Calcium disturbances in the critically ill coincide with elevations of proinflammatory cytokines. The effects of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) on parathyroid hormone (PTH) secretion were investigated. IL-6 and TNF-α had no acute effect on PTH secretion in extracellular Ca2+ concentrations of 0.5, 1.25 and 3.0 mM. In contrast to TNF-α, cultures for 24 h in the presence of 10 ng/mL of IL-6 showed decreased PTH secretion by 51% and 29% in 0.5 mM and 1.25 mMCa2+ respectively. Neither IL-6 nor TNF-α, affected cytoplasmic Ca2+ of the cells. We conclude that PTH secretion in vitro can be suppressed by IL-6 at clinically relevant concentrations. This suppression may aggravate hypocalcemia of the critically ill and attenuate the conventionally strong stimulation of the PTH release by reduction in serum calcium.

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