Regulation of submaxillary gland muscarinic receptors during heat acclimation

Binding properties of submaxillary gland muscarinic receptors and agonist-induced saliva secretion were studied in rats subjected to heat acclimation. The maximal binding capacity for the muscarinic antagonist N-[3H]methyl-4-piperidyl benzilate was increased from control value of 0.21 to 0.40 pmol/mg protein within 1-2 days of heat acclimation. The increase in the number of muscarinic receptors per gland (100%) was by far higher than the increase in tissue weight (20%), indicating higher density of receptors in the acinar cells of the treated rats. High levels of receptors coincided with the appearance of high-affinity binding sites for muscarinic agonists (oxotremorine, pilocarpine and carbamylcholine), and with reduced tissue sensitivity to pilocarpine. After 4-8 weeks of heat acclimation, the number of receptors as well as tissue response to pilocarpine returned to control levels. These results suggest a functional correlation between the transient upregulation muscarinic receptors in the submaxillary gland and the physiological activity in salivary secretion, and indicate that the high-affinity muscarinic receptors may attenuate saliva secretion during the initial phase of heat acclimation.     

Long-term heat adaptation results in an enhanced efficiency of muscarinically-induced water secretion in rat submaxillary glands

1. Carbamylcholine-induced 86Rb+ and 36Cl- efflux, as markers of calcium mobilization and water secretion, respectively, were studied during 30 days of heat acclimation (at 34 degrees C) in rat submaxillary gland slices using perifusion techniques. 2. The fractional rate of 36Cl- efflux was markedly elevated with acclimation, reaching its maximal level on day 30, while that of 86Rb+, after an initial rise, returned to non-acclimated control levels. The total carbamylcholine-induced efflux of both ions markedly increased throughout the 30 days' acclimation. 3. The rapid increase in ion fluxes was accompanied by a transient increase in Na+ concentrations in the gland and a decrease in the saliva. 4. The data suggest that the acclimation-induced increase in secretory capacity is bi-phasic: initially, a rapid transient rise in ion fluxes accompanies a transient rise in muscarinic receptor density (Kloog et al., 1985). 5. Long term acclimation is characterized by increased efficiency of the cellular secretory mechanism(s), as demonstrated by the chronically increased efflux of ions.     

A comparison of the effects of vasoactive intestinal polypeptide on secretion from the submaxillary gland of the sheep and pig

The effects, on secretion of fluid and protein from the submaxillary gland of intracarotid injections of acetylcholine or vasoactive intestinal polypeptide (VIP), and intracarotid infusions of VIP during a background of muscarinic stimulation, were examined in sheep and pigs. Intracarotid injections of VIP produced secretion of saliva from the ovine gland which continued after administration of atropine, phentolamine and propranolol. The protein concentration of this saliva was over 5-fold greater than that secreted in response to acetylcholine. Intracarotid injection of VIP did not evoke secretion from the porcine submaxillary gland but increased 3-fold the protein concentration in saliva evoked by subsequent intracarotid injection of acetylcholine. Intracarotid infusions of VIP in sheep produced dose-related increases in both flow (up to 1.9-fold) and protein concentration (up to 42-fold) of submaxillary saliva secreted in response to a background infusion of bethanechol. In pigs, intracarotid infusions of VIP at 0.015, 0.15 and 1.5 nmol/min produced increases in both flow and protein concentration of bethanechol-evoked saliva. The increases in protein concentration (up to 2.8-fold) were dose-related, but the increases in flow were not, being ca. 25% with each dose of VIP. The experiments provide evidence that VIP may effect mobilization of protein into saliva even in a species (pig) in which VIP does not evoke secretion of fluid.     

Body surface temperatures of jerboas (Allactaga) in uniform thermal environments

Summary Body surface temperatures of threeAllactaga elater and oneA. hotsoni were measured by infrared radiography at ambient temperatures of 1° to 42°C. In each test the radiant temperature of environmental surfaces was the same as air temperature.At ambient temperatures of 40–42°C, the temperature of the entire body surface was close to ambient temperature. As ambient temperature was lowered toward 1°C, forehead and back temperatures became increasingly greater than ambient temperature (Fig. 3), indicating an increasing thermal flux across these parts of the body. Forehead and back temperatures were linear functions of ambient temperature below thermoneutrality and behaved as expected according to a model of thermal exchange developed here. The surface temperature of the extraordinarily large pinnae remained close to ambient temperature down to 10°C (Fig. 3), indicating that deep pinna temperature likely falls with decreasing ambient temperature and that the pinnae, despite their size, are not major sites of heat loss at low ambient temperatures.     

Immunocytochemical identification of enkephalinergic neurons in the hypothalamic magnocellular preoptic nucleus of the goldfish,Carassius auratus

Summary Secretory granule area and glycoprotein concentration of the saliva in the submaxillary gland of rats were measured during various stages of acclimation to heat at 34±1° C. Granule size decreased by 18% during the first five days of heat acclimation (0.025<p<0.05) after which period it increased to reach 118% of the control levels after 28 days (p<0.05). Glycoprotein concentration in the saliva of stimulated glands rose above control levels, reaching a maximum between the 2nd and 5th day of acclimation (p<0.05). It was concluded that the initial decrease in granule size reflects a decrease in glycoprotein content following an increase in salivary flow known to occur at high ambient temperatures. The subsequent increase in granule size is considered an adaptation of the gland to continuous stimulation. The rise in salivary glycoprotein concentration suggests increased efficiency of the secretory mechanism.Supported by the joint research fund of the Hebrew University-Hadassah School of Dental Medicine founded by the Alfa Omega Fraternity and the Hadassah Medical Organization     

Regulation mode of evaporative cooling underlying a strategy of the heat-tolerant FOK rat for enduring ambient heat

Compared with other rat strains, the inbred FOK rat is extremely heat tolerant. This increased heat tolerance is due largely to the animal's enhanced saliva spreading abilities. The aims of the present study were to 1) quantify the heat tolerance capacity of FOK rats and 2) determine the regulatory mode of the enhanced salivary cooling in these animals. Various strains of rats were acutely exposed to heat. In the heat-intolerant strains, saliva spreading was insufficient and the core temperature (Tc) rose rapidly. In contrast, FOK rats maintained an elevated Tc plateau (39.5 +/- 0.7 degrees C) for 5-6 h over a wide range of ambient temperatures (Ta) (37.5-42.5 degrees C). In hot environments the FOK rats secreted copious amounts of saliva and spread it over more than the entire ventral body surface. FOK rats had a low Tc threshold for salivation, and the salivation rate increased linearly in proportion to the Tc deviation from the threshold. No strain difference or temperature effect was observed in the saliva secretion rate from in vitro submandibular glands perfused by sufficient doses of ACh. These results suggest that 1) the ability of FOK rats to maintain a moderate steady-state hyperthermia (39.5 +/- 0.7 degrees C) over a wide Ta range is enabled by a lowered threshold Tc for salivation and functional negative-feedback control of saliva secretion and 2) strain differences in ability to endure heat stress are mainly attributable to changes in the thermoregulatory control system rather than altered secretory abilities of the salivary glands.     

Regulation of heat shock-induced alterations in the release of prostaglandins by the uterine endometrium of cows

Maternal heat stress in cattle may disrupt pregnancy by elevating uterine prostaglandin F(2alpha) (PGF(2alpha)) secretion. The objectives of this study were to determine the effects of elevated temperature (42 degrees C) in vitro upon 1) prostaglandin secretion by endometrial tissue; 2) the actions of extracellular regulators of uterine PGF [conceptus secretory proteins (bCSPs) and platelet-activating factor, (PAF)]; 3) the activity of the cyclooxygenase-endoperoxidase enzyme complex (PG synthetase); and 4) the activity of the endometrial PG synthesis inhibitor present in the endometrium from pregnant cattle. Endometrial explants at Day 17 of the estrous cycle produced more PGF than PGE(2) while elevated temperature caused increased PGF secretion but did not affect PGE(2) secretion. Elevated temperature did not reduce the ability of bCSPs or PAF to suppress release of PGF. The heat shock-induced increase in PGF at Day 17 was not due to the direct effects on PG synthetase, because PGF production from a cell-free cotyledonary microsomal enzyme preparation was reduced at elevated temperature. The activity of the cytosolic inhibitor of cyclooxygenase present in the endometrium of Day-17 pregnant cows could be reduced but not eliminated at 42 degrees C. We conclude that in vitro heat stress induces PGF secretion from the bovine uterine endometrium at Day 17 after estrus. This increase is not accompanied by the loss of regulatory capacity of conceptus products or increased activity of PG synthetase.     

Effect of cold air inhalation on core temperature in exercising subjects under heat stress

Whether increasing respiratory heat loss (RHL) during exercise under heat stress can contain elevation of rectal temperature (Tre) was examined. Eight men cycled twice at 45-50% their maximum work rate until exhaustion at ambient temperature and relative humidity of 38 degrees C and 90-95%, respectively. They inspired either cold (3.6 degrees C) or ambient air in random sequence. When subjects breathed cold air during 23 min of exercise, a ninefold increase in RHL was observed vs. similar work during hot air inhalation (32.81 vs. 3.46 W). Respiratory frequency (f) and rate of rise in Tre decreased significantly (P less than or equal to 0.004 and P less than or equal to 0.002, respectively). The rise in skin temperature in each inhalant gas condition was accompanied by a parallel almost equal increase in core temperature above basal (delta Tre) for equivalent gains in skin temperature. The increase in tidal volume and decreased f in the cold condition allowed more effective physical conditioning of cold inspirate gas in the upper airways and aided RHL. Cold air inhalation also produced a significant (P less than or equal to 0.05) decrease in heart rate vs. hot air inhalation in the final stages of exercise. Insignificant changes in O2 consumption and total body fluid loss were found. These data show that cold air inhalation during exercise diminishes elevation of Tre and suggest that both the intensity and duration of work can thus be extended. The importance of the physical exchange of heat energy and any physiological mechanisms induced by the cold inspirate in producing the changes is undetermined.     

Arginine vasopressin does not mediate heat loss in the tail of the rat

It has been reported that hypothermia induced by arginine vasopressin (AVP) is brought about by a coordinated response of reduced thermogenesis in brown adipose tissue (BAT) and increased heat loss through the tail of rats. However, it is well known that AVP is one of the strongest peripheral vasoconstrictors. Whether the AVP-induced hypothermia is associated with an increase in heat loss through the tail is questionable. Therefore, the present study assessed the relationship between the effects of AVP on tail skin temperature and the induced hypothermic response, and to determine if peripheral AVP administration increases heat loss from the tail. Core, BAT and tail skin temperature were monitored by telemetry in male Sprague–Dawley rats before and after intraperitoneal administration of AVP or vasopressin receptor antagonist. We also analyzed simultaneously of the time-course of AVP-induced hypothermic response and its relationship with changes in BAT temperature, and effect of AVP on grooming behavior. The key observations in this study were: (1) rats dosed with AVP induced a decrease in heat production (i.e., a reduction of BAT thermogenesis) and an increase of saliva spreading for evaporative heat loss (i.e., grooming behavior); (2) AVP caused a marked decrease in tail skin temperature and this effect was prevented by the peripheral administration of the vasopressin V1a receptor antagonist, suggesting that exogenous AVP does not increase heat loss in the tail of rats; (3) the vasopressin V1a receptor antagonist could elevate core temperature without affecting tail skin temperature, suggesting that endogenous AVP is involved in suppression of thermogenesis, but not mediates heat loss in the tail of rats. Overall, the present study does not support the conclusion of previous reports that AVP increased tail heat loss in rats, because AVP-induced hypothermia in the rat is accompanied by a decrease in tail skin temperature. The data indicate that exogenous AVP-induced hypothermia attributed to the suppression of thermoregulatory heat production and the increase of saliva spreading for evaporative heat loss.     

Comparison of the effector mechanisms during endotoxin fever in the adult rabbit.

In unanaesthetized adult rabbits an intravenous dose of E. coli endotoxin evoked a febrile rise in colonic temperature at ambient temperatures of 9 to 31 degrees C. The rise in colonic temperature and oxygen consumption did not depend on the ambient temperature, while, among the heat loss effectors, in warmer environments only the depression of respiratory heat loss and in cooler environments only ear skin vasoconstriction contributed to the febrile rise in colonic temperature. In moderately warm environments the endotoxin first induced a maximum inhibition of respiratory frequency and this was followed by vasoconstriction. Later, a transient rise in oxygen consumption occurred. During defervescence the timing of the effectors was reversed. The results showed that a febrile response is not necessarily characterized by simultaneous changes in the thermoregulatory effector mechanisms.     

Thermal salivation in rats anesthetized with barbiturates,chloralose, urethane and ketamine

1. The relationship between thermal salivation (TS) and thermoregulation was studied in anesthetized rats.2. Of the 6 anesthetics used, ketamine-anesthetized rats secreted the largest amount of saliva. Salivation, however, was thermal and not induced by ketamine itself.3. Ketamine-anesthetized rats readily secreted saliva at core temperatures less than 40°C but TS was remarkably enhanced by hyperthermia of 40–42.5°C.4. The equilibrium phase in the triphasic heat response of core temperature was a consequence of equilibrium between heat gain and heat loss by salivation.     

The origin of immunoglobulins in salivary secretion of sheep.

A comparative study was made on the secretion of IgG1 and IgA into parotid and submaxillary saliva of sheep. The purpose of the study was to examine the suggestion that in the external secretory organs of ruminants there is an inverse relationship between the capacity to selectively transfer IgG1 and the development of the IgA secretory system. Despite a marked difference in the secretion of IgA between the parotid and submaxillary salivary glands, the magnitude of selective transfer of IgG1 was similar. Thus, there appears to be no relationship between the selective transfer of IgG1 and the secretion of IgA into the saliva of sheep.     

Effect in vivo of beta-adrenergic stimulation, angiotensin II, dibutyryl cyclic AMP, and theophylline on tonin concentration in rat saliva and submaxillary gland.

Tonin (an enzyme present in rat submaxillary gland and saliva) has previously been shown to be able, unlike renin and reninlike substances, to release angiotensin II either directly by acting on an appropriate substrate or from angiotensin I. The administration of a beta-adrenergic drug, isoproterenol, produces a rise of tonin concentration in saliva without affecting its concentration in the submaxillary gland. Prior administration of a beta blocker, propranolol, partially prevents this effect. The administration of theophylline increases the tonin concentration in both saliva and the submaxillary gland, whereas dibutyryl cyclic AMP increases tonin concentration in the former. These results suggest that beta-adrenergic stimulation enhances both tonin release into the saliva and tonin synthesis in the submaxillary gland, and that these effects might be mediated by cyclic AMP. Infusion of angiotensin II blocked the stimulatory effect of isoproterenol on salivary tonin. 1Sar-8Ile-angiotensin II is both a weak antagonist of angiotensin II in this respect and a strong agonist in terms of blocking the effect of isoproterenol another role mirrored in other physiological mechanisms of derivatives of angiotensin II.     

Temperature regulation in adult quail (Colinus virginianus) during acute thermal stress

1. Evaporative heat loss, O2 consumption, CO2 production, and internal body temperature were measured in unanesthetized, unrestrained bobwhite (Colinus virginianus) at specific ambient temperatures (Ta). 2. No significant change in body temperature occurred at any Ta tested, but metabolic heat production (H) increased from 42.17 W/m2 at Ta 35 degrees C to 102.89 W/m2 at Ta 10 degrees C. 3. Evaporative heat loss (E) increased approximately two-fold from Ta 10-35 degrees C, with E/H increasing exponentially over the same temperature range. 4. No significant change in thermal insulation occurred from Ta 10-30 degrees C. 5. Combined convective and radiative heat transfer for the bobwhite was 2.96 W/m2 X C from Ta 10-35 degrees C.     

甜椒细胞质小分子量热激蛋白基因(CaHSP18)的cDNA克隆与表达

用RT-PCR和RACE-PCR技术,从热激处理的甜椒叶片总RNA中扩增出了细胞质小分子量热激蛋白(sHSP)全长779 bp的cDNA基因序列,包含一个480 bp开放阅读框,编码159个氨基酸.Southern杂交结果表明在甜椒基因组中有该基因的小的多基因家族.Northern结果显示该基因在甜椒根、茎、叶中的表达受热激和低温的诱导.原核表达分析表明该基因在高温以及低温条件下可以提高大肠杆菌的生存能力.     

Thoracic temperature,shivering, and flight in the monarch butterfly,Danaus plexippus (L.)

Summary Monarch butterflies, Danaus plexippus (L.), display a warm-up behavior characterized by wingstrokes of small amplitude. Thoracic temperature during this shivering and during fixed flight was measured by means of a smallbead thermistor inserted into the thorax. At ambient temperatures of 15–16°C, once shivering is initiated the thoracic temperature rises at a maximum rate of 1.3°C/min, and a thoracic temperature 4.0°C greater then ambient is produced (Table 1). Fixed flight at these low ambient temperatures results in a similar rate of increase in thoracic temperature, and a similar temperature excess is produced (Fig. 3). At ambient temperatures between 22 and 35°C the thoracic temperature of an animal starting to fly rises at a faster rate, 3.6°C/min, and reaches a greater excess, 7.9°C (Fig. 4). The wingbeat frequency of animals in fixed flight increases with increasing thoracic temperature (Fig. 2). In the absence of direct solar radiation, shivering typically occurs prior to flight at low ambient temperatures (13–17°C), and the resulting increase in thoracic temperature allows monarch butterflies to fly at these cool temperatures.I thank Miss Janice Ruppert and Mr. C. J. Doughty for their valuable technical assistance. The co-operation of the administrators of New Brighton Beach State Park in permitting me to collect in the park is appreciated. Financial support for this study was provided in part by a faculty research grant from the University of California.     

Functional acclimation of Japanese quail to simulated high-altitude

Summary Japanese quail,Coturnix coturnix japonica, which were acclimated to a simulated altitude of 6100 m for six weeks were compared with control quail maintained at sea level. Body weight initially decreased in both groups, and by the end of six weeks the altitude quail weighed an average of 8% less than the control quail (Fig. 1). Compared with the controls, the altitude birds exhibited mean increases in hematocrit ratio and blood hemoglobin concentration of 31 and 37% respectively (Fig. 2). Blood volume was 36% higher in the altitude acclimated quail, while plasma volume was unchanged (Fig. 3). Exposure to chronic hypoxia resulted in hypertrophy of the right ventricle, while left ventricular mass was unchanged (Fig. 4). Rates of O₂ consumption (VO₂) at 5°C were continuously recorded as ambient PO₂ was slowly reduced from 155 to 30 torr. VO₂ was significantly higher at any given PO₂ in the altitude quail (Fig. 5). Exposure to reduced PO₂ resulted in a significantly greater decrease in body temperature in the control quail than in the altitude acclimated birds (Fig. 6).     

Thermoregulation during pentobarbital and ketamine anesthesia in rats

1.) Core temperature, tail temperature, metabolic heat production, and evaporative heat loss were measured in rats exposed to various ambient temperature conditions. 2.) Control rats increased heat production in the cold and heat loss in a warm environment, thus maintaining a relatively constant core temperature. 3.) Pentobarbital anesthesia reduced the thermoregulatory responses and caused core temperature to vary considerably with ambient temperature. Ketamine anesthesia resulted in minor thermoregulatory deficits. 4.) It is concluded that ketamine can be used in thermal physiological studies that require an anesthetised preparation, although it is not completely devoid of inhibitory effects on thermoregulatory responses.     

Exercise in the heat: Effects of dinitrophenol administration

1. 1.|Dinitrophenol (DNP) was administered to rats in two equal dosages (20 mg/kg, 30 min interval); the second injection was followed immediately by exercise (9.14 m/min) in the heat (30°C) or at room temperature (21°C).

2. 2.|At 21°C control (saline-treated) rats manifested a mean endurance of 94 min which was reduced to 32 min among DNP-treated animals.

3. 3.|At 30°C, control rats ran for 65 min (δT_re/min = 0.05°C) while DNP-treated animals had a mean endurance of only 12 min (δT_re/min = 0.22°C).

4. 4.|DNP-treated rats (30°C) manifested no decrements in tail-skin heat loss (δT_sk/min = 0.17°C vs 0.10°C) or saliva secretion (0.78 g/min, DNP vs. 0.19 g/min, control) for their brief treadmill duration.

5. 5.|The increased metabolic heat production of DNP severely reduced performance.

Central alpha-MSH,energy balance,thermal balance,and antipyresis

Intracerebroventricular administration of alpha-MSH in young adult rats enhanced metabolic rate and caused a dose-dependent suppression of food intake, exhibiting a coordinated catabolic pattern. However, the thermoregulatory effects did not seem to be coordinated: the rising heat production was accompanied by a practically simultaneous tendency for rise in heat loss (skin vasodilatation), and the final core temperature either increased or decreased depending on which rise prevailed. The effect on heat loss possibly explains the antipyretic properties of the peptide.