Changes in hypothalamic estrogen receptor-containing cell numbers in response to feed restriction in the female lamb

The mechanism whereby undernutrition enhances the ability of estradiol (E) to inhibit reproductive activity is unknown. This study aimed to determine the effect of feed restriction on E receptor (ER)-containing cell numbers i n the female sheep hypothalamus. Ovariectomized lambs at 7 months of age re ceived either ad libitum (AL; n = 5) or restricted (FR; n = 10) levels of f eed intake. Lambs were weighted weekly and FR lambs fed to lose approximate ly 15% of their initial body weights over 7 weeks, at the end of which jugu lar blood samples were collected at 10-min intervals for 5 h to assess the patterns of LH release. After blood collection, lambs were euthanized and h ypothalami collected for immunocytochemical detection of ER. Based on LH se cretory profiles, FR lambs were subdivided into two groups. The first group (FR + LH; n = 5) exhibited patterns of LH release similar to AL controls. LH secretion in the second group (FR-LH; n = 5) was obviously suppressed. N umbers of ER-containing cells did not differ significantly (p > 0.10) among treatment groups in the bed nucleus stria terminalis, anterior hypothalami c area and arcuate nucleus. ER-containing cell numbers were greater (p < 0. 05) in the preoptic area (POA) but less (p < 0.05) in the ventromedial/vent rolateral hypothalamus (VMH/VLH) for FR-LH lambs compared to AL animals. No tably, for both the POA and VMH/VLH, ER-containing cell numbers in the FR LH animals were intermediate and did not differ (p > 0.10) from either FR- LH or AL lambs. These results suggest that feed restriction differentially alters ER-containing cell numbers in specific regions of the ovine hypothal amus (numbers increased in the POA but decreased in the VMH/VLH). These cha nges may, at least in part, represent a mechanism whereby undernutrition en hances the ability of E to inhibit reproduction.