Hypothalamic Modulation of Growth Hormone Secretion in the Rhesus Monkey: Evidence from Intracerebroventricular Infusions of Glucose, Free Fatty Acid, and Ketone Bodies

To evaluate the hypothalamus as a possible site of metabolic modulation of GH secretion, we studied the GH response to insulin hypoglycemia (IHG) and nicotinic acid (NA)- induced FFA depression in the absence and presence of third ventricular (ivt) infusions of glucose, oleic acid (Ol-Ac), or /3- hydroxybutyrate (/βOHB). Four rhesus monkeys had been prepared for chronic remote iv and ivt infusions as well as blood sampling from the adjacent room. Statistical evaluation used a two-way analysis of variance and individual comparisons with Tukey's Studentized range test. The GH response (area under the curve ± SE) to IHG was significantly reduced by a concomitant ivt glucose infusion (control, 1.0 ± 0.1; IHG, 12.1 ± 3.3; IHG plus ivt glucose, 7.0 ± 1.2 μg/L-120 min). The GH response to FFA depression was significantly reduced by ivt Ol-Ac or jSOHB infusion (control, 6.0 ± 1.0; NA, 51.5 ± 4.1; Na plus Ol- Ac, 31.2 ± 1.3; NA plus /βOHB, 38.6 ± 3.5 Mg/L-300 min). Introcerebroventricular infusions of glucose, Ol-Ac, or /βOHB alone had no effect on plasma GH, glucose, FFA, or /βOHB concentrations. These results provide evidence for a hypothalamic site of metabolic modulation of GH secretion in the rhesus monkey. This does not exclude an additional effect directly at the pituitary gland.