Anaemia and marrow blood flow in the rat.

An increase in bone marrow blood flow has been previously described in anaemic rabbits and dogs. We examined the effect of haemorrhage and haemolysis in female Sprague-Dawley rats, with the hypothesis that high blood flow was related to hyperplasia of bone marrow tissue and that the increase would affect bone as well. Blood flow was measured in tibia and femur by the microspheres trapping method. Chronic anaemia was accompanied at day 32 by a marked increase (factor of 1.7-1.9) in blood flow to bone marrow and to bone. On the other hand, no increase in blood flow was observed in chronic compensated anaemia, showing that anaemia per se and not stimulation of erythropoiesis was responsible for the increase. We then explored the effect on blood flow of two factors associated with anaemia. Erythropoietin 4 U/d for 4 d failed to induce any increase in bone and marrow blood flow. Systemic hypoxia (76 mmHg for 3 d) reduced the fraction of cardiac output conveyed to bone and marrow by 40-50%, but this decrease was more than compensated by an increase in cardiac output. We conclude that neither erythropoietin nor low tissue pO2 is the direct cause for the increase in bone and marrow blood flow observed in anaemia.

Bone loss and bone blood flow in paraplegic rats treated with calcitonin, diphosphonate, and indomethacin.

Sham-operated (SO) and paraplegic rats were treated from the day of operation during a period of 4 or 6 weeks with salmon calcitonin 4 IU/kg/day or a diphosphonate (APD) 1mM/kg/day or indomethacin 2.5 mg/kg/day. The consequence of spinal cord section on the femur and tibia is a loss of mineral which affects predominantly trabecular bone (-24 and -13% in calcium content for the tibial metaphysis and the whole bone, respectively, when compared with the SO controls), a twofold increase in bone blood flow as measured by the technique of the microspheres trapping, a moderate decrease of the 72 hour 45Ca accretion rate in the bone shaft, and an increase in the number of metaphyseal osteoclasts in the tibia. In paraplegics, all three drugs inhibit bone loss to some degree, calcitonin and indomethacin being mostly effective on the cortical bone of the shaft, and APD tremendously increasing the trabecular network of the metaphysis. APD is the only drug to exhibit a significant effect on the calcium content of the bones of the SO controls, but some effect is apparent for calcitonin on X-rays and histological preparations. The increase in bone blood flow in paraplegics is unaffected, this point being discussed in view of the hypothesis of the resorptive action of prostaglandins produced by newly formed vessels. 45Ca accretion rate increases in the shaft of calcitonin-treated paraplegics, whereas it decreases in APD-treated controls and paraplegics. The number of osteoclasts decreases in paraplegics treated with calcitonin and indomethacin, and increases in both controls and paraplegics treated with APD.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of orchidectomy on bone metabolism in aging rats.

We have shown that orchidectomy in postpubertal 55-day-old rats led beyond 2 months to a decrease in bone growth and loss of weight. At 1 month postorchidectomy, we observed a three-fold increase in bone blood flow, an increase in calcium accretion rate, and an increase in the number of osteoclasts in the metaphysis. In the present experimental study, orchidectomy was performed in 1-year-old rats when bone growth in length was no longer measurable. In the tibia and femur we observed a decrease in bone volume, a still more rapid decrease of bone calcium during the first postoperative month, a thinning of the cortical width, an initial increase in calcium accretion rate (+20% when compared to 31 days controls) followed by a decrease at 120 days (-22% and -11% when compared to controls for tibia and femur respectively), a 29% increase in bone blood flow, and an increase in the number of osteoclasts. We conclude that androgen deprivation in young and old animals leads to a modified bone architecture, independent of the androgen impact on bone growth.

Growth and bone haemodynamic responses to castration in male rats. Reversibility by testosterone.

Orchidectomy in postpubertal 55 day old rats, compared to sham-operated controls, led beyond 2 months to a decrease in body weight (87% of controls by 120 d), tibial length (97% of controls) and in tibial calcium content (85% of controls). Bone plasma flow increased three times to reach a peak at 31 days; it was decreased but no significantly at 86 and 120 days. The number of osteoclasts was maximal at 51 days (X 2.3) and was still elevated at 120 days. The calcium accretion rate increased briefly at 31 days (110% of controls) and was diminished at 86 and 120 days (78% of controls). The initial 'physiological' changes in the tibia occurred before any weight change and might be directly due to the lack of androgens. They can be interpreted as inducing the conditions for enhanced bone resorption. Testosterone replacement therapy, initiated after the initial haemodynamic response, inhibited the negative effect of castration on bone growth.

Uptake of colloids by bone is dependent on bone blood flow.

In rat the uptake of colloids by the femur and tibia is dependent on bone plasma flow even if other factors modulate the relationship. We warn Nuclear Medicine scientists against the use of colloid uptake measurement as a marker of the bone macrophagic population, especially in situations associated with modified bone plasma flow.