Abstract
Background: The expression and overexpression of luteinizing hormone receptor in the canine adrenal gland cortex has been reported. Therefore, it was hypothesized that a luteinizing hormone (LH)-dependent form of Cushing's syndrome (CS) could exist in dogs.
Aim: Assess whether the adrenal gland post ovariectomy exhibits greater response to ACTH stimulation. Evaluate whether the adrenal gland responds to hCG stimulation by increasing the release of cortisol. Consider whether hCG stimulus testing would be useful as a diagnosis for possible cases of LH-dependent Cushing’s syndrome
Methods: Cortisol concentrations were measured from healthy female dogs (n=16) at baseline and following ACTH stimulation before and 2 months after gonadectomy (OVx). Cortisol concentrations were also measured from female dogs with CS (n=14) following administration of hCG (5000 IU). A post-hCG cortisol concentration of greater than140 nmol/L was used to define dogs with LH-dependent Cushing's syndrome.
Results: In normal female dogs, both pre- and post-stimulation cortisol concentrations increased following OVx (P=0.002 and P=0.0003, respectively). In female dogs with CS, cortisol concentrations increased following stimulation with hCG in 57% (8/14; P=0.002). Age at the time of OVx was associated (P=0.015) with the cortisol response to hCG (8 [5-9] years vs. 3.5 [2-6] years, P=0.0013).
Conclusion: Based on these results, a LH-dependent form of CS occurs in spayed female dogs and that it is more likely to occur when female dogs are spayed later in life

Key words: aberrant receptors, Cushing's syndrome, gonadectomy, hCG, luteinizing hormone