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The aim of this study was to determine the impact of surgical disconnection of the fetal hypothalamus and pituitary on the fetal prolactin response to different photoperiods. Disconnection of the hypothalamus (HPD) or a sham operation was carried out at around day 110 of gestation (term = 145 +/- 3 days). Before surgery, pregnant ewes were maintained under a photoperiod of 12 h light:12 h dark. After surgery, ewes carrying HPD fetuses (n = 10) or intact fetuses (n = 13) were exposed to either a long day (16 h light:8 h dark) or a short day (8 h light:16 h dark) regimen until day 143 of gestation. Thyrotrophin-releasing hormone (50 micrograms) was administered intrafetally at days 130-135 of gestation and chlorpromazine (a dopaminergic antagonist) was administered to all sheep fetuses at days 141-142 of gestation. Mean fetal prolactin concentrations were significantly higher in the long day group (HPD: 37.3 +/- 11.3 ng ml-1; intact: 71.0 +/- 16.2 ng ml-1) than in the short day group (HPD: 9.0 +/- 4.8 ng ml-1; intact: 34.2 +/- 16.0 ng ml-1). In the intact group, fetal prolactin concentrations increased significantly between day 6 and day 30 of exposure to either photoperiod. However, in the HPD group, fetal prolactin increased with increasing exposure to the long day photoperiod and decreased with increasing exposure to the short day photoperiod.(ABSTRACT TRUNCATED AT 250 WORDS)

Response of prolactin to different photoperiods after surgical disconnection of the hypothalamus and pituitary in sheep fetuses