A.P. Chiarenza

Decrease in Salivary Secretion by Radiation Mediated by Nitric Oxide and Prostaglandins

Objective: In the present work, we evaluated the effect of exposing the submandibular glands (SMG) to radiation, studying different functional parameters such as salivary secretion, nitric oxide (NO) production, reactive oxygen species formation, prostaglandin (PGE) content and apoptosis. Methods: We irradiated rats in the head and neck region with a single dose of γ-ray radiation of 15 Gy. Two hours after radiation, we measured norepinephrine-induced salivary secretion. After that, the SMG were dissected, and in this tissue, we measured the activity of NO synthase (NOS), the PGE content, the amount of reactive oxygen species, apoptotic cells and mitochondrial inducible NOS (iNOS) expression. Results: We found that radiation decreased salivary secretion when 10 and 30 µg/kg of norepinephrine was administered via the right femoral vein. We observed that iNOS activity was reduced and PGE content increased after radiation in SMG, indicating that NO and PGEs may participate in salivary secretion. The expression of mitochondrial NOS was increased after radiation leading to the formation of large amounts of NO that acts as a proapoptotic signal. In fact, we observed an augmentation in apoptotic cells. In this study, we also observed an increase in lipid peroxidation induced by radiation that may contribute to tissue damage. Conclusions: Our results indicate that radiation induced a decrease in salivary secretion and SMG iNOS activity, meanwhile the PGE content, the lipid peroxidation and apoptosis increased in the tissue. These modifications decrease salivary secretion.

Reduced methacholine-induced submandibular salivary secretion in rats with experimental periodontitis

OBJECTIVE Saliva is the first barrier to the entry of bacteria and viruses into the body and is considered a necessary instrument in oral health. Intraperitoneal injection of lipopolysaccharide endotoxins results in submandibular gland (SMG) hyposalivation. The objective of present studies was to assess if periodontitis, a chronic inflammatory disease caused by oral bacteria, alters cholinergic-induced SMG salivary secretion. DESIGN An experimental periodontitis model (EP) (cotton thread ligature around the neck of the first lower molars) was used. Male Wistar rats (300-380g) were randomly divided into 3 groups: control, 7 days-bilateral EP and 7 days-unilateral EP (to study if there were different effects at the ipsilateral and contralateral side). The following determinations were performed in SMG: (1) dose-response curves to the cholinergic agonist methacholine, (2) prostaglandin E (PGE) content, (3) inducible nitric oxide synthase (iNOS) activity and (4) histology of gland sections. RESULTS The molars with EP, no matter the group, exhibited significant and similar bone loss (p<0.001). Bilateral EP reduced methacholine-induced salivary secretion (p<0.05, dose 1μg/kg; p<0.001, dose 3-30μg/kg), increased PGE content (p<0.01), stimulated iNOS activity (p<0.05). Ipsilateral glands of unilateral EP animals presented lower methacholine-induced salivary secretion (p<0.05, dose 3μg/kg; p<0.001, dose 10-30μg/kg), and higher PGE content than contralaterals (p<0.001). In turn, at 3 and 10μg/kg of methacholine, contralateral glands showed significantly lower secretion than control animals (p<0.001). Histological studies of glands revealed partial loss of secretor granular material and periductal oedema in the bilateral and unilateral EP groups as compared to controls. CONCLUSIONS As far as we know, the present results demonstrate for the first time that EP reduces methacholine-induced SMG salivary secretion.

Effects of cadmium on the function and structure of the rat salivary glands

The effects of sub-chronic cadmium (Cd) administration on the structure and subsequent secretory responses of the submaxillary and parotid glands to sialagogues were investigated. Female Wistar rats were injected subcutaneously with cadmium chloride (3.0 mg/kg body weight), 4 times a week for 2, 3 or 4 weeks. Functional and histopathological studies were done 3 days after the last injection. Dose-response curves for norepinephrine and methacholine were obtained. After 2 weeks of Cd administration significant changes in the secretory response to these sialogogues were observed. The dose-response curves after pretreatment with Cd for 3 weeks were also shifted to the right, but the response showed recovery when compared with that of 2-week treated animals. Parotid amylase concentration was also diminished by Cd. Treated rats had reduced acinar diameters, and an increase in acinar cell nuclei per field in both the submaxillary and parotid glands. Thus sub-chronic administration of ionized Cd produces morphological and functional changes in rat salivary glands. Moreover, the extent of tubular and acinar damage matches the degree of gland dysfunction as judged by the diminution of secretory responses to sialagogues.

Adrenergic receptors and secretory responses of the rat submandibular salivary gland after periodic incisor reduction

The lower and upper incisors of female rats were repeatedly reduced every 48 hr for 21 days. A marked enlargement of the submandibular glands was observed at the end of this period. One day after the final reduction, dose dependent curves to phenylephrine and isoproterenol were obtained in relation to salivary flow rates. Secretory responses, expressed as mg/gland, showed that the dose response curve to the alpha1-adrenomimetic drug was not modified by treatment while that for isoproterenol was shifted to the right of the control. When the responses were expressed as microg of saliva/mg of wet tissue, the dose-response curve to both agonists was shifted to the right in the incisor-reduced group. (Activation of alpha2-adrenergic receptors by clonidine did not inhibit the responses to phenylephrine in the incisor-reduced rats.) Radioligand binding assays of alpha1-, beta- and alpha2-receptors did not show differences between control and experimental glands in terms of densities (Bmax) or affinities (Kd). The lack of correlation between the decrease in alpha2- and beta-mediated responses and the radioligand bindings suggests that postreceptor mechanisms are involved in the diminished secretory responses of the rat submandibular gland after periodic reduction or amputation of incisors.

Effects of chronic hypoxia on the secretory responses of rat salivary glands.

Female Wistar rats were placed for 3 weeks in a simulated chamber evacuated by a vacuum pump and maintained at 40.5 kPa (7100 m). Dose-response curves were obtained through the sequential injection, via the femoral vein, of increasing doses of methacholine, methoxamine, isoprenaline and substance P. The secretory activity in the parotid gland after exposure to chronic hypoxia was significantly decreased for all agonists studied, and the submaxillary gland showed the same behaviour except in relation to isoprenaline, which did not show a significant difference compared to controls. These data suggest that changes in the number or sensitivity of autonomic receptors and/or alterations in the intracellular signals caused by hypoxia may be involved in the reduction in salivary secretory responses.

Actividad del sistema neuronal LHRH en un modelo animal de retraso del crecimiento

OBJECTIVE Mild and chronic energy restriction results in growth retardation with puberal delay, a nutritional disease known as nutritional dwarfing (ND). The aim of the present study was to assess the profile of hypothalamic luteinizing hormone-releasing hormone (LHRH) release, at baseline and under glutamate stimulation, in ND rats to elucidate gonadotrophic dysfunction. Reproductive ability during refeeding was also studied. MATERIAL AND METHODS At weaning, 60 male rats were assigned to two groups of 30 animals each: a control and an experimental group. Control rats were fed ad libitum with a balanced rodent diet. The experimental group received 80% of the diet consumed by the control group for 4 weeks. After 4 weeks of food restriction, the ND group was fed freely for 8 weeks. Ten rats from each group were sacrificed every 4 weeks for assays. RESULTS At week 4, body weight and length were significantly diminished in the experimental group vs. the control group (p<0.001). No changes were observed in LHRH baseline release, pulse frequency or amplitude in the experimental group compared with the control group at any time. However, under glutamate stimulation, LHRH release was significantly higher in ND rats than in control rats at week 4 (p<0.05). Refeeding the ND group allowed the rats to reach overall growth and reproductive ability. CONCLUSIONS The results of the present study suggest that the response to the facilitatory effect of glutamate on LHRH release in post-restricted ND rats is probably related to a lesser central nervous system maturation in relation to their chronological age. The adequate somatic growth and normal reproductive ability attained with refeeding suggest the reversibility of the two energetically costly processes compromised by global, mild and chronic food restriction.

Daily changes in β-adrenergic sensitivity of rat submandibular gland. Correlation with β-adrenoceptor rhythm.

Abstract Neurons from the superior cervical ganglia (SCG) innervate the submandibular gland and release noradrenaline during the dark phase of the daily photoperiod. Since in the pineal, another structure innervated by sympathetic neurons, nocturnal activation of the SCG is associated with β-adrenergic sub- and super-sensitivity rhythms, the possible existence of similar phenomena in the rat submandibular gland was assessed. Wistar female rats, kept on a 14:10 light/dark cycle (light from 06:00 to 20:00 h), were sacrificed at 09:00, 14:00, 20:00, 24:00 and 04:00 h. β-Adrenoceptors were studied by 3 H-dihydroalprenolol binding to membrane preparations. The equilibrium dissociation constant ( K d ) did not change as a function of time while significant daily variations in maximal binding values ( B max ) were observed with a peak at 20:00 h. Changes in B max correlated with a high response of adenylate cyclase to isoproterenol. In addition, when the response in salivary flow to isoproterenol was measured, a shift to the left (about 1 logarithmic unit) in dose–response curves was observed at 19:00–20:00 h as compared to 08:00–09:00 h. These daily variations in isoproterenol responsiveness seem not to depend on the pattern of eating since a 24-h starvation or a nocturnal starvation for 16–18 days did not abolish the morning–evening differences in the salivary flow response to isoproterenol. Rather, the results suggest that the daily variations in isoproterenol response correlate with β-adrenergic super- and sub-sensitivity phenomena associated with the circadian release of noradrenaline from SCG neurons.

Dietas ricas en grasa y composición corporal a lo largo de dos generaciones. Estudio experimental

INTRODUCTION AND OBJECTIVE Despite recent findings reported on the nutritional factors that induce epigenetic changes, little information is available at early ages. This study analyzed in an experimental model, over two generations, potential changes in body composition and potential expression of epigenetic changes as the result of the intake of isoenergetic diets with different fat levels. MATERIALS AND METHODS At weaning, Wistar female rats were divided into two groups that were fed either a control diet (fat=7% w/w) or a high-fat diet (15% w/w). Rats were mated at 70 days (M(1)) and their pups (P(1)) were the first generation; P(1) rats were mated at 70 days (M(2)) and their pups (P(2)) represented the second generation. At weaning, mothers and pups (M(1), M(2) and P(1), P(2)) were measured body weight (W) and composition (% body fat, %BF), and total skeleton bone mineral content (BMC), expressed as %BMC, using chemical and DXA methods respectively. RESULTS At weaning, high-fat diet groups M(2) and P(2) showed significant increases in W and %BF (p<0.05); increased %BF values were already found in the M(1) and P(1) groups (p<0.001). By contrast, %BMC significantly decreased in M(2) and P(2) rats (p<0.001). CONCLUSION This study demonstrates the need to review certain eating habits to avoid perpetuation of unhealthy patterns generation after generation.