Dietary protein modulates circadian changes in core body temperature and metabolic rate in rats

Continuous body temperature as a window into adolescent development

Continuous body temperature is a rich source of information on hormonal status, biological rhythms, and metabolism, all of which undergo stereotyped change across adolescence. Due to the direct actions of these dynamic systems on body temperature regulation, continuous temperature may be uniquely suited to monitoring adolescent development and the impacts of exogenous reproductive hormones or peptides (e.g., hormonal contraception, puberty blockers, gender affirming hormone treatment). This mini-review outlines how traditional methods for monitoring the timing and tempo of puberty may be augmented by markers derived from continuous body temperature. These features may provide greater temporal precision, scalability, and reduce reliance on self-report, particularly in females. Continuous body temperature data can now be gathered with ease across a variety of wearable form factors, providing the opportunity to develop tools that aid in individual, parental, clinical, and researcher awareness and education.

Nutritional ecology and ecological immunology in degus: Does early nutrition affect the postnatal development of the immune function?

Environmental conditions experienced by developing animals have an impact on the development and maturity of the immune system. Specifically, the diet experienced during early development influences the maintenance and function of the immune system in young and adult animals. It is well known that exposure to low-protein diets during early development are related to an attenuation of immunocompetence in adulthood. While this functional linkage has been widely studied in altricial models' mammals, it has been little explored how the nutritional history modulates the immune function in precocial animals. We evaluated the effect of dietary protein consumed during early development on the immune function and the oxidative costs in the precocial Caviomorph rodent Octodon degus, or degu. We evaluated components of the acute phase response (APR) and oxidative parameters before and after immune challenge. We found that after the immune challenge, the juveniles on the low-protein dietary treatment exhibited an attenuation of body temperature but showed higher levels of lipid peroxidation than juvenile degus on the high-protein diet. We did not find a significant effect of the interaction between diet and immune challenge on body mass, levels of inflammatory proteins, nor in the total antioxidant capacity. Our results suggest that some components of the immune function and the oxidative status in the degu can be modulated by diet during development. However, the modulation would depend on the immune variables analyzed, and the characteristics of the immune system of precocial rodents.

Protein malnutrition prevents heat conservation induced by amino acid infusion during general anesthesia in rats

The intravenous administration of an amino acid (AA) mixture during general anesthesia reduces anesthesia-induced hypothermia. AA-induced skeletal muscle protein synthesis and thermogenesis play important roles in the antihypothermic effects of AAs. We hypothesized that a preanesthetic dietary protein deficiency impairs the antihypothermic effects of AAs during general anesthesia due to a reduction in thermogenesis caused by a decrease in muscle protein synthesis. Sprague-Dawley rats were divided into 4 groups: fed a control diet plus saline (CON-SAL) or the AA mixture (CON-AA), and fed a protein-free diet plus saline (PF-SAL) or the AA mixture (PF-AA). SAL solution or AA mixture solution was infused for 180 minutes during sevoflurane anesthesia, and rectal temperatures were measured. Rectal temperatures were significantly higher in the CON-AA group than in the PF-AA group 90 to 180 minutes after initiating the intravenous infusion of the test solutions. There was no significant difference between the PF-SAL and PF-AA groups. Plasma insulin concentrations were significantly higher in the CON-AA group than in the PF-AA group (P < .05). The phosphorylation states of protein kinase B, mammalian target of rapamycin, and eukaryotic initiation factor 4E-binding protein 1 were significantly greater in the CON-AA group than in the PF-AA group (P < .05, P < .05, and P < .01, respectively). Our results indicated that a dietary protein deficiency before general anesthesia impaired the antihypothermic effects of an AA mixture infusion during general anesthesia by decreasing muscle protein synthesis through the insulin-stimulated phosphoinositide 3-kinase/protein kinase B/mammalian target of rapamycin complex 1 signaling pathway followed by metabolic heat production.

Dissociated Oxygen Consumption and Carbon Dioxide Production in the Post-Cardiac Arrest Rat: A Novel Metabolic Phenotype

BACKGROUND

The concept that resuscitation from cardiac arrest (CA) results in a metabolic injury is broadly accepted, yet patients never receive this diagnosis. We sought to find evidence of metabolic injuries after CA by measuring O2 consumption and CO2 production (VCO2) in a rodent model. In addition, we tested the effect of inspired 100% O2 on the metabolism.

METHODS AND RESULTS

Rats were anesthetized and randomized into 3 groups: resuscitation from 10-minute asphyxia with inhaled 100% O2 (CA-fraction of inspired O2 [FIO2] 1.0), with 30% O2 (CA-FIO2 0.3), and sham with 30% O2 (sham-FIO2 0.3). Animals were resuscitated with manual cardiopulmonary resuscitation. The volume of extracted O2 (VO2) and VCO2 were measured for a 2-hour period after resuscitation. The respiratory quotient (RQ) was RQ=VCO2/VO2. VCO2 was elevated in CA-FIO2 1.0 and CA-FIO2 0.3 when compared with sham-FIO2 0.3 in minutes 5 to 40 after resuscitation (CA-FIO2 1.0: 16.7±2.2, P<0.01; CA-FIO2 0.3: 17.4±1.4, P<0.01; versus sham-FIO2 0.3: 13.6±1.1 mL/kg per minute), and then returned to normal. VO2 in CA-FIO2 1.0 and CA-FIO2 0.3 increased gradually and was significantly higher than sham-FIO2 0.3 2 hours after resuscitation (CA-FIO2 1.0: 28.7±6.7, P<0.01; CA-FIO2 0.3: 24.4±2.3, P<0.01; versus sham-FIO2 0.3: 15.8±2.4 mL/kg per minute). The RQ of CA animals persistently decreased (CA-FIO2 1.0: 0.54±0.12 versus CA-FIO2 0.3: 0.68±0.05 versus sham-FIO2 0.3: 0.93±0.11, P<0.01 overall).

CONCLUSIONS

CA altered cellular metabolism resulting in increased VO2 with normal VCO2. Normal VCO2 suggests that the postresuscitation Krebs cycle is operating at a presumably healthy rate. Increased VO2 in the face of normal VCO2 suggests a significant alteration in O2 utilization in postresuscitation. Several RQ values fell well outside the normally cited range of 0.7 to 1.0. Higher FIO2 may increase VO2, leading to even lower RQ values.