EFFECTS OF TESTOSTERONE ON THE RAT RENAL MEDULLARY VASOPRESSIN RECEPTOR CONCENTRATION AND THE ANTIDIURETIC RESPONSE

The renal concentrating ability declines with age in humans and animal s. Studies suggest that the concentrating defect is due to a decrease in renal vasopressin sensitivity. With ageing, expression of the renal vasopressin V-2 receptor in rat is impaired; the normal receptor expr ession is restored by testosterone treatment. The effect of testostero ne on the renal sensitivity to vasopressin was investigated in young r ats. Male rats after orchidectomy and chronic antiandrogen cyproterone acetate treatment, and female rats after chronic testosterone phenylp ropionate treatment, were used. The plasma arginine-vasopressin (AVP) and testosterone concentrations, and the antidiuretic responses to AVP and the V-2 agonist deamino[8-D-arginine]-vasopressin (dDAVP) after v olume loading were measured, and the renal [H-3]AVP binding density wa s determined. The plasma AVP level decreased slightly, but not signifi cantly, in male rats after orchidectomy and cyproterone acetate treatm ent, but did not alter in female rats after testosterone treatment. Th e AVP and dDAVP sensitivities decreased in male rats after orchidectom y and cyproterone acetate administration, and increased in female rats treated with testosterone, as compared with the animals with a normal gonadal function. [H-3]AVP binding to the renal inner medullary membr anes was decreased following orchidectomy or antiandrogen treatment in male rats, and increased in testosterone-treated female rats. The res ults suggest that testosterone may play a physiological role in mainte nance of the V-2 vasopressin receptor expression and hence in the norm al urinary concentrating ability in rat.