Neural lobe function in aged Wistar/Tw strain rats showing polydipsia and polyuria

Neural lobe function in male rats of the Wistar/Tw strain was studied at 3, 7 and 16-18 months of age. A significant rise in the serum arginine vasopressin (AVP) level was noted in 16-18-month-old rats showing polydipsia and polyuria. The content and concentration of AVP in the neural lobe of aged rats were significantly less than those of younger animals (3 and 7 months). These results point out an enhancement of AVP release from the neural lobe of aged rats. The reduction in urinary volume in aged rats subjected to 24 hours of water deprivation was less than those in younger animals. No increase in urinary sodium, potassium and chloride concentrations was observed in aged rats, and the decrease in electrolyte excretion from urine during the dehydration period was less in aged rats than younger ones. These results suggest that the antidiuretic response to osmotic stimuli was reduced in aged rats. The administration of AVP to aged rats resulted in a significant decrease in water intake and urinary volume, but AVP administration did not induce any change in the electrolyte balance. Therefore, it is concluded that the main cause of the development of polydipsia and polyuria is the decline in renal function but not in neurosecretory activity, although exogenous AVP can effectively reduce water intake and urinary output in aged rats.     

The effect of pitressin on esophageal blood flow of the dog.

In a previous study on canine esophagus, we reported that intravenous infusion of isoproterenol caused mucosal (i.e., mucosal + submucosal) vasodilation only in the lower esophageal sphincter (but not in the body) and muscularis vasodilation only in the body (not in the lower esophageal sphincter). In the present study, we have investigated in dogs whether these esophageal tissues also exhibit a similar difference in their vasoconstrictory response to intravenous infusion of pitressin. All measurements were made before (basal) and after infusion of 0.02 U pitressin.min-1.kg-1 for 15 min. Pitressin significantly decreased portal venous pressure and blood flow, and increased vascular resistance of all tissues of the esophagus. This vasoconstriction of the tissues, however, was higher in the squamous mucosa of the body than in the columnar mucosa of the lower esophageal sphincter. In contrast, it was higher in the smooth muscle of the lower esophageal sphincter than in the striated muscle of the body. These data together with those of our previous report on isoproterenol demonstrate that pitressin causes a pronounced vasoconstriction in those esophageal tissues where isoproterenol had no effect. Conversely, pitressin causes least vasoconstriction in those tissues where isoproterenol produced a significant vasodilation. These differences could be the result of partial agonist actions or differences in receptor density or in receptor-effector coupling mechanism.     

The modifying action of calcium antagonists on postirradiation thymidinemia]

Single and long-term per os administration of verapamil, a calcium antagonist, changes the thymidine content of nonirradiated mouse blood. The changes observed depend upon verapamil concentration in the blood. The postirradiation thymidinemia level is the lowest in animals exposed at the time when the thymidine content was minimized by the agent administered.