osmotic regulation of vasopressin and renin in spontaneously hypertensive rats abnormalities in the vasopressin and renin systems have been reported in spontaneously hypertensive rats shr therefore studies were performed to evaluate the responsiveness of these systems to changes in plasma osmolality and sodium concentration these variables were manipulated in vivo by intraperitoneal administration of distilled water isotonic saline or hypertonic saline to 8 and 18weekold shr and normotensive wistarkyoto rats wky animals were decapitated 30 minutes later and trunk blood was collected the hypertonic saline injections resulted in an increase in plasma osmolality and serum sodium at both ages p less than 0001 serum vasopressin was higher in all groups of animals receiving hypertonic saline 1200 mosmkg h2o p less than 005 but the magnitude of increase was not significantly different in the shr and wky at either age serum renin activity was lower in shr than in wky following acute decreases in serum sodium at 8 weeks but it was the same for both strains at 18 weeks both kidney renin content and concentration were lower in shr than in wky at 18 weeks but not at 8 weeks therefore the suppressed renin response to acute osmotic challenge in 8weekold shr is not the consequence of reduced kidney renin content the vasopressin response to osmotic stimulation also was evaluated in vitro using hypothalamoneurohypophyseal explants obtained from 5 8 and 18weekold shr and wkyabstract truncated at 250 words