Disturbed release of growth hormone in mature dogs: a comparison with congenital growth hormone deficiency
Rijnberk, A.; van Herpen, H.; Mol, J.A.; Rutteman, G.R.
Veterinary Record 133(22): 542-545
1993
ISSN/ISBN: 0042-4900 PMID: 8116157 Document Number: 413003
An acquired defect in growth hormone secretion in mature dogs has been associated with some forms of generalised alopecia. To elucidate the pathogenesis of the disturbance in growth hormone release, the plasma concentrations of growth hormone and insulin-like growth factor I (IGF-I) were measured in two 7-year-old Poodles with alopecia and, for comparison, in 2 young German Shepherd dogs with congenital hyposomatotropism (pituitary dwarfism). In the Poodles the basal concentrations of growth hormone were low, although often above the detection limit of the assay. The concentrations of IGF-1 were in the reference range for healthy Poodles. No growth hormone could be detected in the plasma of the German Shepherd dogs and the concentrations of IGF-1 were very low. Stimulation with clonidine and growth hormone releasing hormone (GHRH) before and after repeated injections of GHRH did not result in increases in growth hormone concentrations in plasma. The concentrations of growth hormone in the Poodles fluctuated at low levels during the test period. In the German Shepherd dogs the levels of growth hormone remained unmeasurable during the stimulation tests. It was concluded that in the 2 Poodles the basal concentrations of growth hormone were sufficient to maintain IGF-I concentrations, and thus the release of growth hormone was considered appropriate. Based upon measurements of urinary corticoids and a review of the literature it is suggested that the lack of a growth hormone response to stimulation was due to the enhanced release of somatostatin as a result of mild and fluctuating hyperadrenocorticism. This mild hyperadrenocorticism seems to explain one form of alopecia for which, probably in part erroneously, names such as growth hormone responsive dermatosis and adult-onset growth hormone deficiency have been introduced.