Renal vasopressin receptor expression and function in rats following spaceflight

It has been suggested there is a decreased renal responsiveness to vasopres sin following spaceflight and that this may be the mechanism for the increa sed urine flow that is observed following return to normal gravity. In the present study, we have therefore measured vasopressin receptor expression a nd activity in kidneys taken from rats 1 and 14 days following spaceflight of 15 days duration. Measurements of renal vasopressin Vt and VI, receptor mRNA expression by quantitative RT-PCR demonstrated Little difference at ei ther 1 day or at 14 days following return from space. Evaluation of H-3-lab eled arginine vasopressin binding to membranes prepared from kidneys indica ted that the majority of the vasopressin receptors were Vt receptors. Furth ermore, the data suggested that binding to vasopressin V-2 or VI, receptors was unaltered at 1 day and 14 days following spaceflight. Similarly, the a bility of vasopressin to stimulate adenylate cyclase suggested no change in vasopressin V2 receptor activity in these animals. These data suggest that , whatever changes in fluid and electrolyte metabolism are observed followi ng spaceflight, they are not mediated by changes in vasopressin receptor nu mber or vasopressin-induced stimulation of adenylate cyclase.