Attenuated pulse size, disorderly growth hormone and prolactin secretion with preserved nyctohemeral rhythm distinguish irradiated from surgically treated acromegaly patients

Background: Radiation induces time-dependent loss of anterior pituitary function, attributed to damage of the pituitary gland and hypothalamic centres. The development of growth hormone deficiency (GHD) in irradiated acromegaly patients is not well defined. Objective: Detailed analysis of spontaneous 24-h GH and prolactin (PRL) secretion in relation to other pituitary functions and serum IGF-I concentrations in an attempt to find criteria for GHD in acromegalic patients with a GH response < 3 μg/l during the insulin tolerance test (ITT). Design: Plasma hormone profiles obtained by 10 min sampling for 24 h in postoperatively irradiated acromegalic patients, compared with patients cured by surgery only and matched healthy controls. Setting/participants: University setting. Fifteen subjects in each group. Outcome measures: GH and PRL secretory parameters quantified by deconvolution, cluster, cosinor and approximate entropy (ApEn) analyses, IGF-I concentrations. Results: Irradiation attenuated pulsatile secretion of GH and PRL, but total PRL secretion was unchanged. GH and PRL secretory regularity were diminished. Circadian timing remained intact. Pulsatile GH secretion and IGF-I were correlated (R = 0.30, P = 0.04). Criteria of pulsatile GH secretion = 12 μg/l/24 h and ApEn = 0.800 separated 12 of 15 irradiated patients from all others. Conclusion: Irradiated acromegaly patients with a subnormal GH response to ITT have very limited spontaneous GH secretion, with specific attenuation of the size of GH bursts and a highly irregular pattern, but with retained diurnal properties. These patients are thus likely GH-deficient and might benefit from GH replacement.