Subcutaneous injections of oestradiol benzoate in oil, resulting in a sustained elevation of circulating oestradiol levels, induced an initial suppression of LH secretion, followed by a positive discharge of LH in castrated male and female and in intact male marmosets. Oestrogen-induced LH release (producing maximum LH concentrations 24 h after the injection) was observed in 75% of castrated males and females. A positive discharge of LH occurred in 50 % of intact males 28\p=n-\36h after

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... n administration. The experimental production of a preovulatory type of LH discharge after oestradiol administration (positive feedback) in intact and ovariectomized females has been well documented for rats (Caligaris,