Modulation of the anabolic effect of synthetic human parathyroid hormone fragment-(I-34) in the bone of growing rats by variations in the dosage regimen.

1. The influence of the time of the day of the administration of synthetic human parathyroid hormone fragment-(1-34) [hPTH-(1-34)] on its anabolic effect in bone was investigated in 23 60-day-old female Wistar rats. Rats were randomly assigned to the groups vehicle control morning, hPTH-(1-34)-treated morning, vehicle control afternoon and hPTH-(1-34)-treated afternoon, and once daily received a subcutaneous injection of 8 micrograms of hPTH-(1-34)/100 g body weight for 11 days. The increase in net intestinal calcium absorption and the increase in calcium balance were not influenced by the time of day of hPTH-(1-34) treatment. Four days after cessation of treatment, the net intestinal calcium absorption and calcium balance in hPTH-(1-34)-treated rats were not different from those of the control rats. 2. Modulation of the anabolic effect by variation of the hPTH-(1-34) dosage regimen was investigated in 43 60-day-old female Wistar rats. Rats were randomly assigned to the groups vehicle control, environmental control, 8 micrograms of hPTH-(1-34)/100 g body weight every 3 days for 24 days, 8 micrograms of hPTH-(1-34)/100 g body weight every 2 days for 16 days, 8 micrograms of hPTH-(1-34)/100 g body weight every day for 8 days, 4 micrograms of hPTH-(1-34)/100 g body weight twice a day for 8 days and 2.7 micrograms of hPTH-(1-34)/100 g body weight three times a day for 8 days. In all cases, the total dose of hPTH-(1-34) received was 64 micrograms/100 g body weight.(ABSTRACT TRUNCATED AT 250 WORDS)