16 WEEKS OF HEXARELIN THERAPY IN AGED DOGS - EFFECTS ON THE SOMATOTROPIC AXIS, MUSCLE MORPHOLOGY, AND BONE METABOLISM

Hexarelin (HEXA; 500 mu g/kg/die, s.c.) was administered for 16 weeks to sir old beagle dogs. The treatment consisted of three on-drug perio ds spaced by two off-drug periods. During each on period, the growth h ormone (GH) peak response to HEXA initially increased and then dropped to pretreatment values. Each time, a wash-out interval restored the s ame pattern of GH responsiveness. HEXA significantly augmented the ind ices of spontaneous pulsatility of GH, but plasma insulin-like growth factor I levels did not change during treatment. HEXA apparently reduc ed bone resorption since it significantly decreased the urinary concen tration of lysylpyridinoline, a bone matrix component. Bone formation apparently was not affected since unchanged levels of alkaline phospha tase were recorded. In three of six old dogs, HEXA induced an improvem ent of some morphological and biochemical muscular indices, evaluated in muscle specimens that, instead, remained unchanged in a group of yo ung untreated controls. These findings indicate that HEXA effectively releases GH and primes the pituitary of old dogs, and strengthen the v iew that in aging, GH secretion mag be restored by pharmacological mea ns. It would also appear that HEXA-induced GH release improves some in dices of body composition in old dogs.