Pituitary oxytocin and vasopressin content of rats flown on COSMOS 2044

Abstract

Preliminary studies in rats (COSMOS 1887) suggested that levels of posterior pituitary hormones were reduced by exposure to spaceflight. To confirm these preliminary findings, we obtained pituitary tissue from rats flown for 14 days on COSMOS 2044. Posterior pituitary content of oxytocin (OT) and vasopressin (VP) were measured in these tissues as well as those from ground-based controls. The synchronous control group had feeding and lighting schedules synchronized to those in the spacecraft and were maintained in flight-type cages. Another group was housed in vivarium cages; a third group was tail suspended (T), a method used to stimulate microgravity. Flight rats showed an average reduction of 27% (P less than 0.05) in pituitary OT and VP compared with the three control groups. When hormone content was expressed in terms of pituitary protein (micrograms hormone/mg protein), the average decrease in OT and VP for the flight animals ranged from 20 to 33% (P less than 0.05) compared with the various control groups. Reduced levels of pituitary OT and VP were similar to preliminary measurements from the COSMOS 1887 mission and appear to result from exposure to spaceflight. These data suggest that changes in the rate of hormone secretion or synthesis may have occurred during exposure to microgravity.

Altered gravity downregulates aquaporin-1 protein expression in choroid plexus

“…However, it was shown that AVP and ANP, respectively, have stimulatory and inhibitory effects on the choroidal CSF secretion (23,29). In rats, adaptation to spaceflight induces decreases in hypothalamic (6) and neurohypophyseal AVP content (13) and increases in choroidal NP receptor number (12) and cGMP content (C. Carcenac, S. Herbuté, C. Masseguin, L. Mani-Ponset, D. Maurel, R. Briggs, A. Gü ell, and J. Gabrion, unpublished observations). It is important to note that cGMP is produced in choroidal cells after activation of the guanylate cyclase domain of the biologically active NP receptors (30), particularly when the CSF production is reduced (29).…”