Growth hormone-releasing activity in the hypothalamus of animals of different species

Hypothalamic extracts from the dog, rabbit, mouse, kitten, pigeon, and frog were found to decrease the growth hormone (GH) content of rat pituitary glands. Comparable cerebral cortical extracts were completely inactive in this test. These results broaden previous observations on the existence of a GH-releasing factor (GRF) in the hypothalami of mammals and show the presence of GRF activity in birds and amphibians.