PTH and osteoporosis: This well-known reversal of the sustained resorptive PTH action to bone mineral accretion with pulsatile PTH secretion is used in medicine with injections of synthetic PTH analog, teriparatide (TPTD), to treat osteoporosis [33], Application of TPTD is a circadian event, because a circadian 8 h admnistration to osteoporotic postmenopausal women completely abolished nocturnal circadian CTX rhythm [33] (Figure 8A), while a 20 h injection did not (Figure 8B).