Blood flow of the submandibular gland in sodium-depleted and -loaded rats: effect of nitric oxide synthase inhibition

Different role of isoproterenol and NOS inhibitors on salivary ducts of rats

OBJECTIVES

Nitric oxide (NO) is a diffusible intracellular messenger that is present in saliva. Chronic treatment with isoproterenol, a beta receptor agonist, stimulates the release of NO from acinar cells and induces salivary gland hypertrophy. The aim of this study was to investigate the effect of NO synthesis inhibitors and isoproterenol on rat salivary glands. We analyzed salivary gland weight and the number of ducts per unit area (0.5mm(2)) by NADPH-diaphorase histochemistry (to identify the presence of the enzyme NO synthase-NOS) and haematoxylin-and-eosin (HE).

METHODS

For 8 days male Wistar rats received daily single intraperitoneal injections of saline or a NOS inhibitor (40mg/kg N(omega)-nitro-L-arginine L-NOARG or N(omega)-nitro-l-arginine methyl ester L-NAME). This was followed, 30min later, by subcutaneous injection of isoproterenol (2 or 5mg/kg) or saline.

RESULTS

Isoproterenol increased parotid and submandibular gland weights. Isoproterenol (2mg/kg) induced a decrease of ducts per unit area inversely correlated to the weight of the parotid gland. This effect was augmented by L-NAME. In the submandibular gland L-NAME attenuated isoproterenol (2mg/kg) weight increase. In the submandibular gland isoproterenol and NOS inhibitors induced an increase in ducts per unit area (HE and NADPH-diaphorase). No effect was observed in the sublingual gland.

CONCLUSION

To our knowledge this is the first description of isoproterenol and NOS inhibitors increasing duct density in the submandibular gland. Our results corroborate the hypothesis that NO plays different roles in parotid and submandibular glands.

Comparative haemodynamic studies of resting and active skeletal muscle in anaesthetised rats: role of nitric oxide

Our previous studies have indicated that nitric oxide takes part in the basal regulation of vascular tone in skeletal muscle. The purpose of this study was to investigate whether nitric oxide has a role in the active hyperaemic response of a working muscle in a resting subject. Haemodynamic effects of nitric oxide synthase (NOS) inhibition (L-NAME, 10 mg/kg/30 min i.v. infusion) were determined simultaneously in the resting m. quadriceps femoris and in the working (breathing) m. rectus abdominis in anaesthetised rats (86Rb accumulation technique). L-NAME increased blood pressure and total peripheral resistance (TPR) while it decreased cardiac output. Blood flow (BF) decreased and vascular resistance (VR) increased both in resting (BF: 8.91+/-1.97-->5.92+/-2.59 ml/min/100 g, p<0.05: VR: 106+/-29.9-->212+/-113 R, p<0.01) and working (BF: 17.0+/-4.78-->6.93+/-2.15 ml/min/100 g, p<0.001; VR: 57.0+/-18.5-->160+/-56.7 R, p<0.01) muscle following NOS inhibition, but the percentile change of BF was higher in the working muscle (59%) than in the resting one (34%, p<0.001). There was a positive correlation between the cardiac output and the blood flow of the resting muscle with or without L-NAME administration, but blood flow of the working muscle failed to have any correlation with the cardiac output in control animals. However, L-NAME administration decreased both the cardiac output and the blood flow and similarly to the resting muscle a positive correlation was found. In conclusion, the haemodynamic effects of NOS inhibition are higher in working muscle than in the resting one: the nitric oxide may have important role in vasodilatation during muscle activity.

Role of nitric oxide in the regulation of blood flow in the rat submandibular gland during carotid artery occlusion

The possible involvement of nitric oxide in the preservation of blood flow to the rat submandibular gland after uni- or bilateral occlusion of the common carotid was studied. Glandular blood flow and mean blood pressure were monitored before, during and after carotid occlusion in the presence and absence of the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine-methyl-ester (L-NAME). To calculate vascular resistance, the local perfusion pressure distal to the point of occlusion was also measured. In normal rats, uni- or bilateral carotid occlusion resulted in an immediate decrease in ipsilateral glandular blood flow. After the cessation of carotid occlusion, hyperaemia was observed in the submandibular gland. Both local perfusion pressure and vascular resistance decreased during carotid occlusion. In the group pretreated with L-NAME, trends in blood-flow responses to uni- or bilateral occlusion were identical to those registered in the control groups, though the magnitude of the alterations was significantly less. The well-maintained glandular blood flow was due to functioning vascular anastomoses and compensating dilatation of glandular blood vessels. Nitric oxide had only a restrained effect on this compensatory mechanism.

Alteration by cadmium of rat submandibular gland secretory function and the role of the l-arginine/nitric oxide pathway

The effects of cadmium, l-arginine (nitric oxide precursor) and N(omega)-nitro-l-arginine methyl ester (l -NAME) as a nitric oxide synthesis inhibitor and cotreatment of them on rat submandibular secretory function were studied. Pure submandibular saliva was collected intraorally by micro polyethylene cannula from anaesthetized rats using pilocarpine as secretagogue. Fourteen days treatment with 10 mg l(-1)cadmium as cadmium chloride in drinking water caused significant alterations on salivary function. Salivary flow rate, total protein concentration and amylase activity of saliva were decreased while secretion of calcium was increased by cadmium. Two weeks treatment of rats with l -arginine (2.25%) in drinking water caused an increase in submandibular gland weight. Flow rate was reduced by l-NAME. The total protein concentration of saliva was increased by l-arginine while decreased by l-NAME. Calcium concentration of saliva was reduced by l-arginine and increased by l-NAME. Cotreatment of cadmium with l-arginine prevented cadmium-induced reduction of flow rate while l-NAME cotreatment potentiated cadmium-induced reduction of flow rate. l-arginine showed a preventive effect on cadmium-induced decrease of protein concentration and reached control levels. l-arginine potentiated cadmium-induced increase of saliva calcium concentration. It is confirmed that nitric oxide (NO) has a role in salivary gland function. It is also concluded that cadmium inhibitory effects on salivary gland function are modulated by the NO system as it is observed that the cadmium inhibitory effect on submandibular gland function is diminished by l-arginine and extended by l-NAME. Considering the properties of cadmium substitution for calcium in many intracellular events, different types of alterations can be discussed.