Immunohistochemical analysis from a previous investigation (Cosmos 1887) suggested
preferential effects on hypophysiotropic principles involved in the regulation
of growth hormone secretion and synthesis. To provide an additional, more penetrating
analysis, this study attempted to complement immunohisto- chemical analysis
of growth hormone-releasing factor (GRF) and somatostatin (SS) staining with
quantitative, in situ assessments of messenger RNAs encoding the precursors
for both these hormones.
Longitudinally bisected hypothalami were sectioned 20 µm thick and stained
with a conventional avidin-biotin-immunoperoxidase procedure. For GRF, a polyclonal
antiserum raised in rabbits against synthetic rat GRF[1-43] was used; for SS
an antiserum against SS-28 was employed. For in situ hybridization, plasmid
was linearized, and labeled antisense probes were generated using SP6 RNA polymer-
ase and 35-S-UTP. Sections were dehydrated and exposed to x-ray films, later
coated with a liquid autoradiographic emulsion, then finally developed. Cell
and grain counting procedures were used to compare the strengths of mRNA signals
on autoradiographic material.
The results complement and extend analyses of the previous study, which showed
roughly comparable decrements in both SS and GRF-IR in the median eminence of
flight animals; though, in this study flight hypophysiotropic fibers were more
severely depleted. In comparison to synchronous and tail-suspended animals,
the ppGRF mRNA signal in the arcuate nucleus of flight animals was significantly
reduced, while ppSS mRNA levels were not significantly altered. While this effect
on indices of ppGRF mRNA levels may be representative of an influence exerted
at the level of ppGRF gene transcription, alternate explanations (e.g., effects
on mRNA stability) cannot be discounted.
Sawchenko, P.E. et al.: Effects of Spaceflight on Hypothalamic Peptide Systems
Controlling Pituitary Growth Hormone Dynamics. Journal of Applied Physiology,
supl., vol. 73, no. 2, 1992, pp. S158-S165.
Sawchenko, P.E. et al.: Growth Hormone Regulation, Synthesis and Secretion
in Microgravity: II. Hypothalamic GH-Releasing Factor, Somatostatin Immunoreactivity,
and mRNA Levels in Microgravity. Final Reports of the U.S. Experiments Flown
on the Soviet Biosatellite Cosmos 2044. Vol. 2. J.P. Connolly, R.E. Grindeland,
and R.W. Ballard, eds., NASA TM-108802, 1994, pp. 173-182.
¥ = publication of related ground-based study