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Enhancement of Parathyroid Hormone-Stimulated Bone Resorption by Poly-L-Lysine^*

LAWRENCE G. RAISZ, PIERRE J. BERGMANN, JESUS H. DOMINGUEZ and MARLENE A. PRICE

Department of Medicine, University of Connecticut Health Center Farmington, Connecticut 06032

Address requests for reprints to: Dr. Lawrence G. Raisz, Division of Endocrinology and Metabolism, University of Connecticut Health Center, Department of Medicine, Farmington, Connecticut 06032.

Abstract

Poly-L-lysine (PL II; mol wt, 1000–4000) was added to fetal rat bones cultured in a chemically defined medium (BGJ) containing bovine serum albumin in the presence and absence of parathyroid hormone (PTH). Bone resorption was measured by the release of previously incorporated ⁴⁵Ca. The addition of PL II at concentrations of 3–100 µ/ml enhanced the stimulation of bone resorption by submaximal doses of PTH but had little effect on ⁴⁵Ca release from control unstimulated cultures. Higher concentrations of PL II produced inhibition of ⁴⁵Ca release. Dialysis of PL II did not alter enhancement or inhibition by PL II. PL II did not increase sensitivity to PTH in serumsupplemented cultures. Higher molecular weight PL II preparations were less effective. PL II did not enhance the resorptive response to 1,25-dihydroxyvitamin D, prostaglandin E₂, osteoclast- activating factor, or bacterial endotoxin. The mechanism of the selective ability of PL II to enhance the response to low concentrations of PTH is unknown but may be due to the ability of this basic polypeptide to interfere with binding of PTH to sites other than the hormone receptor or to block degradation of PTH by bone.

Footnotes

^* This work was supported by Research Grant AM-18063 from the NIAMDD, NIH, and a grant from the Fonds National de la Recherche Scientifique, Beige.

Fulbright-Hays Scholar of the Council for International Exchange of Scholars.

Nutrition Scholar of the American College of Physicians.

Received October 2, 1978.