[Effect of parathormone on bone blood flow in rats--possible role of NO]

Parathyroid hormone (PTH)--besides its main osteotrophic action--exerts also vascular effect demonstrated formerly also in bones. The aim of the presented work was to verify this effect of PTH using the radioactive microsphere method and to ascertain simultaneously whether NO does participate or not in this effect of PTH. We performed two experiments which were arranged in the same way, as follows: group I--controls, group II--PTH, group III--L-NAME, group IV--L-NAME + PTH. Parathyroid hormone 1.34 fragment (Sigma, USA) was administered to each animal 6-12 minutes before the injection of radioactive microspheres in the dose of 3 micrograms in the experiment A, 10 micrograms in the experiment B. NG-nitro-L-arginin methyl ester (Sigma, USA) was given in the food for ten days before the experiment in the concentration of 0.025% in experiment A, 0.05% in experiment B.

We present the results of experiment A in the part "Results" of the paper briefly in percentages--they are similar to the results of experiment B, but without statistical significance. Administration of PTH increased statistically significantly the microsphere uptake in tibia and distal femur and also the blood flow in both bones, increased the cardiac output and lowered blood pressure. Administration of L-NAME alone induced decrease of the heart rate only. After the injection of PTH to the rats fed L-NAME there was--compared to the injection of PTH only--the blood flow through both bones significantly lower. The observed increase in the bone blood flow as well as changes in the general circulation show that i.v. injection of PTH under the experimental conditions used does induce vasodilatation in female rats. Influence of these changes by the administration of L-NAME indicates possible participation of the nitric oxide (NO) in the observed effect of PTH on the vessles.