Cyclic Hormonogenesis in Gray Collie Dogs: Interactions of Hematopoietic and Endocrine Systems*

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Abstract
Cortisol, ACTH, T4, and T3 concentrations were determined in six cyclic hematopoietic (CH) dogs to determine if hormonal cycles were a feature of this hematopoietic disorder. It was determined that there were 12- to 14-day cycles of these hormones in CH dogs. Plasma cortisol and ACTH concentrations peaked 4-8 days after the onset of neutropenia and were concurrent with peak neutrophil counts. The peak ACTH concentration occurred 1-2 days before or concurrent with the cortisol peak concentration. T4 and T3 peak concentrations were opposite the cortisol cycles, and maximal concentrations were seen when cortisol levels were lowest. ACTH, GH-releasing factor and TRH response tests were performed in the CH dogs. No frank deficiencies in hormone production were seen with the ACTH, GH-releasing factor, and TRH responses in CH dogs relative to those in normal dogs. It was concluded that cyclic hormonogenesis is a central feature of CH disease. These findings are the first demonstration of extrahematopoietic system cyclicity in this rare disease and suggest the presence of common regulatory factors in the hematopoietic and endocrine systems.