A comparison of the effects of bovine parathyroid hormone 1-34 and methylated prostaglandin E2 analogues on plasma calcium and inorganic phosphate levels in immature chickens and rats.

The relative effects of bovine parathyroid hormone 1-34 (bPTH-(1-34] and prostaglandin (PG)E2 analogues, 16,16-dimethyl PGE2 and 11,16,16-trimethyl PGE2, on plasma calcium, inorganic phosphate (Pi), and osmolality in 12-day-old chickens were compared. bPTH-(1-34) and 16,16-dimethyl PGE2 were similarly tested for effects on plasma Ca and Pi in immature (3-week-old) rats. PGs administered iv in a saline vehicle (20 micrograms 16,16-dimethyl PGE2 or 125 micrograms 11,16,16-trimethyl PGE2/100 g body wt, respectively) produced significant hypercalcaemic effects in chicks compared with vehicle-injected controls at times ranging from 15 to 90 min, similar to those obtained with bPTH-(1-34) (3.3 micrograms/100 g body wt). The PGE2 analogues injected in chicks also produced significant increases in plasma Pi compared with controls at 15 and 45 min, while those treated with PTH showed smaller, nonsignificant plasma Pi responses. Little change in plasma osmolality was seen in chicks following injection with either bPTH-(1-34) or 16,16-dimethyl PGE2, although a small but significant increase in this parameter was seen in chicks treated with 11,16,16-trimethyl PGE2. Acute labelling of chicks with 32P incorporated into the 16,16-dimethyl PGE2 injection vehicle indicated a decreased exit of Pi from the blood as the mechanism underlying the PG-mediated hyperphosphataemic response. This type of response was not seen following bPTH-(1-34) injection in chicks.(ABSTRACT TRUNCATED AT 250 WORDS)