Summary
The development of the ability of the kidney to concentrate urine was studied in normal
and propylthiouracil-treated rats by measuring urinary sodium concentration and osmolarity
at different ages. It was shown that the normal animals, but not the PTU-treated ones
were able to concentrate urine at 35 days of age. The response of the hypothalamo-neurohypo-physeal
axis (AVP system) and that of the kidney were investigated in the two categories of
animals at 35 days of age by measuring concomitantly the AVP content of the hypothalamus
and neurohypophysis, the AVP plasma concentration and the natremia and plasma osmolarity
at various intervals after intraperitoneal injection of a 5% NaCl solution. In normal,
as well as in PTU-treated rats, salt load did not lead to significant modifications
of the hypothalamic AVP con-tent. In comparison with normal rats, the neurohypophysis
of the PTU-treated ones released AVP more slowly, but with a similar amplitude. In
normal rats, the plasma AVP concentration was already maximal 30 min after salt load
and then decreased and returned to the normal value at 2 hrs; at the same time, the
natremia and plasma osmolarity also recovered their normal value. In contrast, the
plasma AVP concentration as well as the natremia remained high 1 h 30 after salt load
in PTU-treated rats. It is concluded that PTU-treated young rat is unable to compensate
the salt load in normal delays. Beside the slowing in AVP release by neurohypophysis
and decreased AVP plasma level, the responsiveness of the kidney seems to be altered.
Key-Words:
Developing Rat
-
PTU Treatment
-
Salt Load
-
Vasopressin
-
Hypothalamus
-
Neurophypophysis
-
Natremia
-
Plasma and Urine Osmolarity
