Growth Hormone-Releasing Activity in Plasma of Normal and Hypophysectomized Rats

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Abstract
Growth hormone (GH)-releasing activity in plasma of normal or hypophysectomized male rats was investigated by the method of in vivo depletion of growth hormone in rat pituitaries. Plasma from rats hypophysectomized about 3 months previously depleted pituitary growth hormone when injected into the carotid artery of 40-day-old recipient rats. This activity was absent in plasma of rats hypophysectomized for only a week and from plasma of normal rats of the same age as the hypophysectomized rats. The GH-releasing activity of plasma from long-term hypophysectomized rats appeared to be of neural origin, since it was not present in aortic plasma 10 min. after elimination of the cranial circulation.