Rats on calcium-deficient diets developed hypocalcemia, hyperparathyroidism and 
hypertension and showed an increase in plasma catecholamines. Adrenal gland 
catecholamines were decreased while tyrosine hydroxylase (TH) and dopamine 
beta-hydroxylase (DBH) were found to be increased, as compared to controls. In 
contrast, no significant differences were found between controls and 
parathyroidectomized rats in plasma catecholamines, and catecholamines, TH and 
DBH of the adrenal gland. These findings seem to indicate that the genesis of 
hypertension in rats on a low calcium diet is secondary to hyperparathyroidism 
caused by a low calcium diet. Furthermore, some relation between catecholamines 
and parathyroid hormone seems to exist in the regulation of blood pressure in 
rats.