Amylase activity, glycoprotein and electrolyte concentration in rat's submaxillary salivary gland during heat acclimation.

1. Amylase activity, glycoproteins, Na and K concentrations were measured in submaxillary salivary gland of the rat during heat acclimation (34 degrees C). 2. Acclimation resulted in a decrease in glycoprotein concentration and amylase activity, whereas Na and K concentrations and the Na/K ratio increased. 3. It is suggested that heat acclimation results in an increase in glandular activity leading to increased water secretion and depletion of the glycoprotein store. The decrease in amylase activity is probably due to liver atrophy which occurs during prolonged heat exposure.     

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.     

Altered responsiveness to parasympathetic activation of submaxillary salivary gland in the heat-acclimated rat

Submaxillary salivary gland responsiveness during the heat acclimation procedure (34 +/- 1 degree C) was studied in the rat. Gland responsiveness was evaluated by measuring saliva flow rate of the anesthetized animals following either parasympathetic nerve stimulation or i.v. application of pilocarpine. A thirty percent decrease in glandular responsiveness for the two modes of stimulation was measured during the first 10 days of acclimation. Following 60 days of acclimation recovery was observed. It is concluded that decreased responsiveness of the heat-acclimated gland is a glandular event. Increased saliva flow occurring at the initial phase of acclimation is apparently due to changes in the thermoregulatory center.     

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.     

Screening of biochemical parameters in the orthodontic treatment with the fixed appliances: A follow-up study

The aim of this study was to assess the changes in vital salivary parameters such as calcium, phosphorous, alkaline phosphatase, buffering capacity, pH, flow-rate and Oral Hygiene Index (OHI) in fixed orthodontic treatment patients during the retention period. In this study, saliva samples were collected from 35 patients before de-bonding (T₀) and after 4 to 5 weeks of de-bonding or on retention period (T₁). The biochemical parameters such as calcium, phosphorous and alkaline phosphatase levels were measured with saliva samples. Additionally, flow-rate, buffering capacity, pH and OHI levels was also measured. The current study results showed reduction in calcium, alkaline phosphatase, pH, flow-rate and OHI levels during T₁ (p < 0.05). However, phosphorous and buffering capacity levels were increased at T₁. The phosphorous levels showed non statistically significant difference when compared between T₀ and T₁ (p = 0.42). The remaining salivary parameters showed statistically significant difference when compared between T₀ and T₁ (p < 0.05). The present study concludes that there was a statistically significant decrease in the calcium, alkaline phosphatase, pH, flow rate and OHI values a month after de-bonding and increased in the buffering capacity values.     

Heat acclimation in rats: modulation via lipid polyunsaturation

Heat acclimation of rats has been shown to enhance endurance of rat hearts to ischemic insult and acute heat stress. Common protective features have been shown to be operative during both these stress-inducing conditions. To explore the role of membrane lipid composition in the adaptive response, we analyzed two major parameters that impact membrane dynamics and order, the nonesterified cholesterol levels and the acyl chain composition of phospholipids, in rat heart and salivary glands, both major thermoregulatory organs, in short- and long-term heat-acclimated rats. Before exposure to heat, control salivary gland tissue has a higher cholesterol-to-phospholipid mole ratio (0.32 +/- 0.02) than heart (0.14 +/- 0.01), and the acyl chains of its phospholipids are 50% more saturated. The remodeling strategies of the tissues after exposure to heat differed. Heart cholesterol levels increased after short-term heat acclimation (approximately 50%), whereas salivary gland cholesterol levels decreased in acute heat stress and long-term heat acclimation (approximately 32%). Remodeling of phospholipid acyl chains, particularly an increase in docosahexaenoic acid, was a protective strategy in both tissues (57% in heart and >100% in salivary glands). Modifying membrane lipid composition by treating rats with liposomes composed of egg phosphatidylcholine (PC) before exposure to heat resulted in a 38% increase in endurance to thermal stress. The density and affinity of muscarinic receptors of submaxillary salivary glands, involved in the acclimation response, were measured in control and PC liposome-treated rats, and then both groups were subjected to short-term heat acclimation. After PC treatment the well-established compensatory upregulation of the muscarinic receptors and concomitant decrease in their affinity was blunted. The substantial increase in the thermal endurance of heat-challenged intact rats after treatment with PC liposomes (600 vs. 200 min) suggests that membrane lipid composition plays a role in the ability of these tissues to respond to heat stress.     

Interrelationships between heat acclimation and salivary cooling mechanism in conscious rats

1. Adaptation of salivary cooling mechanism during acclimation to heat (34 degrees C) and its role in thermoregulation of the rats was studied on conscious rats with either one submaxillary gland chronically cannulated or both submaxillaries ligated. 2. During heat stress (40 degrees C) acclimated rats showed a decrease both in rectal temperature threshold for salivation (Tre-TS), in salivary flow rate and in Tre (hyperthermic plateau). Animals survived for extended periods and rats with ligated glands survived 40% less than non-ligated rats. 3. For both cannulated and ligated rats short term acclimation (5 days) was the most effective. 4. It is suggested that earlier activation of salivation mechanism is associated with the decreased hyperthermic plateau and that the decreased salivary flow rate allows better control of water balance of the animals. Consequently, survival period during heat stress is extended.     

Plasma aldosterone and sweat sodium concentrations after exercise and heat acclimation

This investigation was designed to determine the relationship between the levels of plasma aldosterone and eccrine sweat gland sodium excretion following exercise and heat acclimation. Ten subjects exercised at 45% of their maximal O2 uptake in a hot (40 degrees C), moderately humid (45% relative humidity) environment for 2 h/day on ten consecutive days. Acclimation was verified by significant reductions in exercise heart rate, rectal temperature, and heat storage, as well as significant elevation of resting plasma volume (12%, P less than 0.05) and exercise sweat rate on day 10 compared with day 1 of acclimation. During exercise, the concentration and total content of sodium in sweat as well as plasma aldosterone were significantly decreased from day 1 to day 10. The ratio of sweat sodium reabsorbed to plasma aldosterone concentration was significantly increased from day 1 to day 10 after both 1 and 2 h of exercise. These data indicate that plasma aldosterone concentrations decrease following heat acclimation; and eccrine gland responsiveness to aldosterone, as represented by sweat sodium reabsorption, may be augumented through exercise and heat acclimation.     

In vivo secretory responses of submandibular glands in streptozotocin-diabetic rats to sympathetic and parasympathetic nerve stimulation

Submandibular gland responses to sympathetic and parasympathetic nerve stimulation were studied in streptozotocin-diabetic rats. Morphologically, the acinar cells in control glands were relatively uniform in size and contained electron-lucent granules. The granular ducts were distinguished by the presence of electron-dense granules. With the exception of intracellular lipid droplets and the presence of a few autophagosomes in diabetic glands, no consistent differences in acinar cell structure were observed. In contrast, the diameter of the granular ducts and the granule content of their cells were less in diabetic glands. At 3 weeks sympathetic flow rate, salivary protein concentration, and total protein output were unaffected by diabetes. Sympathetic flow rate was greater at 3 months, and the concentration of protein in the saliva was lower. In 6-month diabetic rats flow rate remained increased, but protein concentration and total protein output were reduced. The decrease in salivary protein concentration at 3 and 6 months was accompanied by a reduction in secretory granule release from acinar and granular duct cells. No consistent differences in flow rate, protein concentration, protein output, or secretory granule release were observed following parasympathetic stimulation. We conclude that the effects of diabetes on nerve-stimulated flow rate and protein release depend on the duration of diabetes and the type of stimulation, and are independent of one another.     

Thermoregulatory activity in the rat: effects of hypohydration, hypovolemia and hypertonicity and their interaction with short-term heat acclimation

Hypothalamic temperature thresholds to heat-induced (40 degrees C ambient temperature) tail vasodilation (Vth) and salivation (Sth) as well as salivary flow rate and volume were studied in conscious rats, hypohydrated (24 hr water deprivation), hypovolemic (20% dextran sc), hypertonic (1M NaCL po), hypertonic and hypovolemic and heat-acclimated (5 days at 34 degrees C) before and after hypohydration. Sth was elevated in hypohydrated, hypovolemic, hypertonic and heat-acclimated hypohydrated rats concomitantly with a remarkable decrease in saliva volume, flow rate and heat tolerance. Heat acclimation alone resulted in a reduction in Vth, Sth, salivary flow and volume. Vth was not affected by hypohydration, but was elevated following hypovolemia and combined hypovolemia and hypertonicity. It is concluded that alterations in both plasma volume and osmolarity, which may occur during hypohydration, play a major role in the alteration in thermoregulatory responses during hypohydration. Heat acclimation does not improve tolerance during hypohydration. Thus, during hypohydration, the control of body fluids overrides thermoregulation.     

Early detection in saliva of polypeptides associated to isoproterenol-induced mouse parotid hypertrophy

Chronic administration of isoproterenol (IPR) results in a marked hypertrophy and in the induction of a group of putative proline-rich polypeptides in the mouse parotid glands. Some of these polypeptides (pps C-G) have been considered as molecular markers of the parotid gland enlargement. Given the secretory character of polypeptides C-G, the polypeptide composition of mouse saliva was used to monitor the IPR-induced salivary gland hypertrophy. Whole saliva was collected after an oral administration of pilocarpine (PIL). Under those conditions, PIL provoked a massive salivary secretion both in normal control mice and during the whole course of the IPR-induced gland enlargement. Striking changes in the polypeptide composition of saliva obtained from chronically IPR-stimulated animals were observed. Those changes consisted basically in the appearance and progressive increase in concentration of parotid polypeptides C-G and in the progressive diminution in concentration of a couple of normal salivary polypeptides (polypeptides A-B). The appearance of new polypeptides in saliva could be established unequivocally within the 24 h following the trophic adrenergic stimulation. On the other hand, salivary polypeptides induced in response to a single administration of IPR could be demonstrated as late as 7-9 days after the stimulation. Accordingly, detection of parotid polypeptides C-G in PIL-produced saliva obtained from IPR-stimulated mice has proved to be a highly advantageous method to evaluate salivary gland hypertrophy both at very early stages after the trophic stimulation and late after the occurrence of the trophic episode.     

Effects of exposure to high temperatures on serum,urine and sweat concentrations of iron and copper

The objective of this research was to determine the acute effect of a maximum test until exhaustion in normothermia and hyperthermia, and after repeated exposure to heat at high temperatures on the homeostasis of Fe and Cu.The sample was composed of twenty-nine male university students. The participants were divided into a control group (CG) and an experimental group (EG). All of them underwent an incremental test until exhaustion in normothermia and hyperthermia before and after the repeated exposure of EG to heat at high temperatures, consisting of 9 heat acclimatisation sessions in the sauna. Samples of urine and blood were taken before and after each test. Additionally, sweat samples were collected in the hyperthermia test. The samples were frozen at −80 °C for further analysis by ICP-MS.None of the metal concentrations in serum were affected by hyperthermia or exposure to heat. Urinary Fe increased in CG in the hyperthermia test before Heat exposure at High Temperature (HEHT)(p < 0.05) and in both groups after HEHT (p < 0.05). In EG there was an increase in the urinary excretion of Cu after HEHT (p < 0.01) in both trials. Fe suffered a decrease in sweat in EG after exposure to heat (p < 0.05).The concentrations of Fe and Cu in serum were not affected by acute exercise and exposure to high temperatures. However, there was a decrease in excretion of Fe in sweat due to HEHT, and an increase in urinary excretion in both. Therefore, we think that in conditions of high temperatures for long periods of time, attention should be paid to the body levels of these metals.     

The involvement of boar submaxillary salivary gland secretions in boar-induced precocious puberty attainment in the gilt

The involvement of secretions from boar submaxillary salivary glands in mediating the induction of precocious puberty in the gilt was investigated as follows. Forty-eight Large White × (Large White × Landrace) prepubertal gilts from 12 litters were randomly allocated within litters by weight, to four treatment groups of six, in two replicates, at 145 days of age. Treatments commencing at a mean group age of 165 days, were: (1) control (no boar exposure); (2) gilts exposed to a mature sialectomised boar (submaxillary salivary glands were removed at 9 weeks of age); (3) gilts exposed to a mature sham-operated boar; (4) gilts exposed to a mature unoperated boar.Boar exposure occurred for 30 min per day for 75 days, or until pubertal oestrus was observed. Gilts showing pubertal oestrus were removed and slaughtered. Ovaries were examined to confirm reproductive status. Gilts failing to exhibit oestrus by 240 days of age were slaughtered and nominally ascribed a pubertal age of 245 days. Age at puberty was significantly earlier in all three boar-exposed treatments than in the control treatment (P<0.05 for treatments 2 and 3, P<0.001 for treatment 4; median ages at puberty being 227.0, 203.5 , 202.0 and 179.0 days for treatments 1 to 4 respectively). No frothy saliva was ever produced by the sialectomised boar, and chromatographic analysis of saliva produced by the sham-operated boar during mating revealed very low levels of 16-androstene pheromones, while levels in the unoperated boar's saliva were normal. These results provide further evidence for an important role of boar salivary pheromones in the induction of precocious puberty attainment in the gilt.     

Cortisol and progestin release, heart rate and heart rate variability in the pregnant and postpartum mare, fetus and newborn foal

The mechanisms leading to parturition in the horse in many aspects differ from those in other species. Pregnancy is maintained not by progesterone but by 5α-pregnanes and the progestin precursor pregnenolone originates from the fetus. As parturition approaches, the fetal adrenal switches from pregnenolone to cortisol synthesis but it is not known whether cortisol crosses the placenta. We hypothesized that in parallel to fetal cortisol release, cortisol in the maternal circulation increases before foaling and this increase can be determined in both saliva and plasma. In addition, maternal, fetal and neonatal heart rate and heart rate variability were measured. In 25 pregnant mares, saliva for cortisol analysis was collected 4 times daily from 15 days before to 5 days after foaling. In 13 mares, in addition, fetomaternal electrocardiogram (ECG) recordings were made and blood samples for progestin and cortisol analysis were collected once daily. Heart rate (HR) was recorded until 5 days after foaling. The heart rate variability (HRV) variables standard deviation of the beat-to-beat (RR) interval (SDRR) and root mean square of successive RR differences (RMSSD) were calculated. From Days 15 to 4 before parturition, progestin concentration increased (peak 267 ± 42 ng/mL) and decreased thereafter (P < 0.05, day of foaling 113 ± 18 ng/mL). A prepartum increase in maternal cortisol concentrations was evident in blood (P < 0.05) and saliva (P < 0.05) and paralleled the decrease in progestin concentrations. In mares, HR remained constant during the last days of pregnancy but decreased within one day after parturition (P < 0.05) while maternal HRV did not change. In the fetus and neonate, HR increased from before to after birth (P < 0.05) indicating increasing demands on the cardiovascular system with adaptation to extrauterine life.     

Thyroid gland function during cross adaptation to heat and cold in man

Plasma thyroxine (T₄), triiodothyronine (T₃) and thyrotropin (TSH) levels were monitored in 10 healthy euthyroid male subjects of the age group 20 to 30 years before and during heat and cold acclimatisation schedule in a sequential manner. The subjects were exposed to 45C DB and 30% relative humidity in a hot chamber for 2 hours daily for 8 consecutive days. Subsequently they were exposed to cold for 4 hours daily at 10C for 21 days. The mean plasma T₄ and T₃ concentration before exposure to heat were 7.87±0.82 ug/dl and 159.8±9.1 ng/dl respectively. A significant decrease in both T₄ (p<0.05) and T₃ (p<0.01) levels to mean values of 6.4±0.76g/dl and 129±7.9 ng/dl was recorded on day 4 of exposure to heat. Further significant decrease (p<0.05) over the preceding T₃ levels was observed on day 8 of heat exposure. Plasma T₄ and T₃ on day 21 of cold exposure was not significantly different from the levels reckoned after last day of heat exposure but was significantly lower than the pre-exposure values. Throughout the thermal stress schedule there was no change in the TSH levels. These observations suggest that a decrease in thyroid hormone levels during exposure to heat might be an adaptive process which continues even during cold acclimatisation.     

Salivary Melatonin in Relation to Depressive Symptom Severity in Young Adults

Reduced levels of melatonin have been associated with severe depression. The aim was to investigate the correlation between salivary melatonin and dimensional measures of depressive symptom severity in young adult psychiatric patients. Levels of melatonin were analyzed in six saliva samples during waking hours from 119 young adult patients under outpatient psychiatric care. Melatonin levels were tested for association with the severity of depressive symptoms using the self-rating version of the Montgomery Åsberg Depression Rating Scale (MADRS-S). Where possible, depressive symptoms were assessed again after 6±2 months of treatment. Response was defined as decrease in MADRS-S by ≥50% between baseline and follow-up. Patients with levels of melatonin in the lowest quartile at bedtime had an increased probability of a high MADRS-S score compared to those with the highest levels of melatonin (odds ratio 1.39, 95% CI 1.15–1.69, p<0.01). A post hoc regression analysis found that bedtime melatonin levels predicted response (odds ratio 4.4, 95% CI 1.06–18.43, p<0.05). A negative relationship between salivary melatonin and dimensional measures of depressive symptom severity was found in young patients under outpatient psychiatric care. Bedtime salivary melatonin levels may have prognostic implications.     

Effects of heat acclimation on sweating during graded exercise until exhaustion

The aim of the present study was to test the hypothesis that the sweating during graded exercise until exhaustion in a temperate environment would be greater after heat acclimation. Six healthy young males performed an exercise–heat stress acclimation protocol during 9 days. Before (PRE) and after (POS) the acclimation protocol they performed a graded exercise until exhaustion and the sweat loss during exercise increased after acclimation (3.94±1.10, PRE, and 4.86±1.70 g m⁻² min⁻¹, POS; p<0.05). The results showed that daily prolonged exposures to exercise-heat stress increased sweating during a graded and short duration exercise in a temperate environment.     

Na+-Glucose Cotransporter SGLT1 Protein in Salivary Glands: Potential Involvement in the Diabetes-Induced Decrease in Salivary Flow

Oral health complications in diabetes include decreased salivary secretion. The SLC5A1 gene encodes the Na⁺-glucose cotransporter SGLT1 protein, which not only transports glucose, but also acts as a water channel. Since SLC5A1 expression is altered in kidneys of diabetic subjects, we hypothesize that it could also be altered in salivary glands, contributing to diabetic dysfunction. The present study shows a diabetes-induced decrease (p < 0.001) in salivary secretion, which was accompanied by enhanced (p < 0.05) SGLT1 mRNA expression in parotid (50%) and submandibular (30%) glands. Immunohistochemical analysis of parotid gland of diabetic rats revealed that SGLT1 protein expression increased in the luminal membrane of ductal cells, which can stimulate water reabsorption from primary saliva. Furthermore, SGLT1 protein was reduced in myoepithelial cells of the parotid from diabetic animals, and that, by reducing cellular contractile activity, might also be related to reduced salivary flux. Six-day insulin-treated diabetic rats reversed all alterations. In conclusion, diabetes increases SLC5A1 gene expression in salivary glands, increasing the SGLT1 protein content in the luminal membrane of ductal cells, which, by increasing water reabsorption, might explain the diabetes-induced decrease in salivary secretion.     

Advanced Glycation End Products Increase Salivary Gland Hypofunction in d-Galactose-Induced Aging Rats and Its Prevention by Physical Exercise

A declined salivary gland function is commonly observed in elderly people. Advanced glycation end products (AGEs) are believed to contribute to the pathogenesis of aging. Although physical exercise is shown to increase various organ functions in human and experimental models, it is not known whether it has a similar effect in the salivary glands. In the present study, we evaluated the AGEs burden in the salivary gland in the aging process and the protective effect of physical exercise on age-related salivary hypofunction. To accelerate the aging process, rats were peritoneally injected with D-galactose for 6 weeks. Young control rats and d-galactose-induced aging rats in the old group were not exercised. The rats in the physical exercise group ran on a treadmill (12 m/min, 60 min/day, 3 days/week for 6 weeks). The results showed that the salivary flow rate and total protein levels in the saliva of the d-galactose-induced aging rats were reduced compared to those of the young control rats. Circulating AGEs in serum and secreted AGEs in saliva increased with d-galactose-induced aging. AGEs also accumulated in the salivary glands of these aging rats. The salivary gland of aging rats showed increased reactive oxygen species (ROS) generation, loss of acinar cells, and apoptosis compared to young control mice. However, physical exercise suppressed all of these age-related salivary changes. Overall, physical exercise could provide a beneficial option for age-related salivary hypofunction.     

The effects of saliva collection,handling and storage on salivary testosterone measurement

Several endocrine parameters commonly measured in plasma, such as steroid hormones, can be measured in the oral fluid. However, there are several technical aspects of saliva sampling and processing that can potentially bias the validity of salivary testosterone measurement. The aim of this study was to evaluate the effects caused by repeated sampling; 5 min centrifugation (at 2000, 6000 or 10,000g); the stimulation of saliva flow by a cotton swab soaked in 2% citric acid touching the tongue; different storage times and conditions as well as the impact of blood contamination on salivary testosterone concentration measured using a commercially available ELISA kit. Fresh, unprocessed, unstimulated saliva samples served as a control. Salivary testosterone concentrations were influenced neither by repeated sampling nor by stimulation of salivary flow. Testosterone levels determined in samples stored in various laboratory conditions for time periods up to 1 month did not differ in comparison with controls. For both genders, salivary testosterone levels were substantially reduced after centrifugation (men F = 29.1; women F = 56.17, p < 0.0001). Blood contamination decreased salivary testosterone levels in a dose-dependent manner (men F = 6.54, p < 0.01, F = 5.01, p < 0.05). Salivary testosterone can be considered A robust and stable marker. However, saliva processing and blood leakage can introduce bias into measurements of salivary testoterone using ELISA. Our observations should be considered in studies focusing on salivary testosterone.