Benzodiazepines Inhibit Thyrotropin (TSH) -Releasing Hormone-Induced TSH and Growth Hormone Release from Perifused Rat Pituitaries*

The perifusion technique was used to investigate the action of diazepam (DZ), a benzodiazepine molecule known to compete for TRH receptor binding in rat pituitary, on TRHinduced TSH and GH release. The release kinetics for the two hormones from quartered pituitaries were measured in response to a 6-min pulse of TRH (10 nM), without or with DZ addition for a period of 30 min before and during the TRH pulse, plus an additional 15-min period. The dynamic patterns of TSH and GH release in response to TRH were characterized by a rapid increase in hormone release, declining slowly over the next 20 min. The rate of release represented 2.98 ± 0.02 (±SE) and 1.75 ± 0.06 times the corresponding basal level for TSH and GH, respectively, when evaluated over the first 15 min of the response to TRH. Addition of increasing doses of DZ suppressed the stimulatory effect of TRH in a dose-related manner, with an ID60 of 3 nM for both TSH and GH. The maximal effect of DZ was obtained with a concentration of 10 nM for both ho...