Engineering topics
Publications and source records attributed to Krasnov, I..
The function of pineal exposed to microgravity and spaceflight is studied. It is found that the spaceflight resulted in a stress response as indicated by adrenal hypertrophy, that gonadal function was compromised, and that the pineal may be linked as part of the mechanisms of the response noted.
Pituitary levels of oxytocin (OT) and vasopressin (VP) were measured in rats exposed to 14 days of spaceflight (FLT) as well as in ground-based controls; one group synchronously maintained in flight-type cages with similar feeding schedules (SYN), one group in vivarium cages (VIV), and a group of tail suspended (SUS) animals. Flight rats had significantly less (p less than 0.05) pituitary OT and VP (4.48 +/- 0.31 and 7.48 +/- 0.53 mg hormone / mg protein, n = 5) than either the SYN (6.66 +/- 0..59 and 10.98 + 1.00, n = 5), VIV (6.14 +/- 0.40 and 10.98 +/- 0..81, n = 5) or SUS (5.73 +/- 0.24, n = 4) control groups, respectively. The reduced levels of pituitary OT and VP are similar to measurements made on rats from the previous 12.5 day Cosmos 1887 mission and appear to be a direct result of exposure to spaceflight.
Six key metabolic enzymes plus glutaminase and glutamate decarboxylase, as well as glutamate, aspartate and GABA, were measured in 11 regions of the hippocampal formation of synchronous, flight and tail suspension rats. Major differences were observed in the normal distribution patterns of each enzyme and amino acid, but no substantive effects of either microgravity or tail suspension on these patterns were clearly demonstrated.
Immunohistochemical analyses of hypothalamic hormones carried out on tissue from rats flown on an earlier flight (Cosmos 1887) suggested preferential effects on hypophysiotropic principles involved in the regulation of growth hormone secretion and synthesis. We found that staining in the median eminence for peptides that provide both stimulatory (growth hormone-releasing factor, or GRF) and inhibitory (somatostatin, SS) influences on growth hormone secretion were depressed in flight animals relative to synchronous controls, while staining for other neuroendocrine peptides, cortocotropin-releasing factor and arginine vasopressin, were similar in these two groups. While this suggests some selective impact of weightlessness on the two principal central nervous system regulators of growth hormone dynamics, the fact that both GRF- and SS-immunoreactivity (IR) appeared affected in the same direction is somewhat problematic, and makes tentative any intimation that effects on CNS control mechanisms may be etiologically significant contributors to the sequelae of reduced growth hormone secretion seen in prolonged space flight. To provide an additional, and more penetrating, analysis we attempted in hypothalamic material harvested from animals flown on Cosmos 2044 to complement immunohistochemical analyses of GRF and SS staining with quantitative, in situ assessments of messenger RNAs encoding the precursors for both these hormones.
The secretory capacity of growth hormone (GH) and prolactin (PRL) cells prepared from rats flown in space on the 12.5 day mission of Cosmos 1887 and the 14 day mission of Cosmos 2044 was evaluated in several post-flight tests on earth. The results showed statistically significant and repeatable decrements in hormone release, especially when biological assays (rather than immunological assays) were used in the tests. Significant and repeatable intracellular changes in GH cells from the flight animals were also found; most important were increases in the GH-specific cytoplasmic staining intensities and cytoplasmic areas occupied by hormone. Tail suspension of rats for 14 days, an established model for mimicking musculo-skeletal changes seen in spaceflown rats, results in some changes in GH and PRL cell function that were similar to those from spaceflown animals. Our results add to a growing body of data that described deconditioning of physiological systems in spaceflight and provide insights into the time frame that might be required for readaptation of the GH/PRL cell system upon return to earth.
Possible effects of reduced gravity on central hypophysiotropic systems controlling growth hormone (GH) secretion were investigated in rats flown on Cosmos 1887 and 2044 biosatellites. Immunohistochemical (IHC)staining for the growth hormone-releasing factor (GRF), somatostatin (SS), and other hypothalamic hormones was performed on hypothalami obtained from rats. IHC analysis was complemented by quantitative in situ assessments of mRNAs encoding the precursors for these hormones. Data obtained suggest that exposure to microgravity causes a preferential reduction in GRF peptide and mRNA levels in hypophysiotropic neurons, which may contribute to impared GH secretion in animals subjected to spaceflight. Effects of weightlessness are not mimicked by hindlimb suspension in this system.
Preliminary studies in rats (COSMOS 1887) suggested that levels of posterior pituitary hormones were reduced by exposure to spaceflight. To confirm these preliminary findings, pituitary tissue from rats flown for 14 days on Cosmos 2044 is obtained. Posterior pituitary content of oxytocin (OT) and vasopressin (VP) were measured in these tissues as well as those from ground-based controls. The synchronous control group had feeding and lighting schedules synchronized to those in the spacecraft and were maintained in flight-type cages. Another group was housed in vivarium cages; a third group was tail suspended (T), a method used to simulate microgravity. Flight rats showed an average reduction of 27 in pituitary OT and VP compared with the three control groups. When hormone content was expressed in terms of pituitary protein (microg hormone/mg protein), the average decrease in OT and VP for the flight animals ranged from 20 to 33 percent compared with the various control groups. Reduced levels of pituitary OT and VP were similar to preliminary measurements from the Cosmos 1887 mission and appear to result from exposure to spaceflight. These data suggest that changes in the rate of hormone secretion or synthesis may have occurred during exposure to microgravity.
Frontal lobe samples of rat brains flown aboard Cosmos 1887 were processed for the study of muscarinic (cholinergic) and GABA (benzodiazepine) receptors and for immunocytochemical localization of the neurotransmitter gamma-aminobutyric acid (GABA) and glial fibrillary acidic protein (GFAP). Although radioactive labeling of both muscarinic cholinergic and GABA (benzodiazepine) receptors proved to be successful with the techniques employed, distinct receptor localization of individual laminae of the frontal neocortex was not possible since the sampling of the area was different in the various groups of animals. In spite of efforts made for proper orientation and regional identification of laminae, it was found that a densitometric (quantitation of autoradiograms) analysis of the tissue did not contribute to the final interpretation of the effects of weightlessness on these receptors. As to the immunocytochemical studies the use of both markers, GFAP and GABA antiserum, confirmed the suitability of the techniques for use in frozen material. However, similar problems to those encountered in the receptor studies prevented an adequate interpretation of the effects of micro-G exposure on the localization and distribution of GABA and GFAP. This study did, however, confirm the feasibility of investigating neurotransmitters and their receptors in future space flight experiments.
One of the most interesting concomitants to spaceflight and exposure to microgravity has been the disturbing alteration in calcium metabolism and resulting skeletal effects. It was recognized as early as 1685 (cited in Kitay and Altschule, 1954) that the pineal of humans calcified with age. However, little can be found in the literature relating calcification and pineal function. Given the link between exposure to microgravity and perturbation of calcium metabolism and the fact that the pineal is apparently one of the only soft tissues to calcify, researchers examined pineal calcium content following the spaceflight. Researchers concluded that the spaceflight resulted in a stress response as indicated by adrenal hypertrophy, that gonadal function was compromised, and that the pineal may be linked as part of the mechanism of the responses noted.
Pituitary levels of oxytocin (OT) and vasopressin (AVP) were measured in rats exposed to 12.5 days of spaceflight (FLT) as well as ground-based controls, one group synchronously maintained in flight-type cages with similar feeding schedules (SYN), and one group in vivarium cages (VIV). Flight rats had significantly less (p less than 0.05) pituitary OT and AVP(1.10 plus or minus 0.04 and 1.69 plus or minus 0.07 micron g, n=5) than either the SYN(1.60 plus or minus 0.08 and 2.11 plus or minus 0.04 micron g, n=5) or VIV (1.54 plus or minus 0.03 and 2.10 plus or minus 0.09 micron g, n=5) control groups, respectively. Because the FLT group mean body weight was significantly less (p less than 0.05) than either control group, the pituitary hormone content was also calculated on the basis of posterior pituitary protein content. When calculated in this manner, pituitary OT in the FLT rats (5.09 plus or minus 0.15 micron g/mg protein) was significantly less (p less than 0.05) than SYN(7.66 plus or minus 0.39 micron g/mg protein) or VIV controls (8.11 plus or minus 0.64 micron g/mg protein). Pituitary AVP was also less in the FLT animals (7.80 plus or minus 0.13 micron g/mg protein) compared to either SYN(9.84 plus or minus 0.51, p less than 0.05) or VIV controls (11.01 plus or minus 0.76, p less than 0.05). The reduced levels of pituitary OT and AVP may have resulted from increased hormone secretion resulting from the combined effects of water deprivation and the stress of the novel microgravity environment.
The individual fibers of any individual muscle vary greatly in enzyme composition, a fact which is obscured when enzyme levels of a whole muscle are measured. The purpose of this study was therefore to assess the changes due to weightless on the enzyme patterns composed by the individual fibers within the flight muscles. In spite of the limitation in numbers of muscles examined, it is apparent that: (1) that the size of individual fibers (i.e., their dry weight) was reduced about a third, (2) that this loss in dry mass was accompanied by changes in the eight enzymes studied, and (3) that these changes were different for the two muscles, and different for the two enzyme groups. In the soleus muscle the absolute amounts of the three enzymes of oxidative metabolism decreased about in proportion to the dry weight loss, so that their concentration in the atrophic fibers was almost unchanged. In contrast, there was little loss among the four enzymes of glycogenolysis - glycolysis so that their concentrations were substantially increased in the atrophic fibers. In the TA muscle, these seven enzymes were affected in just the opposite direction. There appeared to be no absolute loss among the oxidative enzymes, whereas the glycogenolytic enzymes were reduced by nearly half, so that the concentrations of the first metabolic group were increased within the atrophic fibers and the concentrations of the second group were only marginally decreased. The behavior of hexokinase was exceptional in that it did not decrease in absolute terms in either type of muscle and probably increased as much as 50 percent in soleus. Thus, their was a large increase in concentration of this enzyme in the atrophied fibers of both muscles. Another clear-cut finding was the large increase in the range of activities of the glycolytic enzymes among individual fibers of TA muscles. This was due to the emergence of TA fibers with activities for enzymes of this group extending down to levels as low as those found in control soleus muscles. It would be interesting to know if this represents a transition stage, and whether with prolonged weightlessness most of the fibers would be transformed into a low glycogenolytic type.
The objectives of the 1887 mission were: (1) to determine if the results of the SL-3 pituitary gland experiment (1) were repeatable; and (2) to determine what effect a longer mission would have on the rat pituitary gland growth hormone (GH) system. In the 1887 experiment two issues were considered especially important. First, it was recognized that cells prepared from individual rat pituitary glands should be considered separately so that the data from the 5 glands could be analyzed in a statistically meaningful way. Second, results of the SL-3 flight involving the hollow fiber implant and HPLC GH-variant experiments suggested that the biological activity of the hormone had been negatively affected by flight. The results of the 1887 experiment documented the wisdom of addressing both issues in the protocol. Thus, the reduction in secretory capacity of flight cells during subsequent extended cell culture on Earth was documented statistically, and thereby established the validity of the SL-3 result. The results of both flight experiments thus support the contention that there is a secretory lesion in pituitary GH cells of flight animals. The primary objective of both missions was a clear definition of the effect of spaceflight on the GH cell system. There can no longer be any reasonable doubt that this system is affected in microgravity. One explanation for the reason(s) underlying the better known effects of spaceflight on organisms, viz. changes in bone, muscle and immune systems may very well rest with such changes in bGH. In spite of the fact that rats in the Cosmos 1887 flight were on Earth for two days after flight, the data show that the GH system had still not recovered from the effects of flight. Many questions remain. One of the more important concerns the GRF responsiveness of somatotrophs after flight. This will be tested in an upcoming experiment.
It is now known that the pineal organ can interact with many endocrine and nonendocrine tissues in a regulatory fashion. Given its key role in the regulation of melatonin synthesis, its high concentration, and that its levels may persist longer than the more rapidly changing melatonin, it was felt that serotonin might give a more accurate assessment of the effects of microgravity on pineal function following recovery of animals from flight. Five-hydroxyindole acetic acid (5-HIAA), a major metabolite of serotonin metabolism, was also measured. One of the most interesting concomitants to spaceflight and exposure to microgravity has been the disturbing alteration in calcium metabolism and resulting skeletal effects. Given the link between exposure to microgravity and perturbation of calcium metabolism and the fact that the pineal is apparently one of the only soft tissues to calcify, pineal calcium content was examined following spaceflight.