Pelage insulation, litter size, and ambient temperature impact maternal energy intake and offspring development during lactation

Energy balance during lactation critically influences survival and growth of a mother's offspring, and hence, her reproductive success. Most experiments have investigated the influence of a single factor (e.g., ambient temperature [T_a] or litter size) on the energetics of lactation. Here, we determined the impact of multiple interventions, including increased conductive heat loss consequent to dorsal fur removal, cold exposure (T_a of 5 °C versus 23 °C), and differential lactational load from litters of different sizes (2 or 4 pups), on maternal energy balance and offspring development of Siberian hamsters (Phodopus sungorus). Lower T_a, fur removal, and larger litters were associated with increased maternal food consumption. Females exposed to multiple challenges (e.g., both fur loss and lower T_a) ate substantially more food than those exposed to a single challenge, with no apparent ceiling to elevated food intake (increases up to 538%). Thus, energy intake of dams under these conditions does not appear to be limited by feeding behavior or the size of the digestive tract. Housing at 5 °C attenuated pup weight gain and increased pup mortality to more than 5 times that of litters housed at 23 °C. Increases in the dam's conductive heat loss induced by fur removal did not affect pup weight gain or survival, suggesting that effects of low T_a on pup weight gain and survival reflect limitations in the pups’ ability to ingest or incorporate energy.     

Evidence of a greater onset threshold for sweating in females following intense exercise

We evaluated the hypothesis that females would show a greater postexercise hypotension and concurrently a greater increase in the onset threshold for sweating. Fourteen subjects (7 males and 7 females) of similar age, body composition, and fitness status participated in the study. Esophageal temperature was monitored as an index of core temperature while sweat rate was measured by using a ventilated capsule placed on the upper back. Subjects cycled at either 60% (moderate) or 80% (intense) of peak oxygen consumption followed by 20-min recovery. Subjects then donned a liquid-conditioned suit used to regulate mean skin temperature. The skin was then heated (∼4.3°C·h⁻¹) until sweating occurred. Esophageal temperatures were similar to baseline before the start of whole body warming for all conditions. The postexercise threshold values for sweating following moderate and intense exercise were an esophageal temperature increase of 0.10 ± 0.02 and 0.22 ± 0.04°C, respectively for males, and 0.15 ± 0.03 and 0.34 ± 0.01°C, respectively for females. All were elevated above baseline resting (P < 0.05) and a significant sex-related difference was observed for sweating threshold values following intense exercise (P < 0.05). This was paralleled by a greater decrease in mean arterial pressure in females at the end of the 20-min recovery (P < 0.05). In conclusion, females demonstrate a greater postexercise onset threshold for sweating, which is paralleled by a greater postexercise hypotensive response following intense exercise.     

Body temperature daily rhythm adaptations in African savanna elephants (Loxodonta africana)

The savanna elephant is the largest extant mammal and often inhabits hot and arid environments. Due to their large size, it might be expected that elephants have particular physiological adaptations, such as adjustments to the rhythms of their core body temperature (T(b)) to deal with environmental challenges. This study describes for the first time the T(b) daily rhythms in savanna elephants. Our results showed that elephants had lower mean T(b) values (36.2 +/- 0.49 degrees C) than smaller ungulates inhabiting similar environments but did not have larger or smaller amplitudes of T(b) variation (0.40 +/- 0.12 degrees C), as would be predicted by their exposure to large fluctuations in ambient temperature or their large size. No difference was found between the daily T(b) rhythms measured under different conditions of water stress. Peak T(b)'s occurred late in the evening (22:10) which is generally later than in other large mammals ranging in similar environmental conditions.     

Role of Noradrenergic Innervation of Brown Adipose Tissue in Thermoregulatory Deficits Following Prenatal Alcohol Exposure

The development of thermoregulation in newborns is delayed by prenatal alcohol exposure in an animal model of moderate maternal drinking. Newborn mammals generate heat primarily via nonshivering thermogenesis in brown adlpose tissue (BAT), which is activated by the sympathetic nervous system. In this study, the effects of prenatal alcohol exposure on the development of the sympathetic innervation of BAT was investigated by assessing the concentration of norepinephrine (NE) in interscapular BAT. Pregnant dams were given either a liquid diet with 35% of the calories derived from alcohol, a liquid diet without alcohol to control for any effects of the liquid diet administration, or ad libitum food and water. Interscapular brown adipose tissue was excised from 5-, 10-, and 20-day-old male and female offspring. At 5 days of age, alcohol-exposed pups had significantly lower NE concentrations than did pups in either control group. However, 20-day-old alcohol-exposed pups had significantly higher NE concentrations than either control group. These results suggest a delay in the development of the sympathetic activation of BAT thermogenesis, followed by a compensatory overactivation. These findings may have important implications for understanding the mechanisms underlying thermoregulatory deficits seen after prenatal alcohol exposure. In addition, these results suggest that maternal alcohol consumption may increase the risk of sudden infant death syndrome, which has been linked to inappropriate BAT thermogenesis.     

Mathematical modeling of thermal and circulatory effects during hemodialysis

Intradialytic hypotension (IDH) is one of the most common complications of hemodialysis (HD) treatment. The initiating factor of IDH is a decrease in blood volume, which is related to an imbalance between ultrafiltration (UF) and refilling rate. Impaired reactivity of resistance and capacitance vessels in reaction to hypovolemia plays possibly a major role in the occurrence of IDH. These vessels also fulfill an important function in body temperature regulation. UF‐induced cutaneous vasoconstriction would result in a reduced surface heat loss and an increase in core temperature. To release body heat, skin blood flow is increased at a later stage of the HD treatment, whereby possibly IDH can occur. The aim of the study is to develop a mathematical model that can provide insight into the impact of thermoregulatory processes on the cardiovascular (CV) system during HD treatment. The mathematical procedure has been created by coupling a thermo‐physiological model with a CV model to study regulation mechanisms in the human body during HD + UF. Model simulations for isothermal versus thermoneutral HD + UF were compared with measurement data of patients on chronic intermittent HD (n = 13). Core temperature during simulated HD + UF sessions increased within the range of measurement data (0.23°C vs. 0.32 ± 0.41°C). The model showed a decline in mean arterial pressure of ?7% for thermoneutral HD + UF versus ?4% for isothermal HD + UF after 200 min during which relative blood volume changed by ?13%. In conclusion, simulation results of the combined model show possibilities for predicting circulatory and thermal responses during HD + UF.     

Rebound hyperthermia follows ethanol-induced hypothermia in rats

We have recently described a telemetry/micro-computer system to monitor core temperatures in rats. We implant a miniature transmitter (Mini-mitter) into the peritoneal cavity of the rat, allowing us to obtain temperatures around the clock without handling the animals or disturbing the light-dark cycle. In the present study we describe the temperature effects of ethanol doses ranging from 2 to 6 g/kg. Baseline temperatures were collected for 2 days before drug was administered. Subsequent computer analysis then allowed us to compare experimental results in each animal with its own baseline temperature to allow for individual and circadian temperature differences. In preliminary studies we observed the well-known dose-dependent hypothermic effect of ethanol. However, by observing animals continually over 4 days we also observed a period of rebound hyperthermia beginning at about the time of complete ethanol elimination and persisting for several days. During this period daytime temperatures remained at the normally high night-time level. This may be evidence of a mild abstinence syndrome, or alternatively, may be due to a disruption of the normal circadian temperature rhythm.Preliminary work presented at the 33rd Fall Meeting of the American Society of Pharmacology and Experimental Therapeutics, Louisville, KY, August 1982, and at the 28th Annual Meeting of the Western Pharmacology Society, Jan. 20–25, 1985, Tahoe City, CA     

Fever evoked by macrophage inflammatory protein-1 (MIP-1) injected into preoptic or ventral septal area of rats depends on intermediary protein synthesis

Macrophage inflammatory protein-1 (MIP-1), a novel cytokine composed of α/β subunits, is released from macrophages during infection, MIP-1 injected intravenously in the rabbit or into the anterior hypothalamic, preoptic area (AH/POA) of the rat causes an intense fever, which is not blocked by prostaglandin synthesis inhibitors, ibuprofin or indomethacin, respectively. The purpose of this study was to determine the role of de novo protein synthesis on the fever evoked by MIP-1 applied to thermosensitive cells of the AH/POA. Guide cannulae were implanted bilaterally above the AH/POA or ventral septal area (VSA) and medially above the third cerebral ventricle in each of 11 male Sprague-Dawley rats. Following postoperative recovery, body temperature (T_b) was monitored by a colonic thermistor probe. The bilateral microinjection of MIP-1 in a dose of 14 pg per 0.5 μ1 into the AH/POA caused a biphasic elevation in T_b to 0.9 ± 0.2 °C within 3.0 h, and persisted for over 6.0 h. An identical injection of MIP-1 into the VSA increased T_b biphasically to 0.1 ± 0.1 °C within 1.0 h and to 0.8 ± 0.3 °C within 3.0 h. The infusion into the third ventricle of 80 μg/10 μ1 of the inhibitor of protein synthesis, anisomycin, either 10 or 30 min before the microinjection of MIP-1 into the AH/POA, attenuated significantly the rise in T_b for 1.0 to 3.0 h or 2.5 to 3.0 h, respectively. These results coincide with the earlier finding that anisomycin inhibits both endotoxin- and IL-1β-induced fevers. Further, the synthesis of a new protein factor may be required functionally for the initiation and maintenance of a fever whose mechanism of induction apparently is metabolically independent of the cyclooxygenase pathway.     

Neuronal responses in the rat's thalamus to scrotal heating

Summary Twenty-one single neurons from the rat's thalamus were recorded as they responded to scrotal skin thermal stimulation. Eighteen of them were warm und three inverse-warm cells. After the injection of Lidocain (Xylocain) into the scrotal skin, the response of each neuron was abolished. Eight neurons could be followed until the drug effect had disappeared; their responsiveness was fully restored. External application of Xylocain had the same effect as intracutaneous injection, apart from longer time intervals before the effect became apparent. From this, conclusions are drawn on the origin of the thalamic responses, and speculations are made on the functional role of warm and inverse-warm cells.This project was supported by the Deutsche Forschungs-gemeinschaft, SFB 114 (BIONACH)     

Variations in behavioral thermoregulation in the young pig over 24 hour periods.

Young pigs were trained to make a response to obtain a reinforcement of radiant heat. The animals were kept by themselves in a temperature-controlled light-proof room. Some pigs were kept in constant light, some were subjected to a light/dark cycle, and some were first fed ad lib and then deprived of food. The results were analysed by fitting a cosine curve using regression methods and evidence of a circadian rhythm was obtained under all conditions and at ambient temperature between 5 degrees and 20 degrees centrigrade. Most pigs had a peak demand for heat during the true daytime, but in two pigs the peak occurred at night.     

Generation of temperature profiles for elements of the human body

Calculation of steady-state temperature distributions throughout cylindrical elements of the human body result in sets of data pairs (u_i, r_i), i = 1,2, …, n, where u_i is the tissue temperature at radial distance r_i. A novel empirical relation of the form u = a(b − r)^c is proposed and a non-linear least squares algorithm is used to fit a curve of this form to sets of experimental data and hence generate temperature profiles. The parameter a has a value which is close to that of the core temperature of the element, the parameter b has a value which is very slightly larger than the normalised radius of the element (i.e. unity), and the parameter c lies within the range −1 < c < 1.