Effect of growth hormone and pamidronate on bone blood flow, bone mineral and IGF-I levels in the rat

So far it is not known whether the growth hormone (GH) has an effect on the local blood circulation in bones. Using male rats we studied the local blo od circulation in the tibia and the distal end of the femur (by means of th e uptake of Sr-85-microspheres), the density and ash weight of the tibia, t he urinary excretion of pyridinoline (PD) and deoxypyridinoline (DPD) as an indicator of bone resorption and the blood levels of IGF-I after the admin istration of human GH (4 mg/kg s.c, daily for 4 weeks) and/or bisphosphonat e pamidronate (Aredia, CIBA-Geigy, administered in the dose of 3 mg/kg i.p. on day 1, 2, 9 and 10). The rats were divided into four groups: 1. control s, 2. GH, 3, pamidronate, 4. GH plus pamidronate. After the administration of GH, we observed a significant increase in bone blood flow (and in the up take of Sr-85-microspheres), a decrease in the density and ash weight of th e tibia and increased urinary excretion of PD and DPD; IGF-I levels in the blood were non-significantly elevated. Simultaneously administered pamidron ate inhibited all significant effects of GH and it also decreased the IGF-I levels in rats treated with GH. After the administration of pamidronate it self the bone density and ash weight of the tibia were increased and urinar y DPD excretion was decreased. In view of the known vascular effects of IGF -I, we assume that the increase in bone blood flow after the administration of GH and its reduction after simultaneous administration of pamidronate c ould be mediated by the changes of IGF-I blood levels, although the effect of pamidronate on IGF-I is still not clear. Regarding the role of blood cir culation in rat bones, we consider that our present results are further evi dence for the relationship between the blood circulation in bones and bone resorption, although these results do not show how active is bone blood cir culation in the regulation of bone tissue metabolism.