Dietary Salt Sensitivity and Bone in a Spaceflight Model

摘要

It is well known that the amount of salt in the diet affects blood pressure. Eight to thirty percent of patients who develop hypertension can be described as salt-sensitive because they manifest high blood pressure when consuming salt-rich diets. High salt diets affect not only the cardiovascular system but are also thought to worsen osteoporosis unless the amount of calcium in the diet is also relatively high. This is because there is an obligatory excretion of calcium in amounts proportional to the amount of sodium in the diet. Using a rat model for human hypertension (the Dahl salt-sensitive and salt-resistant strains). Dr. Thierry-Palmer from the Morehouse School of Medicine has found no differences in the amount of calcium excreted in the urine that seemed to relate to the level of dietary salt, but has found some differences in vitamin D metabolism magnified by the level of dietary salt. Vitamin D is a component of the calcium endocrine system that functions to facilitate the transport of calcium in and out of the kidney, intestine, and bone. In the absence of differences in the renal handling of calcium, we collaborated to explore the possibility that the vitamin D abnormalities might be connected to some differences in bone. Static and dynamic studies were made of the femurs in Dahl salt-sensitive and salt-resistant rats. The static studies involved measurements of mineral content and strength in the bones of animals fed normal amounts of dietary salt (0.4). No differences were found in the mineral content or strength of bones from salt-sensitive or salt-resistant male or female juvenile rats. The dynamic studies used the same measurements to evaluate the responses of bone to a spaceflight model in female rats fed high or low levels of dietary salt. Females were studied because the vitamin D differences were found in females only. Salt-sensitive rats tended to grow more rapidly than salt-resistant animals and weighed more than the resistant species. Given that bone mineral content of weight-bearing bones is related to body weight, the values in the salt-sensitive animals tended to be higher than in the salt-resistant animals.