Experimental modification of rat pituitary growth hormone cell
function during and after spaceflight.
Hymer, W. C., R. E. Grindeland, T. Salada, P. Nye, E. J. Grossman, and
P. K. Lane.
Department of Biochemistry and Molecular Biology, The Pennsylvania
State University, University Park, PA 16802, NASA Ames Research
Center, Moffett Field, CA 94035, Lockheed Engineering & Sciences
Company, Moffett Field, CA 94035
APStracts 3:0009A, 1996.
Spaceflown rats show a number of flight-induced changes in the
structure and function of pituitary growth hormone (GH) cells after
in vitro postflight testing (Hymer, W.C., et. al., J. Appl. Physiol.
73(2), 151S-157S, 1992). In order to evaluate the possible effects of
microgravity on GH cells themselves, a passive cell culture system
was used during an 8 day spaceflight experiment on the Space Shuttle.
Freshly dispersed anterior pituitary gland cells from young adult
male rats were seeded into 4.4 ml capacity glass vials containing
either serum or serum-free media +/- 1 [mu]M hydrocortisone (HC)
(2x105 cells/vial), sealed, and loaded into Shuttle middeck 19 hours
before launch. Five different cell preparations were used: the entire
mixed-cell population of various hormone producing cell types; cells
of density < 1.071 g/cm3 (band 1); cells of density >1.071
g/cm3 (band 2) and finally, cells prepared from either the dorsal or
ventral parts of the gland. Three sets of vials (165/set) were
prepared; one served as the ground control to the flight set while
the other was used to determine the amount of GH that was released
between the time of cell seeding and launch. Seven hrs after Shuttle
landing media were removed for GH analyses by a) immunoassay, b)
bioassay (tibial line width increase after injection into
hypophysectomized rats) and c) HPLC sizing columns to evaluate
apparent molecular weights of secreted GH variants. Fresh media were
added to some cell-containing vials in order to do a 6 day postflight
culture recovery test while other cells were challenged with growth
hormone releasing hormone (GHRH, 2x10-9M) during a 3 hr test to
evaluate GH cell responsiveness to secretagogue. Finally, some cells
were recovered from the vial surface by trypsinization, stained for
intracellular GH with GH antisera and analyzed by either flow
cytometry or digital image analysis. Relative to ground controls
bioactive GH (bGH) released from dense cells during flight was
reduced in HC-free medium, but was increased in HC-containing medium;
these changes continued into the postflight culture period. Band 1
and mixed cells usually showed opposite HC-dependent responses.
Intracellular GH levels were usually lower in flight cells. Release
of bGH from ventral (but not dorsal) flight cells was reduced by one
-half. Responses to GHRH challenge after flight were modest to non
-existent. GH cell numbers were not affected by microgravity exposure,
but the cytoplasmic area occupied by GH in dense cells was
significantly greater. Collectively the data establish that the
changes we previously reported in the release of GH from cells of
spaceflown animals during postflight testing also occur when cells
themselves are put in microgravity. Furthermore, they show that the
chemistry and cellular makeup of the culture system modifies the
responses of GH cells to microgravity. As such, these cells offer a
system to identify gravisensing mechanisms in secretory cells in
future microgravity research.
Received 18 January 1995; accepted in final form 28 September
1995.
APS Manuscript Number A58-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96