The effect of intravenous growth hormone infusion on cerebrospinal fluid somatostatin levels in the rhesus monkey

CSF was continuously withdrawn over 13 days from the cervical subarachnoid space of two rhesus monkeys during the intravenous infusion of saline or human growth hormone (GH) and samples collected during sequential 2 h periods were assayed for somatostatin (SRIF). SRIF-like immunoreactivity (SRIF-LI) concentrations were decreased during GH infusion as compared to saline infusion (P less than 0.005) and the maximal effect occurred during the hours of darkness (18.00-06.00 h). Since in vivo GH administration stimulates hypothalamic SRIF-LI release, CSF SRIF-LI does not appear to be derived primarily from the hypothalamus but rather from extrahypothalamic brain by a mechanism inhibited by GH.