EXPERIMENTAL MODIFICATION OF RAT PITUITARY GROWTH-HORMONE CELL-FUNCTION DURING AND AFTER SPACEFLIGHT

Space-flown rats show a number of flight-induced changes in the struct ure and function of pituitary growth hormone (GH) cells after in vitro postflight testing (W. C. Hymer, R. E. Grindeland, I. Krasnov, I. Vic torov, K. Motter, P. Mukherjee, K. Shellenberger, and M. Vasques. J. A ppl. Physiol. 73, Suppl.: 151S-157S, 1992). To evaluate the possible e ffects of microgravity on growth hormone (GH) cells themselves, freshl y dispersed rat anterior pituitary gland cells were seeded into vials containing serum +/- 1 mu M hydrocortisone (HC) before flight. Five di fferent cell preparations were used: the entire mixed-cell population of various hormone-producing cell types, cells of density < 1.071 g/cm (3) (band 1), cells of density > 1.071 g/cm(3) (band 2), and cells pre pared from either the dorsal or ventral part of the gland. Relative to ground control samples, bioactive GH released from dense cells during flight was reduced in HC-free medium but tvas increased in HC-contain ing medium. Band 1 and mixed cells usually showed opposite HC-dependen t responses. Release of bioactive GH from ventral flight cells was low er; postflight responses to GH-releasing hormone challenge were reduce d, and the cytoplasmic area occupied by GH in the dense cells was grea ter. Collectively, the data show that the chemistry and cellular makeu p of the culture system modifies the response of GH cells to micrograv ity. As such, these cells offer a system to identify gravisensing mech anisms in secretory cells in future microgravity research.