint of colonic steady state cell renewal and as a possible tool for the study of in vivo steady state cell renewal.

Effect of parathyroidectomy on the fasting-refeeding response in the rat colon.

Following fasting and refeeding, the colonic epithelium of the rat exhibits a marked hyperplasia. This response is of a similar magnitude but of a longer duration to that observed in mice. This response is not affected by reducing serum calcium levels to those reported to alter normal tissue proliferation in vivo.

Effect of lumenal contents on colonic cell replacement.

Recent studies have shown that the rate of colonic cell renewal can be altered through fasting and refeeding, which produces a marked depression and transient stimulation, respectively. In the present study, the role of physical versus nutritional stimulation in the colonic fasting-refeeding response and the renewal of the functional colonic compartment were evaluated via a nondestructive colonic ligation procedure. The results reported herein suggest that physical stimulation by lumenal factors is in part required to initiate the colonic hyperplasia seen after refeeding. Blood-borne nutritional factors, in the absence of physical stimulation, cannot alone stimulate colonic cell production. Additional evidence is presented which suggests that this physical stimulation may be manifested through the lumenal distension produced by the newly ingested food materials. The results are discussed from the viewpoint of influencing the functional colonic compartment and physiological capacity.

Fasting and refeeding: cell kinetic response of jejunum, ileum and colon.

Following a period of fasting, feeding a normal diet results in a burst of DNA synthesis in the crypts of the colonic epithelium. This is due largely to a prompt entry of cells, blocked in G1, into S. Peak levels of S cellularity exceed 4 times the fasting, and 2 times the normal fed control values. Refeeding a low residue diet (soluble casien, glucose and corn oil) results in a return to control levels of proliferative activity, but no hyperplasia. However, in jejunum and ileum, refeeding is followed by a return to near control levels of proliferation with only a slight overshoot in S phase cellularity. During the fasting period, the ileal crypt proliferative compartment (Pc-zone) and total crypt cellularity decline significantly. These changes are accompanied by an increase in the total cycle time, due to an equivalent lengthening of the G1 and S phase. Following refeeding, there is a reduction in the cycle time and a gradual return to the control values for the Pc-zone size and cellularity. In the colon, fasting has no effect on the Pc-zone size or total crypt cellularity. There is an approximate doubling of the cycle time due solely to an increase in G1. Following refeeding there is an increase in the Pc-zone size and crypt cellularity and a marked shortening of the cycle time. Evidence that a G1 cycle blockade is induced in the colon by fasting is given by a lenghening of the G1 period and by stathmokinetic studies employing vincristine.

Influence of adriamycin and adriamycin-radiation combination on jejunal proliferation in the mouse.

The influence of adriamycin and adriamycin-radiation combinations on posttreatment proliferative activity of the mouse jejunum was examined by measuring [3H]thymidine incorporation. Single doses of 5 or 10 mg/kg produced a transient reduction in the proliferative activity, while 1 mg/kg had little effect. After 10 mg/kg, there was a rapid decrease in the number of mitotic figures, followed by a gradual decrease in the number of and rate of DNA synthesis in S-phase cells. A compensatory epithelial hyperplasia characterized by an enlarged crypt proliferative population and shortened mitotic cycle duration was observed beginning 48 hr after treatment. Multiple doses of adriamycin totalling 10 mg/kg inhibited cell production to a greater extent than the equivalent single dose. In combination with 1000 R, adriamycin (5 mg/kg) given from 96 hr before to 72 hr after irradiation reduced the amount of postirradiation proliferation.

Combined-modality oncotherapy with cyclophosphamide (NSC-26271) and radiotherapy: control of murine mastocytoma.

We investigated the effects of cyclophosphamide, alone and in combination with a 1,000-R/week radiotherapy schedule, on the growth of solid P815X2 tumors in 12-week-old male DBA/2 mice. Single-dose treatments of 150 mg cyclophosphamide/kg were given to animals bearing tumors of different ages. Such treatment of young tumors resulted in proportionately greater degrees of regression and steeper regrowth curves than did treatment of older tumors. Although slopes of regrowth curves differed greatly, time to regrowth (to pretreatment size) was the same for all age classes of tumors. Graded weekly exposures of 50-250 mg/kg for 4 weeks resulted in dose-dependent increases in incidence of complete remission, duration of remission (time to regrowth), and mean animal life-spans. The combination of radiotherapy to the tumor and 75, 150, or 225 mg cyclophosphamide/kg/week resulted in better local tumor control than occurred with radiotherapy or the drug alone. However, a dose-dependent increase in radiosensitivity of the gastrointestinal mucosa included in radiotherapy fields was observed. A 3-week course of radiotherapy plus 75 mg cyclophosphamide/kg/week (which is tolerated by the mucosa) increased animal lifespans to 165% of those of controls.

The modification of gastrointestinal tolerance and responses to abdominal irradiation by chemotherapeutic agents.

Groups of male DBA/2 mice were irradiated with partial abdominal exposures of x radiation ranging from 100 to 1,600 rads. Concomitant with radiation exposure and at 1 or 4 hours prior to, and at 1, 6, 24, or 48 hours after irradiation, various chemotherapeutic agents were administered, i.e., methotrexate, Cytoxan, adriamycin and BCNU. The results suggest that excessive gastrointestinal toxicity may result if aggressive chemotherapy is closely spaced with radiation exposure for the treatment of abdominal neoplasms. However, adjustment of dose and time patterns based on the proliferative responses of the mucosa may circumvent such toxicity to a large extent.

Treatment of solid P815x2 murine mastocytoma with adriamycin (NSC-1231127): toxity limitations.

The efficacy of adriamycin (NSC-123127), given as weekly or as 5-day-per-week doses, on the control of solid P815X2 murine mastocytomas was severely limited by hematopoietic and gastrointestinal toxicity. Although daily or weekly drug schedules both elicited dose responsiveness in terms of tumor control, no dose level of drug increased the life-span of tumor bearing animals.

Intestinal cell proliferation during fractionated abdominal irradiation.

In the mouse, at normal steady state of cell proliferation, the compensatory proliferative response to intestinal irradiation is such that when radiation exposures totalling 1,000 R are concentrated over the first few days of the week, summated proliferative activity for the entire week is near control levels. Symmetrically distributed exposures over a five-day treatment week (200 R daily, and especially 333 R on Monday, Wednesday and Friday) result in depressed levels of overall weekly proliferation. In these instances, the weekend break is particularly crucial. Similar results were obtained when the one-week measurement period was inserted between the third and fifth week of abdominal therapy, except in this instance, 200 R per day did not result in sub-control levels of proliferation, whereas 333 R on M, W and F, continued to do so. The intestine seems able to maintain its barrier epithelium for extended periods of diminished cell input, provided such is not too severe and that it seems from decreased cell production rate per crypt rather than from crypt attrition. A partial explanation for this relative tolerance is given by the finding that the vast majority of proliferative cells, even those irradiated and rendered permanently incapable of further division, succeed in migrating up the villus and hence help to maintain a barrier epithelium. In that sense, nearly all cell divisions become useful, even in the face of repeated exposures.

Damage and recovery assessment of the mouse jejunum to abdominal X-ray and adriamycin treatment.

The influence of adriamycin on the post-irradiation proliferative response of the mouse jejunum was examined. Doses of either 5 or 10 mg/kg of adriamycin administered immediately after abdominal irradiation reduced the LD50/7 days by 300-400 R. Neither dosage of the drug reduced the number of surviving crypts, as measured by the crypt isolation and microcolony techniques, for a given radiation exposure. However, both drug dosages reduced the amount of post-irradiation compensatory hyperplasia, as measured by 3H-thymidine incorporation.

A technical improvement in the radioimmunoassay of cyclic-AMP.

An improvement in the technique for the radioimmunoassay of cyclic-AMP, wherein ammonium sulfate precipitation is replaced with zirconyl phosphate gel, is presented. This substitution produces a more stable pellet than that obtained with ammonium sulfate. This greatly reduces a potential source of error due to pellet instability.

Time/dose relationships in experimental radiation cataractogenesis.

The response of the mammalian lens to fractionated radiation exposures was evaluated as a model system for predicting delayed radiation effects on normal tissue. Only the heads of male Ha/ICR mice were irradiated with 14 different time-dose schedules and followed for cataractous changes. A log-log plot of dose vs time yielded a line with a slope of 0.303 and ordinate intercept of 1050 R; a similar plot for dose vs fraction number yielded a slope of 0.382 and ordinate intercept of 835 R. Results suggest that the lenticular response to radiation may be a useful model for studying late effects.

Time/dose relationships in abdominal irradiation: a definition of principles and experimental evaluation.

We have drawn upon the work of numerous investigators to formulate a model describing the principles governing the acute response of the intestinal epithelium to cytotoxic agents. Tolerance (exposure required to kill 50 per cent of the animals) to abdomen-only irradiation was measured experimentally in the mouse using a total of 17 time/dose fractionation schedules. The principle determinants of intestinal response to fractionated radiation therapy were magnitude of each fraction and the introduction of regular recovery intervals during the course of treatment. The roles of exposure per week, exposures per day, and radiation days per week were also examined. The log-log plots of endpoint v. either number of fractions or overall treatment time yielded straight lines with slopes of 0 with 54 and 0 with 59 and y intercepts of 1,270 and 812 rets respectively. The single dose for 50 per cent acute intestinallethality (LD50/6 days) was 1,610 R. It would appear that the acute intestinal tolerance to fractionated irradiation is, in the mouse, extremely dependent upon fraction number and overall treatment time. The biological basis for intestinal tolerance to cytotoxic agents is discussed in light of the results of these studies and the model initially described.

A non-destructive method for measuring intestinal cell transit time.

Villous exfoliation of intestinal epithelial cells, which had been previously labeled in the crypt with 125I-iododeoxy-uridine, can be detected by thyroidal accumulation of the liberated 125I-. The latter can be monitored externally. The interval between labeled precursor injection and the steep portion of the thyroid activity accumulation curve corresponds to the intestinal cell transit time, as measured by destructive techniques, in three animal species. The technique allows estimations of intestinal cell transit time to be made on an individual basis, and can be expeditiously applied to large animals. Very small tracer doses are required for detection.

Control of local tumor growth with combined fractionated radiotherapeutic and chemotherapeutic regimens.

A treatment concept for the control of tumor growth utilized weekday radiotherapy and weekend chemotherapy. Mice were given sc injections of P815X2 mastocytoma cells on the lower back (day 0) and separated into the following treatment groups: 5-day/week X-irradiation, adriamycin alone at either 5 mg/kg body wt (days 6 and 13) or 2 mg/kg (days 5, 12, and 19), and combined radiotherapy and chemotherapy. Untreated controls had a mean tumor volume of 2.77 cm-3 and a mean survival time of 24 days. Adriamycin alone at 5 mg/kg resulted in an eventual tumor of 70 percent of the control value at death, whereas at 2mg/kg the tumor volume was 60 percent of control. After radiotherapy only, tumor size was 52 percent of control. Irradiation plus either 5 or 2 mg drug per kg body wt resulted in tumor volumes of 23 and 30 percent, respectively, of control values. Although no treatment regimen prolonged survival, the marked reduction in local tumor growth with combination therapy indicates that it may be a useful concept in future cancer therapy.

Responses of an experimental solid tumour to irradiation: A comparison of modes of fractionation.

Several radiotherapeutic schedules compatible with continued structural-functional integrity of the gastrointestinal (GI) mucosa were compared utilizing the P815X2 murine mastocytoma grown as a solid subcutaneous tumour. Both the tumour and underlying normal tissues were irradiated during the treatments. The tumour exhibited a Do that increased from 210 rad to 397 rad as the tumour aged and in all instances demonstrated minimal shoulders in survival curves. In spite of a relative radioresistance of cells within the solid tumour, quite effective control of localized disease could be accomplished with radiotherapy schemes compatible with GI tolerance limits. Schedules evaluated utilizing this model included acute exposures to 1122 rad, daily exposure to 187 rad, 5 days/week exposures to 281 rad, twice weekly exposures (561 rad on Mondays and 374 rad on Thursdays) and a high dose, two fractions per day, schedule. Tumours were followed for changes in growth patterns during these schedules. Efficacy of tumour control was determined and schedules were compared on this basis. Aggressive radiotherapy approaching the tolerance limits of any of the fractionation schemes proved most effective.