Serum calcium does not influence the extraction of 125I-bovine parathyroid hormone by the dog liver in vivo.

To gain information regarding the possible influence of serum calcium on the hepatic extraction and early metabolism of the complete molecule of parathyroid hormone (PTH(1-84)) in vivo, we have studied the role of serum calcium on the fractional extraction and clearance of 125iodinated bovine parathyroid hormone, 125I-bPTH(1-84), by the dog liver in vivo. Dog serum calcium was increased by calcium chloride or decreased by sodium EDTA infusions. Hepatic blood flow, fractional hepatic extraction and hepatic clearance were calculated from dilution curves obtained by sampling the hepatic vein after injection of 125I-bPTH(1-84) and reference substances in the portal vein of anesthetized dogs. The gel chromatography profile of the 125I-radioactive substance injected and recovered was also analyzed to confirm results. Each dog was first studied in the basal state and then again after its serum calcium level was modified. Increasing or decreasing the serum calcium by 1.5 and 3 mg/dl in groups of at least five dogs had no effect on the hepatic blood flow, fractional hepatic extraction or hepatic clearance of 125I-bPTH(1-84). A negative correlation was found to exist between hepatic blood flow (ordinate) and fractional hepatic extraction (abscissa) of 125I-bPTH(1-84), both in the basal state (r = -.483, p less than .05, n = 24) and after having modified serum calcium (r = -.548, p less than .01, n = 24). The intercepts on the Y axis and the slopes of these correlations were statistically identical, again indicating that serum calcium had no effect on hepatic blood flow or fractional hepatic extraction.(ABSTRACT TRUNCATED AT 250 WORDS)