Interstitial cell-stimulating hormone-releasing activity of hypothalamic extracts in the dog

The effect of hypothalamic extracts on 17-ketosteroid secretion by the testis of the dog was investigated. Stalk-median eminence extracts produced an increased rate of 17-ketosteroid secretion by the testis but extracts of the anterior hypothalamus caused little or no increase in the testicular output. No effect was obtained after the administration of extracts of the pre-optic, posterior hypothalamic and other brain regions. Stalk-median eminence extracts, after boiling, were still active in stimulating the testis though part of the activity was lost. The extracts failed to increase the testicular output of 17-ketosteroids in the hypophysectomized dog and the response is thus considered to be pituitary-dependent. Furthermore, intracarotid administration of acetylcholine, catechol amines, γ-amino-n-butyric acid (GABA), glutamic acid and aspartic acid did not stimulate testicular 17-ketosteroid secretion.