SYNTHETIC PARATHYROID HORMONE-RELATED PEPTIDE(1-34) FRAGMENT STIMULATES PLACENTAL CALCIUM TRANSFER IN EWES

The influence of synthetic parathyroid hormone related peptide (PTHrp) fragments on placental transfer of Ca was studied in four groups of four single ovine fetuses fitted with catheters chronically implanted into their left jugular vein (for injections) and carotid artery (for blood sampling), and used between days 104 and 118 of gestation. The first received PTHrp(1-34), the second PTHrp(107-138), the third bovine PTH(1-34), and the last (control) group was injected with solvent alone. Each peptide (6 nmol/fetus per day) was injected i.v. three times per day from day 105 until day 116 of gestation. Placental Ca transfer (mmol/24 h per kg fetal wt) from the dam to the fetus was not different in control fetuses (7.1 ± 0.6) and those given PTHrp(107-138) (7.2 ± 0.5), but it was significantly increased by bovine PTH(1-34) (8.6 ± 0.4; P < 0.05) and by PTHrp(1-34) (10.1 ± 0.3; P < 0.01). Both peptides also significantly increased plasma concentrations of 1,25 dihydroxyvitamin D3 (1,25-(OH)2D). These results indicate that PTHrp(1-34) can stimulate placental Ca transfer by increasing 1,25-(OH)2D synthesis, but also possibly by acting directly upon the placenta.