The aim of this study was to verify the possible role of prostaglandin (PG) in the increase in the bone blood flow of female rats after oophorectomy (OOX). In two experiments we determined blood flow in the tibia and distal femur (85Sr-microspheres) and 24-h incorporation of 45Ca and 3H-proline. Acetylosalicyclic acid (ASA, 0.13% in the food for 4 weeks) was used to suppress the production of PG. There was an increase in the bone blood flow after OOX (performed 4 weeks prior to the experiment), no change after ASA alone and significant reduction by ASA of the OOX-induced increase in the bone blood flow. In both groups of OOX females there was a decrease in tibial bone density and ash weight. The changes in 45Ca incorporation were similar to those in the blood flow while the changes in 3H-proline incorporation were not significant. Thus, the effect of ASA, i.e. suppression of the OOX-induced increase in the bone blood flow, is consistent with the possible role of PG (probably PGE2) in the increase in bone blood flow of OOX female rats.
To study the relations between thyroid gland blood flow and the concentration of thyroid-stimulating hormone (TSH) in rats, a graded concentration of endogenous TSH was induced: for a period of 10 days, methylthiouracil was added to the food (Alkiron, Spofa, 0.2%) and in addition, in the respective groups, dried thyroid gland preparation (Thyreoidin, Spofa) in concentrations of 0.01, 0.02, 0.03, 0.04 and 0.05%.
The concentration of TSH was estimated by means of the McKenzie bioassay (results are given in the percentile response index). In addition, the relative weight of the thyroid gland (in mg per 100 g of body weight) was followed and the tissue uptake of radioactive rubidium 86Rb (in % of dose per 1 g of tissue) was recorded as an indicator of changes in the thyroid gland blood flow. The experiment was repeated 3 times in exactly the same way. The course of the changes in groups fed dried thyroid from 0.01 up to 0.05 % was evaluated by means of a regression analysis. Regression lines for the same index (i. e. concentration of TSH, relative weight of the thyroid gland and uptake of 86Rb) in each particular experiment were parallel, i. e. the course of the changes for all 3 repeated experiments was identical. Regression coefficients for all the 3 indices were significantly different from zero. The values for all 3 indices then showed a statistically significant decrease concomitantly with the rising concentration of dried thyroid gland in the food, the course of the changes being very similar. Changes in the uptake of 86Rb in the thyroid gland that are in agreement with changes in the concentration of endogenous TSH are considered as further evidence of a TSH regulatory effect on the thyroid gland blood flow.
Effect of estradiol benzoate (EB, Agofollin Depot Spofa, CSSR, 1 mg s.c. once a week for 4 weeks) on local blood flow through the tibia of intact and oophorectomized (OOX) female rats was studied using the 85Sr-microsphere method. In experiment A, the 85Sr-microsphere uptake and blood flow was increased 4 weeks after OOX and significantly decreased after EB in both the intact and OOX animals. In experiment B (intact female rats), the decrease after EB was confirmed both in microsphere uptake and tibial blood flow (48.8% and 57.1% respectively). No changes in the cardiac output and the marked fall of the uptake of labelled microspheres suggest a local circulatory reaction.
We studied changes in the local circulation and mineralization of the rat tibia under different experimental conditions. Four experiments were performed on a total of 155 female and male rats: after oophorectomy (OOX) or orchidectomy (ORX), after the administration of estradiol benzoate (EB, Agofollin Depot, 1 mg/rat once a week or 5 mg/kg body weight once every 5 days for 4 weeks), or after the administration of testosterone (T, Agovirin Depot, 25 mg/kg body weight once every 5 days for 4 weeks). We estimated 85Sr-microsphere uptake and blood flow in the tibia, density of the tibia, and ash weight per bone volume unit. The scheme of the experiments was uniform: experiment A--females--controls, OOX, EB, OOX + EB; experiment B--males--controls, ORX, EB, ORX + EB; experiment C--females--controls, OOX, T, OOX + T; experiment D--males--controls, ORX, T, ORX + T. A sham operation was performed on the animals in the uncastrated groups. The results showed that OOX and ORX stimulated the uptake of 85Sr-microspheres and bone blood flow and reduced both bone density and ash weight, whereas T inconstantly and EB constantly reduced 85Sr-microsphere uptake and bone blood flow and increased bone density and ash weight in both sham-operated and castrated animals. The described changes in the bone blood flow and mineral content under the given experimental conditions suggest a relation in the regulations of both processes, a possible association with resorption of bone, and the importance of the circulation of blood in the metabolism of bone tissue.
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