Effect of Intraventricular Injection of Dopamine, Norepinephrine, Acetylcholine, and 5-Hydroxytryptamine on Immunoreactive Somatostatin Release into Rat Hypophyseal Portal Blood

TLDR: The effect of several putative neurotransmitters in the regulation of somatostatin release from the median eminence into hypophyseal portal blood was investigated in male rats under urethane anesthesia.

Abstract: The effect of several putative neurotransmitters in the regulation of somatostatin release from the median eminence into hypophyseal portal blood was investigated in male rats under urethane anesthesia. Using a specially designed microfraction collector, hypophyseal portal blood was collected at 15-min intervals into five separate tubes containing 2 N acetic acid. Immunoreactive somatostatin (IRS) in the acid-blood mixtures was extracted with acetone, washed with organic solvents, and determined by RIA. Dopamine, norepinephrine, 5-hydroxytryptamine, or acetylcholine in a dose of 10-8 mol/5 μl freshly prepared 5% glucose solution or 5 nl glucose solution alone was injected into the third ventricle immediately after collection of the first blood sample. In 10 control animals, the mean (±SE) secretion rate and concentration of IRS were 3.90=0.66 pg/min and 628 ± 126 pg/ml before injection of 5% glucose, 2.12 ± 0.28 pg/min and 286 ± 22 pg/ml 15 min after the injection, 1.93 ± 0.17 pg/min and 261 ± 18 pg/ml at...