Enhancement of the GH responsiveness to GH releasing stimuli by lysine vasopressin in type 1 diabetic subjects

OBJECTIVE We tested the possibility that lysine vasopressin (LVP) changes t he GH responsiveness to exogenously administered GH-RH (at its minimal and maximal doses), clonidine (which is thought to stimulate endogenous GH-RH r elease) and arginine (which is thought to inhibit somatostatin) in patients with type 1 diabetes mellitus and normal subjects. DESIGN AND PATIENTS Normal male subjects (NC) and age- and weight-matched i nsulin-dependent diabetic men (DM) with good metabolic control were studied . An iv bolus of LVP at a dose (15 mu g/kg body weight (BW)) lower than the minimal GH releasing effective dose was injected just before the I,V, inje ction of the minimal effective dose of GH-RH (0.035 mu g/ kg BW) in 10 NC a nd 10 DM, the I,V, injection of the maximal effective dose of GH-RH (100 mu g) in 7 NC and 7 DM, the I.V. infusion of arginine (30 g over 30 min) in 7 NC and 8 DM or the oral administration of clonidine (150 pg) in 7 NC and 8 DM. On different occasions, GH stimuli, LVP or normal saline were given al one to the same normal and diabetic subjects. MEASUREMENTS GH responses in the presence and absence of LVP were measured and compared within each group and between normal and diabetic groups. RESU LTS LVP or normal saline administration did not modify the basal concentrat ions of GH in any subject. The administration of GH-RH (at the minimal dose ), arginine or clonidine alone induced significantly higher GH responses in the diabetic subjects than in the normal controls. At the maximal dose GH- RH induced similar GH responses in normal and diabetic subjects. The simult aneous administration of LVP did not change the GH response to any challeng ing stimulation in the normal controls; in contrast, GH-RH- (at both minima l and maximal dose), arginine- and clonidine-induced GH increments were sig nificantly enhanced by LVP in the diabetic subjects. CONCLUSIONS These data show that in diabetic, but not in normal subjects LVP enhances the GH resp onsiveness to secretagogues, such as GH-RH, clonidine and arginine, which a ct through three different mechanisms. These findings suggest that in diabe tes mellitus, vasopressin functions as a primer for various GH responses.