Experimental modification of rat pituitary growth hormone cell function during and after spaceflight

Abstract

Space-flown rats show a number of flight-induced changes in the structure and function of pituitary growth hormone (GH) cells after in vitro postflight testing (W. C. Hymen, R. E. Grindeland, I. Krasnov, I, Victorov, K. Motter, P. Mukherjee, K. Shellenberger, and M. Vasques. J. Appl. Physiol. 73, Suppl.: 151S-157S, 1992). To evaluate the possible effects of microgravity on growth hormone (GH) cells themselves, freshly dispersed rat anterior pituitary gland cells were seeded into vials containing serum +/- microM hydrocortisone (HC) before flight. 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 cells prepared 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 was increased in HC-containing medium. Band 1 and mixed cells usually showed opposite HC-dependent responses. Release of bioactive GH from ventral flight cells was lower; postflight responses to GH-releasing hormone challenge were reduced, and the cytoplasmic area occupied by GH in the dense cells was greater. Collectively, the data show that the chemistry and cellular makeup of the culture system modifies the response of GH cells to microgravity. As such, these cells offer a system to identify gravisensing mechanisms in secretory cells in future microgravity research.

Mammalian pituitary growth hormone: Applications of free flow electrophoresis

“…The biological activity of GH released from heavily granulated rat pituitary GH cells is greater, on a per cell basis, than that released from a less well granulated cell [5]. This differential response could be attributed to a more heterogeneous nature of GH molecular forms contained within the densely granulated cell.…”

“…Finally, many studies support the idea that subpopulations of GH cells are contained in the gland [3,5]. The biological activity of GH released from heavily granulated rat pituitary GH cells is greater, on a per cell basis, than that released from a less well granulated cell [5].…”

“…Cryopoor human plasma was obtained from the American Red Cross. Suspensions of rat anterior pituitary cells were prepared from 200 g male Sprague Dawley rats (Harlan) by trypsiniza-tion [5]. In some experiments, a fraction of 300 mm diameter secretory granules, enriched in GH, was prepared from 0.25 M sucrose + 2 mM ZnCl 2 homogenates of either human or rat pituitary tissues by differential centrifugation [6].…”

“…Concentrations of immunoreactive GH (iGH) contained in human or rat samples were measured using specific polyclonal antisera (final dilution of 1:80 000, rat; 1:250 000, human) exactly as described previously [5]. Concentrations of biologically active GH (bGH) in both human and rat samples were determined using the tibial line bioassay procedure of Greenspan et al [7].…”

“…Cells in fraction 1 were pooled from tubes 16±19; those in fraction 2 (which had higher anodal mobility) were pooled from fractions 25±40. Intracellular GH was extracted from an aliquot of these cells [5] and assayed by immunoassay while the remainder were cultured for 8 days prior to measurement of released iGH and bGH. Cell numbers were insufficient to measure intracellular bGH before or after cell culture.…”