Various Putative Neurotransmitters Affect Growth Hormone (GH) Release in Rats with Anterolateral Hypothalamic Deafferentation of the Medial Basal Hypothalamus: Evidence for Mediation by a GH-Releasing Factor

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Abstract
Anterolateral deafferentation of the rat medial basal hypothalamus was used to eliminate most of the somatostatinergic innervation of the stalk-medium eminence while leaving a functional system producing GH[growth hormone]-releasing factor (GHRF) in the partially deafferented hypothalamus. One week after the operation, the rats were anesthetized, the 3rd ventricle was cannulated, and various putative neurotransmitters were infused for 5 min. Plasma GH levels were measured between 10 and 25 min after infusion. When infused into the 3rd ventricle, acetylcholine (50 .mu.g), substance P (5 .mu.g), dopamine (5 .mu.g) and norepinephrine (2.5 .mu.g) increased plasma GH levels in the deafferented rats but not in the controls, while 5-hydroxytryptamine (5 .mu.g) caused a rise of plasma GH levels in both groups. Histamine (5 .mu.g) failed to alter GH in any of the groups. Apparently acetylcholine, substance P, norepinephrine and dopamine, but not histamine, may increase the secretion of GHRF acting either directly upon the GHRF cells or on neural circuits impinging upon them.