002-23 – The role of oxytocin in the neuroendocrine control of reproduction

The hypothalamic-pituitary-gonadal (H-P-G) axis controls reproductive function, as hypothalamic gonadotrophin-releasing hormone (GnRH) regulates hypophysial release of luteinizing hormone (LH), which is essential for ovulation and steroidogenesis. A limited number of in vitro studies suggest the nonapeptide oxytocin (OT) may influence LH release, however, the precise mechanisms involved are yet to be delineated. This study aimed to elucidate the role of sex steroids in modulating the OT-stimulated LH response by measuring ELISA-determined whole blood LH concentrations in C56BL/6 WT mice, 15, 30 and 60 minutes following intracerebroventricular OT administration in ovariectomized (OVX; n=5) and ovariectomized oestrogen-treated (OVX + E2; n=4 ) females, as well as, gonadectomized (GND; n=7) and gonadectomized testosterone-treated (GND + T; n=5) males. In females the presence of oestrogen elicited a significant rise in LH concentrations 15 min following OT administration (from 0.34 +/- 0.1 to 0.83 +/- 0.25, p=0.049) compared with a tendency to decrease LH concentrations in the absence of oestrogen (from 1.71 +/- 0.54 to 1.25 +/- 0.45, p=0.054). This contrasted with males, whereby GND mice displayed a significant increase in LH concentration 15 min following OT administration (from 1.64 +/- 0.29 to 3.19 +/- 0.17, p=0.003) but with no change in LH concentration observed in the presence of testosterone (from 0.57 +/- 0.05 to 0.64 +/- 0.09, p=0.6). These findings suggest that OT acts on the H-P-G axis to influence LH release in a sex- and sex steroid-dependent manner, but further research is required to delineate the underlying mechanisms.