PhD Candidate Faculty of Veterinary and Agricultural Sciences, The University of Melbourne Werribee, Victoria, Australia
Abstract:
Background: Equine pituitary pars intermedia dysfunction (PPID) is associated with reduced dopamine secretion and many cases are insulin dysregulated (ID), which increases laminitis risk. Dopamine agonists improve insulin sensitivity in other species, but the role of dopamine in insulin regulation in equids is unclear.
Objectives: To determine whether dopamine agonist treatment affects tissue insulin sensitivity and/or the post-prandial insulin response in ID equids, with and without PPID. Animals: Sixteen horses and ponies with ID; eight with concurrent PPID and eight without PPID, paired by age and breed.
Methods: Animals were treated (4 weeks) with pergolide mesylate (2 µg/kg PO SID) or no drug, in a randomized crossover study. A combined glucose and insulin test (CGIT) and standard meal test (SMT; 1.2 g/kg BW starch plus 0.11g/kg BW free sugar) were performed before and after treatment. Glucose and insulin responses were compared using a paired t-tests.
Results: Pergolide had no significant effect on insulin sensitivity as measured by the CGIT (45min glucose and 75min insulin), nor on the glycemic responses to the SMT, in either the PPID or non-PPID groups. However, the area under the curve for insulin following the SMT was significantly reduced in the PPID group following pergolide treatment (47251 ± 5609 μIU/ml/min vs 27655 ± 9089, mean and SEM; P = 0.036). Conclusions and clinical importance: No evidence was found for pergolide modifying systemic insulin sensitivity in insulin resistant equids with or without PPID. However, pergolide may have beneficial post-prandial insulin-lowering effects in PPID cases with ID
