Fate and biological action of human recombinant interleukin 1 beta in the rat in vivo.

The plasma half life of recombinant human interleukin 1 beta (rhIL 1 beta) was determined in rats by measuring the disappearance of the radioactivity of 125I-labeled rhIL 1 beta from the circulation. The plasma clearance showed a biphasic behavior: an initial fast disappearance (half life of about 3 min) was followed by a second slower one (half life of about 4 h). Twenty minutes after a single-dose injection of 125I-labeled rhIL 1 beta most of the radioactivity was concentrated in kidneys, liver and intestine. rhIL 1 beta induced the synthesis of alpha 1-acid glycoprotein (AGP), alpha 1-cysteine proteinase inhibitor (CPI) and beta-fibrinogen mRNA in liver. Half maximal stimulation was elicited by approximately 3000 U of rhIL 1 beta per animal. The mRNA changes for AGP and CPI were followed by corresponding protein increases in serum. Twenty hours after rhIL 1 beta injection, serum AGP rose from 0.7 to 2.5 mg/ml. CPI increased from 0.3 to 1.9 mg/ml 25 h after administration of rhIL 1 beta. Within 20 h after rhIL 1 beta injection, albumin serum concentration showed a strong decrease, preceded by a reduction in hepatic albumin mRNA levels. Neither changes in albumin synthesis nor degradation can explain this decrease suggesting that other mechanisms such as increased transvascular permeability are involved.