Growth hormone and insulin-like growth factor I in German Shepherd dwarf dogs

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Abstract
The roles of growth hormone (GH) and insulin-like growth factor I (IGF I) were studied in 9 German Shepherd dwarf dogs. GH deficiency was evidenced in all dogs by an absence of increase in GH levels in response to clonidine administration. While the mean IGF I concentration in normal adult German Shepherds was 280 .+-. 23 ng/ml and 345 .+-. 50 ng/ml in immature animals, the mean IGF I concentration in the dwarf dogs was 11 .+-. 2 ng/ml (mean .+-. SEM [standard error of the mean], P < 0.001). In the affected animals, plasma thyroxine (T4) levels were only slightly subnormal and there was an increase in these levels in response to TSH administration. Dwarfism in German Shepherds is caused the primary GH-deficiency resulting in low circulating levels of IGF I and IGF I levels in the dog as in man are subject to control by GH.