Abstract
Summary
(1) Ultrafiltrates of partially purified rat hypothalamic extract were capable of inhibiting prolactin release in vitro. (2) These same extracts at a higher dose partially prevented the suckling-induced rise in blood prolactin concentration and lowered the already elevated levels present in suckling rats. (3) The in vivo response to hypothalamic extracts was of short duration and had disappeared within 45 min of the injection. (4) Under these conditions, similarly prepared cortical extracts or oxytocin in doses higher than those found in the extracts had no effect. (5) It is concluded that partially purified hypothalamic extracts from the rat contain a prolactin-inhibiting factor.
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