Retardation by restricted feeding of age-related changes in steroidogenic activity of rat pre- and post-ovulatory follicles.

Reproductive ageing in female rodents is accompanied by changes in circulating peptide and steroid hormones leading to irregular, lengthened oestrous cycles prior to loss of fertility. In this study, the effect of ageing is reported on steroid hormone synthesis within individual ovarian follicles and its retardation by restricted feeding for two groups of ad libitum fed animals (114 and 350 days) and two groups of diet-restricted animals (350 and 600 days). Follicles from ad libitum fed animals of 350 days showed a transition in follicular steroid hormone synthesis to release elevated amounts of oestradiol-17beta on all days of the cycle. This age-related change in follicle steroid release was significantly delayed by maintaining animals on a restricted feeding regime, and was not complete even by 600 days of age. This effect of diet as a means to manipulate ageing of the follicular steroidogenic pathways provides a useful system for investigating the control of reproductive ageing in rodents.

Effect of age and restricted feeding on polypeptide chain assembly kinetics in liver protein synthesis in vivo.

Polypeptide assembly rates during in vivo hepatic protein synthesis were studied as a function of age and restricted feeding in male rats. With ageing the time to assemble the average peptide in the liver of fully-fed rats significantly increased. In young rats maintained on a restricted feeding regime known to retard ageing, the time to assemble the average polypeptide was increased 2.5 times. With ageing the rate of peptide elongation increased so that at 2 years of age the underfed animals assembled peptides at a significantly faster rate than their age-matched controls. The rate of elongation of peptides during hepatic protein synthesis was shown to be directly dependent upon circulating T3 levels rather than the dietary status of the animal. On refeeding young diet restricted rats, polypeptide assembly kinetics did not immediately return to control values although the rate of protein synthesis was significantly increased. Total liver RNA content increased significantly in refed animals allowing for a greater rate of chain initiation to offset the slow rate of chain elongation. A period of 28 days of ad libitum feeding was required before assembly kinetics returned to control values and is probably indicative of a persistent impaired monodeiodination of T4 to T3.

The effects of aging on carbonic anhydrase concentrations in rat liver and skeletal muscle.

The isoenzymes carbonic anhydrase II (CAII) and III (CAIII) have been measured by radioimmunoassay in the livers of male and female rats aged from 21 to 800 days. No sexual dimorphism at 21 days was found, but from 50 to 400 days both isoenzymes show sexual differences. From 600 days onwards, these differences are less apparent. CAIII concentrations in two 'fast' fibre muscles and one 'slow' fibre muscle have been determined. There is no sexual dimorphism in muscle, but a wide variation between individuals was observed. Fast muscles show maximal CAIII levels at 800 days, whereas in slow muscle the concentration of the isoenzyme is declining at this time.

The effects of ageing and chronic dietary restriction on in vivo hepatic protein synthesis in the rat.

Hepatic growth and protein synthesis in vivo was studied with age in ad libitum-fed and dietary restricted rats in which the mean and maximum lifespan was significantly extended. Livers from underfed rats showed significantly lower DNA, RNA and protein contents, and total protein synthesis. The fractional rate of synthesis although initially depressed by restricted feeding, showed no consistent trend with age when compared with control values. The lower fractional rate of synthesis observed in livers from dietary restricted rats at 7 weeks of age is attributable to a significant decrease in ribosomal capacity, with no effect on ribosomal activity being evident. Liver tissue from rats fed ad libitum demonstrated a progressive loss of translational efficiency with age which was delayed by chronic dietary restriction.

The influence of chronic dietary intervention on protein turnover and growth of the diaphragm and extensor digitorum longus muscles of the rat.

Changes in weight, protein, RNA and DNA contents of the E.D.L. and diaphragm muscles were studied in conjunction with aging and chronic dietary restriction. Between weaning and senescence both muscles exhibited progressive decreases in their fractional rates of growth, protein synthesis and protein breakdown; these rates being age for age higher in the diaphragm. Dietary restriction (50% of ad libitum food intake) from weaning onwards retarded muscle growth, particularly at the early stages (i.e. 4 weeks) after its implementation. Here the suppression of protein synthesis was due to the combined effects of piece meal feeding and long term reductions in food intake. Later, muscle sizes and total, but not fractional, synthetic rates were consistently decreased by chronic dietary intervention. The onset of the ageing atrophy may also be delayed by underfeeding. The changes in these 2 muscles have been compared to those in the whole animal and other striated muscles, as previously reported by the authors.

The effect of chronic and acute dietary restriction on the growth and protein turnover of fast and slow types of rat skeletal muscle.

Changes in the growth and protein turnover of the anterior tibialis and soleus muscles were studied in response to acute and chronic dietary restriction (50% of ad libitum intake) between 3 and 149 weeks post partum. The effect of long-term dietary restriction from weaning to senescence was to retard the growth and normal developmental of the two types of skeletal muscle. This was evident from measurements of various parameters of growth, i.e. total protein, RNA and DNA and protein/DNA-P, which were reduced by approximately 50% when compared with age-matched controls. These decreases, however, were not accompanied by a decline in the fractional rate of synthesis (%/day) or ribosomal activity (mg protein/day per mg RNAP). The slowing down of the age-related decline in muscle growth has been attributed to a reduction in RNA capacity (RNA/protein), with similar responses in the fast- and slow-twitch skeletal muscles. The initial effects of piecemeal feeding of this restricted diet on the two types of muscle were also monitored. Short term starvation effects, i.e. 24 hr after feeding a reduced ration, were measured on the protein content and RNA/protein of both the anterior tibialis and soleus muscles; both parameters were unchanged within 24 hr. In contrast, a rapid and significant decline in the ribosomal synthetic activity (mg/d per mg RNAP), and a corresponding fall in the fractional rate of synthesis, occurred within 24 hr of feeding.

Lifetime breeding studies in fully fed and dietary restricted female CFY Sprague-Dawley rats. 1. Effect of age, housing conditions and diet on fecundity.

The capacity of female CFY Sprague-Dawley rats to bear multiple litters when breeding was commenced at increasing ages was assessed under the following conditions: continuous housing with male (GC), intermittent breeding of group (GI) and individually housed (I) fully fed animals, restriction of food intake (DR), refeeding of dietary restricted rats (DRA). The percentage of females pregnant, number of litters produced and total litter size were assessed. The number of litters or percent pregnant was unaffected by individual housing but there was a significantly greater decline in total litter size with increasing age of mother when compared to (GI) rats. The slope of the regression line in (I) was identical to that for (GC) females and may reflect the burden of continuous breeding or the stress of individual housing. Both litter size and overall fertility were decreased by dietary restriction but these females did retain their capacity to breed as late as 937 days in contrast to 720 days for any group of fully fed animals. There was no decline in litter size with increasing age in (DR). Returning (DR) rats to full feeding resulted in a rate of decline in litter size identical to that for (GI). All groups of (DRA) produced a maximum of three litters, commencement of breeding at 750 days resulting in production of a litter as late as 952 days.

Levels of O6-methylguanine acceptor protein in tissues of rats and their relationship to carcinogenicity and aging.

N-nitroso compounds react with cellular DNA to produce various damaging adducts, one of the more important being O6-alkylguanine. DNA restoration is accomplished by transfer of the alkyl group to a cysteine residue of an acceptor protein. The levels of acceptor activity were compared in several tissues from well-fed and dietary-restricted inbred SD rats 30-1,194 days of age. Striking and consistent differences were found in the levels of acceptor activity in different tissues from both groups; these levels corresponded to their sensitivity to tumorigenesis by alkylating agents. Acceptor activity levels were highest in the liver and somewhat less in the spleen; there were significantly lower levels in brain and kidney. The random loss with time in the integrity of DNA may cause alterations in cellular function or limit cellular proliferation, thus leading to senescence and death. DNA repair processes may alter the rate of accumulation of damage, thereby affecting potential longevity. There were no significant age-associated changes in the ability of cells from either dietary group to remove DNA adducts and there was no evidence of alterations in the acceptor protein with age that would compromise its functional activity.

The control of puberty in the dietary restricted female rat.

Food intake, body weight and serum LH, FSH, progesterone and oestradiol-17 beta were monitored from weaning to puberty in fully fed females housed in groups of four or individually and in females individually housed and dietary restricted. Restriction of food intake from weaning delayed the onset of puberty (34-39 days fully fed, 63-189 days dietary restricted) which was achieved at the same body weight as in the fully fed females. Individual housing of fully fed rats resulted in a significant increase in relative and absolute food intake (but not body weight) and a decrease in serum FSH when compared to group housed fully fed animals. Serum FSH and progesterone were significantly decreased in restricted females and serum oestradiol-17 beta significantly increased.

Modification of the oestrous cycle hormonal profile by dietary restriction.

In fully fed female CFY Sprague-Dawley rats there was a significant increase in oestrous cycle length with increasing age and a decrease in the percentage of rats with cycles of regular duration. Modification of the rate of reproductive decline could be achieved by restriction of food intake from weaning. Such animals showed retention of regular cycles to a greater age and there was no age-associated change in the length of the oestrous cycle. In dietary restricted females the serum LH peak occurred earlier in the cycle and serum oestradiol-17 beta rose later than in fully fed animals. Both peaks were of reduced amplitude. Serum progesterone values were reduced overall by dietary restriction. Underfeeding resulted in both an increase in serum FSH values and a significant modification of the serum FSH profile.

In vivo DNA synthesis in the dietary restricted long-lived rat.

Male CFY Sprague-Dawley rats maintained at 50% growth rate of ad libitum fed, age-matched control animals showed a 42% extension in maximum lifespan and an increase in the overall doubling time of the rate of mortality from 102 days to 203 days. The slower growth rate of animals on the restricted diet was reflected in lower DNA, RNA, and protein content of liver, kidney and heart with age. DNA synthesis in vivo measured by the incorporation of 3H-thymidine was severely inhibited in liver, kidney, heart, and abdominal skin, particularly during the first six months of life. The developmental peak in DNA synthesis observed in liver and kidney of ad libitum fed animals before 100 days of age was completely inhibited. No effect of restricted feeding on DNA synthesis in the small intestine was observed; however, DNA synthesis was higher in thymic tissue from the experimental animals. A decrease in RNA content of liver, kidney, and heart preceded any change in protein or DNA in animals subjected to restricted feeding. The capacity for protein synthesis (RNA/DNA ratio) was decreased by restricted feeding and was associated with a reduced protein/DNA ratio indicative of reduced cell size during the first six months of life. The translational activity per ribosome (protein/RNA ratio) was not disturbed by undernutrition in any of the tissues studied.

The effects of aging and chronic dietary restriction on whole body growth and protein turnover in the rat.

Changes in whole body growth, nucleic acids, and protein turnover have been studied in conjunction with ageing and chronic dietary restriction. Normal developmental changes between weaning and senescence included progressive decreases in the fractional rates of growth, protein synthesis, and protein breakdown; the decline in the synthetic rate correlating with decreases in the ribosomal capacity. Dietary intervention was imposed at weaning and involved pair feeding to 50% of the ad libitum food intake. Although this regime slowed whole body growth by retarding the developmental decline in protein turnover, growth was extended into the second and third years of life. The dietary-induced increase in longevity resulting from a retardation of the ageing process(es) appears therefore to be associated with an enhanced turnover of proteins during the major portion of the life span of dietary restricted rats.

Onset of puberty and duration of fertility in rats fed a restricted diet.

Chronic dietary restriction such that the body weight of CFY Sprague-Dawley female rats was 50% that of animals fed ad libitum resulted in enhanced longevity (LD 50 of 1090 days compared to 704 days). All the experimental females had reached puberty by 227 days and 80% were able to conceive and wean young at 510 days, an age beyond that at which the control rats had ceased to breed (450 days). Some (25%) of the experimental rats were able to breed at over 800 days of age.