Functional and proteomic analysis of submandibular saliva in rats exposed to chronic stress by immobilization or constant light.

OBJECTIVE: In this study, we have evaluated the effects of stress on functional and proteomic changes in submandibular saliva of rats. DESIGN: Male adult rats were divided in three groups: IMO (2 h/day of immobilization for 7 days), LL (constant light during 20 days), C (unstressed controls submitted to 14 h light-10h dark cycle). Body weight, food intake and the dry weight of submandibular gland were recorded. Saliva samples, collected under anaesthesia following i.p. administration of isoproterenol and pilocarpine (5 mg/kg), were assayed for total proteins (TP), amylase activity and SDS-PAGE electrophoresis. RESULTS: Body weight, food intake and the dry weight of submandibular gland of IMO rats were lower than those of C and LL groups. The salivary volumes secreted in IMO and LL rats, were significantly higher than in controls. The TP output (µg protein/µg saliva/mg of dry tissue) and amylase activity output (AU/µg of saliva/mg of dry tissue) in IMO were significantly higher than in C and LL animals. The electrophoretic pattern of saliva proteins of LL rats, revealed the absence of a protein band of approximately 25 kDa. This band was composed by the common salivary protein-1 and a prolactin-induced protein as identified by peptide mass fingerprinting. CONCLUSIONS: Differences in body weight and food intake between IMO and LL might be attributed to the sort and intensity of stressors stimuli. The changes in the volume of secreted saliva could be a compensatory mechanism in response to stressors. The increase of total protein in IMO rats and the absence of 25 kDa proteins in LL, would suggest that the submandibular glands respond to the sympathetic nervous system stimuli induced by the stress with an increase of activity of the sympathetic nerves in IMO and a reduction in LL rats.

Modification of the beta- and alpha2-adrenergic sensitivity of rat submandibular glands by environmental stimuli and stress.

In man, the rate of resting salivary secretion can be influenced by environmental stimuli related to light dark cycles or by noxious stimuli (stressors) of psychological origin. The sympathetic branch of the autonomic nervous system and the adrenal medulla play an important part in homeostatic responses. Previous observations have shown that chronic exposure of rats to constant light promotes degranulation of parotid acini and desensitization of submandibular beta-adrenergic receptors. Now the submandibular secretory response elicited by beta- and alpha2-adrenergic agonists was studied in rats chronically exposed to environmental conditions that modified the activities of sympathetic efferents to the pineal, salivary and adrenal glands. Adult male rats were exposed to constant light (LL) or constant darkness (DD) for 20 days, or to stress (2 h daily immobilization) for 14 days. Control animals were kept under the usual lighting conditions and without immobilization. Dose response curves to isoproterenol (i.v), before and after administration (i.v.) of a dose (20 microg/kg) of clonidine were obtained. Beta-adrenergic desensitization was observed in all the experimental groups, while alpha2-adrenergic desensitization was only observed in the stress and LL groups. The results suggest that circulating catecholamines could mediate light and stress effects on submandibular beta-adrenergic secretory responses. Extrasynaptic alpha2-adrenoceptors might modulate the submandibular secretory response when predictable environmental stimuli (daily light phase) or unpredictable stressors raise the concentrations of circulating catecholamines.

Maternal coordination of the daily rhythm of malate dehydrogenase activity in testes from young rats: effect of maternal sympathetic denervation of the pineal gland and administration of melatonin.

Chronic sympathetic denervation of the pineal gland by bilateral removal of the superior cervical ganglia (SCG) was performed on female rats 30 days before impregnation. The offspring, maintained in the dark from birth, had disruption of the malate dehydrogenase circadian rhythm in the testes at 25 days of age. A daily injection of melatonin (1 mg/kg s.c. at 10:00 or 18:00 h) to denervated mothers from the 14th day of pregnancy up to the 10th day postpartum produced one daily phase in the enzyme activity of tests in the offspring. Entrainment of daily enzyme activity also was obtained when the hormone was administered orally to the pups during the postnatal period or when pups were reared by intact (not denervated) foster mothers. The results indicate the involvement of the maternal pineal gland in the maternal transfer of photoperiodic information necessary for the coordination of the circadian system in young rats.

Modification of the beta-adrenergic sensitivity of rat submandibular gland by constant light.

Rats exposed for 2, 5, 10, 20, 35 and 50 days to constant light (CL) showed beta-adrenergic desensitization of the submandibular gland as indicated by dose-response curves to 1.5, 2.0, 3.0, 10.0, 30.0 and 50.0 micrograms/kg isoproterenol. The phenomenon, evident with 1.5, 2.0 and 50.0 micrograms/kg after 2 days at CL, was more intense as time of exposure increased to reach values of about 50% those for controls after 20 days. After 35 and 50 days, desensitization showed some reversion, but the secretory responses were still lower than for controls maintained under a typical photoperiod. In the groups of rats exposed to CL for 20 days, gland wet and dry weights were higher (10%) than those of controls. These changes probably indicate an adaptation of the sympathetic control of salivary secretion induced by environmental illumination.

Effect of chronic constant light on sensitivity of rat submandibular gland.

A consistent difference in the secretory response between submandibular (SM) glands of rats maintained under constant light (CL) during 50 days and those of rats under a photoperiod (14 h light: 10 h dark) was found. We have used alpha 1-adrenergic, muscarinic, peptidergic and beta-adrenergic secretagogue agents to study the secretory response of rat SM glands "in vivo". The response to phenylephrine, methacholine and substance P, was increased by exposure CL, while that to isoproterenol was diminished. The changes in the sensitivity of the secretory response from SM gland of rats under CL might be related to changes in the normal interplay of various receptors as well as to possible alteration in the intracellular signal transduction. It may represent and adaptive process of the nervous control of saliva secretion by environmental light and be of physiological and clinical interest.

Effect of chronic constant light on sensitivity of rat submandibular gland.

A consistent difference in the secretory response between submandibular (SM) glands of rats maintained under constant light (CL) during 50 days and those of rats under a photoperiod (14 h light: 10 h dark) was found. We have used alpha 1-adrenergic, muscarinic, peptidergic and beta-adrenergic secretagogue agents to study the secretory response of rat SM glands [quot ]in vivo[quot ]. The response to phenylephrine, methacholine and substance P, was increased by exposure CL, while that to isoproterenol was diminished. The changes in the sensitivity of the secretory response from SM gland of rats under CL might be related to changes in the normal interplay of various receptors as well as to possible alteration in the intracellular signal transduction. It may represent and adaptive process of the nervous control of saliva secretion by environmental light and be of physiological and clinical interest.

Effect of chronic constant light on sensitivity of rat submandibular gland

A consistent difference in the secretory response between submandibular (SM) glands of rats maintained under constant light (CL) during 50 days and those of rats under a photoperiod (14 h light: 10 h dark) was found. We have used alpha 1-adrenergic, muscarinic, peptidergic and beta-adrenergic secretagogue agents to study the secretory response of rat SM glands [quot ]in vivo[quot ]. The response to phenylephrine, methacholine and substance P, was increased by exposure CL, while that to isoproterenol was diminished. The changes in the sensitivity of the secretory response from SM gland of rats under CL might be related to changes in the normal interplay of various receptors as well as to possible alteration in the intracellular signal transduction. It may represent and adaptive process of the nervous control of saliva secretion by environmental light and be of physiological and clinical interest.

Effect of sympathetic denervation of the pineal gland on maternal co-ordination of the circadian rhythm of alpha-amylase in parotid gland from young rats.

Twenty-five-day-old rats maintained in constant darkness since birth and born from mothers kept in the dark since the 14th day of pregnancy showed a circadian rhythm of alpha-amylase content in parotid glands, which may be explained by a mechanism of maternal co-ordination. Rats in the same conditions, except that their mothers had been submitted to bilateral excision of the superior cervical ganglia 30 days before mating, did not show diurnal variations of alpha-amylase activity in the parotid glands. When ganglionectomized mothers were treated with a daily dose of melatonin (1 mg/kg) from the 14th day of gestation up to the 10th day of lactation, their litters showed significant diurnal variations of amylase in the parotid glands, suggesting a role of the maternal pineal gland in the maternal-fetal and/or maternal-neonatal transfer of photoperiodic information.