We investigated the kinetics of production of the hepatocyte stimulating factor (HSF) by peritoneal exudate- and peripheral circulating blood-polymorphonuclear leukocytes (PMNLs). Effects of the HSFs on alpha-2-macroglobulin (a2M) synthesis and a2M specific gene expression in primary cultured adult rat hepatocytes were also examined. Peritoneal exudate-PMNLs were collected 3 hr after the injection of alkaline-denatured casein into the peritoneal cavity of rats. Secretion of HSF into the culture medium began within 15 min after the start of incubation and practically a full secretion was noted within 3 hr. Lipopolysaccharide or other agents were not required to induce HSF from the PMNLs. Inhibitors of protein or DNA synthesis, cycloheximide, actinomycin D or puromycin, did not inhibit the secretion of HSF by rat PMNLs thereby suggesting that preformed and pooled HSF in the PMNLs was secreted during incubation. Peripheral circulating blood-PMNLs collected from a healthy man did not secrete HSF, in the absence of stimulation but did secrete HSF after vigorous agitation during incubation at 37 degrees C. The PMNL-HSF induced the synthesis of a2M and the accumulation of a2M mRNA in primary cultured rat hepatocytes. However, the effect was evident only with dexamethasone present in the culture medium. Furthermore, the effects of the PMNL-HSFs on a2M and albumin protein synthesis were reciprocal: The PMNL-HSF induced a2M synthesis, whereas it suppressed albumin synthesis.