Role of Nitric Oxide in Control of Growth Hormone Release in the Rat

Previous experiments in this and other laboratories have revealed that nitric oxids (NO) plays a role in controlling the release of corticotropin-releasing hormone (CRH) and luteinizing-hormone-releasing hormone (LHRH). Therefore, we have investigated its role in control of growth hormone (GH) release in conscious rats by microinjecting NG-monomethyl-L-arginine (NMMA), an inhibitor of NO synthase (NOS), into the third ventricle (3V) of conscious, freely moving castrate male rats. An initial blood sample (0.3 ml) was drawn from an indwelling intra-atrial catheter just prior to injection of NMMA [1 mg in 5 microliters of 0.9% NaCl (saline)] into the 3V. To maintain the inhibitory action on NOS, a second injection of NMMA was administered into the 3V 60 min after the first. Additional blood samples (0.3 ml) were removed at 10 min intervals for 120 min. Other animals received injections of the diluent at the same times and volumes as NMMA. Interleukin (IL)-1 alpha (0.06 pmol in 2 microliters saline) was injected into the 3V immediately after the first injection of NMMA, whereas other animals received the NMMA diluent followed by IL-1 alpha. The effects of IL-1 alpha were almost identical to those of NMMA in that there was a dramatic lowering of plasma GH achieved primarily by a reduction in height of the GH pulses without a significant reduction in their number.(ABSTRACT TRUNCATED AT 250 WORDS)