Renal-thyroid interrelationship in normotensive and hypertensive rats

An increase in the weight of the thyroid gland, accompanied by reductions in uptake and release of 131I, serum T 3 and reverse T 3 concentrations and an increase in serum TSH concentration, occurs during the development of renal hypertension in rats. Renal function, as assessed by BUN, serum and urinary creatinine concentrations, and ability to concentrate urine during dehydration, is depressed. The kidneys of both normotensive and renal hypertensive rats contain a thyroid depressing factor (TDF) which inhibits uptake of 131I both in vivo and in vitro as well as inhibiting the lactoperoxidase enzyme in vitro. The kidneys of renal hypertensive rats contain less, and the serum more, TDF than those of normotensive rats. Whether TDF is produced as a result of hypertension per se or as a result of renal damage accompanying hypertension remains for further study. TDF appears to be a peptide with a molecular weight in the range of 400 to 419 daltons.