For the inflight study, venous heparinized blood was drawn either at the Johnson Space Center or the Kennedy Space Center in one to two milliliter aliquots and was obtained at the time of drawing for other medical procedures. Each sample was allowed to settle, and five to seven drops of the buffy coat were placed in Chromosome Medium 1A. Four such cultures were initiated on each person from each blood drawing. The cultures were then incubated for a period of 60 to 70 hours at 37 degrees Celsius. The cells were treated with 0.1 micromilligrams per milliliter (micromg/ml) of Colcemid for two hours. Following the treatment with Colcemid, the cell suspensions were prepared for examination with light microscopy by fixation with methanol:acetic acid at a 3:1 ratio. The slides were prepared with Wright's stain for examination. Chromosomes were technically examined in the metaphase stage of cell division when the chromosomes are separated and paired together. Examiners studied from 100 to 150 cells from each specimen. When chromosome abnormalities were found, the cell was photographed. A karyotype analysis was performed to determine the type of chromosomal aberration. Blood samples were analyzed for chromosome breaks, fragments, deletions, translocation, and exchanges.
Flight Study Results: A total of 79 specimens from the Skylab 2 mission and a total of 70 specimens from the Skylab 3 mission were completely analyzed. Only one specimen from each mission, that of a control subject, showed greater than 8.0% minor structural defects. Aberrations were noticed in 5.0 to 7.9 percent of the cells examined in 16 analyses from Skylab 2, and in 5.0 to 9.0 percent of the cells in six analyses from Skylab 3. One specimen from Skylab 2 showed an unusual rearrangement, not characteristic of the general population. However, the aberrations occurred sporadically throughout, and there was no difference between the crew and the control group with regard to such aberrations. The researchers expected to see 3 to 4 percent of cells with chromosomal aberrations, due to viral illness, after administration of viral vaccines, x-rays, and after exposure to chemicals.
Also, on Skylab 2, the structural rearrangements were more consistent in the postflight period than on Skylab 3. The observations were consistent with repeated exposures to radioactive tracer injections, and it was speculated that the post-flight structural rearrangements might be associated with exposures to radioactive tracers. Overall, the data did not seem to suggest that the external sources of radiation to which the crew were exposed in orbit resulted in an increase in chromosomal aberrations.
There were no individual studies from this mission that demonstrated greater than 8.0% minor structural defects except for one subject, a control. Only in 16 studies did such aberrations appear in 5.0 to 7.9 % of the cells examined. It is expected to see 3 to 4% of cells with chromosomal aberrations due to viral illness, after administration of viral vaccines, x-rays, and after exposure to chemicals. The appearance of one or more structural rearrangements in 250 cells is unusual, however, in this study there is no difference between the crew and the control group in regard to such aberrations, as they occur sporadically throughout. However, on Skylab 2, structural rearrangements were more consistent in the postflight period, which was consistent with the repeated exposure to the radioactive tracer injections. It was speculated that the structural rearrangements postflight were associated with exposure to the radioactive tracers. However, this observation was not found on Skylab 3. Overall, the data does not seem to suggest that the external sources of radiation to which the crew were exposed in orbit resulted in an aberration increase.
SMEAT results: (97) cells with suspected structural defects were photographed and karyotyped. Minor chromosome defects were noted, including both chromatid and isochromatid gaps and breaks, and fragments. The researchers noted that these defects are typically found in a small percentage of otherwise normal individuals; they increase temporarily under certain conditions including exposure to various drugs, viruses, isotope injections and ionizing radiation. The researchers also found a small number of more significant aberrations.
The results of this study seem to indicate that the chamber environment had no deleterious effect on the type of chromosomal aberrations studied in this investigation. The first post-chamber study showed values comparable to the first pre-chamber study. Following isotope injection, the aberrations increased to levels well above the normal range. The crews suffered no obvious illnesses, ingested no drugs, and had no unusual exposure to ionizing radiation during their stay in the chamber, so it appears likely that the aberrations were solely caused by the isotope injections.
Unusual structural rearrangements were noted in the pre-chamber cultures (done prior to any radioisotope injections), and in post-chamber cultures in two of the crewmembers. At the cytogenetic laboratory with which the investigators were affiliated (University of Texas Medical Branch at Galveston), some 13,000 cells were examined annually, and translocations (chromosomes with extra chromatin attached) were rarely seen; chromatid exchanges and dicentrics were rarely seen except in a few expected conditions (none of the crewmembers had these conditions); and rings were rarely seen except in persons with multiple anomalies (the crewmembers did not fall under this category either).
While the number of aberrations found in the Skylab crews were small, they were nevertheless found in all crewmembers during all phases of these chamber studies, and were found both before and after radioisotope injection. It is interesting to note that these same investigators reported the same type of occasional defects in Gemini astronauts both before and after flight.
The conclusion of the Skylab SMEAT study was that the chamber environment itself had no bearing on these results. The findings were deemed less-than-clear-cut due to the confounding of the experiment design by the injection of isotopes for other experiments, and due to the lack of control subjects.