Circulating Concentrations of Insulin‐Like Growth Factor‐1 in Dogs with Naturally Occurring Mitral Regurgitation

Insulin‐like growth factor‐1 (IGF‐1), which mediates most effects of growth hormone, has effects on cardiac mass and function, and plays an important role in the regulation of vascular tone. In humans, an inverse relationship between degree of heart failure (HF) and circulating IGF‐1 concentrations has been found in several studies. In dogs with HF, few studies have focused on IGF‐1. We examined circulating IGF‐1 concentrations in dogs with mitral regurgitation (MR) caused by myxomatous mitral valve disease. Study 1 included 88 Cavalier King Charles Spaniels (CKCSs) with a broad range of asymptomatic MR (median serum IGF‐1:76.7 μg/L; 25–75 percentile, 59.8–104.9 μg/L). As expected, standard body weight and percentage under‐or overweight correlated directly with IGF‐1. MR (assessed in 4 different ways) did not correlate with IGF‐1. In study 2, 28 dogs with severe MR and stable, treated congestive HF had similar serum IGF‐1 concentrations (median, 100.8 g/L; 25–75 percentile, 74.9–156.5 μg/L) as 11 control dogs (79.6 μg/L; 25–75 percentile, 64.1–187.4 μg/L; ( P = .84). In study 3, the plasma IGF‐1 concentration of 15 untreated CKCSs with severe MR was 16.4±24.2 μg/L lower ( P = .02) at the examination when decompensated HF had developed (80.8±30.9 μg/L) than at a visit 1–12 months earlier (97.2±39.8 μg/L), possibly in part due to an altered state of nutrition. The studies document that circulating IGF‐1 concentrations are not altered before development of congestive HF in dogs with naturally occurring MR, but decrease by approximately 20% with the development of untreated HF. In treated HF, circulating IGF‐1 concentrations apparently return to within the reference range.