Inter-organ relation between salivary gland and kidney in lithium excretion. IV. Saturation of inhibitory effect of NaCl on ductal reabsorption of Li+ in beagle dogs.

The inhibitory effect of NaCl coadministration on the reabsorption of Li+ in the salivary ducts and the renal tubules was investigated in beagle dogs. Following the bolus intravenous administration of LiCl (0.145 meq/kg), 50 ml of NaCl solution (100, 200 meq/l) was administered orally each hour, and parotid saliva (Pr) and mandibular-sublingual saliva (MS) were collected under the continuous stimulation of salivation with citric acid. The renal clearance of Li+ increased with the increased concentration of administered NaCl solution. This could be a result of the competitive inhibition of the tubular reabsorption of Li+ by Na+. The salivary clearance of Li+ also tended to increase by the administration of NaCl. These results suggest the existence of a reabsorption process of Li+ in the salivary glands similar to that in the renal tubule. However, when the administered NaCl was increased from 100 to 200 meq/l, the renal clearance was further increased, but the salivary clearance was not. This suggests that the transport capacity of Li+ reabsorption is relatively small in the salivary glands, compared with that in the renal tubule, and that the inhibitory effect of NaCl on Li+ reabsorption had already reached a maximum level when 100 meq/l NaCl was administered.