Establishment and characteristics of four sub-strains of F344 rats reared on various low protein and low energy diets.

Four sub-strains, reared by sib-mating and having for their origin the F344/DuCrj strain of rats, were established by feeding with different levels of low protein and low energy diets, and their characteristics investigated. The amounts of crude protein (CP) and digestible energy (DE) in the four diets were 17.6%-3.0 kcal, 10.5%-2.5 kcal, 8.4%-2.0 kcal, and 10.5%-2.5 kcal, respectively, and the four sub-strains established here were provisionally designated as F344/Tig1, F344/Tig2, F344/Tig3 and F344/Tig4, respectively. Intakes of nitrogen-corrected metabolizable energy (MEn) did not differ, and a large intake of digestible crude protein (DCP) was observed in F344/Tig1 rats. The body weight of rats provided with lower-nutrient diets showed a tendency to decrease until the F2 generation, but no change among the generations was seen subsequently, and the same compiled differences in protein content were maintained. Similar transitions were observed in the lifetime rearing test. Though F344/Tig3 rats, which were reared on minimum nutrients, showed a tendency to delayed puberty, we were easily able to breed four pairs in every generation using procedures similar to those used for other strains of rats. There were no differences among the F344/Tig1 to -3 strains of rats in body length, digestive tract length, or organ weight per body weight, and all the rats had a normal range of biochemical values. But the F344/Tig4 showed a high glutamic-oxaloacetic transaminase (GOT), and a tendency to decreased liver function and a shorter lifespan. These sub-strains of F344 rats clarified differences in fatty acid compositions, such as docosahexaenoic acid (DHA) in serum, liver and the brain. The rats were intended to be useful animal models for the study of nutritional environments and their influence on the memory and learning.     

Development of a diet for long-term raising of F344 rats--relationship between dietary digestible crude protein content and digestible energy content.

Mice and rats are frequently subjected to long-term raising in studies of aging. These animals are usually given growing or breeding diets from a young age. This raising method causes diseases such as chronic nephropathy with proteinuria due to nutritional excess. Consequently, a long-term raising study on male F344/DuCrj rats using nine sorts of diets differing in crude protein (CP; 12, 28, 44%) and digestible energy (DE; 2.8, 3.7, 4.5 kcal/g) contents was carried out. It was found that feed consumption was regulated by DE, not digestible crude protein (DCP) intake. Body weight was controlled within low energy areas, and was not influenced by feed or DCP intake. The liver and kidney weight at 105 weeks of age increased in response to an increase in the level of CP in the diet. Chronic nephropathy was severe in rats fed high protein diets and moderate levels of protein with moderate to high energy diets. Fatty liver and bile duct hyperplasia were found in rats fed a high protein and high energy diet. Few pathological findings of kidney and liver were found in the low protein and low energy diet group. The reduction of disorders attributable to excess energy or inappropriate diet suggests that low protein and low energy diets are most suitable for long-term raising in this strain of rat.     

Differences in survivability among F344 rats.

Important parameters to identify and develop appropriate animal models for longevity science include survivability, age-related disorders, and easy handling of aged individuals. It is found that F334/Du and F344/N have distinctive strain difference in these parameters. The finding suggests F334/Du and F344/N, even though they are historically siblings, need clearly separate identification when used as animal models for aging science, in particular, longevity science.     

Spontaneous calcification in F344/Slc and F344/JCL rats

F344/Slc and F344/JCL rats 2 years of age were histologically examined for the incidence and distribution of calcification. In the male rats of both strains, calcification was observed in the testis, lung, brain, kidney, heart, aorta, cornea, prostate and seminal vesicle respectively. In the female F344/JCL rats, calcification appeared in the kidney, lung, cornea, brain, stomach, ovary and heart. Among these of both sexes, the lung was one of the most affected organs for calcification. On the other hand, calcification in the kidney was more severe and frequent in the females than in the males, suggesting that the sex may be one of enhancing factors for calcification.     

Effect of carbohydrate-enriched diet and subsequent food restriction on life prolongation in Fischer 344 male rats

Increased proportion of carbohydrates (dextrin) in the diet has a life prolonging effect upon male Fischer 344 rats; however, the effect of this diet appears only when the rats aged from 6 weeks to 6 months are on diet, after this treatment median survival of experimental animals increases by 96 days and the 10th percentile increases on the average by 10 days (n-60). Further maintenance of animals on the same diet has minimum effect: animals being on this diet throughout the whole life exhibit a median lifespan increase by 120 days and an increase in the 10th percentile by 41 days. However, if such animals aged 6 months are transferred to a restricted (60%) food intake regimen (control diet, not enriched with carbohydrate) a further increase in median and 10th percentile lifespan prolongation can be observed reaching 328 and 396 days, respectively as compared to controls. The effects of this early feeding (from 6 weeks to 6 months) with a carbohydrate-enriched diet available ad libitum and food restricted (60% controls) regimen fed from the age of 6 months onwards are additive, the final results being identical as if the animals are kept on the 60% food restricted intake throughout the whole life.     

Resorptive clearance and transepithelial potential difference in capsaicin-treated F344 rats.

The long-term effects of substance P (SP) depletion on epithelial integrity were assessed by measurements of airway transepithelial potential difference (PD) and resorptive clearance. Both techniques are highly sensitive to differences in epithelial permeability. PD (mV) was assayed with a KCl-saturated agar bridge technique in the lower trachea of Fischer 344 rats depleted of SP by neonatal capsaicin treatment. Capsaicin treatment is known to ablate a subpopulation of primary afferent fibers containing SP. Resorptive clearance (clearance in 1 h) was measured with 99mTc-labeled diethylenetriaminepentaacetic acid administered as a 100-microliters (100 microCi) bolus. Depletion of SP by neonatal treatment with capsaicin resulted in a highly significant increase in resorptive clearance (P less than 0.001). There was also a significant difference in PD in the lower trachea, the values being less negative for the capsaicin-treated rats (P less than 0.005). The increase in resorptive clearance may reflect the leakiness of the epithelial membrane, as also suggested by the decrease in PD. Aside from its known involvement as a neurotransmitter in neurogenic inflammation, SP may, under normal physiological conditions, have an additional role in the maintenance of epithelial barrier function.     

Differences of mu-opioid receptors between Lewis and F344 rats

F344 and Lewis rats show different responses to opioids in several experimental paradigms. In this study we have used the specific mu-opioid agonist DAMGO to find out if these differences could be attributed to heterogeneity of mu-opioid receptors. The density of [H3]DAMGO binding sites was similar in the brain cortex and spinal cord of both strains, but DAMGO affinity for mu-opioid receptors was higher in F344 tissues. Moreover, a parallel study of the effects of DAMGO on electrically-evoked twitches of isolated vasa deferentia revealed that this drug was also more effective in F344 preparations. These results suggest that mu-opioid receptors of F344 rats are more sensitive to pharmacological stimulation in vitro, which could be related to a higher drug affinity.     

Effect of long-term administration of a high protein or low protein diet on rat liver. Morphological and biochemical findings

An increase in relative liver weight, the total liver DNA content, hepatocyte volume and the total surface area of the membranes of mitochondria and the granular and smooth endoplasmic reticulum of hepatocytes, but a decrease in the size of the nuclei, were found in adult male rats fed three weeks on a high protein diet compared with animals given a standard laboratory diet. Serum transaminase (ALT, AST) and alkaline phosphatase activity was practically the same as the control values. Rats fed three weeks on a low protein diet showed a decrease in relative liver weight, in the total liver DNA content, in hepatocyte and nuclear volume and in ploidy, and also in the surface area of the membranes of the mitochondria and the smooth and granular endoplasmic reticulum; conversely, the number of binucleate hepatocytes rose. Serum ALT, AST and alkaline phosphatase activity was mildly, but statistically significantly elevated.     

Sex and dietary fat modulate hepatic prostaglandin F2 alpha in F344/N rats.

The study was designed to determine whether sex and fat calories altered hepatic prostaglandin (PG) F2 alpha status; a factor which may reflect susceptibility to cancer development. For 4 weeks, groups of 8 male and 8 female F344/N rats were fed diets with 9% of energy (en%) from linoleate and 15.5, 20, 30 or 40 en% fat. Females had greater hepatic stearate, arachidonate and PGF2 alpha whereas males had greater hepatic myristate, palmitate and oleate. Females also had greater plasma stearate levels. Greater hepatic arachidonate may have stimulated PG production in females. Hepatic oleate increased and hepatic palmitate decreased with increasing en% fat (p < 0.05). Hepatic stearate was greater and hepatic linoleate less when 40 en% fat was fed compared with other levels of dietary fat (p < 0.05). Plasma oleate was greater at 30 or 40 en% fat than at lower levels of fat, whereas plasma linoleate was less at 40 en% than at 15.5% en% fat. The ability of a 30 en% fat diet, containing equal proportions of linoleate and oleate, to suppress hepatic PG production may be related to the effects of dietary fat content and composition on plasma fatty acid profiles. Because suppressed PG production has been linked with suppression of cancer development, dietary recommendations to consume 30 en% fat with a P:M ratio of 1:1 may be cancer-protective.     

Sensitivity of selected drug biotransformation enzymes to dietary protein levels in adult F344 male rats

Adult male Fischer 344 rats were fed inadequate, adequate, and excessive quantities of dietary protein (8, 12, and 22%, respectively) for a period of 14 days. An increase in dietary protein did not increase liver weight but resulted in an increase in cytochrome P-450 content and 7-ethoxycoumarin O-deethylase activity. No significant difference in glutathione S-transferase activity was observed at the three protein levels. The in vivo hepatotoxicity of bromobenzene increased with an elevation in dietary protein intake from 12 to 22%. These data from mature rats follow trends similar to findings we have reported previously with juvenile rats.     

Effect of a soy protein diet on protein and energy metabolism and organ development in protein-restricted growing pigs

Two feeding experiments were carried out with castrated male pigs weighing between 10 and 30 kg to study acute and persisting dietary effects on growth and on protein and energy metabolism in growing pigs. Pigs were fed semi-synthetic isoenergetic and isonitrogenous diets at 50% protein requirement with either soy protein isolate (SPI) or casein (CAS) as sole protein source. Intake of protein and ME amounted to 9% w/w and 1800 kJ x kg BW (-0.62) x d(-1) in Exp. 1, respectively, and 9% w/w and 1430 kJ x kg BW(-0.62) x d(-1) in Exp. 2. The CAS diet was supplemented by Lys, Met, Thr and Trp. In Exp. 1 (acute effects), 18 pigs received the CAS diet for 24 days (period 1); 9 pigs were then switched to a SPI diet whereas 9 pigs continued on the CAS diet for another 31 days (period 2). In Exp. 2, a third period of 31 days was added in which the SPI group was switched back to CAS diet. The control group was fed on the CAS diet throughout Exp. 2 (86 days). Altogether the majority of parameters were not affected neither comparing SPI with CAS in Exp. 1 nor inspecting possible persistence of effects in Exp. 2. In detail, in Exp. 1 SPI compared to CAS feeding resulted in a lower efficiency of protein utilisation and lower protein retention. Attendant upon the lower protein retention an increased energy retention as fat was only observed in tendency. SPI feeding caused a decreased body weight, thyroid weight and increased hepatic carbohydrate content that persisted after the diet was changed back to CAS (Exp. 2).     

Effect of a soy protein diet on protein and energy metabolism and organ development in protein-restricted growing pigs

Two feeding experiments were carried out with castrated male pigs weighing between 10 and 30 kg to study acute and persisting dietary effects on growth and on protein and energy metabolism in growing pigs. Pigs were fed semi-synthetic isoenergetic and isonitrogenous diets at 50% protein requirement with either soy protein isolate (SPI) or casein (CAS) as sole protein source. Intake of protein and ME amounted to 9% w/w and 1800 kJ · kg BW ^{? 0.62} · d ^{? 1} in Exp. 1, respectively, and 9% w/w and 1430 kJ · kg BW ^{? 0.62} · d ^{? 1} in Exp. 2. The CAS diet was supplemented by Lys, Met, Thr and Trp. In Exp. 1 (acute effects), 18 pigs received the CAS diet for 24 days (period 1); 9 pigs were then switched to a SPI diet whereas 9 pigs continued on the CAS diet for another 31 days (period 2). In Exp. 2, a third period of 31 days was added in which the SPI group was switched back to CAS diet. The control group was fed on the CAS diet throughout Exp. 2 (86 days). Altogether the majority of parameters were not affected neither comparing SPI with CAS in Exp. 1 nor inspecting possible persistence of effects in Exp. 2. In detail, in Exp. 1 SPI compared to CAS feeding resulted in a lower efficiency of protein utilisation and lower protein retention. Attendant upon the lower protein retention an increased energy retention as fat was only observed in tendency. SPI feeding caused a decreased body weight, thyroid weight and increased hepatic carbohydrate content that persisted after the diet was changed back to CAS (Exp. 2).