Background and aims: Ghrelin is an orexigenic hormone produced in the stomach and in other organs, exerting a wide range of metabolic functions, including stimulation of GH secretion. Ghrelin secretion is decreased by iv or oral glucose load as well as during euglycemic-hyperinsulinemic clamp and hypoglycemia. We evaluated the circulating ghrelin levels in GH-deficient (GHD) and in GH-sufficient (GHS) patients during GHRH plus arginine test.
Materials and methods: The study group comprised 35 patients, including 20 with pituitary tumors, 12 with empty sella, 2 with short stature, and 1 with post-traumatic isolated GH deficiency. According to the results of GHRH plus arginine test, 14 patients were defined as GHD and 21 as GHS. Patients with central hypothyroidism, hypocorticism, and hypogonadism had been on replacement therapy for at least 3 months at the moment of the study. Blood samples were collected every 20 min up to 60 min after GHRH and arginine administration.
Results: By definition, GH response to GHRH plus arginine was higher in GHS than GHD group (p<0.0001). Basal serum ghrelin levels were not different in the two groups and did not correlate with body mass index, GH, IGFI and insulin concentrations. After GHRH plus arginine, serum ghrelin decreased significantly in both groups, with percent decreases ranging 13.3-66.6% in GHD patients (p=0.001) and 7.2-42.2% in GHS patients (p=0.004), with no significant difference in the two groups (p=0.12).
Conclusion: Our results show that ghrelin secretion is not modulated by acute GH increase observed in GHS subjects during GHRH plus arginine infusion. The similar decrease of serum ghrelin after GHRH plus arginine stimulation in both GHS and GHD subjects demonstrated that there is no negative feedback of GH on ghrelin secretion.