Growth hormone responses to growth hormone-releasing hormone and clonidine in dogs with Cushing's syndrome.
The effects of clonidine, a growth hormone (GH) secretagogue, acting at the hypothalamic level and synthetic GH-releasing hormone (GHRH), a physiological stimulus of somatotrophs, on GH secretion were measured in 11 dogs with Cushing's syndrome. Eight healthy dogs served as controls. After the administration of GHRH the dogs with hyperadrenocorticism had a mean (SEM) GH peak of 11.2 (2.5) ng ml-1 which was significantly lower than the peak of 48.6 (13.4) ng ml-1 observed in the healthy dogs. Similarly, the GH response to clonidine was inhibited in the dogs with hyperadrenocorticism, the mean GH peak being 9.3 (3.3) ng ml-1 compared with 135.6 (43.3) ng ml-1 in the control dogs. No significant difference between the GH responses to GHRH and clonidine was observed in the dogs with Cushing's syndrome, the areas under the response curves being 567.9 (78.2) and 478.0 (102.6) ng.min ml-1, respectively. These results demonstrate that the function of somatotrophs is abnormal in dogs with Cushing's syndrome. There is evidence that the likely action of clonidine in dogs is to inhibit the release of somatostatin and the results therefore suggest that the effect of an excess of glucocorticoid in the dog is probably not mediated through an increase in somatostatin tone.
Regnier
A
A
Small Animal Clinic, School of Veterinary Medicine, Toulouse, France.
Garnier
F
F
D000818:Animals; D003000:Clonidine / Q000494:pharmacology*; D003480:Cushing Syndrome / Q000378:metabolism / Q000662:veterinary*; D004283:Dog Diseases / Q000378:metabolism*; D004285:Dogs; D005260:Female; D013006:Growth Hormone / Q000097:blood* / Q000378:metabolism; D013007:Growth Hormone-Releasing Hormone / Q000502:physiology*; D008297:Male; D011863:Radioimmunoassay / Q000662:veterinary
D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone; D003000:Clonidine