Parathyroid Hormone Secretion Is Controlled by Both Ionized Calcium and Phosphate During Exercise and Recovery in Men

Context: The mechanism by which PTH is controlled during and after exercise is poorly understood due to insufficient temporal frequency of measurements. Objective: The objective of the study was to examine the temporal pattern of PTH, PO4, albumin-adjusted calcium, and Ca2+ during and after exercise. Design and Setting: This was a laboratory-based study with a crossover design, comparing 30 minutes of running at 55%, 65%, and 75% maximal oxygen consumption, followed by 2.5 hours of recovery. Blood was obtained at baseline, after 2.5, 5, 7.5, 10, 15, 20, 25, and 30 minutes of exercise, and after 2.5, 5, 7.5, 10, 15, 20, 25, 30, 60, 90, and 150 minutes of recovery. Participants: Ten men (aged 23 ± 1 y, height 1.82 ± 0.07 m, body mass 77.0 ± 7.5 kg) participated. Main Outcome Measures: PTH, PO4, albumin-adjusted calcium, and Ca2+ were measured. Results: Independent of intensity, PTH concentrations decreased with the onset of exercise (−21% to −33%; P ≤ .001), increased thereafter, and were higher than baseline by the end of exercise at 75% maximal oxygen consumption (+52%; P ≤ .001). PTH peaked transiently after 5–7.5 minutes of recovery (+73% to +110%; P ≤ .001). PO4 followed a similar temporal pattern to PTH, and Ca2+ followed a similar but inverse pattern to PTH. PTH was negatively correlated with Ca2+ across all intensities (r = −0.739 to −0.790; P ≤ .001). When PTH was increasing, the strongest cross-correlation was with Ca2+ at 0 lags (3.5 min) (r = −0.902 to −0.950); during recovery, the strongest cross-correlation was with PO4 at 0 lags (8 min) (r = 0.987–0.995). Conclusions: PTH secretion during exercise and recovery is controlled by a combination of changes in Ca2+ and PO4 in men. PTH rapidly decreased and then increased during exercise, it peaked in the first minutes of recovery before decreasing below baseline. Changes in Ca2+ and PO4 were related to the changes in PTH.