Bioavailability of intranasal scopolamine in normal subjects.

The bioavailability of scopolamine in three dosage forms was compared in 12 healthy nonsmoking male volunteers. Subjects received 0.4-mg doses of scopolamine bromide in intravenous (i.v.), intranasal (i.n.), or oral (p.o.) dosage forms on three occasions, with at least 2 weeks separating the doses. Scopolamine concentrations in plasma were determined with a combined reverse-phase liquid chromatographic-radioreceptor binding assay. Saliva volume and flow rate and percent suppression of control flow rate were determined from each sample. Absorption after i.n. and po scopolamine administration was rapid; plasma concentrations [1680 (i.n.) and 164 pg/mL (p.o.)] peaked within 1 h of dosing [0.37 (i.n.) and 0.78 h (p.o.)], respectively. i.n. and i.v. scopolamine suppressed salivary flow rate to similar extents (95% and 99.7%), respectively. Times to reach maximum effect were 1.05 and 0.27 h after i.n. and i.v. dosage, respectively. Absolute intranasal bioavailability, calculated from the area under the drug concentration vs time curve, was found to be significantly greater than that of p.o. scopolamine (83% vs 3.7%, p < 0.05). The i.n. route may provide a noninvasive, reliable, fast, and effective route for administering scopolamine.

Changes in sympathoadrenal response to standing in humans after spaceflight.

Plasma catecholamine levels and cardiovascular responses to standing were determined in astronauts before and after several Space Shuttle missions. Blood pressure, heart rate, and cardiac output were measured and blood samples for catecholamine analyses were drawn at the end of the supine and standing periods. Supine plasma norepinephrine and epinephrine concentrations increased 34 and 65%, respectively, on landing day compared with before flight. Standing on landing day resulted in a 65 and 91% increase in plasma norepinephrine and epinephrine, respectively. Supine and standing norepinephrine levels remained elevated 3 days after landing while epinephrine levels returned to preflight levels. On landing day, supine heart rate and systolic blood pressure increased 18 and 8.9%, respectively, and standing heart rate and diastolic blood pressure were elevated by 38 and 19%, respectively. On standing, stroke volume was decreased by 26% on landing day compared with before flight. Collectively, these data indicate that the decreased orthostatic function after spaceflight results largely from the decreased stroke volume. Possible mechanisms contributing to this condition are discussed.

Acute effects of head-down tilt and hypoxia on modulators of fluid homeostasis.

In an effort to understand the interaction between acute postural fluid shifts and hypoxia on hormonal regulation of fluid homeostasis, the authors measured the responses to head-down tilt with and without acute exposure to normobaric hypoxia. Plasma atrial natriuretic peptide (ANP), cyclic guanosine monophosphate (cGMP), cyclic adenosine monophosphate (cAMP), plasma aldosterone (ALD), and plasma renin activity (PRA) were measured in six healthy male volunteers who were exposed to a head-down tilt protocol during normoxia and hypoxia. The tilt protocol consisted of a 17 degrees head-up phase (30 minutes), a 28 degrees head-down phase (1 hour), and a 17 degrees head-up recovery period (2 hours, with the last hour normoxic in both experiments). Altitude equivalent to 14,828 ft was simulated by having the subjects breathe an inspired gas mixture with 13.9% oxygen. The results indicate that the postural fluid redistribution associated with a 60-minute head-down tilt induces the release of ANP and cGMP during both hypoxia and normoxia. Hypoxia increased cGMP, cAMP, ALD, and PRA throughout the protocol and significantly potentiated the increase in cGMP during head-down tilt. Hypoxia had no overall effect on the release of ANP, but appeared to attenuate the increase with head-down tilt. This study describes the acute effects of hypoxia on the endocrine response during fluid redistribution and suggests that the magnitude, but not the direction, of these changes with posture is affected by hypoxia.

Alterations in renal stone risk factors after space flight.

Exposure to the microgravity environment of space produces a number of physiological changes of metabolic and environmental origin that could increase the potential for renal stone formation. Metabolic, environmental and physicochemical factors that influence renal stone risk potential were examined in 24-hour urine samples from astronauts 10 days before launch and on landing day to provide an immediate postflight assessment of these factors. In addition, comparisons were made between male and female crewmembers, and between crewmembers on missions of less than 6 days and those on 6 to 10-day missions. Results suggest that immediately after space flight the risk of calcium oxalate and uric acid stone formation is increased as a result of metabolic (hypercalciuria, hypocitraturia, pH) and environmental (lower urine volume) derangements, some of which could reflect residual effects of having been exposed to microgravity.

Alteration in human mononuclear leucocytes following space flight.

Reduced in vitro mitogen-stimulated proliferative responses have routinely been observed from astronauts' mononuclear leucocytes following space flight. This study investigated the effect of space flight on subpopulations of peripheral blood mononuclear cells from 30 shuttle astronauts prior to launch, upon landing and 3 days after flight. The total number of peripheral blood leucocytes, granulocytes and monocytes were increased after space flight (5.7 +/- 0.2 versus 7.0 +/- 0.2; 3.1 +/- 0.1 versus 5.0 +/- 0.1; and 0.16 +/- 0.02 versus 0.25 +/- 0.28 x 10(3) cells/mm3, respectively) whereas lymphocytes were decreased (2.2 +/- 0.1 versus 1.7 +/- 0.1 x 10(3) cells/mm3). Flow cytometry analysis on Ficoll-Hypaque isolated mononuclear cells upon landing revealed significant decreases in T-inducer (CD4+, Leu-8+; 32 +/- 2 versus 23 +/- 2%) and T-cytotoxic lymphocytes (CD8+, CD11b-; 17 +/- 1 versus 12 +/- 1%), and increases in monocytes (CD14+; 13 +/- 1 versus 21 +/- 1%) compared to pre-flight and post-flight samples whereas B cells (CD19+), T-helper (CD4+, Leu-8-) and T-suppressor (CD8+, CD11b+) populations did not change. Additional phenotypic analysis of these mononuclear leucocytes from 10 crew members upon landing revealed a reduction in natural killer (NK) cells (CD16+ or CD56+; 9 +/- 1 versus 3 +/- 1%) and an increase in monocytes that were negative for insulin and insulin-like growth factor-1 (IGF-1) receptor expression. Flow cytometric analysis indicated these hormone receptor negative monocytes were smaller and less granular than receptor positive monocytes. Therefore, a novel population of monocytes may be released into the peripheral blood during the stress of space flight or upon landing. These findings may explain some of the diverse in vitro immunological and endocrine changes observed in crew members following space flight.

Metabolic changes observed in astronauts.

Study of metabolic alterations that occur during space flight can provide insight into mechanisms of physiologic regulation. Results of medical experiments with astronauts reveal rapid loss of volume (2 L) from the legs and a transient early increase in left ventricular volume index. These findings indicate that, during space flight, fluid is redistributed from the legs toward the head. In about 2 days, total body water decreases 2 to 3%. Increased levels of plasma renin activity and antidiuretic hormone while blood sodium and plasma volume are reduced suggest that space flight-associated factors are influencing the regulatory systems. In addition to fluid and electrolyte loss. Skylab astronauts lost an estimated 0.3 kg of protein. Endocrine factors, including increased cortisol and thyroxine and decreased insulin, are favorable for protein catabolism. The body appears to adapt to weightlessness at some physiologic cost. Readaptation to Earth's gravity at landing becomes another physiologic challenge.

Insulin-like growth factor-I binds selectively to human peripheral blood monocytes and B-lymphocytes.

Insulin-like growth factor-I (IGF-I) is a potential modulator of responses to a variety of immunological challenges. Previous studies have suggested that specific IGF-I receptors are present on peripheral blood leukocytes, including polymorphonuclear leukocytes, lymphocytes, and monocytes. We sought to determine what type of IGF receptor was present on peripheral blood mononuclear cells and which types of cells possessed these receptors. Binding of [125I]IGF-I to mononuclear cells was inhibited by both unlabeled IGF-I and insulin, insulin being 200-fold less potent than IGF-I. Covalent affinity labeling with [125I]IGF-I, followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography, revealed a specific binding species with an apparent mol wt of 130 kDa. Two color flow cytometric analysis of mononuclear cells stained with mouse monoclonal antibodies specific for the human IGF-I receptor, the human insulin receptor, and monoclonal antibodies directed against specific monocyte and lymphocyte subset cell surface antigens revealed that both IGF-I receptors and insulin receptors were present on nearly all monocytes and B-lymphocytes, but were present on only 2% of T-lymphocytes. We conclude from these data that among human peripheral blood nonactivated mononuclear cells, IGF-I binds to specific type I IGF receptors found predominantly on monocytes and B-lymphocytes.

Pharmacokinetic consequences of spaceflight.

Spaceflight induces a wide range of physiological and biochemical changes, including disruption of gastrointestinal (GI) function, fluid and electrolyte balance, circulatory dynamics, and organ blood flow, as well as hormonal and metabolic perturbations. Any of these changes can influence the pharmacokinetics and pharmacodynamics of in-flight medication. That spaceflight may alter bioavailability was proposed when drugs prescribed to alleviate space motion sickness (SMS) had little therapeutic effect. Characterization of the pharmacokinetic and/or pharmacodynamic behavior of operationally critical medications is crucial for their effective use in flight; as a first step, we sought to determine whether drugs administered in space actually reach the site of action at concentrations sufficient to elicit the therapeutic response.

Hypergravity signal transduction in HeLa cells with concomitant phosphorylation of proteins immunoprecipitated with anti-microtubule-associated protein antibodies.

We have shown that hypergravity (35g) stimulates production of inositol 1,4,5-trisphosphate (IP3) and decreases adenosine 3',5'-cyclic monophosphate (cAMP) levels in HeLa cells. IP3 production rapidly increased 1.5- and 2.1-fold greater (P less than 0.05) than the control after 2- and 5-min exposures to 35g, respectively. The intracellular cAMP levels, determined in the presence of isobutylmethylxanthine, were decreased by 11% (P less than 0.05) and 16% (P less than 0.01) relative to the control after 10- and 20-min exposures to 35g, respectively. The phosphorylation of proteins which were immunoprecipitated by antibodies recognizing microtubule-associated proteins (ipMAPs) was also apparent after exposure of these cells to hypergravity. In the detergent-insoluble fraction, phosphorylation of a 115-kDa protein was significantly enhanced compared to the control after a 5-min exposure to 35g. In the detergent-soluble fraction, phosphorylation of a 200-kDa protein was observed served after a 20-min exposure to 35g. Our study suggests that IP3 and cAMP may act as second messengers in hypergravity signal transduction. Phosphorylation of ipMAPs in both the detergent-soluble and -insoluble fractions suggests that cytoskeletal structures may be influenced by gravity.

Immunoreactive prohormone atrial natriuretic peptides 1-30 and 31-67; existence of a single circulating amino-terminal peptide.

Sep-Pak C18 extraction of human plasma and radioimmunoassay using antibodies which recognize atrial natriuretic peptide (99-128) and the prohormone sequences 1-30 and 31-67 resulted in mean values from 20 normal subjects of 26.2 (+/- 9.2), 362 (+/- 173) and 368 (+/- 160) pg/ml, respectively. A high correlation coefficient between values obtained using antibodies recognizing prohormone sequences 1-30 and 31-67 was observed (R = 0.84). Extracted plasma immunoreactivity of 1-30 and 31-67 both eluted at 46% acetonitrile. In contrast, chromatographic elution of synthetic peptides 1-30 and 31-67 was observed at 48 and 39% acetonitrile, respectively. Data suggest that the radioimmunoassay of plasma using antibodies recognizing prohormone sequences 1-30 and 31-67 may represent the measurement of a unique larger amino-terminal peptide fragment containing antigenic sites recognized by both antisera.

Dexamethasone effects on creatine kinase activity and insulin-like growth factor receptors in cultured muscle cells.

We examined the effects of dexamethasone on creatine kinase (CK) activity and insulin-like growth factor I (IGF-I) binding in two skeletal muscle-derived cell lines (mouse, C2C12; rat, L6) and in one cardiac muscle-derived cell line (rat, H9c2). Dexamethasone treatment during differentiation of cultured cells caused a dose-dependent increase in CK activity as well as an increase in the degree of myotube formation in C2C12 and L6, whereas H9c2 cells did not exhibit significant CK activities during culture or dexamethasone treatment. Dexamethasone treatment of C2C12 did not stimulate proliferation in differentiating cultures, but a dose-dependent increase in the number of nuclei was observed for L6 concomitant with increased CK activity. In L6 the increased CK activity may therefore reflect a dose-dependent increase in proliferation. Short-term (48 hr) treatment of C2C12 with dexamethasone (20 nM) did not appear to alter myoblast fusion but reversibly increased CK activity. In C2C12 the observed increase in CK, alanine aminotransferase (ALT), and aspartate aminotransferase (AST) activities with dexamethasone treatment suggest modulation of protein expression and/or turnover. Although the data for dexamethasone effects on CK activities varied in each of the cell lines, consistent behavior was observed in all three cell lines when IGF-I binding was examined. IGF-I binding to dexamethasone-treated cells (50 nM for 24 hr the day prior to confluence) resulted in an increased number of available binding sites, with no effect on the binding affinities. Affinity cross linking and autoradiography indicated that the increase in IGF-I binding was the result of dexamethasone up-regulation of type I IGF receptors. Our data for all three muscle cell lines suggest that similar heterologous hormone receptor modulation of type I IGF receptor sites occurs with dexamethasone treatment.

Pharmacokinetics and oral bioavailability of scopolamine in normal subjects.

The pharmacokinetics and bioavailability of scopolamine were evaluated in six healthy male subjects receiving 0.4 mg of the drug by either oral or intravenous administration. Plasma and urine samples were analyzed using a radioreceptor binding assay. After iv administration, scopolamine concentrations in the plasma declined in a biexponential fashion, with a rapid distribution phase and a comparatively slow elimination phase. Mean and SE values for volume of distribution, systemic clearance, and renal clearance were 1.4 +/- 0.3 liters/kg, 65.3 +/- 5.2 liters/hr, and 4.2 +/- 1.4 liters/hr, respectively. Mean peak plasma concentrations were 2909.8 +/- 240.9 pg/ml following iv administration and 528.6 +/- 109.4 pg/ml following oral administration. Elimination half-life of the drug was 4.5 +/- 1.7 hr. Bioavailability of the oral dose was variable among subjects, ranging between 10.7 and 48.2%. The variability in absorption and poor bioavailability of oral scopolamine indicate that this route of administration may not be reliable and effective.

Assessing applicants to the NASA flight program for their renal stone-forming potential.

Spaceflight could provoke formation of kidney stones, in part by causing hypercalciuria and hyperphosphaturia. Applicants for spaceflight who have metabolic or environmental derangements to begin with might be particularly susceptible to stone formation in space. We, therefore, analyzed 24-h urine samples for stone-forming risk factors in 104 male applicants before their selection into the astronaut-mission specialist corps. The urinary environment was abnormally supersaturated with calcium oxalate in 25.0% of applicants, brushite in 36.5%, and monosodium urate in 66.3%, predisposing these applicants to crystallization of stone-forming calcium salts. This high level of supersaturation was caused by both "metabolic" and environmental disturbances. Thus, hypercalciuria was found in 11.5% of applicants, hyperoxaluria in 2.9%, hyperuricosuria in 18.3% and hypocitraturia in 5.8%. Environmental derangements were generally more prominent, as indicated by low urine volume of less than 2 L.d-1 in 84.6%, high urinary phosphate in 24.4%, and high urinary sodium in 10.6% of applicants. The results suggest that most of the abnormal stone risk factors disclosed among applicants for spaceflight programs were environmental in origin.

Cholesterol in serum lipoprotein fractions after spaceflight.

Cholesterol, triglycerides, very low density lipoprotein cholesterol (VLDL-C), low density lipoprotein cholesterol (LDL-C), and high density lipoprotein cholesterol (HDL-C) were measured in blood samples from 125 crewmembers on the first 24 space shuttle flights. Samples were obtained before, immediately after, and 3-23 days after spaceflight. On landing day, only HDL-C was significantly changed from its preflight level; it had decreased 12.8%. Later in the postflight period, total cholesterol and LDL-C as well as HDL-C decreased significantly. Possible causes of these decreases in estimated cholesterol content of lipoprotein fractions include increased levels of thyroxine during flight and reduced physical activity. The postflight decrease in HDL-C is not considered to have clinical significance for shuttle astronauts, but lipoproteins and apolipoproteins should be measured in blood drawn during longer missions.

Effect of antiorthostatic bed rest on hepatic blood flow in man.

Physiological changes that occur during exposure to weightlessness may induce alterations in blood flow to the liver. Estimation of hepatic blood flow (HBF) using ground-based weightlessness simulation models may provide insight into functional changes of the liver in crewmembers during flight. In the present study HBF, indirectly estimated by indocyanine green (ICG) clearance, is compared in 10 subjects during the normal ambulatory condition and antiorthostatic (-6 degrees) bed rest. Plasma clearance of ICG was determined following intravenous administration of a 0.5-mg.kg-1 dose of ICG to each subject on two separate occasions, once after being seated for 1 h and once after 24 h of head-down bed rest. After 24 h of head-down bed rest, hepatic blood flow did not change significantly from the respective control value.

The endocrine system in space flight.

Hormones are important effectors of the body's response to microgravity in the areas of fluid and electrolyte metabolism, erythropoiesis, and calcium metabolism. For many years antidiuretic hormone, cortisol and aldosterone have been considered the hormones most important for regulation of body fluid volume and blood levels of electrolytes, but they cannot account totally for losses of fluid and electrolytes during space flight. We have now measured atrial natriuretic factor (ANF), a hormone recently shown to regulate sodium and water excretion, in blood specimens obtained during flight. After 30 or 42 h of weightlessness, mean ANF was elevated. After 175 or 180 h, ANF had decreased by 59%, and it changed little between that time and soon after landing. There is probably an increase in ANF early inflight associated with the fluid shift, followed by a compensatory decrease in blood volume. Increased renal blood flow may cause the later ANF decrease. Erythropoietin (Ep), a hormone involved in the control of red blood cell production, was measured in blood samples taken during the first Spacelab mission and was significantly decreased on the second day of flight, suggesting also an increase in renal blood flow. Spacelab-2 investigators report that the active vitamin D metabolite 1 alpha, 25-dihydroxyvitamin D3 increased early in the flight, indicating that a stimulus for increased bone resorption occurs by 30 h after launch.

A sensitive radioreceptor assay for determining scopolamine concentrations in plasma and urine.

A sensitive and reliable procedure for the quantitation of low picogram levels of scopolamine in plasma and urine is described. The method consists of two steps, a preparative extraction step using C18 columns (Sep-Pak), followed by an analytical quantitation step involving a muscarinic radioreceptor assay. The extraction efficiency of the C18 columns was 85-95% for both plasma and urine over a wide concentration range. When [3H]methyl scopolamine is used as a tracer, the assay can detect picogram concentrations (greater than 25 pg) of scopolamine (base) in plasma and urine. The applicability of the procedure for therapeutic drug monitoring of scopolamine was demonstrated by using the method to determine plasma levels in humans after transdermal administration.