The growth hormone response to hexarelin in patients with different hypothalamic-pituitary abnormalities

We evaluated the GH-releasing effect of hexarelin (Hex; 2 μg/kg, iv) and GHRH (1 μg/kg, iv) in 18 patients (11 males and 7 females, aged 2.5- 20.4 yr) with GH deficiency (GHD) whose hypothalamic pituitary abnormalities had been previously characterized by dynamic magnetic resonance imaging (MRI). Ten patients had isolated GHD, and 8 had multiple pituitary hormone deficiency. All patients were receiving appropriate hormone replacement therapy. Twenty-four prepubertal short normal children (11 boys and 13 girls, aged 5.9-13 yr, body weight within ±10% of ideal weight) served as controls. MRI studies revealed an ectopic posterior pituitary at the infundibular recess in all patients. A residual vascular component of the pituitary stalk was visualized in 8 patients with isolated GHD (group 1), whereas MRI showed the absence of the pituitary stalk (vascular and neural components) in the remaining 10 patients (group 2), of whom 8 had multiple pituitary hormone deficiency and 2 had isolated GHD. In the short normal children, the mean peak GH response to GHRH (24.8 ± 4.4 μg/L) was significantly lower than that observed after Hex treatment (48.1 ± 4.9 μg/L; P <0.0001). In the GHD patients of group 2, the mean peak GH responses to GHRH (1.4 ± 0.3 μg/L) and Hex (0.9 ± 0.3 μg/L) were similar and markedly low. In the patients of group 1, the GH responses to GHRH (8.7 ± 1.3 μm/L) and Hex (7.0 ± 1.3 μg/L) were also similar, but were significantly higher that those observed in group 2 (P <0.0001). In the whole group of patients, a significant correlation was found between the GH peaks after Hex and those after GHRH (r = 0.746; P <0.0001). In this study we have confirmed that the integrity of the hypothalamic pituitary connections is essential for Hex to express its full GH-releasing activity and that Hex is able to stimulate GH secretion in patients with GHD but with a residual vascular component of the pituitary stalk.