Physiological levels and action of dehydroepiandrosterone in Yucatan miniature swine

The biological role of dehydroepiandrosterone (DHEA) and its less active sulphated conjugate DHEAS was investigated in two experiments using Yucatan miniature swine. In experiment 1, plasma levels of both DHEA(S) among males were greater than female pigs that ranged in age from 0.3 to 84 mo old (P < 0.0001). In males, DHEA(S) were related inversely to serum triglycerides; DHEA was positively related to triglycerides in females (P < 0.01). In experiment 2, four 2-yr old male pigs, used as their own control, showed a 5% decrease in body weight, 11% increase in energy expenditure, 88% increase in lipid, and 100% decrease in glucose utilization (P < 0.0001) in response to DHEA vs. placebo treatments when adjusted for body weight. Plasma DHEA(S) were not different between treatment conditions. Glucose tolerance and plasma insulin levels were not different from controls. In vivo response to norepinephrine indicated beta-adrenergic sensitivity was altered by DHEA. Present findings suggest DHEA and/or its hormone products are important in modulating energy expenditure and lipid utilization for energy in male animals. The role of DHEA in energy metabolism and the difference between sexes warrant further investigation.

Cyclic food restriction, insulin and mammary cell proliferation in the rat

We reported recently that weight cycling significantly increased the incidence of mammary cancer in virgin female rats that were pretreated with N-methyl-N-nitrosourea. The present study investigated the effect of weight cycling on mammary epithelial cell proliferation and its relationship to changes in plasma insulin, estrogen, progesterone and urinary corticosterone in 30 female virgin Sprague-Dawley rats. Animals were fed a modified AIN-76A diet containing 24.6% corn oil by weight. Weight-cycled (WC) rats were food restricted daily by either 33% or 50% of non-restricted controls for 1 week followed by 3 weeks compensatory refeeding and weight recovery over 18 weeks or 4.5 weight cycles. WC rats consumed 6-10% less food than controls (P = 0.01) but showed a 71-89% greater efficiency of food utilization for growth (P < 0.0001) than controls. There were no differences in total weight gain during treatment. Mammary lobuloalveolar and ductal cell proliferation of WC rats, measured by 5-bromo-2'deoxyuridine labelling, increased in a dose-response fashion, P = 0.03, P = 0.06 respectively in comparison to controls. Energy and substrate utilization measured by indirect calorimetry indicated WC animals expended less energy (P = 0.005) and utilized less glucose (P = 0.0001) and protein (P = 0.006) during restriction, and less lipid during recovery (P = 0.05) than controls. There were no significant differences in hormone levels between groups. Multiple regression analysis with plasma insulin, estrogen, progesterone and urinary corticosterone as independent variables (r = 0.947, r2 = 0.897, P = 0.003) showed that plasma insulin was the only significant predictor (P < 0.01) of mammary cell proliferation. In accord with this observation, tyrosine-phosphorylated activation of insulin receptor substrate-1, detected by immunoprecipitation and Western immunoblot analysis in mammary tumors of WC rats from our previous study, was 3-5 times greater than in non-restricted controls (P < 0.01). Present findings suggest that weight cycling in rats increases risk of breast cancer development via insulin stimulated mammary cell proliferation.

Cyclic food restriction alters substrate utilization and abolishes protection from mammary carcinogenesis female rats

We tested the hypothesis that cyclic food restriction abolishes protection against mammary carcinogenesis. Virgin female Sprague Dawley rats (n = 159) were injected intraperitoneally with 25 mg/kg n-methyl-n-nitrosourea at 50 d of age. Eleven days later, rats were given free access to a 24.6 g fat/100 g AIN-76A diet (ad lib-c), fed in two meals (me-c), or fed in two meals restricted in weight by 33% for 1 wk followed by 3 wk of compensatory refeeding (me-r) for 18 wk or 4.5 restriction cycles. Energy and substrate utilization of 15 rats from each group was measured by indirect calorimetry. The me-r rats ate and weighed less (P < 0.0001), had a greater efficiency of food utilization (P < 0.01), and had a 12% higher incidence of mammary cancer (P < 0.0001) than ad lib-c rats after adjusting for the effect of final body weight. Resting metabolic rate was not different among groups, but me-r rats used less glucose during restriction and more glucose and less lipid for energy during body weight recovery than me-c rats (P < 0.0001). Increased energy efficiency and the shift in utilization of glucose and fatty acids followed closely the effects of cyclic food restriction and meal feeding on mammary carcinogenesis.

Increased lipolysis to beta-adrenergic stimulation after dehydroepiandrosterone treatment in rats

Young adult male rats were treated with 4 mg dehydroepiandrosterone (DHEA)/100-g diet for 4 wk or were fed the same purified diet unadulterated (51 carbohydrate:20 fat: 23.5 protein; wt/wt). After 1 wk body weight and fat mass of the DHEA-fed rats were significantly less than the controls. By the end of week 3, fat-free mass of the DHEA rats was less than the controls. Neither food intake nor resting metabolism, measured by indirect calorimetry, was different between groups. Isolated epididymal adipocytes of DHEA rats were significantly smaller and isoproterenol (x 10(7) M) stimulation of glycerol release was 53% greater (P < 0.01) than the controls. Basal rate of glycerol release increased significantly for both groups in response to the adenosine inhibitor adenosine deaminase; there were no significant interaction effects. Inhibition of lipolysis by the adenosine analogue phenylisopropyladenosine was similar between groups. Findings support the hypothesis that DHEA reduces adiposity directly by increased lipolysis, but the mechanism of action does not involve a change in the antilipolytic function of adenosine.

Dietary modulation of pancreatic carcinogenesis: calories and energy expenditure

Physical activity (exercise) is a lifestyle factor that has received little attention with regard to its role in the etiology and/or prevention of cancer. These studies examined the effects of treadmill exercise on the early stages of pancreatic carcinogenesis initiated by azaserine in rats. Male Lewis rats were treated with azaserine at 2 weeks of age and weaned to experimental protocols at 3 weeks of age. Two experiments were undertaken; treadmill exercise began at 6 weeks of age (Experiment 1) or at 13 weeks of age (Experiment 2). Rats were exercised for 15-20 min/day and for 3-5 days/week. Treadmill speed and angle of incline were adjusted to afford a range of exercise intensities. The development of putative preneoplastic lesions of the pancreatic acinar cells (henceforth termed foci) was evaluated by quantitative stereological analysis using light microscopy. In Experiment 1, exercise resulted in a known paradoxical reduction in food intake by about 15% of the intake of the sedentary group fed ad libitum. The burden of azaserine-induced foci was decreased by approximately 37%, and this was attributed to the well known effects of reduced caloric intake in these young, rapidly growing rats. In Experiment 2, the higher intensity treadmill exercise group had an increased focal burden, compared to their sedentary pair-fed controls. Importantly, this enhancement occurred despite a reduction in food intake and body fat stores in this treadmill exercise group. These experiments demonstrate that exercise may suppress or promote carcinogenesis, depending upon the stage in the life cycle of the animal.

Effect of type and amount of dietary fat on the enhancement of rat mammary tumorigenesis by exercise

The effect(s) of treadmill exercise and type and amount of dietary fat on the process of mammary tumorigenesis was investigated. Female Sprague-Dawley rats were fed a purified 5% fat diet (AIN-76A) from 21 to 64 days of age. At 50 days of age each rat was intubated p.o. with 5 mg 7,12-dimethylbenz(a)anthracene (DMBA). Fourteen days after DMBA, the rats were randomized into one of three diet groups: 5% fat as corn oil, 24.6% fat as corn oil, or 24.6% fat as a mixture of palm (21.8%) and corn oil (2.8%). The combination of palm and corn oil provided the same amount of linoleic acid per g as the 5% corn oil diet. Half the animals receiving each diet were exercised on a treadmill at a speed of 20 m/min, 1 degree incline, 15 min/day, 5 days/week, and were designated as the moderate intensity treadmill exercise group (MITE). The remaining animals were exercised at a speed of 2 m/min, 1 degree incline, 15 min/day, 5 days/week, and were designated as the low intensity treadmill exercise group (LITE). The experiment was terminated 154 days after DMBA was administered. The median tumor-free time was significantly shortened in MITE rats receiving the 24.6% fat, corn oil-formulated diet in comparison to LITE rats receiving the same diet (43 day vs. 62 day, P = 0.028). Similarly, tumor appearance was more rapid in MITE rats consuming the low fat corn oil diet in comparison to the low fat diet-fed LITE group (57 day vs. 67 day, P = 0.046). Exercise exerted no effect on the rate of tumor appearance in rats that received the 24.6% palm and corn oil mixture, (58 day, MITE, vs. 62 day, LITE, P = 0.502). Mean body weight gains were similar among groups, although MITE rats consistently weighed more than LITE rats consuming the same diet. Gross carcass composition was unaffected by either the level of exercise or the amount of dietary fat consumed. The data indicate that moderate intensity treadmill exercise for a short duration, that is without effect on carcass fat content, can stimulate mammary tumorigenesis in rats fed low or high fat diets. This effect can be influenced by the type of dietary fat ingested.

Effect of exercise on the induction of mammary carcinogenesis

Although data reported in several epidemiological investigations indicate that reduced consumption of dietary fat and increased levels of physical activity are associated with reduced risk for breast cancer, the results of some studies do not support these observations. Underlying this situation is the unanswered question about whether degree of body fatness, which is affected by dietary composition, total caloric intake, and energy expenditure, is the critical determinant affecting breast cancer risk. The objective of this work was to establish whether increasing energy expenditure by exercise would reduce the occurrence of mammary carcinomas induced by 7,12-dimethylbenz[a]anthracene (DMBA) in animals consuming a high fat diet to the level of occurrence observed in sedentary animals consuming a low fat diet. Female Sprague-Dawley rats were obtained at 21 days of age and maintained on a 5% (w/w) corn oil diet (AIN-76A) until they were 64 days of age. At 50 days of age, rats received either 5 mg DMBA or the solvent in which the carcinogen was dissolved. Fourteen days after DMBA intubation they were randomized into one of three groups: 5% fat (w/w), sedentary; 24.6% fat (w/w), sedentary; or 24.6% fat (w/w), exercised. Animals were exercised on a motor-driven treadmill at a belt speed of 20 m/min and a 1-degree incline for 15 min/day, 5 days/week for 18 weeks. Feeding a high fat versus a low fat diet increased the number of breast cancers induced and the rate at which they appeared in agreement with previous investigations. However, rather than retarding the development of tumors as was hypothesized, moderate treadmill exercise increased the incidence and number of cancers induced and shortened cancer latency in comparison to animals that received either the high fat or low fat diet and were sedentary. Body composition was not altered by the exercise regime imposed, although these animals weighed more than either sedentary group. These data document a heretofore unreported effect of a moderate level of aerobic work on breast cancer induction.

Effect of D,L-2-difluoromethylornithine and endocrine manipulation on the induction of mammary carcinogenesis by 1-methyl-1-nitrosourea

The purpose of this investigation was to establish an efficient route and dose regime for the long-term administration of tamoxifen in the study of mammary tumorigenesis in the rat. The second objective of this work was to determine whether treatment with D,L-2-difluoromethylornithine (DFMO), a synthetic inhibitor of the enzyme ornithine decarboxylase, would reduce the occurrence of mammary cancers in tamoxifen-treated or ovariectomized rats. A total of 265 female Sprague-Dawley rats were assigned to one of two experimental protocols. All animals were injected with 50 mg 1-methyl-1-nitrosourea (MNU) per kg body wt at 50 days of age. In experiment 1, beginning 7 days after the injection of the carcinogen, animals were assigned to one of six groups which received either 0, 1 or 5 mg tamoxifen citrate per kg AIN-76A purified diet in addition to either no DFMO or a 0.125% w/v solution of DFMO as the drinking water. The experiment was terminated 180 days following carcinogen treatment. Treatment with tamoxifen resulted in a dose-dependent reduction in cancer incidence, and the number of cancers induced and significantly prolonged the median cancer-free time. This effect was also accompanied by a decrease in the rate of body weight gain. Treatment with DFMO delayed latency and reduced tumor number. DFMO in addition to tamoxifen (1 mg/kg diet) further prolonged latency. In experiment 2 each animal was assigned to one or four treatment groups when its first palpable mammary tumor was detected. At that time each was either ovariectomized or sham-operated. In addition, the rats were either provided no DFMO or a 0.5% w/v solution of DFMO as the drinking water. The study was terminated 35 weeks following carcinogen injection. Ovariectomy significantly inhibited the occurrence of additional mammary tumors. Ovariectomy plus DFMO was more effective than ovariectomy alone in reducing tumor number. Collectively, these observations indicate that suppression of polyamine biosynthesis via the systemic administration of DFMO inhibits the development of ovarian hormone insensitive mammary tumors.

Effect of tamoxifen and D,L-2-difluoromethylornithine on the growth, ornithine decarboxylase activity and polyamine content of mammary carcinomas induced by 1-methyl-1-nitrosourea

The effect of combined treatment with D,L-2-difluoromethylornithine (DFMO) and tamoxifen on the growth status, ornithine decarboxylase (ODC) activity and polyamine content of established 1-methyl-1-nitrosourea (MNU)-induced mammary tumors was investigated. DFMO treatment, a 0.125% solution provided as drinking water, inhibited the rate of tumor occurrence and reduced the number of mammary tumors induced by a high dose of MNU (50 mg/kg body weight) during the first 120 days post-carcinogen treatment. Tamoxifen was administered daily via s.c. injection (25 micrograms/100 g body weight) to tumor-bearing rats in both treatment groups, i.e. control and DFMO-treated, for a 30-day period beginning 120 days after carcinogen. Tamoxifen treatment induced tumor regression but the percentage of regressing, static or growing tumors was no different in the presence or absence of DFMO. Whereas the mammary tumors of DFMO-treated rats had reduced ODC activity and lower polyamine concentrations in comparison to the tumors of untreated animals, tamoxifen had no effect on these parameters independent of its effect on tumor growth status. DFMO did not increase the efficacy of tamoxifen in inducing tumor regression.

Effect of concentration of D,L-2-difluoromethylornithine on murine mammary carcinogenesis

The appearance of chemically induced mammary gland carcinomas in virgin female Sprague-Dawley rats was blocked by the administration of D,L-2-difluoromethylornithine (DFMO) in drinking water during the stage of tumor promotion. Rats were given injections s.c. at 50 days of age with either 35 mg of 1-methyl-1-nitrosourea (MNU) per kg of body weight or the 0.9% NaCl solution in which the carcinogen was dissolved. At 57 days of age, the rats were each randomly allocated to one of 14 treatment groups. Ten groups (five solvent treated and five MNU treated) were assigned to treatments consisting of 0.00, 0.0625, 0.125, 0.25, or 0.50% (w/v) solution of DFMO in their drinking water; two MNU-treated groups were placed on or removed from DFMO treatment (0.5%; w/v) at 90 days post-carcinogen exposure; and two carcinogen-treated groups received either putrescine (0.5-g/kg diet) or putrescine and DFMO (0.5%; w/v) throughout the experiment. The study was terminated 183 days after carcinogen treatment. All doses of DFMO exerted a protective effect against the induction of mammary cancer; however, only the feeding of the 0.125% and the 0.5% solutions of DFMO resulted in a significant reduction in cancer incidence. The average number of cancers per rat was reduced, and cancer-free time was extended at all concentrations of DFMO. The protective effect of DFMO was sustained following withdrawal of treatment at 90 days post-MNU injection. Feeding putrescine in conjunction with DFMO treatment partially blocked the inhibitory activity of DFMO. DFMO treatment did not affect food or water intake; body weight gain; the weight of ovaries, uterus, adrenal glands, liver, kidney, or spleen; or the periodicity of the estrous cycle. These data provide evidence of an inhibitory effect of DFMO against mammary cancer induced by MNU which cannot be attributed to a systemic toxic effect of this compound.

Effect of D,L-alpha-difluoromethylornithine on murine mammary carcinogenesis

The development of chemically-induced mammary gland carcinomas in rats was dramatically suppressed by provision of a 1% solution of D,L-alpha-difluoromethylornithine (DFMO) in drinking water. Treatment with DFMO significantly reduced cancer incidence and the average size and number of cancers per rat and prolonged the cancer-free time. DFMO appears to be effective in blocking some aspect of the promotion stage of chemically induced mammary carcinogenesis in the rat.