A parathyroid-related peptide induces transcaltachia (the rapid, hormonal stimulation of intestinal Ca2+ transport)

PTH-related peptide (PTHrP) has been shown to be responsible for the hormonal hypercalcemia of malignancy. Previously, we demonstrated that both 1,25(OH)2-vitamin D3 and the N-terminal fragment of PTH (1-34) stimulates the rapid transport of Ca2+ (transcaltachia) in the perfused chick intestine. Since there is a sequence homology between these two hormones in the n-terminal fragment, in this study we examined the effect of PTHrP(1-40) on stimulation of transcaltachia in the perfused chick duodenum. The results indicate that the maximal stimulation of transcaltachia occurs at 50 pM PTHrP(1-40), and that the dose-response curve is biphasic in nature. Perfusion with 25 pM, 50 pM, 100 pM or 200 pM PTHrP(1-40) for 40 min increases the transport of Ca2+ in perfused intestine 1.8-, 3.0-, 2.4- and 1.6-fold, respectively. The response is rapid, occurring within 10 min of introduction of the PTHrP. The Ca2+ channel inhibitor nifedipine, which is known to abolish the transcaltachic effect elicited by 1,25(OH)2 vitamin D3, also inhibited the rapid transport of Ca2+ stimulated by PTHrP(1-40). The transcaltachic effect of PTHrP(1-40) may be mediated by a signal transduction pathway in which Ca2+ channels are activated.