ldopa restores amplitude of growth hormone pulses in old male rats to that observed in young male rats 35 male spraguedawley rats 18 months old were injected subcutaneously with the catecholamine precursor ldihydroxyphenylalanine ldopa 100 mgkg twice daily or vehicle alone for 8 days in an attempt to increase the amplitude of growth hormone gh pulses in old male rats 40 of young rats had at least one gh pulse greater than 600 ngml over a 65 h sampling period whereas only 22 of old vehicletreated rats had pulses of similar amplitude treatment of old rats with ldopa increased the number of animals showing elevated gh pulses to 53 young animals had mean gh concentrations of 1365 140 ngml over the 65 h sampling period whereas vehicletreated old animals had mean gh levels of 952 77 ngml p less than 005 treatment of old animals with ldopa increased mean plasma gh concentrations to 1329 112 ngml p less than 005 which was not significantly different from gh values in young rats pituitary gh concentration was less in old than in young rats 301 274 vs 370 174 microgramsmg protein p less than 005 ldopa increased pituitary gh concentrations in old rats to 318 322 microgramsmg protein which was not significantly different from that in either young or old vehicletreated animals hypothalamic somatostatin content in both rostral and caudal areas was lower in old than in young rats p less than 001 and ldopa had no significant effect on somatostatin content these data indicate that ldopa can increase the amplitude of gh pulses and elevate mean plasma gh in old male rats to levels present in young male rats probably by increasing hypothalamic catecholamines