HUMAN GRANULOSA-LUTEAL CELLS SECRETE PARATHYROID HORMONE-RELATED PROTEIN INVIVO AND INVITRO

The presence of mRNA transcripts and/or immunoreactivity for PTH-related protein (PTHrP) in several normal mammalian tissues suggests a possible paracrine or autocrine role for this hormone. Since immunohistochemical studies of human ovary demonstrate the presence PTHrP immunoreactivity in this tissue, we wondered if ovarian follicular fluid (OVFF) might contain PTHrP. We retrospectively analyzed 28 OVFF samples obtained at ova harvest in 21 women undergoing in vitro fertilization. Fourteen samples contained significant adenylate cyclase-stimulating activity in a PTHrP-sensitive bioassay. In a subsequent prospective analysis, 41 of 45 freshly obtained OVFF samples demonstrated significant activity. This bioactivity was completely neutralized by antisera to PTHrP, but was unaffected by antisera to PTH. Fifteen OVFF samples were also analyzed in a sensitive 2-site immunoradiometric assay for PTHrP, and all 15 demonstrated significant levels of the hormone. The PTHrP levels did not correlate with the presence of an ovum in the follicle or with follicular fluid calcium. Short term (24- to 48-h) cultures of granulosa-luteal cells established from 5 OVFF samples demonstrated constitutive secretion of PTHrP using the immunoradiometric assay. Neither progesterone nor estrogen affected basal secretion. RNase protection analysis of cellular RNA prepared from cultured granulosa-luteal cells demonstrated the presence of mRNA for PTHrP in these cells. We conclude that 1) human OVFF obtained after stimulation with FSH and LH contain high concentrations of PTHrP; and 2) the granulosa-luteal cell is capable of secreting PTHrP both in vivo and in vitro.