Norepinephrine and Dopamine Injection Into Lateral Brain Ventricle of the Rat and Growth Hormone-Releasing Activity in the Hypothalamus and Plasma

The effect of norepinephrine (NE) or dopamine (DA) on the growth hormonereleasing (GRF) activity in the hypothalamus and plasma of intact or hypophysectomized rats was studied by administering the catecholamines into the lateral ventricle of the brain. Growth hormone-releasing activity was evaluated by the depletion of pituitary growth hormone produced by intracarotid injection of hypothalamic extracts or plasma. NE and DA at doses known to be effective in depleting GH from the pituitary (0.5 μg) induced in intact and hypophysectomized rats disappearance of GRF activity from the hypothalamus and its appearance in plasma from hypophysectomized but not from intact rats. Unlike adrenergic compounds, serotonin (0.5 μg) was inactive. In intact rats NE given intraventricularly induced a depletion of pituitary GH activity at doses from 0.05 to 0.0025 μg. Dopamine at a dose of 0.005 μg was inactive. These results, while pointing to a hypothalamic site of action for the GH-releasing effect of catecholamines, tend to suggest that norepinephrine is the synaptic transmitter which releases GRF from its neurosecretory neurons. (Endocrinology86: 1376, 1970)