A Comparative Study of Plasma Vasopressin Levels and V₁ and V₂ Vasopressin Receptor Properties in Congenital Hypothyroid Rat Under Thyroxine or Vasopressin Therapy

Summary

The effects of propylthiouracil (PTU) treatment on the plasma vasopressin level, on the number of hepatic (V₁) or renal (V₂) Vasopressin receptors and on the hormone-sensitive adenylate cyclase activity in the kidney of developing rats were studied in parallel. In addition, we investigated the corrective effects of thyroxine therapy on the plasma vasopressin level and parameters related to the liver, and the effects of vasopressin therapy on the parameters related to the kidney. As already reported in the case of the number of V₂ receptors and adenylate cyclase activity in the kidney, the deficient plasma vasopressin level in hypothyroid rats was completely corrected by two daily physiological doses of thyroxine given from birth to the age of sacrifice (1 month). Unlike the V₁ receptors, the V₂ receptors are known to be highly dependent on their specific circulating ligand. Since, first of all, the deficit was similar in the numbers of V₁, and V₂ receptors in hypothyroid rats, and, secondly, the treatment of hypothyroid rats by two daily physiological doses of long lasting vasopressin was found ineffective to recover the deficit in the number of V₂ receptors, it can be concluded that thyroid deficiency directly alters vasopressin receptor biosynthesis in both liver and kidney, instead of acting via the depressed plasma vasopressin level.

Key-Words

Developing Rat - Hypothyroidism - Plasma Vasopressin - V₁ and V₂ Receptors - Adenylate Cyclase Activity - Thyroxine and Vasopressin Therapy