Endocrine Abstracts

Gonadotrophs have previously been shown to be the predominant source of C-type natriuretic peptide (CNP) in the anterior pituitary, and CNP causes enhanced cGMP accumulation in αT3-1 gonadotrophs. However, the biological role of CNP in gonadotrophs remains elusive. In the current study, we examined the molecular and functional characteristics of the gonadotroph natriuretic peptide system. Using two well-characterised gonadotroph cell lines of different developmental origin (αT3-1 and LβT2), we first examined the expression of components of the natriuretic peptide system. Both αT3-1 and LβT2 cells expressed CNP, GC-A and GC-B, soluble guanylyl cyclase α and β subunits, and protein kinase G by PCR analyses. To determine whether the receptors were functional, cGMP enzymeimmunoassays were used to measure the response to ANP, CNP and the nitric oxide donor, sodium nitroprusside (SNP), in the presence of 1 mM IBMX. As expected, αT3-1 cells responded in a concentration-dependent manner to ANP, CNP and SNP. However, LβT2 cells appeared more responsive to ANP than CNP, and had a blunted SNP response. To determine the functional consequence of CNP signalling in these cells, we examined CNP effects on cell proliferation and gene transcription. CNP failed to significantly alter cell proliferation (by cell counting) or cell cycle distribution (by flow cytometry) in either cell line. However, when αT3-1 and LβT2 cells were transiently transfected with deletion constructs of the human αGSU promoter, CNP caused significant stimulation of reporter gene activity in LβT2 cells (between 2.9±0.5-fold and 6.3±0.9-fold, **), without significantly affecting the αGSU promoter in αT3-1 cells. These concentration-dependent effects of CNP in LβT2 cells were independent of MAPK activity, but mimicked by ANP, suggesting a cGMP-dependent effect. These data reveal an active natriuretic peptide system in gonadotroph cell lines, suggesting that CNP is an autocrine regulator of gonadotrophs. Funded by a BBSRC Project Grant (BBD0015601).