The effect of the mitochondria-targeted, plastoquinone-containing antioxidant SkQ1 on the lifespan of outbred mice and of three strains of inbred mice was studied. To this end, low pathogen (LP) or specific pathogen free (SPF) vivaria in St. Petersburg, Moscow, and Stockholm were used. For comparison, we also studied mole-voles and dwarf hamsters, two wild species of small rodents kept under simulated natural conditions. It was found that substitution of a LP vivarium for a conventional (non-LP) one doubled the lifespan of female outbred mice, just as SkQ1 did in a non-LP vivarium. SkQ1 prevented age-dependent disappearance of estrous cycles of outbred mice in both LP and non-LP vivaria. In the SPF vivarium in Moscow, male BALB/c mice had shorter lifespan than females, and SkQ1 increased their lifespan to the values of the females. In the females, SkQ1 retarded development of such trait of aging as heart mass increase. Male C57Bl/6 mice housed individually in the SPF vivarium in Stockholm lived as long as females. SkQ1 increased the male lifespan, the longevity of the females being unchanged. SkQ1 did not change food intake by these mice. Dwarf hamsters and mole-voles kept in outdoor cages or under simulated natural conditions lived longer if treated with SkQ1. The effect of SkQ1 on longevity of females is assumed to mainly be due to retardation of the age-linked decline of the immune system. For males under LP or SPF conditions, SkQ1 increased the lifespan, affecting also some other system(s) responsible for aging.
We tested the winter immunity enhancement hypothesis (WIEH) on male desert hamsters (Phodopus roborovskii) kept under long-day (LD) and short-day (SD) photoperiods. We assumed that under SD in a laboratory, the adaptive humoral immune responsiveness to the antigenic challenge would be enhanced due to the lack of winter physical stressors and food shortages and/or because of the action of an endogenous winter bolstering mechanism, while under LD the immune responsiveness would be suppressed by the activity of the reproductive system. The results support the WIEH in part. We did not find a difference in antibody production in response to sheep erythrocytes between SD and LD hamsters, but SD males had the lower number of granulocytes and the higher number of lymphocytes in white blood cell counts. Reproductive activity was lower in SD males. These males demonstrated an increase in their mass-specific resting metabolic rate, their mass-specific maximal metabolic rate and their level of cortisol. The result of a generalized linear model analysis indicates the negative effect on secondary immunoresponsiveness to sheep erythrocytes of mid-ventral gland size, the organ characterizing individual reproductive quality, and designates a tradeoff between antibody production and reproductive effort. The mass-independent maximal metabolic rate also negatively affected antibody production, indicating a tradeoff between maximal aerobic performance and the adaptive immune function. The higher stress in SD males seems to be the most likely reason for the lack of the effect of daylight duration on antibody production.
Characteristics of innate (nonspecific) and acquired T cell immunity, resting metabolic rate, hor monal and reproductive status, morphological traits of maturation and aggressive behavior were studied in two sample groups of Campbell's dwarf hamster males (Phodopus campbelli Thomas, 1905) selected in three generations for high and low humoral immune response to sheep red blood cells (SRBC). The groups of males with low and high immune responses (LIR and HIR, respectively) to SRBC did not differ statistically in the intensity of delayed type hypersensitivity cutaneous response to phytohemagglutinin (T cell immunity test), the activity of the peroxidase-endogenous hydrogen peroxide system of neutrophils (characteristic of the innate immunity state), the white blood cell counts, the resting metabolic rate, body weight, anogenital distance at the age two months, testosterone level in the blood before immunization and at the peak of sec ondary immune response to SRBC, or the blood cortisol level in response to social conflict (encountering). LIR males had a significantly higher background blood cortisol level and were less aggressive (reaction to the stranger male). The midventral sebaceous gland was less developed in them at the age of two months. We observed no differences in the time of first litter birth after uniting LIR and HIR males in pairs with intact females; however, females in pairs with LIR males had smaller numbers of pups in the litter. The results of comparison do not favor the immunocompetence handicap hypothesis, which assumes the existence of a trade off between the immunocompetence and reproductive effort.
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