Determination of bioactive rat parathyroid hormone (PTH) concentrations in vivo and in vitro by a 2-site homologous immunoradiometric assay.
A new homologous 2-site assay for rat parathyroid hormone (IRMA), developed by Immutopics, Inc., has been evaluated and compared with a bone cell cAMP bioassay. Circulating PTH for adult rats assayed with this IRMA are in the range 10-15 pg/ml, and of the same order of magnitude as published values for biologically active PTH. The standard curve for the IRMA was linear over the range 3.4-240 pg/ml of rPTH 1-34, and serum samples diluted in parallel with the standard curve. The within-assay and between-assay coefficients of variation ranged from 5.2% (n = 18) to 7.6% (n = 24) and 8.3% (n = 16) to 26.4% (n = 10), respectively. Serum PTH values (mean +/- S.E.) for parathyroidectomized rats were 3.5 +/- 0.6 pg/ml (n = 18) versus 10.3 +/- 1.4 pg/ml (n = 16) for intact non-mated rats. Calcium injections suppressed circulating PTH by 50%. Lactating rats had serum PTH levels 5-fold higher and vitamin D deficient rats 60-fold higher than non-mated controls. PTH secreted from parathyroid cells in vitro was in the range 60-490 pg/ml as determined by the IRMA. These values represented 86.0 +/- 9.0% of the comparable bioassay values, indicating that the IRMA detects only bioactive PTH.
Schultz
V L
VL
Dental Research Center, University of North Carolina, Chapel Hill 27599-7455.
Garner
S C
SC
Lavigne
J R
JR
Toverud
S U
SU
D000818:Animals; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000032:analysis / Q000378:metabolism*; D005260:Female; D015592:Immunoradiometric Assay; D010280:Parathyroid Glands / Q000166:cytology* / Q000378:metabolism; D010281:Parathyroid Hormone / Q000032:analysis / Q000097:blood* / Q000378:metabolism; D016105:Parathyroidectomy; D011247:Pregnancy; D051381:Rats; D017207:Rats, Sprague-Dawley; D012044:Regression Analysis
D010281:Parathyroid Hormone; D000242:Cyclic AMP