[Role of IGF-I and NO on regulation of regional blood circulation in the bones of rats].

UNLABELLED

We present the results of two experiments aimed at the role of IGF-I and NO in the regulation of bone blood flow. In the first experiment A we determined the blood circulation in tibia and distal part of femur and the blood level of IGF-I after oophorectomy (OOX, 4 weeks before the experiment) and/or administration of NG-nitro-L-arginin methyl ester (L-NAME, Sigma, USA, 0.05% in the food for 10 days before the experiment). In the second experiment B we checked up the possibility of correlation between the bone blood flow and IGF-I level in female rats control and after the administration of estradiol (Agofollin Depot, Biotika, Slovak Republic, 1 mg s.c., two times weekly, for 4 weeks before the experiment). The bone blood flow was ascertained by means of 85-Sr microsphere (NEN, USA) technique, IGF level was estimated with Rat IGF-I RIA kit (DSL, USA).

RESULTS

Experiment A: group I: controls--sham operation, group II: oophorectomy (OOX), group III: L-NAME + sham operation, group IV: OOX + L-NAME. OOX elevated the 85-Sr microsphere uptake and bone blood flow in tibia and distal femur. The administration of L-NAME to non-castrated females lowered significantly the blood flow in the femur only, whereas in OOX females it inhibited completely the usual OOX-induced increase in circulatory indicators in both bones. IGF-I level was higher after OOX, administration of L-NAME did not exert any effect on it. Experiment B: group I: control females, group II: estradiol. After the administration of estradiol, there was marked decrease in the uptake of 85-Sr microspheres and blood flow in both bones, decrease in body weight, cardiac output, heart rate, blood pressure and also in the blood level of IGF-I. Density and ash weight of the tibia were elevated. Important results found in the group I of experiment B seem to be the correlations between the blood level of IGF-I and 85-Sr microsphere uptake in tibia (r = 0.68, p < 0.01), between IGF-I and blood flow in tibia (r = 0.54, p < 0.05) and between IGF-I and 85-Sr microsphere uptake in distal femur (r = 0.55, p < 0.05). However, in the group II of females after estradiol no significant dependence could be demonstrated. The results support the conception of the role of IGF-I and NO in the regulation of local blood flow also in the bones of rats. The possible sequence of the interrelations could be as follows: OOX--increase in the blood level of IGF-I--increase in the production of NO--vasodilatation and increase in the bone blood flow. Significant correlations between the blood level of IGF-I and bone blood flow represent further evidence of the participation of IGF-I in the regulation of bone blood flow in rats.