Morphometric Studies on the Effects of Dehydration on the Renin-immunopositive Cells in the Kidney of the Mongolian Gerbil (<I>Meriones unguiculatus</I>)

Effects of dehydration on the total area of the kidney occupied by renin-immunopositive cells were morphometrically studied on parasagittal sections by an image-analyzing system in the Mongolian gerbils. Changes in the body weight and plasma osmolarity were simultaneously measured to compare with morphometric data. The body weight decreased rapidly at the beginning, and gradually after 10 days of dehydration. On the other hand, the plasma osmolarity showed no significant change at 2 days, increased gradually after 5 days, and reached a plateau after 15days. Similarly, the total area of renin-positive cells showed no significant changes at 2 days, increased remarkably after 5 days, and reached a plateau after 15 days. These findings suggest that the plasma osmolarity and total area of renin-positive cells showed no significant changes at the beginning of dehydration because the increase in the plasma osmolarity was compensated by the expenditure of inter- and intra-cellular fluid, and the total area of renin-positive cells was increased in response to the acceleration of renin synthesis stimulated by the increase in the plasma osmolarity after a certain period of dehydration. The total area seemed to be maintained on a certain level because the further increase in the plasma osmolarity was suppressed by the excretion of electrolytes from the body in proportion to the water loss after a long period of dehydration.