Relationships between IGF-I, cortisol, and osteocalcin in peripheral plasma of growing pigs

Osteocalcin is a bone specific protein which is secreted by mature osteoblasts and is measurable in peripheral blood plasma. In growing female pigs (n = 6) osteocalcin was measured in daily blood samples between an age of 125 to 238 days and the values were compared to IGF-I and cortisol. Mean concentrations of osteocalcin were 158 +/- 2.7 ng/ml and the concentrations were significantly correlated to those of IGF-I (r = 0.12 p < or = 0.01 n = 581) and cortisol (r = 0.13 p < or = 0.01 n = 503). Both hormones and less pronounced osteocalcin revealed a rhythm-like pattern with a period of 10-14 days. In addition, rhythm-like variations with a period of about 5 weeks are visible. The highest correlation was found between IGF-I and cortisol both within the animals (r = 0.28, n = 508, p < or = 0.001) and between the individuals (r = 0.94, n = 6, p < or = 0.01). Thus a dialog between IGF-I and cortisol may be assumed. A possible physiological role is discussed.