A comparison of the effects of bovine parathyroid hormone 1–34 and methylated prostaglandin E 2 analogues on plasma calcium and inorganic phosphate levels in immature chickens and rats

Abstract

The relative effects of bovine parathyroid hormone 1–34 (bPTH-(1–34)) and prostaglandin (PG)E 2 analogues, 16,16-dimethyl PGE 2 and 11,16,16-trimethyl PGE 2, on plasma calcium, inorganic phosphate ( P i), and osmotality in 12-day-old chickens were compared, bPTH-(1–34) and 16,16-dimethyl PGE 2 were similarly tested for effects on plasma Ca and P i in immature (3-week-old) rats. PGs administered iv in a saline vehicle (20 μg 16,16-dimethyl PGE 2 or 125 μg 11,16,16-trimethyl PGE 2/100 g body wt, respectively) produced significant hypercalcaemic effects in chicks compared with vehicle-injected controls at times ranging from 15 to 19 min, similar to those obtained with bPTH-(1–34) (3.3 μg/100 g body wt). The PGE 2 analogues injected in chicks also produced significant increases in plasma P i compared with controls at 15 and 45 min, while those related with PTH showed smaller, nonsignificant plasma P i responses. Little change in plasma osmolality was seen in chicks following injection with either bPTH-(1–34) or 16,16-dimethyl PGE 2, although a small but significant increase in this parameter was seen in chickes treated with 11,16,16-trimethyl PGE 2. Acute labelling of chicks with 32P incorporated into the 16,16-dimethyl PGE 2 injection vehhicle indicated a decreased exit of P i from the blood as the mechanism underlying the PG-mediated hyperphosphataemic response. This type of response was not seen following mediated hyperphosphataemic response. This type of response was not seen following bPTH-(1–34) injection in chicks. Both 16,16-dimethyl PGE 2 (20 μg/100 g body wt) and bPTH-(1–34) (6.6 μg/100 g body wt) injected iv into rats produced significant hypercalcaemic responses compared with controls at 45 min, although they were small compared to those in chicks. A small but significant hyperphosphataemia was also seen in response to the PG but not to bPTH-(1–34) at 45 min.