Gastrointestinal (GI) function plays a critical role in the absorption and bioavailability of orally administered drugs. Further, the GI tract plays a pivotal role in the bioavailability of nutrients. The availability of energy depends on intake, absorption, storage, and utilization. The absorption and bioavailability of ingested compounds depend on physiological factors such as GI motility, splanchnic blood flow, and pH of gastric secretions.
Changes in albumin and creatinine are established indices for hepatic and renal function. Previous studies looking at albumin creatinine ratios found a 10 percent change depending on the length of bed rest. The normal ratio is .8-.13 mg/dl creatinine and 3.7-5.2g/dl albumin. Individual values are usually consistent under controlled conditions.
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The residence time of a drug within the human body, described using pharmacokinetics, is governed by its absorption from the site of administration and clearance. Clearance is directly related to the dose of a drug, and inversely related to the systemic exposure (area under the concentration versus time curve or AUC) of the drug. Important parameters affecting the pharmacokinetics of many drugs include blood flow (potentially affecting absorption, systemic distribution and/or clearance), hepatic, and renal function. The liver (hepatic) and kidney (renal) are the two primary organs of metabolism and excretion, respectively. Not surprisingly, the pharmacokinetics of many drugs is altered in patients who have hepatic dysfunction. Hepatic clearance is governed by two key physiological factors: hepatic arterial and portal vein blood flow and the liver's intrinsic metabolizing enzyme activity.
Albumin and creatinine concentrations were monitored to assess general “clearance organ” function. Indices are well established and are readily used in clinical settings. Albumin was tested in blood serum while creatinine was tested in both urine and blood serum.
This experiment has concluded in ground-based studies sponsored by the National Aeronautics and Space Administration's Human Adaptation and Countermeasures Division. This experiment was conducted during Bed Rest Campaigns 1 and 3A. LSDA doesn't expect to receive results from this study.