Effects of spaceflight on rat pituitary cell function.

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 postflight tests on Earth. The results showed statistically significant and repeatable decrements in hormone release, especially when biologic (rather than immunologic) 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 musculoskeletal changes in rats flown in space, resulted in some changes in GH and PRL cell function that were similar to those from animals flown in space. Our results add to a growing body of data that describe 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 on return to Earth.