Reduced starch granule number per chloroplast in the dpe2/phs1 mutant is dependent on initiation of starch degradation.

An Arabidopsis double knock-out mutant lacking cytosolic disproportionating enzyme 2 (DPE2) and the plastidial phosphorylase (PHS1) revealed a dwarf-growth phenotype, reduced starch content, an uneven distribution of starch within the plant rosette, and a reduced number of starch granules per chloroplast under standard growth conditions. In contrast, the wild type contained 5-7 starch granules per chloroplast. Mature and old leaves of the double mutant were essentially starch free and showed plastidial disintegration. Several analyses revealed that the number of starch granules per chloroplast was affected by the dark phase. So far, it was unclear if it was the dark phase per se or starch degradation in the dark that was connected to the observed decrease in the number of starch granules per chloroplast. Therefore, in the background of the double mutant dpe2/phs1, a triple mutant was generated lacking the initial starch degrading enzyme glucan, water dikinase (GWD). The triple mutant showed improved plant growth, a starch-excess phenotype, and a homogeneous starch distribution. Furthermore, the number of starch granules per chloroplast was increased and was similar to wild type. However, starch granule morphology was only slightly affected by the lack of GWD as in the triple mutant and, like in dpe2/phs1, more spherical starch granules were observed. The characterized triple mutant was discussed in the context of the generation of starch granules and the formation of starch granule morphology.

Sumoylation of eIF4A2 affects stress granule formation.

Regulation of protein synthesis is crucial for cells to maintain viability and to prevent unscheduled proliferation that could lead to tumorigenesis. Exposure to stress results in stalling of translation, with many translation initiation factors, ribosomal subunits and mRNAs being sequestered into stress granules or P bodies. This allows the re-programming of the translation machinery. Many aspects of translation are regulated by post-translational modification. Several proteomic screens have identified translation initiation factors as targets for sumoylation, although in many cases the role of this modification has not been determined. We show here that eIF4A2 is modified by SUMO, with sumoylation occurring on a single residue (K226). We demonstrate that sumoylation of eIF4A2 is modestly increased in response to arsenite and ionising radiation, but decreases in response to heat shock or hippuristanol. In arsenite-treated cells, but not in hippuristanol-treated cells, eIF4A2 is recruited to stress granules, suggesting sumoylation of eIF4A2 correlates with its recruitment to stress granules. Furthermore, we demonstrate that the inability to sumoylate eIF4A2 results in impaired stress granule formation, indicating a new role for sumoylation in the stress response.

[PROPERTIES OF SACCHAROMYCES CEREVISIAE VOLUTIN GRANULES UNDER CONDITIONS OF THE CHANGE OF SPACE WEATHER].

In this work, the impact of space weather on the staining and the motility of volutin granules ("dancing bodies") in vacuoles of yeast Saccharoniyces cerevisiae with normal and changed phosphoric metabolism was studied. It was showed that the installed ear- lier relation between metachromatic reaction of volutin granules and galactic cosmic rays was confirmed by DAPI-staining of inorganic polyphosphates in cells S. cerevisiae UCM Y-517. The inverse correlation of efficiency of DAPI-staining of volutin granules with some solar activity indexes was observed. During the period of study, the rhythmicity of motile volutin granules in the studied cultures (S. cerevisiae UCM Y-517, S. cerevisiae CRY, S. cerevisiae CNX) was marked. The strains S. cerevisiae UCM Y-517 and CRY, both with unmodified phosphoric metabolism, showed the same rhythmicity of mobile volutin granules. However, this rhythmicity in the strain CNX, which cannot synthesize exopolyphosphatases PPX1 and PPN1 (CF 3.6.1.11), was changed. The volutin granule motion coincided with the rhythmicity of galactic cosmic rays within the period of 9 days. It can be suggested that "dancing bodies" are synchronized with rhythms of galactic cosmic rays. Observed differences between mutant and parental strains may indirectly indicate participation of polyphosphates in the reaction of cells on the changes of space weather pa- rameters. Thus, correlating variability of staining and motion of polyphosphate-containing volutin granules under action of cosmophysical factors may be an evidence of possible key role of phosphoric metabolism in sensitivity of yeast cells to space weather changes.

Intramedullary megakaryocytes internalize released platelet factor 4 and store it in alpha granules.

BACKGROUND: Megakaryocytes express and store platelet factor 4 (PF4) in alpha granules. In vivo, PF4 is a clinically relevant, negative regulator of megakaryopoiesis and hematopoietic stem cell replication. These findings would suggest a regulated source of free intramedullary PF4. OBJECTIVES: Define the source of free intramedullary PF4 and its intramedullary life cycle. METHODS: We interrogated both murine and human bone marrow-derived cells during megakaryopoiesis in vitro by using confocal microscopy and enzyme-linked immunosorbent assay. With immunohistochemistry, we examined in vivo free PF4 in murine bone marrow before and after radiation injury and in the setting of megakaryocytopenia and thrombocytopenia. RESULTS: Exogenously added human PF4 is internalized by murine megakaryocytes. Human megakaryocytes similarly take up murine PF4 but not the related chemokine, platelet basic protein. Confocal microscopy shows that internalized PF4 colocalizes with endogenous PF4 in alpha granules and is available for release on thrombin stimulation. Immunohistochemistry shows free PF4 in the marrow, but not another alphagranule protein, von Willebrand factor. Free PF4 increases with radiation injury and decreases with megakaryocytopenia. Consistent with the known role of low-density lipoprotein receptor-related protein 1 in the negative paracrine effect of PF4 on megakaryopoiesis, PF4 internalization is at least partially low-density lipoprotein receptor-related protein 1 dependent. CONCLUSIONS: PF4 has a complex intramedullary life cycle with important implications in megakaryopoiesis and hematopoietic stem cell replication not seen with other tested alpha granule proteins.

Melatonin protects rat cerebellar granule cells against electromagnetic field-induced increases in Na(+) currents through intracellular Ca(2+) release.

Although melatonin (MT) has been reported to protect cells against oxidative damage induced by electromagnetic radiation, few reports have addressed whether there are other protective mechanisms. Here, we investigated the effects of MT on extremely low-frequency electromagnetic field (ELF-EMF)-induced Nav activity in rat cerebellar granule cells (GCs). Exposing cerebellar GCs to ELF-EMF for 60 min. significantly increased the Nav current (INa ) densities by 62.5%. MT (5 µM) inhibited the ELF-EMF-induced INa increase. This inhibitory effect of MT is mimicked by an MT2 receptor agonist and was eliminated by an MT2 receptor antagonist. The Nav channel steady-state activation curve was significantly shifted towards hyperpolarization by ELF-EMF stimulation but remained unchanged by MT in cerebellar GC that were either exposed or not exposed to ELF-EMF. ELF-EMF exposure significantly increased the intracellular levels of phosphorylated PKA in cerebellar GCs, and both MT and IIK-7 did not reduce the ELF-EMF-induced increase in phosphorylated PKA. The inhibitory effects of MT on ELF-EMF-induced Nav activity was greatly reduced by the calmodulin inhibitor KN93. Calcium imaging showed that MT did not increase the basal intracellular Ca(2+) level, but it significantly elevated the intracellular Ca(2+) level evoked by the high K(+) stimulation in cerebellar GC that were either exposed or not exposed to ELF-EMF. In the presence of ruthenium red, a ryanodine-sensitive receptor blocker, the MT-induced increase in intracellular calcium levels was reduced. Our data show for the first time that MT protects against neuronal INa that result from ELF-EMF exposure through Ca(2+) influx-induced Ca(2+) release.

[The estimation of age-related sensitivity of the retinal pigment epithelium of Japanese quail (Coturnix japonica) to the light damage].

The effect of blue light damage (445-455 nm, 4 J/cm2) to retinal pigment epithelium (RPE) subcellular structures was investigated in 4 age risk groups (9, 25, 40 and 52 weeks) of Japanese quail Coturnix japonica by light and electron microscopy. The indicator of biological aging of RPE was age-related accumulation of lipofuscin granules: 5-6-fold increase in their quantity increasing by 5-6 times in quails at 52 weeks. The main photo-induced changes observed after 24 h of the photo radiation were located in the blood-retinal barrier, such as loss of homogeneity of Bruch's membrane, disorganization of basal processes, deformations of the nuclei and mitochondria shapes. Those effects ofphotobleaching were more expressed in young birds. But for the older 52-week age birds it was not so noticeable, because their retinal pigment epithelium structures had disorders which were similar to those in younger birds after photodamage.

Effects of adult-generated granule cells on coordinated network activity in the dentate gyrus.

Throughout the adult life of most mammals, new neurons are continuously generated in the dentate gyrus of the hippocampal formation. Recent work has documented specific cognitive deficits after elimination of adult hippocampal neurogenesis in rodents, suggesting that these neurons may contribute to information processing in hippocampal circuits. Young adult-born neurons exhibit enhanced excitability and have altered capacity for synaptic plasticity in hippocampal slice preparations in vitro. Still, little is known about the effect of adult-born granule cells on hippocampal activity in vivo. To assess the impact of these new neurons on neural circuits in the dentate, we recorded perforant-path evoked responses and spontaneous network activity from the dentate gyrus of urethane-anesthetized mice whose hippocampus had been focally X-irradiated to eliminate the population of young adult-born granule cells. After X-irradiation, perforant-path responses were reduced in magnitude. In contrast, there was a marked increase in the amplitude of spontaneous γ-frequency bursts in the dentate gyrus and hilus, as well as increased synchronization of dentate neuron firing to these bursts. A similar increase in gamma burst amplitude was also found in animals in which adult neurogenesis was eliminated using the GFAP:TK pharmacogenetic ablation technique. These data suggest that young neurons may inhibit or destabilize recurrent network activity in the dentate and hilus. This unexpected result yields a new perspective on how a modest number of young adult-generated granule cells may modulate activity in the larger population of mature granule cells, rather than acting solely as independent encoding units.

Activity-dependent expression of RNA binding protein HuD and its association with mRNAs in neurons.

The dendritic trafficking of RNA binding proteins (RBPs) is an important posttranscriptional process involved in the regulation of synaptic plasticity. For example, HuD RBP binds to AU-rich elements (AREs) in the 3' untranslated regions (3'UTR) of immediate-early gene (IEG) transcripts, whose protein products directly affect synaptic plasticity. However, the subcellular localization of HuD RBPs and associated mRNAs has not been investigated following neuronal stimulation. Immunofluorescence analysis revealed activity-dependent dendritic localization of HuD RBPs following KCl stimulation in hippocampal neurons, while immunoprecipitation demonstrated the association of HuD RBP with neuronal mRNAs encoding neuritin, Homer1a, GAP-43, Neuroligins, Verge and CAMKIIalpha. Activity-dependent expression of HuD involves activation of NMDAR as NMDA receptor 1 knockout mice (Nr1(neo-/-)) exhibited decreased expression of HuD. Moreover, translational regulation of HuD-associated transcripts was suggested by its co-localization with poly-A-binding protein (PABP) as well as the cap-binding protein (eIF4E). We propose that post-transcriptional regulation of neuronal mRNAs by HuD RBPs mediates protein synthesis-dependent changes in synaptic plasticity.

A novel class of mRNA-containing cytoplasmic granules are produced in response to UV-irradiation.

Nucleic acids are substrates for different types of damage, but little is known about the fate of damaged RNAs. We addressed the existence of an RNA-damage response in yeast. The decay kinetics of GAL1p-driven mRNAs revealed a dose-dependent mRNA stabilization upon UV-irradiation that was not observed after heat or saline shocks, or during nitrogen starvation. UV-induced mRNA stabilization did not depend on DNA repair, damage checkpoint or mRNA degradation machineries. Notably, fluorescent in situ hybridization revealed that after UV-irradiation, polyadenylated mRNA accumulated in cytoplasmic foci that increased in size with time. In situ colocalization showed that these foci are not processing-bodies, eIF4E-, eIF4G-, and Pab1-containing bodies, stress granules, autophagy vesicles, or part of the secretory or endocytic pathways. These results point to the existence of a specific eukaryotic RNA-damage response, which leads to new polyadenylated mRNA-containing granules (UV-induced mRNA granules; UVGs). We propose that potentially damaged mRNAs, which may be deleterious to the cell, are temporarily stored in UVG granules to safeguard cell viability.

Stress induces the assembly of RNA granules in the chloroplast of Chlamydomonas reinhardtii.

Eukaryotic cells under stress repress translation and localize these messenger RNAs (mRNAs) to cytoplasmic RNA granules. We show that specific stress stimuli induce the assembly of RNA granules in an organelle with bacterial ancestry, the chloroplast of Chlamydomonas reinhardtii. These chloroplast stress granules (cpSGs) form during oxidative stress and disassemble during recovery from stress. Like mammalian stress granules, cpSGs contain poly(A)-binding protein and the small, but not the large, ribosomal subunit. In addition, mRNAs are in continuous flux between polysomes and cpSGs during stress. Localization of cpSGs within the pyrenoid reveals that this chloroplast compartment functions in this stress response. The large subunit of ribulosebisphosphate carboxylase/oxygenase also assembles into cpSGs and is known to bind mRNAs during oxidative stress, raising the possibility that it plays a role in cpSG assembly. This discovery within such an organelle suggests that mRNA localization to granules during stress is a more general phenomenon than currently realized.

UVA1 radiation (340-400 nm) interferes with the perforin-granule system of CD8hi+ cytotoxic T lymphocytes in vitro.

UVA1-irradiation was introduced as an innovative and effective phototherapy of atopic dermatitis (AD) and other skin diseases. In AD, a defect of a central apoptosis inducing effector system involved in immunoregulation and immune defense, i.e., the system of perforin-granules in cytotoxic T lymphocytes (CTL), was recently reported: perforin-reduction and perforin-hyperreleasability. We now investigated UVA1-effects on the perforin-granule system in vitro. Peripheral blood CTLs were exposed in vitro to 10-100 J/cm2 UVA1 (340-400 nm), and to 30-150 mJ/cm2 UVB (280-315 nm) as a control. A time-dependent perforin-granule release was induced by phorbol 12-myristate 13-acetate (PMA) and ionomycin. This release was inhibited dose-dependently by UVA1, but not by UVB. An UVA1-dose dependent pattern of sensitive (80%) and insensitive (20%) individuals was found. The kinetics of perforin release in AD-CTLs, i.e. hyperreleasability, was normalized by 50 J/cm2 UVA1 in vitro. Sodium azide as a quencher of reactive oxygen species prevented the UVA1-mediated inhibition of perforin-granule release. Our data demonstrate for the first time a dose- and wavelength-dependent UVA1-effect in vitro on a major effector system of cytotoxic lymphocytes, the system of perforin-granules. This might contribute to the further understanding of immunomodulatory UVA1-effects in vivo.

Raising the bar: how HIF-1 helps determine tumor radiosensitivity.

Through a poorly understood mechanism, tumors respond to radiation by secreting cytokines which inhibit endothelial cell apoptosis, thereby limiting treatment response by minimizing vessel damage. We have recently discovered that this pathway is governed by a major angiogenesis regulator, hypoxia-inducible factor-1 (HIF-1). We uncovered dual mechanisms initiated by radiation that both simultaneously lead to HIF-1 activation: (1) reoxygenation-induced stabilization of the HIF-1 dimer through free radical intermediates, and (2) reoxygenation-mediated depolymerization of hypoxia-induced translational suppressors known as stress granules. These findings have implications both for understanding the basic science of hypoxic signaling in tumors, and for discovering novel methods of enhancing conventional anti-tumor therapeutics in the clinic. In this article, we will highlight the apparent importance of free radical species in protecting tumor vasculature, stress granules in regulating hypoxic gene expression, and HIF-1 in regulating tumor sensitivity to ionizing radiation. The potential therapeutic utility of these findings will also be explored, with emphasis placed on putative targets in these pathways which may enhance tumor radiotherapy.

Serial scrape smear cytology of radiation response in normal and malignant cells of oral cavity.

Serial scrape smears were taken from 111 patients receiving radiotherapy for squamous cell carcinoma of the oral cavity. The surface of the tumour and the normal mucosa on the opposite side was scraped before and after delivery of various fractions of radiotherapy and were evaluated by light microscopy. The number of cells exhibiting changes like multinucleation, micronucleation, nuclear budding, binucleation and cytoplasmic granulation were counted. The results were expressed as abnormality per 1000 cells. Each parameter showed a statistically significant increase with radiation dose in both normal and malignant oral cells. In the normal mucosal cells the mean values after 6Gy and 24Gy respectively were 0.83 and 2.91 (p<0.001) for cells with multinucleation, 1.83 and 4.42 (p<0.001) for micronucleation, 2.58 and 5.15 (p<0.001) for nuclear budding, 5.92 and 12.58 (p<0.001) for binucleation, and 3.67 and 7.17 (p<0.001) for cytoplasmic granulation. On the other hand, in malignant cells, the mean values before and after treatment with 24 Gy respectively, were 3.14 and 7.08 (p<0.001) for cells with multinucleation, 1.05 and 5.97 (p<0.001) for micronucleation, 2.54 and 8.82 (p<0.001) for nuclear budding 7.11 and 27.93 (p<0.001) for binucleation and 5.32 and 12.02 (p<0.001) for cytoplasmic granulation. The study showed that there is a dose-related increase in multinucleation, micronucleation, nuclear budding, binucleation and cytoplasmic granulation after various fractions of radiotherapy in both normal and malignant oral cells, however these changes are more marked in the malignant cells.

A photoreactive fluorescent marker for identifying eosinophils and their cytoplasmic granules in tissues.

Here we describe a simple histochemical technique that provides an improved approach to identifying eosinophil components in tissues through the formation of photoreactive complexes that produce stable fluorescent emissions. This method worked readily with histological tissue sections 6-60 microm thick, which were fixed in neutral buffered formalin (NBF), and with cell suspensions similarly fixed and unfixed. Deep red (>605 nm) fluorescent emissions were produced by eosinophil-specific granules when exposed to broadband excitation spectra from a 100-W mercury lamp source (510-590 nm), as well as single-wavelength excitations from both an argon laser (488 nm) and a UV-visible laser (514 nm). The fluorophore-granule complex emissions increased in intensity during the first minute of continuous photoexcitation, then remained stable (>10 min). All nonspecific autofluorescence phenomena associated with these tissues were photobleached in the first minute, including areas of background Biebrich scarlet binding where photoreactive complexes were not formed (i.e., collagen), indicating environmental influences on the fluorophore. This technique allows the visualization of eosinophil granules over a greater period of time than is usually permissible with standard fluorescent markers. Therefore, techniques such as confocal microscopy can be utilized to their fullest extent, providing much more detailed information on the location and distribution of the cytoplasmic contents of eosinophils.

Intracellular effect of ultrashort electrical pulses.

A simple electrical model for biological cells predicts an increasing probability for electric field interactions with cell substructures of prokaryotic and eukaryotic cells when the electric pulse duration is reduced into the sub-microsecond range. The validity of this hypothesis was verified experimentally by applying electrical pulses with electric field intensities of up to 5.3 MV/m to human eosinophils in vitro. When 3-5 pulses of 60 ns duration were applied to human eosinophils, intracellular granules were modified without permanent disruption of the plasma membrane. In spite of the extreme electrical power levels applied to the cells thermal effects could be neglected because of the ultrashort pulse duration. The intracellular effect extends conventional electroporation to cellular substructures and opens the potential for new applications in apoptosis induction, gene delivery to the nucleus, or altered cell functions, depending on the electrical pulse conditions.

Radiation induced cell loss in rat submandibular gland and its relation to gland function.

PURPOSE: To understand early and late radiation-induced loss of function of the submandibular gland, changes in cell number were documented and correlated with data on gland function. Modulation of the radiation effect by sialogogues was used to investigate possible mechanisms of action. MATERIALS AND METHODS: Rats were irradiated with a single dose of 15 Gy of X-rays after pre-treatment with either saline, the muscarinic receptor agonists methacholine or pilocarpine, the adrenergic receptor agonist phenylephrine or methacholine plus phenylephrine. Before and 1-240 days after irradiation, submandibular saliva flow rate was measured. At the same time points and from comparable animals submandibular glands were carefully extirpated, weighed and prepared for light microscopic examination. RESULTS: Soon after irradiation (<30 days) no significant loss of cells was observed, whereas the gland function was severely compromised. Sialogogue pre-treatment attenuated the radiation-induced loss of gland function. At later intervals a considerable loss of acinar cells and to a lesser extent loss of granular convoluted tubule cells were observed. Gland function subsequently declined slowly. Pre-treatment with sialogogues gave transient protection against cell loss and loss of gland function. CONCLUSIONS: The lack of cell loss observed soon after irradiation indicates that the observed reduction in gland function was caused by a compromised functioning of the acini. The later loss of cells is probably due to death of cells that normally proliferate, leading to a further reduced secretory capacity. Protection of gland morphology and function by sialogogues at later times must therefore involve resistance of progenitor cells to radiation-induced cell death.

Effect of 24 hours light on circadian rhythms of secretory enzymes and morphology of rat von Ebner's glands.

Von Ebner's glands of the rat are minor salivary serous glands in the posterior portion of the tongue. They secrete two digestive enzymes, lingual lipase and amylase. In this investigation, circadian rhythm in feeding was established under a normal 12 h light/12 h dark cycle, with the rats eating primarily during the dark period. At lights on, the size of the acinar cells and the area of the inclusive secretory granules, and the amount of digestive enzyme activity (lingual lipase and amylase) remaining in the gland was significantly less than in the mid-afternoon, after very little daylight food consumption. However, after 7 days of continuous light the circadian rhythm was altered: the food consumption during the normal night-time hours (5 p.m. to 8 a.m.) went from 88% of total 24 h food consumption to 45%, and during normal daylight hours (8 a.m. to 5 p.m.) from 12% to 55%. These changes were correlated with histometric findings of a near reversal of the areas of acinar cells and secretory granules of a.m. and p.m. samples under continuous light. Lingual lipase activity in the glands went from 35% under 12 h light to 61% under continuous light in the a.m. and from 65% to 39% in the p.m. Amylase activity also showed nearly a reversal in activity remaining in the gland, from 36% at 12 h light to 58% at 24 h light in the a.m. and 64% to 41% for the p.m. samples. These results indicate that the von Ebner's glands of the rat have a circadian rhythm of secretion and storage of secretory proteins that is subject to light entrainment similar to that seen in other exocrine glands such as the parotid and pancreas.

An ultrastructural study of the biostimulative effect of He-Ne laser radiation on the early postnatal differentiation of the rat submandibular gland.

Submandibular gland of the rat during the first week of postnatal development was used for the study of the ultrastructural changes after the He-Ne laser radiation. In the experimental group we observed an increase of the dark cells with greater quantity of the granular endoplasmic reticulum and an increased number of specific secretory granules. These changes show positive biostimulative effect of He-Ne laser radiation on the morphologic differentiation of the submandibular gland of the rat in the early postnatal period.

Acute and protracted radiation effects on small intestinal morphological parameters.

PURPOSE: To compare the responses of small intestinal morphological parameters after acute and protracted doses of radiation. MATERIALS AND METHODS: Male C57BL6 mice were examined 6, 24 and 72 h after whole body gamma-irradiation, given either as an acute 5 Gy dose, or as a protracted (continuous) dose of 20 cGy per day for 25 days to a total dose of 5 Gy. Many different structural parameters at both the light microscopical and ultrastructural levels were assessed quantitatively. RESULTS: At different time points following both schedules there were changes in the number of villous enterocytes, goblet cells, lamina propria cells and mitotic figures. Ultrastructural changes occurred in the epithelium. Many of the parameters that showed changes following the protracted schedule appeared to be returning to normal within 3 days of the cessation of radiation, a finding which was in contrast with the acute dose. The protracted schedule produced increases in the number of Paneth cells and in the length of enterocyte microvilli. CONCLUSIONS: Many of the responses that occurred after the protracted schedule suggest that adaptive mechanisms may be being triggered following persistent exposure to radiation.

Protection against irradiation-induced damage to salivary glands by adrenergic agonist administration.

PURPOSE: Irradiation [IR]-induced damage to major salivary glands is an entity first described at the beginning of our century, yet its underlying mechanism is still enigmatic. Exposure of the salivary glands to IR is often inevitable when delivering radiotherapy for malignancies of the head and neck region. Frequently, this results in rapidly developing, life-long severe xerostomia for which no adequate prevention or treatment is available. The purpose of this study was to examine the role of secretion granules in serous cells of the parotid (P) and submandibular (SM) glands as mediators in the IR-induced salivary damage. Functional parameters (flow rate and gland weight), and total body weight were examined at both early term (4 days) and extended term (2 months) post-IR in male Wistar rats exposed to 15 Gy of head and neck irradiation following stimulation for granule secretion (degranulation). METHODS AND MATERIALS: At 4 days, it was demonstrated that IR reduced P flow rate, P gland weight, total body weight, and submandibular/sublingual gland weight by 89, 33, 30, and 32% (p < 0.01), respectively, while SM flow rate was not altered significantly. At 2 months, these parameters were reduced by 59, 37, 31, and 37%, respectively, and the SM flow rate was reduced by 39% (p < 0.01). RESULTS: Pilocarpine, a muscarinsic agonist which, albeit its efficacy as a salivary watery secretion stimulator, causes only limited degranulation, did not protect significantly any of the reduced parameters at either term. In contrast, cyclocytidine, an adrenergic agonist that is a very potent salivary degranulating agent, protected the P against the weight loss at 4 days and 2 months, and against the flow rate reduction at 2 months. The P weight and flow rate were protected to the extent that their values were not significantly different than those of the nonirradiated controls. Cyclocytidine also partially protected against the body weight reduction at 2 months. Our results emphasize the importance of secretion granules as mediatory agents in IR-induced P damage, and more so at the extended term. The demonstrated protective role of adrenergic agonists against IR damage to the P may be of importance in the clinical setting.