Step-by-step protocol to perfuse and dissect the mouse parotid gland and isolation of high-quality RNA from murine and human parotid tissue

Macroscopic identification and surgical removal of the mouse parotid gland is demanding because of its anatomic location and size. Moreover, the mouse parotid gland contains high concentrations of RNases, making it difficult to isolate high-quality RNA. So far, appropriate methods for optimal perfusion-fixation and dissection of mouse parotid glands, as well as the isolation of high quality RNA from this tissue, are not available. Here we present a simple, optimized, step-by-step surgical method to perfuse and isolate murine parotid glands. We also compared two common RNA extraction methods (RNeasy Mini Kit versus TRIzol) for their yields of high-quality, intact RNA from human and murine parotid gland tissues that were either snap-frozen or immersed in RNAlater stabilization solution. Mouse parotid tissue that was perfused and immersed in RNAlater and human samples immersed in RNAlater exhibited the best RNA quality, independent of the isolation method.

Early radiation effects on muscarinic receptor-induced secretory responsiveness of the parotid gland in the freely moving rat

Although the salivary glands have a low rate of cell turnover, they are relatively radiosensitive. To study the possible mechanism behind this inherent radiosensitivity, a rat model was developed in which saliva can be collected after local irradiation of the parotid gland without the use of anesthetics or stressful handling. Saliva secretion was induced by the partial muscarinic receptor agonist pilocarpine (0.03-3 mg/kg) with or without pretreatment with the beta-adrenoceptor antagonist propranolol (2.5 mg/kg), or the full muscarinic receptor agonist methacholine (0.16-16 mg/min), and measured during 5 min per drug dose before and 1, 3, 6 and 10 days after irradiation. The maximal secretory response induced by pilocarpine plus propranolol was increased compared to that with pilocarpine alone but did not reach the level of methacholine-induced secretion, which was about five times higher. One day after irradiation a decrease in maximal pilocarpine-induced secretion was observed (-22%) using the same dose of pilocarpine that induces 50% of the maximal response (ED(50)), in both the absence and presence of propranolol, indicating that the receptor-drug interaction was not affected by the radiation at this time. The secretory response to methacholine 1 day after irradiation, however, was normal. At day 3 after irradiation, the maximal methacholine-induced secretion was also affected, whereas pilocarpine (+/-propranolol)-induced maximal secretion decreased further. At day 6 after irradiation, maximal secretory responses had declined to approximately 50% regardless of the agonist used, whereas ED(50) values were still unaffected. No net acinar cell loss was observed within the first 10 days after irradiation, and this therefore could not account for the loss in function. The results indicate that radiation does not affect cell number or receptor-drug interaction, but rather signal transduction, which eventually leads to the impaired response. We hypothesize that the early radiation effect, within 3 days, may be membrane damage affecting the receptor-G-protein signaltransfer. Later critical damage, however, is probably of a different nature and may be located in the second-messenger signal transduction pathway downstream from the G protein, not necessarily involving cellular membranes.

An investigation of parotid gland function and histopathology in autoimmune disease-prone mice of different age groups

This work aimed to characterize parotid gland function in autoimmune disease-prone murine strains (MRL/n, MRL/l and NZB/W) in relation to increasing age and to relate the extent of functional impairment to the intensity of histopathologic changes observed at the different ages. Pilocarpine-stimulated parotid saliva was collected to assess salivary flow rate and composition. Parotid tissue was then removed for histopathologic assessment. Parotid flow rates were not significantly reduced in autoimmune strains compared to controls but were reduced with age in NZB/W mice and in males of the C57 (control) strain. Age-related salivary compositional changes were present in MRL/l mice and in male NZB/W mice. Focal lymphocytic adenitis increased with age in prevalence and intensity in both sexes. The functional and histopathologic changes were not closely correlated. These results suggest that the parotid gland of autoimmune disease-prone mice provides only a poor replication of the salivary changes in human Sjögren's syndrome. Nevertheless, both the functional and histopathological changes developing in these strains, even though of limited extent, are significantly influenced by age.

Lack of acute effects of methotrexate on rat parotid salivary gland function

Like other cytotoxic drugs, methotrexate (MTX) produces adverse reactions in oral tissues. Parotid gland function was examined, in vivo and in vitro, 18 h after MTX administration (15 mg/kg, i.p.). No salivary effects could be detected consistently. In addition, the integrity of the oral mucosa remained intact. Thus, at this dose, MTX does not exert an acute cytotoxic effect either on a rapidly replicating oral tissue like the mucosa, or on tissue with a slow turnover rate like the parotid.

5-Hydroxytryptamine modulation of rat parotid salivary gland secretion

5-Hydroxytryptamine (5-HT) has been reported to produce significant responses in blowfly salivary glands, but little information is available concerning its action on mammalian salivary glands. When 5-HT (0.1 mumol/L to 10 mumol/L) is infused i.a. into anesthetized rats, no salivary secretion is obtained from either parotid or submandibular glands. However, when 5-HT is infused along with a threshold concentration of acetylcholine (0.1 mmol/L), potentiation of parotid secretory response is seen with 5-HT (1 mumol/L, 260% increase; 10 mumol/L, 146% increase). Substance P (0.3 mumol/L) combined with 5-HT (1 mumol/L) also resulted in a potentiation of parotid secretion (160% increase). Protein and calcium concentrations were not altered during such treatments. No potentiation of submandibular secretion was noted. Experiments in vitro with parotid cell aggregates exhibited no potentiation associated with the combined use of 5-HT and carbachol, as measured by amylase secretion and inositol trisphosphate accumulation. The experiments indicate that 5-HT substantially modulates parotid salivary secretion in vivo; however, the in vitro findings suggest that 5-HT does not act directly on surface glandular receptors. The magnitude of the in vivo potentiation could very well implicate circulating or released 5-HT as a physiological modulator of endogenous neurotransmitter action.

The modulatory effects of leukotrienes C4 and D4 on methacholine- and substance P-induced salivary secretion in rats

Although certain prostaglandins have been found to be inhibitory to nerve-evoked salivary flow, little is known of the effects the leukotrienes on salivary secretion. It was the purpose of this investigation to examine the effects of leukotrienes C4 (LTC4) and D4 (LTD4) on salivary secretion in the rat, using methacholine or substance P to induce basal secretion, and to test whether or not the observed effects of these eicosanoids were receptor-mediated by using the leukotriene receptor blocker FPL-55712. Methacholine (3 x 10(-4) M), or substance P (1 x 10(-6) M) was infused intra-arterially to stimulate secretion and saliva was collected separately from the parotid gland and the submandibular gland of anesthetized rats. LTC4 and LTD4 (each at 1 x 10(-9) to 1 x 10(-6) M) were found to reduce methacholine- and substance P-induced salivary flow in a dose-related manner. Salivary protein concentration and amylase activity were not significantly altered by the leukotrienes; however, arginine-esterase activity, stimulated by substance P, was increased by both leukotrienes. FPL-55712 (1 x 10(-8) M) was shown to reduce the inhibitory effects of LTC4 and LTD4, suggesting the involvement of leukotriene receptors for these agents in their action.

Fluid secretion rates from mouse and rat parotid glands are markedly different following pilocarpine stimulation

1. Parotid saliva production in two commonly employed laboratory animals, mouse and rat, was studied following pilocarpine stimulation. 2. When normalized to body wt, average parotid saliva output rates in mice were 3-4-fold greater than those observed in rats. When parotid salivary flow rates were normalized to gland weight, mice still displayed 2-3-fold higher values than rats. 3. The Na+ and K+ content of parotid saliva showed small differences between the two species, while saliva from rats contained 3-fold higher protein levels than observed with mice.

Effects of substance P and substance P antagonists on rat salivary secretion

The intra-arterial infusion of substance P produced dose-related responses of both parotid and submandibular salivary secretion in anesthetized rats. The substance P-induced secretion in both glands was inhibited by the substance P analogues [D-Arg1, D-Trp7.9, Leu11]-substance P and [D-Arg1, D-Pro2, D-Trp7.9, Leu11]-substance P, but not by [D-Pro2, D-Trp7,9]-substance P. The profiles of protein and calcium levels obtained with substance P-induced salivary secretion for both glands were similar to those produced by acetylcholine stimulation and were not altered by the substance P analogues.