It has been suggested that excess parathyroid hormone (PTH) in chronic renal failure (CRF) or chronic administration of PTH to normal rats caused derangements in norepinephrine and phospholipid metabolism of brain synaptosomes, because of an increase in their resting levels of cytosolic calcium which may induce a decrease in synaptosomal content of ATP. In the study presented here, the resting levels of cytosolic calcium in brain synaptosomes were measured in six groups of rats including: (1) normal rats; (2) rats with CRF of 21-days duration; (3) normocalcemic parathyroidectomized rats with CRF of 21-days duration; (4) rats with CRF of 21-days duration treated with verapamil from day 1 of CRF; (5) normal rats treated with verapamil for 21 days; and (6) normal rats treated with PTH for 21 days. Resting levels of cytosolic calcium of brain synaptosomes of CRF rats (437 +/- 18.0 nM) and normal rats treated with PTH (428 +/- 5.6 nM) were significantly (P less than 0.01) higher than those of normal rats (345 +/- 9.0 nM), normal rats treated with verapamil (354 +/- 8.7 nM), CRF rats treated with verapamil (361 +/- 12.9 nM), or CRF-parathyroidectomized rats (363 +/- 8.2 nM). There were no significant differences between the values of the last three groups of rats.(ABSTRACT TRUNCATED AT 250 WORDS)