Effects of hypophysectomy and ovariectomy on hepatic estrogen receptor content in the turtle, Chrysemys picta

Abstract

Estrogen receptor (ER) content in the cystosol and nuclear extract of the liver of adult female Chrysemys picta (control females) was measured in February, May, early June, and late June. Both cystosolic (C) and nuclear (N) hepatic ER content rose from low levels (C: 189 ± 19; N: 52 ± 23 fmol/g tissue) in February to significantly higher levels in May (C: 437 ± 15; N: 124 ± 25 fmol/g tissue) before declining to lower values in early June (C: 298 ± 19; N: 118 ± 20 fmol/g tissue) and late June (C: 274 ± 22; N: 89 ± 13 fmol/g tissue). This pattern of seasonal variation in hepatic ER content was also observed in gonadectomized females. Levels of hepatic ER content in ovariectomized turtles fluctuated in the same manner as those found in control females. However, elevations in hepatic ER contents were not observed in hypophysectomized females. Removal of the pituitary resulted in a drastic reduction in the May value (316 ± 49 fmol/g tissue) of cystosolic ER content and a complete blockade in a rise of nuclear ER content in the liver of the turtle. Nuclear hepatic ER content remained at around 50 fmol/g tissue throughout the months of May and June. The two surgeries procedures caused no significant changes in the ER's affinity for estrogen. The present findings demonstrate a direct control of the pituitary over hepatic ER content which signifies important pituitary regulation of the vitellogenic process, at the liver level, during the spring reproductive season.