As part of mitonuclear communication, retrograde and anterograde signaling helps maintain homeostasis under basal conditions. Basal conditions, however, vary across phylogeny. At the cell-level, some mitonuclear retrograde responses can be quantified by measuring the constitutive components of oxidative stress, the balance between reactive oxygen species (ROS) and antioxidants. ROS are metabolic by-products produced by the mitochondria that can damage macromolecules by structurally altering proteins and inducing mutations in DNA, among other processes. To combat accumulating damage, organisms have evolved endogenous antioxidants and can consume exogenous antioxidants to sequester ROS before they cause cellular damage. ROS are also considered to be regulated through a retrograde signaling cascade from the mitochondria to the nucleus. These cellular pathways may have implications at the whole-animal level as well. For example, birds have higher basal metabolic rates, higher blood glucose concentration, and longer lifespans than similar sized mammals, however, the literature is divergent on whether oxidative stress is higher in birds compared with mammals. Herein, we collected literature values for whole-animal metabolism of birds and mammals. Then, we collected cellular metabolic rate data from primary fibroblast cells isolated from birds and mammals and we collected blood from a phylogenetically diverse group of birds and mammals housed at zoos and measured several parameters of oxidative stress. Additionally, we reviewed the literature on basal-level oxidative stress parameters between mammals and birds. We found that mass-specific metabolic rates were higher in birds compared with mammals. Our laboratory results suggest that cellular basal metabolism, total antioxidant capacity, circulating lipid damage, and catalase activity were significantly lower in birds compared with mammals. We found no body-size correlation on cellular metabolism or oxidative stress. We also found that most oxidative stress parameters significantly correlate with increasing age in mammals, but not in birds; and that correlations with reported maximum lifespans show different results compared with correlations with known aged birds. Our literature review revealed that basal levels of oxidative stress measurements for birds were rare, which made it difficult to draw conclusions.

There is ample evidence that cell membrane architecture contributes to metabolism and aging in animals; however, the aspects of this architecture that determine the rate of metabolism and longevity are still being debated. The 'membrane pacemaker' hypothesis of metabolism and of aging, respectively, suggest that increased lipid unsaturation and large amounts of polyunsaturated fatty acids (PUFAs) in cell membranes increase the cellular metabolic rate as well as the vulnerability of the cell to oxidative damage, thus increasing organismal metabolic rate and decreasing longevity. Here, we tested these hypotheses by experimentally altering the membrane fatty acid composition of fibroblast cells derived from small and large breed dogs by incubating them in a medium enriched in the monounsaturated fatty acid (MUFA) oleic acid (OA, 18:1) to decrease the total saturation. We then measured cellular metabolic parameters and correlated these parameters with membrane fatty acid composition and oxidative stress. We found that cells from small dogs and OA-incubated cells had lower maximal oxygen consumption and basal oxygen consumption rates, respectively, which are traits associated with longer lifespans. Furthermore, although we did not find differences in oxidative stress, cells from small dogs and OA-treated cells exhibited reduced ATP coupling efficiency, suggesting that these cells are less prone to producing reactive oxygen species. Membrane fatty acid composition did not differ between cells from large and small dogs, but cells incubated with OA had more monounsaturated fatty acids and a higher number of double bonds overall despite a decrease in PUFAs. Our results suggest that increasing the monounsaturation of dog cell membranes may alter some metabolic parameters linked to increases in longevity.

Anxiety is the most prevalent mental disorder among adults in the United States and females tend to have significantly higher rates of anxiety compared with men. Common treatments for anxiety include usage of selective serotonin reuptake inhibitors (SSRIs) and tricyclic antidepressants, however, sex differences in the efficacy of these drugs exist. In this study, we were interested in determining if acutely manipulating serotonin mechanisms at the whole‐animal level affects cellular metabolism and oxidative stress in primary fibroblast cells from clomipramine‐treated Sprague‐Dawley rats. Our groups included a female and male control group that was injected with a saline solution, a female and male group that was injected with a low dosage of clomipramine, and a female and male group of rats that were injected with a high dosage of clomipramine. We then compared cellular oxygen consumption rates, rates of glycolysis and oxidative stress parameters in primary fibroblasts grown from each of the groups described above. We found that clomipramine‐treated rats had significantly lower rates of glycolysis and glycolytic capacity, regardless of sex. Coupling efficiency was significantly higher in male rats compared with female rats across treatment groups. Our data suggest that in female rats reduced glutathione (GSH) is nonsignificantly reduced, yet lipid peroxidation (LPO) damage still accumulates, meaning that enzymatic antioxidants may be acting to reduce any continual increases in LPO damage. This is a metabolically costly process that may be happening because of our drug treatments. Our results provide further evidence of sex differences in the behavioral and metabolic responses to short‐term clomipramine treatment. Continued investigation into these sex differences may reveal their potential for improving our understanding of how different therapeutic interventions may be better suited for treating males and females.

Life‐history theory posits that differences in reproductive strategies may dictate lifespans of organisms. Animals that have higher investments in reproduction in terms of litter size and frequency of litters tend to have shorter lifespans. The accumulation of oxidative stress damage has been proposed to be a cost of reproduction and a mediator of life‐histories among animals, however, the implications of reproduction on oxidative stress still remain unclear. We tested physiological consequences of reproduction on metabolism and oxidative stress of Sprague‐Dawley Rats (Rattus norvegicus) with various reproductive experiences at the cell level. We grew primary dermal fibroblasts from Sprague‐Dawley rats which have the potential of having large litters frequently. Cells were isolated from virgin females, primiparous females, multiparous females, and reproductively‐experienced males. We measured basal oxygen consumption (OCR), proton leak, ATP production, spare respiratory capacity, coupling efficiency and glycolysis using a Seahorse XF96 oxygen flux analyzer. Additionally, we measured rates of RS (reactive species) production, reduced glutathione (GSH), mitochondrial content, and lipid peroxidation (LPO) damage to quantify oxidative stress. There were no significant differences in any OCR or glycolytic parameters across any of our groups. However, reproductively‐experienced females had significantly lower rates of LPO damage as compared with virgin females and males, as well as nonsignificant decreases in GSH concentration. Decreases in LPO damage and GSH indicate that reproductively‐experienced females potentially use their endogenous antioxidant system to combat delirious effects of increased metabolism during reproduction. Our results suggest that reproduction may, in fact, have a protective effect in females.