Abstract
Copper salts induce ovulation in the estrous rabbit, 1 2 a species which normally ovulates only after copulation. The natural mating stimulus, which results in the release of luteinizing hormone from the adenohypophysis, involves the hypothalamus and the pituitary stalk 3 and includes both adrenergic and cholinergic components. 4
Bischoff 5 suggested that copper activated the hypophysis by toxic stimulatory effects on the nervous system. The idea appeared to be confirmed by the results of Brooks, 3 who found that copper failed to induce ovulation in rabbits whose hypophyseal stalks had been severed, and Harris, 6 who reported that very weak dosages of copper acetate injected directly into the third ventricle stimulated the ovulatory response.
We were led to doubt that copper-induced ovulation is purely a nerve-stimulation phenomenon when dibenamine and atropine, in dosages adequate to block the copulation stimulus from reaching the hypophysis, 4 , 7 failed to prevent copper acetate from activating the release of an ovulatory surge of LH. 8 It therefore seemed desirable to test the hypothesis that copper might exert its stimulatory action directly upon the anterior pituitary.
Sexually mature female rabbits ranging in weight from 2.5 to 4.3 kg were employed; in this study. To insure an estrous condition, each animal was treated with 85 μg estradiol benzoate on 2 successive days prior to copper administration, for ovulation is not induced by copper in anestrous rabbits. 9 A control series of 10 females revealed that the estrogen alone would not stimulate LH release. The hypophysis was approached parapharyngeally as in earlier studies, 10 11 and 4 attempts were made at 5 or 10s minute intervals to inject a total of 0.15 ml of 0.1% copper acetate, buffered with 0.1% sodium acetate, 12 directly into the pars distalis.
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