Seasonal differences in function of the hypothalamic-hypophysial-ovarian axis in weaned primiparous sows

Primiparous sows were fed to appetite during lactations that occurred during winter or summer, and 11.4 +/- 0.4 pigs per litter were weaned at 23.5 +/- 0.1 days of age. Sows were slaughtered at 0 or 72 h after weaning or blood samples were collected until 24 h after onset of oestrus. Sows that lactated during summer consumed less food and lost more (P less than 0.05) weight, heartgirth and backfat than those that lactated during winter. Weaning-to-oestrus interval was greater (P less than 0.05) in summer (224 +/- 25 h) than in winter (93 +/- 13 h). Content of GnRH in the hypothalamus and concentrations of LH in the anterior pituitary and serum were lower (P less than 0.05) after weaning in summer than winter. The numbers of visible ovarian follicles less than 5 mm in diameter at weaning were lower (P less than 0.05) in summer than in winter. In contrast to LH, FSH concentration in serum was higher (P less than 0.10) in summer than winter, but FSH values in the anterior pituitary were lower (P less than 0.05) in summer than in winter. Post-weaning patterns of secretion of oestradiol and follicular development differed between winter and summer. For example, in some sows weaned during the summer, transient surges of oestradiol occurred repeatedly during 0 to 280 h after weaning without provoking surges of LH. These results indicate that the period of post-weaning anoestrus in summer is prolonged because of altered activity of the hypothalamic-pituitary axis, possibly because of changes in sensitivity to the feedback of oestradiol. Lower feed intake during lactations that occur during summer may predispose the endocrine system to the aberrations.     

Cholesterol and lipoprotein dynamics in a hibernating mammal

Hibernating mammals cease feeding during the winter and rely primarily on stored lipids to fuel alternating periods of torpor and arousal. How hibernators manage large fluxes of lipids and sterols over the annual hibernation cycle is poorly understood. The aim of this study was to investigate lipid and cholesterol transport and storage in ground squirrels studied in spring, summer, and several hibernation states. Cholesterol levels in total plasma, HDL and LDL particles were elevated in hibernators compared with spring or summer squirrels. Hibernation increased plasma apolipoprotein A-I expression and HDL particle size. Expression of cholesterol 7 alpha-hydroxylase was 13-fold lower in hibernators than in active season squirrels. Plasma triglycerides were reduced by fasting in spring but not summer squirrels. In hibernators plasma β-hydroxybutyrate was elevated during torpor whereas triglycerides were low relative to normothermic states. We conclude that the switch to a lipid-based metabolism during winter, coupled with reduced capacity to excrete cholesterol creates a closed system in which efficient use of lipoproteins is essential for survival.     

Seasonal torpor and normothermic energy metabolism in the Eastern chipmunk (Tamias striatus)

To assess the changes in thermoregulatory characteristics that accompany the seasonal expression of torpor we measured seasonal differences in body mass adjustments, body temperature (T _b) and metabolic rate (MR) in both summer- and winter-acclimated individuals from a species of food-storing hibernator, the Eastern chipmunk (Tamias striatus). Torpor occurred only in the winter and was associated with lower normothermic T _b, during inter-bout arousal periods than in the summer. Chipmunks increased body mass before the initiation of torpor in winter, and steadily lost mass as the hibernation season progressed. Torpor expression was correlated to initial mass gain, with the individuals who showed the largest mass increase in the fall showing the highest degree of torpor. Acclimation to winter-like conditions produced a decline in normothermic MR at all ambient temperatures examined. The findings indicate that torpor expression is accompanied by a decrease in T _b and MR during normothermy, indicating that a conservation of energy metabolism occurs, not only in torpor, but also during the inter-bout arousal periods.     

长江口及邻近海域夏、冬季浮游病毒丰度分布

应用荧光显微计数法,对2006年夏季和2007年冬季长江口浮游病毒丰度(virus direct count,VDC)进行了检测.结果表明:夏季该海域VDC在2.22×106～9.97×107个·ml-1,高值分布在近海B区(122.5°-123.5°E)的表层海域;冬季VDC在1.99×106～2.66×107个·ml-1,高值分布在近岸A区(120.5°-122.5°E)海域,且由近岸向外海逐渐降低.夏季VDC与浮游细菌生物量、叶绿素含量关系密切,与营养盐相关性不显著(P＞0.05);冬季VDC与浮游细菌、营养盐含量关系密切,与叶绿素a含量相关性不显著(P＞0.05).夏季VDC显著高于冬季(P＜0.01),且两季的分布特征存在不同,此种差异主要与浮游细菌、浮游植物等病毒寄主的分布有关.冬季的营养盐含量也是影响其浮游病毒分布的重要因素.     

Surviving the Cold, Dry Period in Africa: Behavioral Adjustments as an Alternative to Heterothermy in the African Lesser Bushbaby (Galago moholi)

Behavioral and physiological adaptations are common and successful strategies used by small endothermic species to adjust to unfavorable seasons. Physiological adaptations, such as heterothermy, e.g., torpor, are usually thought to be more effective energy-saving strategies than behavioral adjustments. The African lesser bushbaby, Galago moholi, is physiologically capable of torpor but expresses heterothermy only under conditions of extreme energy limitation, suggesting that it has evolved alternative strategies to compensate energetic bottlenecks. We hypothesized that Galago moholi survives the unfavorable winter period, without —or only rarely— employing torpid phases to save energy, by using behavioral thermoregulation. We compared the ecology and behavior of Galago moholi in summer and winter by telemetric tracking and examined food availability by determination of arthropod and gum availability. We found a significant increase in huddling behavior and a significant increase in the use of enclosed and insulated sleeping sites during winter, as well as a reduction in nightly activity. Galago moholi hunted for insects significantly less in winter than in summer, and increased gum intake in winter, when gum showed an increase in energy content. The availability of high-quality food, albeit in low quantities, presumably enables Galago moholi to stay normothermic throughout the cold, dry period and to focus on reproduction activities. We propose that Galago moholi favors ecological and behavioral adjustments over torpor because these are sufficient to meet energy requirements of this species, and their advantages (flexibility, unrestricted activity, and reproduction) outweigh the energetic benefits of heterothermy.     

Seasonal differences in mineral content, distribution and leakage of sweet pepper seeds

Pepper seed quality is sensitive to variations in climatic conditions during seed development, which might be associated with accumulation, distribution and leakage of mineral elements from the seeds. This was examined in hybrid seeds of sweet pepper (Capsicum annuum L. cv.‘Hazera’ 1195) in two experiments during two growing seasons. The mean daily temperature (day/night) and daily total radiation receipt during seed development were 27.9/23.2°C and 8.63 kW m^?2 in the summer and 18.3/ 14.9°C and 3.18 kW m^?2 in the winter, respectively. Seeds developed in the summer had lower percentage of seedling emergence and leaked a larger portion (45%) of their K content into the water medium than in winter‐developed seeds. Summer seeds accumulated more K and Cl, but less P, Mg, Ca and the weight ratio of linoleic acid to oleic acid was lower than in the winter seeds. The season did not significantly affect N, S and total fatty acids. The most abundant element on the seed coat surface was K in the summer and Ca in the winter seeds. The cotyledon and endosperm of the summer seeds contained relatively higher ratios of K and Ca and lower ratios of P and Mg than the winter seeds. Transportation of mineral nutrients appeared to be involved in the effect of heat and moisture stresses on emergence quality of the pepper seeds.     

Effects of Intracisternally Injected Serotonin on Cerebral Blood Flow in Cats During Winter and Summer,and After Dark Exposure

This investigation reports on two experiments: (a) The examination of the effects of intracisternally injected serotonin on cerebral blood flow and systemic pressure in cats during winter (1/10–3/7) and summer (7/6–9/3) at a latitude of 39' 40, and (b) the effects of similarly injected serotonin on the same parameters in 11 cats after exposure to 3 days of continuous darkness during the summer months. Serotonin (5 mg) injected intracisternally produced significant decreases in cerebral blood flow and systemic pressure that lasted from 60 to 180 min after injection. Blood flow decreases, expressed as percentage change from baseline, seen during winter (n = 24) periods were significantly greater [analysis of variance (ANOVA), p < 0.02] from decreases seen during summer (n = 25) periods. Following serotonin injection, systemic pressure decreases between the winter and summer cats were not significantly different. Eleven summer cats were subjected to 3 days of continuous darkness before being injected with serotonin. Blood flow decreases in the dark-exposed cats were significantly (p < 0.05) greater than those seen in normal light-exposed cats, whereas systemic pressure changes were not different. These studies suggest that the seasonal photoperiod may affect the sensitivity of cerebral vessels to intracisternally injected serotonin in cats.     

Seasonal Dependent Effects of Flooding on Plant Species Survival and Zonation: a Comparative Study of 10 Terrestrial Grassland Species

Past research has provided compelling evidence that variation in flooding duration is the predominant factor underlying plant species distribution along elevation gradients in river floodplains. The role of seasonal variation in flooding, however, is far from clear. We addressed this seasonal effect for 10 grassland species by testing the hypothesis that all species can survive longer when flooded in winter than when flooded in summer. We carried out an inundation experiment under simulated conditions of summer and winter flooding in the greenhouse. The results showed that all species survived longer under winter floods than under summer floods. However, responses upon flooding were species-specific. All summer flood-tolerant species had high tolerance for winter floods as well, but summer flood sensitive species survived either a little longer, or dramatically longer when flooded under simulated winter conditions. Next, we examined whether winter or summer survival best predicted the lower distribution limits of the species as measured in a natural flooding gradient after an extremely long winter flood. We found a strong significant relationship between the lower distribution limits of species in the field and their tolerance to summer floods, although we measured the lower limits 14 years after the latest major summer flood. In contrast, no such significant relationship existed with species tolerance to winter floods. Some relatively intolerant species occurred at much higher floodplain elevations as was expected from their tolerance to winter inundation in the experiments. This suggests that zonation patterns as created by occasional summer floods may be maintained for a long time, probably due to the limited ability of species to re-colonise lower positions in the floodplain.     

Unraveling seasonality in population averages: an examination of seasonal variation in glucose levels in diabetes patients using a large population-based data set

It has been shown that the population average blood glucose level of diabetes patients shows seasonal variation, with higher levels in the winter than summer. However, seasonality in the population averages could be due to a tendency in the individual to seasonal variation, or alternatively due to occasional high winter readings (spiking), with different individuals showing this increase in different winters. A method was developed to rule out spiking as the dominant pattern underlying the seasonal variation in the population averages. Three years of data from three community-serving laboratories in Israel were retrieved. Diabetes patients (N?=?3243) with a blood glucose result every winter and summer over the study period were selected. For each individual, the following were calculated: seasonal average glucose for all winters and summers over the period of study (2006-2009), winter-summer difference for each adjacent winter-summer pair, and average of these five differences, an index of the degree of spikiness in the pattern of the six seasonal levels, and number of times out of five that each winter-summer difference was positive. Seasonal population averages were examined. The distribution of the individual's differences between adjacent seasons (winter minus summer) was examined and compared between subgroups. Seasonal population averages were reexamined in groups divided according to the index of the degree of spikiness in the individual's glucose pattern over the series of seasons. Seasonal population averages showed higher winter than summer levels. The overall median winter-summer difference on the individual level was 8?mg/dL (0.4?mmol/L). In 16.9% (95% confidence interval [CI]: 15.6-18.2%) of the population, all five winter-summer differences were positive versus 3.6% (95% CI: 3.0-4.2%) where all five winter-summer differences were negative. Seasonal variation in the population averages was not attenuated in the group having the lowest spikiness index; comparison of the distributions of the winter-summer differences in the high-, medium-, and low-spikiness groups showed no significant difference (p?=?.213). Therefore, seasonality in the population average blood glucose in diabetes patients is not just the result of occasional high measurements in different individuals in different winters, but presumably reflects a general periodic tendency in individuals for winter glucose levels to be higher than summer levels.     

Unraveling Seasonality in Population Averages: An Examination of Seasonal Variation in Glucose Levels in Diabetes Patients Using a Large Population-based Data Set

It has been shown that the population average blood glucose level of diabetes patients shows seasonal variation, with higher levels in the winter than summer. However, seasonality in the population averages could be due to a tendency in the individual to seasonal variation, or alternatively due to occasional high winter readings (spiking), with different individuals showing this increase in different winters. A method was developed to rule out spiking as the dominant pattern underlying the seasonal variation in the population averages. Three years of data from three community-serving laboratories in Israel were retrieved. Diabetes patients (N?=?3243) with a blood glucose result every winter and summer over the study period were selected. For each individual, the following were calculated: seasonal average glucose for all winters and summers over the period of study (2006–2009), winter-summer difference for each adjacent winter-summer pair, and average of these five differences, an index of the degree of spikiness in the pattern of the six seasonal levels, and number of times out of five that each winter-summer difference was positive. Seasonal population averages were examined. The distribution of the individual's differences between adjacent seasons (winter minus summer) was examined and compared between subgroups. Seasonal population averages were reexamined in groups divided according to the index of the degree of spikiness in the individual's glucose pattern over the series of seasons. Seasonal population averages showed higher winter than summer levels. The overall median winter-summer difference on the individual level was 8?mg/dL (0.4?mmol/L). In 16.9% (95% confidence interval [CI]: 15.6–18.2%) of the population, all five winter-summer differences were positive versus 3.6% (95% CI: 3.0–4.2%) where all five winter-summer differences were negative. Seasonal variation in the population averages was not attenuated in the group having the lowest spikiness index; comparison of the distributions of the winter-summer differences in the high-, medium-, and low-spikiness groups showed no significant difference (p?=?.213). Therefore, seasonality in the population average blood glucose in diabetes patients is not just the result of occasional high measurements in different individuals in different winters, but presumably reflects a general periodic tendency in individuals for winter glucose levels to be higher than summer levels. (Author correspondence: anneke@clalit.org.il)     

Distribution and dynamic of 137Cs in arboreal plants

Dynamics of 137Cs specific activity (SA) in woody plants was examined. It was found that interseasonal variations of SA are connected mainly with precipitations and related oxygen in soil as well as Eh level. The rate of daily variation in SA in an individual tree can reach 19%. Acropetal or basipetal 137Cs distribution in the bole depends on physiological condition category (PCC) of a tree, weather and environment; SA ratio of higher and lower PCC depends on the same factors. In winter compared to summer higher SA correlation of tree separate parts was observed. Trees with 137Cs acropetal distribution in bark had proven lower general CA level.     

Distribution Pattern of Photosynthetic Picoplankton and Heterotrophic Bacteria in the Northern South China Sea

The environmental regulation of plcoplankton distribution in the northern South China Sea was examined In winter and summer of 2004. The average abundance of Synechococcus, Prochlorococcus, and heterotrophlc bacteria was lower In winter （30, 21, and 780×10^3 cells/cm^3, respectively） than In summer （53, 85, and 1 090×10^3 cells/cm^3, respectively）, but the seasonal pattern was opposite for plcoeukaryotlc phytoplankton （4 500 and 3 200 cells/cm^3 In winter and summer, respectively）. Synechococcus, picoeukaryotes, and bacteria were most abundant in the nutrient-rich coastal zone and continental shelf, but Prochlorococcus was most abundant In the continental slope and open ocean. The vertical distribution of each photosynthetic group and heterotrophlc bacteria changed between the two seasons. Synechococcus populations with apparently different phycoerythrobilin content occurred at many stations In the summer. In addition, two different populations of Prochlorococcus were found： （i） small, weakly fluorescing cells in the surface layer; and （ii） larger, strongly fluorescent cells In the deep layer. The distribution pattern of photosynthetic plcoplankton and heterotrophlc bacteria depends on environmental effects and their ecophyslologlcal differences. The distribution of Synechococcus appeared to be related to nutrient availability, whereas the distribution of Prochlorococcus appeared to be limited by temperature. Synechococcus was the only plcophytoplankton with a consistent strong relationship with bacteria.     

Winter fish community structures across floodplain backwaters in a drought year

We examined fish community structures in floodplain backwaters in the Kiso River, Central Japan, in an uncommon drought year. Nine floodplain backwaters with varying levels of flood inundation frequency were surveyed for winter fish communities, and measured for local environmental variables in summer and winter periods. The winter fish community was better represented, with less diverse and physiologically tolerant species in backwaters with a decreasing flood pulse frequency. The temporal frequency of hypoxic conditions (dissolved oxygen of <2 mg l^?1) and chlorophyll a in summer explained the heterogeneity of the fish community along the gradient of inundation frequency, while no variables measured in winter had an explanatory power. These results suggest that drought-induced, infrequent flood pulses in the autumn–winter period limited the dispersal opportunity of fishes, and thus maintained community structures selected by summer limiting factors until the survey took place in winter. Future comparisons of our data with those in non-drought years would provide important implications to the sustainable management of floodplains for wintering fishes against the increasing probability of future flow regime changes.     

Nitrogen excretion and changes in blood components during emersion of the subtidal spider crab Maia squinado (L.)

Survival ability of Maia squinado to emersion and subsequent reimmersion was determined in winter and summer conditions. Male spider crabs were less tolerant of emersion than females. Emersion (up to 24 h in summer and to 48 h in winter) induced a marked reduction of nitrogen excretion, especially ammonia excretion. Increase in blood ammonia content was rapid and very high in summer (1750 micromol l(-1)), but non-lethal levels. Estimation of the body ammonia overload showed that only 30% of unexcreted ammonia accumulated in blood. The ammonia release at reimmersion indicated that ammonia also accumulated in other body compartments. Increase in blood urate content, which indirectly reduces ammonia production, was similar at both seasons. Emersed M. squinado was rapidly resorting to anaerobic metabolism, especially in summer when its blood haemocyanin content is low. A strong hyperglycemia was developed in the first 12 h of emersion at both seasons. Mortality occurring beyond 24 h of reimmersion, when the body ammonia overload is cancelled and the recovery of most of blood components is achieved, remains unexplained.     

Myoglobin content in skeletal muscles of hibernating ground squirrels rises in autumn and winter

The content of myoglobin (Mb) in skeletal muscles of Arctic Yakutian ground squirrel (Citellus undulatus Pallas) was measured in the active euthermic summer and prehibernating autumn animals as well as in hibernating and awake animals in winter. The myoglobin content in winter, irrespective of the state of the animal, was found to be about three times higher than in summer. The content of myoglobin in autumn was also two-fold increased compared to summer, suggesting that high myoglobin level is necessary for hibernation. Analysis of biochemical data available suggests that the increase in myoglobin content in winter is probably related to a high oxygen demand of muscles at the first stage of arousal (non-shivering thermogenesis) when rectal temperature rises from 0 to 10-12 degrees C. At this stage, the oxygen-dependent processes in muscles proceed under the conditions when peripheral blood flow is blocked and anaerobic glycolysis is switched off.     

Choice of feeding station in Atlantic salmon, Salmo salar, parr: effects of predation risk, season and life history strategy

The current speed at which underyearling salmon parr held feeding stations was examined from late summer to early winter in laboratory flume tanks that offered a choice between (a) areas with high water flow, high food availability but high predation risk and (b) areas with low flow, little food but shelter from predators. In August, those fish that would become smolts aged 1 + (and which by late winter formed the upper modal group, UMG, of the bimodal size distribution) adopted positions in faster currents than did the fish which would take a further year to reach the smolt stage (the lower modal group, LMG). However, the chosen current speed of UMG fish decreased through the period of study, so that by December all fish were found in areas of low flow, and hence little food. Both date and water temperature had independent effects on the chosen current speed of UMG fish.
The effect of predation risk was investigated using a model trout. A brief sight of this predator caused 47% of fish that had been in the main, exposed currents to move to slacker, sheltered areas; they took 1 h, on average, to return to their previous position. The fish that remained in position upon seeing the predator reduced their rate of tail beating, presumably increasing crypticity. Eventual UMG parr were less likely than were LMG fish to move away upon seeing a predator. The fish moved to faster currents than normal 2–3 h after seeing the predator, possibly compensating for the earlier reduction in feeding rate.     

Thermoregulatory anatomy of pronghorn (Antilocapra americana)

We have found that pronghorn (Antilocapra americana) use external heat exchange with the environment and internal heat exchange between the carotid artery rete and cavernous venous sinus blood to regulate body temperature. Now we have investigated the relationship between the histological structure of the skin, cephalic veins, and carotid rete–cavernous sinus system and the physiological mechanisms pronghorn use, and whether their thermoregulatory anatomy has adaptive advantages. We harvested tissue samples of skin, three veins (i.e., angularis oculi vein, dorsal nasal vein, and facial vein), and the carotid rete–cavernous sinus system from four pronghorn, two culled in summer and two in winter, and examined each histologically. The three veins had the typical structure of veins with large lumina and thin walls. The carotid rete consisted of small (0.1–0.5 mm) arterioles with a density of ~10/mm², intertwined with veins (~2/mm²), enclosed within the cavernous sinus; a structure ideal for heat exchange. We concluded that the main function of the dorsal nasal and facial veins is to return cold blood to the body to effect whole body cooling. The cavernous sinus is supplied with warm blood by the palatine veins in winter and cold blood by the deep facial veins in summer, an arrangement different to that in other ungulates, such as sheep, in which the angularis oculi vein supplies the cavernous sinus. Pronghorn skin is richly supplied with blood vessels that facilitate convective heat loss in summer. In winter, the number of coarse and fine hairs per square millimeter increases more than in European deer to form a thick pelage that minimizes heat loss. In summer, the pelage is shed because hair follicles involute. Unlike in other ungulates, pronghorn skin has little adipose tissue. The number of apocrine glands increases in winter rather than in summer. We concluded that the glands have a reproductive/social function rather than a thermoregulatory one. In summary, our study shows that the thermoregulatory anatomy is consistent with our physiological data and has adaptive advantages that help explain the survival of pronghorn in an arid habitat characterized by extreme temperature variation and sparse vegetation.     

Photosynthetic Acclimation of Erythrophleum guineense and Dalbergia odorifera to Winter Low Temperature in a Marginal Tropical Area

In marginal tropical areas, air temperature in winter usually decreases by 10℃ compared with summer at night/day. Although tropical plants are sensitive to low temperature, the mechanism underlying photosynthetic acclimation of tropical trees to winter low temperature is unclear. To address this question, the photosystem I (PSI) and photosystem II (PSII) activities, and energy distribution in PSI and PSII were examined in summer and winter in two tropical high quality timber tree species Erythrophleum guineense and Dalbergia odorifera grown in a marginal tropical area (21°54′N, 101°46′E). Our results indicated that the photosynthetic apparatus of Eguineense and Dodorifera was maintained stable in winter. The effective quantum yield of PSII decreased significantly in winter, but non photochemical quenching (NPQ) significantly increased. In winter, cyclic electron flow (CEF) was significantly stimulated in both species, which was significantly and positively correlated with NPQ. Meanwhile, the stimulation of CEF led to an increase in P700 oxidation ratio and the over reduction of PSI acceptor side was prevented. Antimycin A (a specific inhibitor of PGR5 dependent CEF) significantly aggravated PSII photoinhibition under high light in both species. These results suggested that stimulation of CEF is an important mechanism for photosynthetic acclimation to winter low temperature in a marginal tropical area in the two tropical tree species.     

Diving through the thermal window: implications for a warming world

Population decline and a shift in the geographical distribution of some ectothermic animals have been attributed to climatic warming. Here, we show that rises in water temperature of a few degrees, while within the thermal window for locomotor performance, may be detrimental to diving behaviour in air-breathing ectotherms (turtles, crocodilians, marine iguanas, amphibians, snakes and lizards). Submergence times and internal and external body temperature were remotely recorded from freshwater crocodiles (Crocodylus johnstoni) while they free-ranged throughout their natural habitat in summer and winter. During summer, the crocodiles'' mean body temperature was 5.2 ± 0.1°C higher than in winter and the largest proportion of total dive time was composed of dive durations approximately 15 min less than in winter. Diving beyond 40 min during summer required the crocodiles to exponentially increase the time they spent on the surface after the dive, presumably to clear anaerobic debt. The relationship was not as significant in winter, even though a greater proportion of dives were of a longer duration, suggesting that diving lactate threshold (DLT) was reduced in summer compared with winter. Additional evidence for a reduced DLT in summer was derived from the stronger influence body mass exerted upon dive duration, compared to winter. The results demonstrate that the higher summer body temperature increased oxygen demand during the dive, implying that thermal acclimatization of the diving metabolic rate was inadequate. If the study findings are common among air-breathing diving ectotherms, then long-term warming of the aquatic environment may be detrimental to behavioural function and survivorship.     

Tracheobronchial and upper airway blood flow in dogs during thermally induced panting

Tracheobronchial blood flow increases two- to fivefold in response to isocapnic hyperventilation with warm dry or cold dry air in anesthetized, tracheostomized dogs. To determine whether this response is governed by central nervous system thermoregulatory control or is a local response to the drying and/or cooling of the airway mucosa, we studied eight anesthetized spontaneously breathing dogs in a thermally controlled chamber designed so that inspired air temperature, humidity, and body temperature could be separately regulated. Four dogs breathed through the nose and mouth (group 1), and four breathed through a short tracheostomy tube (group 2). Dogs were studied under the following conditions: 1) a normothermic control period and 2) two periods of hyperthermia in which the dogs panted with either warm 100% humidified air or warm dry (approximately 10% humidified) air. Radiolabeled microspheres (15 +/- 3 micron diam) were injected into the left ventricle as a marker of nasal, lingual, and tracheobronchial blood flow. After the final measurements, the dogs were killed and tissues of interest excised. Results showed that lingual and nasal blood flow (ml.min-1.g-1) increased during panting (P less than 0.01) in both groups and were not affected by the inspired air conditions. In group 1, tracheal mucosal blood flow barely doubled (P less than 0.01) and bronchial blood flow did not change during humid and dry air panting. In group 2, there was a sevenfold increase in tracheal mucosal and about a threefold increase in bronchial blood flow (P less than 0.01), which was only observed during dry air panting.(ABSTRACT TRUNCATED AT 250 WORDS)