HYPERPROLACTINEMIA CAUSED BY LACTATION AND PITUITARY-ADENOMAS IS ASSOCIATED WITH ALTERED SERUM-CALCIUM, PHOSPHATE, PARATHYROID-HORMONE (PTH), AND PTH-RELATED PEPTIDE LEVELS

PRL stimulates systemic release of PTH-related peptide (PTHrP) in anim als. To determine whether hyperprolactinemia causes PTHrP release in h umans, we studied the relationship between PRL and PTHrP in lactating women and patients with PRL-producing pituitary adenomas. Thirty-three lactating women and 16 patients with pituitary adenomas were paired w ith healthy age- and sex-matched controls. Serum total calcium, albumi n, phosphate; PRL, intact PTH, and PTHrP were measured. Mean calcium a nd phosphate levels were higher in lactating women than in control sub jects [2.39 +/- 0.01 v/s. 2.35 +/- 0.01 mmol/L (P < 0.01) and 1.33 +/- 0.03 vs. 1.13 +/- 0.02 mmol/L (P much less than 0.001), respectively] . Mean PTH was lower (2.49 +/- 0.24 vs. 3.17 +/- 0.23 pmol/L; P < 0.04 ) and mean PTHrP was higher than control values (0.93 +/- 0.08 vs. 0.3 8 +/- 0.04 pmol/L; P much less than 0.001). PRL correlated negatively with PTH (P < 0.02) and positively with PTHrP (P < 0.05): Mean calcium , phosphate, and PTH levels were hot different between patients with p ituitary adenomas and control subjects. The mean PTHrP level was highe r in patients with pituitary adenomas (0.75 +/- 0.10 vs. 0.39 +/- 0.07 pmol/L; P < 0.006) and fell significantly with therapy to normalize P RL (P < 0.03). We conclude that PTHrP levels are increased in hyperpro lactinemia caused by lactation and pituitary adenomas. In lactating wo men, the increased PTHrP was associated with higher mean calcium and p hosphate and lower PTH levels. The metabolic consequences of these abn ormalities in hyperprolactinemia require further elucidation.