PROGESTERONE TREATMENT INCREASES PITUITARY OESTRADIOL RETENTION IN THE OVARIECTOMIZED NORMAL FEMALE RAT BUT NOT IN THE MALE NOR IN THE ANDROGEN- OR OESTROGEN-STERILIZED FEMALE RAT

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Abstract
Pituitary retention of [3H]estradiol in ovariectomized rats was measured following in vivo progesterone pre-treatment and found to be significantly increased after 48, 72, 96 and 120 h of pre-treatment. Increased [3H]-estradiol retention was also observed for at least up to 72 h after removal of the progesterone pre-treatment source. This retention was measured as dpm [disintegrations per minute] per mg dry tissue weight. [3H]estradiol retention was also measured in the nuclear fraction of tissues incubated with [3H]-estradiol in vitro. Following 72 h of in vivo progesterone pre-treatment, the nuclear fraction from the pituitary retained significantly more [3H]estradiol than corresponding fractions from non-treated animals. In contrast to ovariectomized females, no increase in [3H]estradiol retention was found in the pituitary of orchidectomized males pre-treated with progesterone for 72 h. [3H]estradiol retention by pituitaries of ovariectomized rats injected on the day of birth with 200 .mu.g estradiol benzoate (OeB) or 500 .mu.g testosterone propionate (TP) was significantly decreased in comparison to control animals. When rats were pre-treated in vivo with estradiol for 6 or 72 h and [3H]estradiol retention was measured 6 or 24 h after this pre-treatment, the OeB and TP treated animals retained significantly less [3H]estradiol under most treatment conditions. Progesterone pretreatment for 24 or 72 h in vivo followed by measurement of [3H]estradiol retention immediately or 6 or 24 h later significantly increased in [3H]estradiol retention for the control animals. The neonatally OeB or TP treated animals differed significantly by not showing increased retention. When [3H]estradiol retention of the pituitary was measured in vitro following homogenization at 0.degree. C and incubation at 37.degree. C for 1 h, the nuclear fraction from both OeB and TP treated animals retained less hormone per unit DNA; this decrease was significant only for the TP animals. Males and androgen- or estrogen-sterilized females have an altered and reduced augmentation of pituitary estradiol retention in response to both estrogen and progesterone pretreatments.