No abstract

The mitogenic effect of epidermal growth factor (EGF) and the characteristics of EGF binding were studied on primary cultures of rabbit proximal tubular cells. EGF was found to be a potent mitogen and stimulated DNA synthesis 18-fold above the level observed in quiescent cells. Using 125I-EGF as a ligand, two classes of specific EGF receptors were identified on the proximal tubular cell in culture, i.e., a high-affinity receptor with a dissociation constant (Kd) of 0.3 nM and maximal binding (Bmax) of 1.7 X 10(4) receptors/cell and a low-affinity receptor with a Kd of 1.9 nM and Bmax of 5.3 X 10(4) receptors/cell. Because angiotensin II (ANG II) appeared to possess many properties common to growth factors, we also examined the interaction of ANG II and EGF on these cells. ANG II was not mitogenic, but it potentiated the mitogenic effect of EGF with a maximal effect at 10(-9) M. The dose-response curve of EGF-induced mitogenesis was shifted to the left in the presence of 10(-9) M ANG II, decreasing the approximate half-maximal stimulatory concentration from 3 X 10(-8) to 5 X 10(-9) M. ANG II also stimulated prostaglandin E2 (PGE2) release, but inhibition of basal and ANG II-stimulated PGE2 synthesis had no effect on mitogenesis. ANG II had no effect on the binding of EGF to the high-affinity receptor from 1 to 20 h and did not alter receptor downregulation. ANG II (10(-9) M) had no effect on cell protein content, RNA and protein synthesis, Na+-H+ antiport, and intracellular free Ca2+ concentration. Higher concentrations of ANG II (5 X 10(-8) to 5 X 10(-6) M) led to a rapid and transient dose-dependent rise in cytosolic free Ca2+ concentration. These studies demonstrate that ANG II potentiates EGF-induced mitogenesis at one or more postreceptor steps that may include small changes in cytosolic Ca2+ concentration.

No abstract

The purpose of this study was to measure bone-regenerative effects of recombinant human bone morphogenetic protein-2 (rhBMP-2) in rat calvarial critical-size defects (CSDs). CSDs (8 mm in diameter) were treated with either 1) 2.2 micrograms rhBMP-2 combined with insoluble collagenous bone matrix (ICBM), 2) 6.5 micrograms rhBMP-2 plus ICBM, 3) ICBM alone, or 4) demineralized bone matrix (DBM), for 7, 14, or 21 days. Multiple linear regression showed that rhBMP-2 had a significant time- and dose-dependent effect on bone regeneration (P < .05). After 7 days, new calcifying cartilage and remineralizing ICBM, with an occasional zone of new woven bone, was evident in defects treated with rhBMP-2/ICBM. By 14 days, both doses of rhBMP-2 reconstituted with ICBM had induced more bone formation than ICBM alone or DBM, and 6.5 micrograms was superior to 2.2 micrograms. There was no evidence of adverse cellular response. This study shows for the first time that rhBMP-2 could restore osseous form to a calvarial defect. In addition, osteoregeneration was accelerated by the higher dose of rhBMP-2.