Hormonal regulation of calcium homeostasis in two breeds of dogs during growth at different rates

Abstract

Growing giant-breed dogs are more susceptible to developing skeletal disorders than small-breed dogs when raised on diets with deficient or excessive Ca content. Differential hormonal regulation of Ca homeostasis in dogs with different growth rates was investigated in Great Danes (GD, n = 9) and Miniature Poodles (MP, n = 8). All animals were raised on the same balanced diet and under identical conditions. Calciotropic and growth-regulating hormones were measured. Production and clearance of 1,25-dihydroxycholecalciferol (1,25[OH]2D3) were investigated with the aid of [3H]-1,25(OH)2D3 and renal messenger RNA abundance of 1 alpha-hydroxylase and 24-hydroxylase. Intestinal, renal, and skeletal Ca handling were evaluated with the aid of 45Ca balance studies. Skeletal development was evaluated by radiology and histomorphometry. Great Danes had greater (P < 0.001) growth rates than MP, as indicated by the 17-fold greater body weight gain, by increased longitudinal growth reflected in the increased (P < 0.05) gain in length of the radius and ulna, and by increased (P < 0.001) growth plate thickness. These findings were accompanied in GD by greater (P < 0.05) plasma GH and IGF-I concentrations. Effects were observed for vitamin D3 metabolism, such as greater (P < 0.01) plasma 1,25(OH)2D3 concentrations due to decreased (P < 0.01) clearance rather than increased production of 1,25(OH)2D3, and decreased (P < 0.01) plasma 24,25-dihydroxycholecalciferol (24,25[OH]2D3) concentrations likely due to competitive inhibition of the production of 24,25(OH)2D3. These findings were accompanied in both breeds by a limited hormonal regulation of Ca and P absorption at the intestinal level, and in GD by increased (P < 0.05) renal reabsorption of inorganic P (Pi) compared with MP, resulting in greater (P < 0.01) Pi retention and greater (P < 0.01) plasma Pi concentrations. Bone turnover, resorption, and formation were greater (P < 0.01) in GD than in MP. In addition, GD had more irregular (P < 0.01) growth plates than MP, accompanied by disorders of endochondral ossification. It is suggested that in GD, increased calcitonin levels and/or a relative deficiency in 24,25(OH)2D3 at the growth-plate level may both be responsible for the retarded maturation of chondrocytes, resulting in retained cartilage cones and osteochondrosis, and this may be a pathophysiological factor for the increased susceptibility of large breed dogs to developing skeletal disorders.

Serum 25-hydroxyvitamin D concentrations in dogs with osteosarcoma do not differ from those of age- and weight-matched control dogs

“…Serum chemistry results were within the reference range for 19/20 dogs with osteosarcoma; one dog had a slight elevation in blood urea nitrogen, but a normal creatinine concentration. Twenty age-and weight-matched control dogs (with unremarkable medical histories and physical evaluations) were paired with osteosarcoma-affected dogs after stratification into groups (Table 1), by factors that have been known to alter vitamin D metabolism (Tryfonidou et al, 2003). Serum biochemical evaluation was performed in both groups of dogs within 1 month of enrollment, and study entry requirements included serum creatinine concentration in the reference range, since renal function has also been shown to affect vitamin D (Mellanby, 2016).…”

Growth plate expression profiling: Large and small breed dogs provide new insights in endochondral bone formation

“…In addition, the morphology and morphometry of the rib growth plate is similar to other rapidly growing growth plates 17. At 21 weeks, both breeds are at the same developmental stage, based on ossification of the secondary ossification centers 15. Histological characteristics of the growth plate of this subset of dogs were consistent with the growth plate characteristics described earlier in Tryfonidou et al13 In the growth plate of the Great Dane, the relative ratio of the hypertrophic zone compared to the total growth plate width was significantly larger (38.3% ± 4.3) compared to the Miniature Poodle (29.4% ± 2.2) while the relative ratio of the proliferative zone was significantly smaller in the Great Danes (61.7% ± 4.7) compared to the Miniature Poodles (70.6% ± 2.2).…”

“…Tissue was obtained from animals used in in vivo experiments described previously 15. All procedures were approved by the Utrecht University Ethics Committee for Animal Care and Use.…”

Composição nutricional e avaliação de rótulo de rações secas para cães comercializadas em Jaboticabal-SP

“…Tryfonidou et al (2003) demonstraram em filhotes de raças gigantes que a reabsorção renal de fósforo inorgânico é maior que a de filhotes de raças pequenas, explicando a retenção orgânica de P e a elevação da fosfatemia verificadas em animais alimentados com excesso de P. Acredita-se que ao redor de 25% dos cães idosos apresentem algum comprometimento da função renal (Crowell e Finco, 1975;Debraekeleer et al, 1999), de modo que a ingestão excessiva de P deve ser evitada para animais nessa faixa etária. Redução da progressão da doença renal, aumento da qualidade e expectativa de vida e regularização das alterações bioquímicas relativas à insuficiência renal crônica foram conseguidas com dietas que apresentavam ao redor de 0,4% de P (Kronfeld, 1994;Finco et al, 1992), valor correspondente a apenas 25% da concentração média encontrada nas rações avaliadas neste trabalho.…”