The effects of acute administration of human parathyroid hormone (1-34) [PTH(1-34)] on the blood pressure of 15 young (mean age +/- SD, 20.9 +/- 1.7 years; 7 males and 8 females) and 11 elderly (78.1 +/- 5.9 years; 4 males and 7 females) normal subjects were compared. The elderly subjects have a slightly, but significantly higher mean basal systolic blood pressure (132.4 +/- 17.7 mmHg) than the young subjects (118.7 +/- 11.4 mmHg), but the basal diastolic and mean blood pressures of the two groups were similar. Intravenous bolus infusion of PTH(1-34) at a dose of 100 U induced transient, but marked hypotension in all subjects. The mean maximal decrease in systolic blood pressure (-delta SBP was significantly more (p less than 0.01) in the elderly subjects (42.5 +/- 13.9 mmHg) than in the young subjects (8.0 +/- 8.9 mmHg), but the maximal decrease in diastolic blood pressure (-delta DBP) was similar in the elderly (25.6 +/- 13.9 mmHg) and young (27.3 +/- 10.9 mmHg) subjects. The maximal decrease in the mean blood pressure (-delta MBP) was also significantly higher (p less than 0.01) in the elderly subjects (31.9 +/- 8.7 mmHg) than in young ones (20.6 +/- 7.6 mmHg). The corrected serum level of calcium (scCa) was significantly (p less than 0.01) lower in the elderly subjects (9.6 +/- 0.2 mg/dl) than in the young ones (10.0 +/- 0.3 mg/dl), and the serum level of C-terminal parathyroid hormone (C-PTH) was significantly higher in the elderly subjects (270 +/- 80 pg/ml) than in the young ones (150 +/- 80 pg/ml).(ABSTRACT TRUNCATED AT 250 WORDS)