Biomedical subjects

J E Heath

Publications and source records attributed to J E Heath.

At least 19 recordsLinked to original sources

PubMed1992

Heat exchange by the pinna of the African elephant (Loxodonta africana).

1. Surface temperatures of the pinnae of four female African elephants were measured at ambient temperatures between 14 and 32 degrees C using infrared thermography. Instantaneous heat losses calculated using those values ranged from 10.67 to 76.2 W under the observed conditions. 2. Using a value of 17 kcal/kg/day, those heat losses account for 0.65-4.64% of the animals' standard metabolic rates, considering one side of one ear only. 3. A model of heat flow across a flat vertical plate was constructed and compared to the actual values. Up to 100% of an African elephant's heat loss needs can be met by movement of its pinnae and by vasodilation. 4. Thermography indicates that the temperature distribution pattern across the pinna changes with ambient temperature and that areas of specialized motor control exist.

Animals↗

PubMed1992

Metabolic rate and evaporative water loss at different ambient temperatures in two species of fox: the red fox (Vulpes vulpes) and the Arctic fox (Alopex lagopus).

1. Resting metabolic rate (RMR) and evaporative water loss (EWL) of adult red and arctic foxes were determined over ambient temperature (Ta) ranges of -13-37 degrees C and -5-30 degrees C as oxygen consumption and amount of water in expired air using an open flow system. 2. The average RMR was 2.60 +/- 0.14 W/kg for the winter red fox, 2.59 +/- 0.14 W/kg for the summer red fox, and 2.35 +/- 0.11 W/kg for the winter arctic fox. 3. The rate of increase of RMR was significant (P less than 0.05) only for Ta range above 27 degrees C. The slopes for this Ta range were 0.152 for the winter red fox, and 0.283 for the winter arctic fox. 4. The upper critical temperature (Tuc) of the red fox is probably between 30 and 32 degrees C. The Tuc of the arctic fox is probably between 26 and 28 degrees C. The lower critical temperatures (Tlc) were not reached. 5. A strong linear relationship between the EWL and Ta was found for Ta range above 27 degrees C. The slopes for this Ta range were 0.523 for the winter red fox, and 1.025 for the winter arctic fox. 6. Probably, there are neither significant intraspecific seasonal nor interspecific differences in the RMR and EWL. The two species seem to differ only in their critical temperatures.

Animals↗

PubMed1992

Thermoregulation and evaporative cooling in the cicada Okanagodes gracilis (Homoptera: Cicadidae).

1. Okanagodes gracilis uses a combination of physiological and behavioral mechanisms to regulate body temperature (Tb) to a prescribed range. 2. High thermal tolerances (48.6 degrees C Tb) and evaporative cooling permit the species to remain active during the hottest parts of the day. 3. The regression of Tb on ambient temperature (Ta) (Y = 0.142X + 34.63) intersects the isothermal line at 40.4 degrees C, below the shade-seeking value of 41.2 degrees C. 4. In the laboratory, weight (water) loss is faster at higher (46 degrees C) than at lower (43 degrees C) temperatures; the cicadas were able to survive mass losses of 25% in the laboratory. 5. Pores in the dorsal thorax and abdomen are the probable sites of water loss. 6. O. gracilis is the first cicada reported that is able to continue activity while simultaneously feeding and evaporatively cooling. 7. Behavioral mechanisms of thermoregulation and the possible thermoregulatory value of the species' coloration are discussed.

Animals↗

PubMed1990

An infrared thermographic study of surface temperature in relation to external thermal stress in the Mongolian gerbil, Meriones unguiculatus.

1. Temperatures of different body surface regions and deep body temperature (Tb) of unrestrained adult Mongolia gerbils exposed to ambient temperatures (Ta) of -10-35 degrees C were measured using infrared (i.r.) thermography and a thermocouple. 2. A strong positive linear relationship between the surface temperature and Ta was found. For Ta range -4-35 degrees C, the slope was lowest for the areas around the eyes and dorsal head, and steepest for the body extremities. At -10 degrees C, surface temperatures of the areas around the eyes and dorsal head were significantly lower then predicted. 3. Tb was lowest at Ta of 25 and 30 degrees C, increased at all temperatures above and up to Ta of -4 degrees C below this range, and began decline at -10 degrees C. 4. The thermoneutral zone (TNZ) is probably between 28 and 32 degrees C, and the absolute lower critical temperature (Tabsl) is probably -4 degrees C. 5. The Mongolian gerbil shows little control of surface temperature and in contrast to larger mammals it has not developed any special thermoregulatory surface areas to regulate heat exchange with its environment. At temperatures below -4 degrees C, this species is unable to maintain the surface temperature of body extremities above the freezing point. 6. It is suggested that the Mongolian gerbil uses mainly behavioral and ecological adaptive strategies to attenuate the stressful effects of its habitat.

Animals↗

PubMed1988

Subchronic toxicity of orally administered (gavage and dosed-feed) theophylline in Fischer 344 rats and B6C3F1 mice.

Theophylline, a methylated xanthine closely resembling caffeine and theobromine, is a widely used pharmaceutical agent for the treatment of respiratory disorders and certain acute cardiovascular conditions. The National Toxicology Program has conducted 13-week subchronic toxicity studies in F344 rats and B6C3F1 mice (10 animals/group) following administration of theophylline via the diet or by gavage. Administration of theophylline in the feed (0, 1000, 2000, and 4000 ppm) resulted in no mortality or body weight effects in F344 rats, but did induce periarteritis of the arteries adjacent to mesenteric lymph nodes and the pancreas, particularly arterioles in the latter. Also observed in rats dosed with theophylline via the diet was an increased severity of chronic nephropathy in males, especially at the high dose. Administration of theophylline at the same concentrations in the feed to B6C3F1 mice resulted in no mortality, but terminal body weights were significantly decreased in all dosed groups. An increased incidence of hepatocellular glycogen depletion was observed in male and female mice, and this change is believed to represent a physiological alteration exacerbated by the administration of theophylline. Administration of theophylline by gavage to F344 rats (0, 37.5, 75, and 150 mg/kg) resulted in the early death of one high-dose male and female and significantly decreased or increased terminal body weights of high-dose males and females, respectively. Similar to the results of the dosed-feed study, male and female rats receiving theophylline by gavage demonstrated a dose-related increase in the incidence and severity of perivascular inflammation of mesenteric arteries. Gavage administration of theophylline to B6C3F1 mice (0, 75, 150, and 300 mg/kg) resulted in the early death of all high-dose females and 3/10 high-dose males and significant depression of terminal body weights in high- and mid-dose males and low-dose females. As in the dosed-feed study, the primary histopathologic change in the mouse subchronic gavage study was hepatocellular glycogen depletion, although in this case it was seen only in females. In summary, the major target organs for orally administered theophylline in 13-week subchronic toxicity studies appear to be the mesenteric arteries in F344 rats and the liver in B6C3F1 mice. On the basis of organ weight changes and/or minor histopathologic effects, many other tissues were also affected, particularly the kidneys in dosed-feed male rats and the uterus in gavage-dosed female rats.

Administration, Oral↗

PubMed1988

Studies on the short-term toxicity of theophylline in rats and mice.

The purpose of these studies was to evaluate the short-term toxicity of theophylline, a compound present in tea and used in a variety of clinical applications. Fourteen-day repeated-dose toxicity studies were conducted in B6C3F1 mice and F344 rats of both sexes. Theophylline was administered in feed (0, 500, 1000, 2000, 4000, and 8000 ppm) or by gavage in corn oil (12.5-twice daily, 25, 50, 50-twice daily, 100, 200, 200-twice daily, and 400 mg/kg). Dosed-feed exposure to theophylline at concentrations up to 8000 ppm induced no significant toxicity except for dose-related uterine hypoplasia in rats. Palatability problems at that level precluded administration of higher concentrations. In the gavage study, 400 mg/kg was acutely toxic for both species, but mice and rats differed in that this same daily dose administered as two separate doses of 200 mg/kg was acutely toxic in rats but not in mice. No dose-related weight gain depression was evident in mice; weight gain was depressed in the majority of dose levels in rats and was pronounced at the higher levels. Clinical signs in mice were squinting and distended testes in males, and in rats, rapid respiration (all doses), squinting, and hunching. Gross necropsies, organ weights, clinical pathology, and pathology identified no target organs in mice, while histopathologic observations in rats suggested heart and stomach as possible target organs. Histopathologic effects in a number of other tissues, including lung, thymus, bone marrow, spleen, and uterus, were considered to reflect agonal changes in treated rats, possibly related to inanition. The results suggest that both species and sex differences exist with respect to sensitivity to theophylline toxicity, with F344 rats being more sensitive than B6C3F1 mice and male rats being more sensitive than female rats.

Animals↗

PubMed1988

Comparison of IR thermography and thermocouple measurement of heat loss from rabbit pinna.

The temperature of the pinnae of male New Zealand White rabbits was measured by use of infrared thermography. At ambient temperatures of 15, 20, and 25 degrees C, the average pinna temperatures were 23.0, 28.7, and 36.2 degrees C, respectively. From these temperatures, average heat loss from the total pinna surface area was calculated to be 2.8, 3.3, and 4.4 W, respectively. Preoptic temperature changes also affect the vasomotor state of the rabbit. At an ambient temperature of 20 degrees C, cooling the preoptic area of the rabbit by approximately 1 degree C resulted in an average pinna temperature of 26.5 degrees C and a heat loss of 2.4 W. Heating the preoptic area by approximately 1 degree C resulted in an average pinna temperature of 33.5 degrees C and a heat loss of 5.4 W. Finally, pinna temperatures were measured by use of a thermocouple and infrared thermography simultaneously. When the pinnae were vasodilated, the thermocouple measurements were consistently higher than the pinna surface temperatures measured thermographically. When the pinnae were vasoconstricted, the thermocouple measurements were consistently lower than the pinna surface temperatures measured thermographically. The discrepancy between the two methods of measurement is discussed.

Algorithms↗

PubMed1988

Oscillating heat flow from rabbit's pinna.

Thermal characteristics of the pinnae of the ears of New Zealand White rabbits (Oryctolagus cuniculus) were measured with an infrared imaging system, and vasomotor oscillations were observed to occur spontaneously in the pinnae of all rabbits at an ambient temperature of 20 degrees C. Measured fluctuations in surface temperature were used to characterize the observed vasomotor oscillations, whereas heat loss from the pinnae was calculated using the mean pinna temperatures. The pulsing related to thermoregulation had a mean frequency of approximately 0.025 Hz with a mean amplitude of approximately 0.35 degrees C. When surface temperature was measured simultaneously from both pinnae of individual rabbits, the thermal pulsing was synchronous in the two pinnae. Many of the characteristics of the vasomotor rhythm measured in the pinnae of rabbits were consistent with an active and controlled oscillation, and a possible thermoregulatory role for a controlled vasomotor oscillation is discussed.

Animals↗

PubMed1986

Integration and central processing in temperature regulation.

Our understanding of the neural control of body temperature has been clarified by research over the past ten years. Overall, ascending thermal inputs are integrated with other thermal and nonthermal inputs, which results in efferent signals with the spatial and temporal characteristics necessary for driving effector organs involved in thermal homeostasis. There is substantial support for the hypothesis that the afferent component of the thermoregulatory system integrates thermal stimuli into several neural patterns, the principal ones being a stepwise, switching response of neuron activity during scrotal thermal stimulation and a proportional response to other thermal inputs. Furthermore, some thermointegrative CNS neurons respond relatively rapidly or slowly during peripheral thermal stimulation, which may be critical in driving behavioral and autonomic motor outputs, respectively. The control of thermoregulatory motor outputs is multifaceted and exhibits proportional, rate-sensitive, and/or on-off regulatory patterns during thermal stimulation. These complex motor patterns indicate the presence of extensive temporal and spatial integration of ascending thermal information. This is supported by the fact that the pattern of efferent nerve activity in various motor systems (e.g. vasomotor) is vastly different from that produced by recordings of primary thermoreceptor activity. Understanding the nature and mechanisms of the CNS transduction of peripheral thermal stimuli to efferent command signals for driving thermoregulatory motor outputs will be a challenging endeavor in the future.

Animals↗

PubMed1976

Metabolic responses of White Pekin ducks to ambient temperature.

Metabolic responses of unrestrained White Pekin ducks, Anas platyrhynchos, were determined at ambient temperatures of -5 degrees, 1 degrees, 10 degrees, 20 degrees, and 30 degrees C. Temperatures from the pectoralis and the subcutaneous back were monitored. Unrestrained ducks exhibited two metabolic states, a high response (540 cc. O2/kg/hr. at 20 degrees C.) and a low response (427 cc. O2/kg./hr. at 20 degrees C). Pectoralis muscle temperature did not vary greatly over the range of ambient temperatures tested and was considered to be a good representative of body temperature.

Animals↗

PubMed1976