Relationship among Insulin Resistance, Growth Hormone, and Insulin-Like Growth Factor I Concentrations in Diestrous Swedish Elkhounds

Background In the dog, the normal estrous cycle includes a prolonged luteal phase. Progesterone stimulates local canine mammary growth hormone (GH) production, which may act systemically and contribute to insulin resistance. Swedish Elkhounds are predisposed to progesterone-related diabetes mellitus, and the relationship among insulin resistance, GH, and insulin-like growth factor I (IGF-I) is of particular interest. Objective To study insulin resistance in relation to GH and IGF-I in nondiabetic Swedish Elkhounds during diestrus. We also assessed whether alterations in these hormones could predict diestrus-linked diseases and all-cause mortality. Animals Eighty-four privately owned female intact Swedish Elkhounds >4years of age. Methods Blood sampling and clinical examination during luteal phase, with a follow-up questionnaire after 20months. Insulin resistance was calculated by homeostasis model assessment (HOMA-IR). Results In multivariable regression analysis, GH was positively associated with HOMA-IR (P=.009). An increase in GH of 1ng/mL was associated with a 12.7% increase in HOMA-IR. Moreover, C-peptide was positively associated with IGF-I (P=.04), and an increase in C-peptide of 0.1ng/mL was associated with a 6.9% increase in IGF-I. Structural equation modeling supported these results. Twenty-three animals were found to have previously unrecognized mammary masses and had higher GH (P<.0001) and IGF-I (P=.007) than dogs without mammary masses (n=61). There was no association between high GH and IGF-I concentrations at sampling and future mammary masses. Conclusion We showed that GH was strongly associated with insulin resistance in older Swedish Elkhounds during diestrus.