Regulation of adenohypophyseal pyroglutamyl aminopeptidase II activity by thyrotropin-releasing hormone and phorbol esters - Dependence on 3,3 ',5 '-triiodo-L-thyronine and gender

Thyrotropin-releasing hormone (TRH) is inactivated by a narrow specificity ectopeptidase, pyroglutamyl aminopeptidase II (PPII), in the proximity of t arget cells. In adenohypophysis, PPII is present on lactotrophs. Its activi ty is regulated by thyroid hormones and 17 beta -estradiol. Studies with fe male rat adenohypophyseal cell cultures treated with 3,3',5'-triiodo-L-thyr onine (T-3) showed that hypothalamic/paracrine factors, including TRH, can also regulate PPII activity. Some of the transduction pathways involve prot ein kinase C (PKC) and cyclic adenosine monophosphate (cAMP). The purpose o f this study was to determine whether T-3 levels or gender of animals used to propagate the culture determine the effects of TRH or PKC, PPII activity was lower in cultures from male rats. In cultures from both sexes, T-3 ind uced the activity. The percentages of decrease due to TRH or PKC were indep endent of T-3 or gender; the percentage of decrease due to cAMP may also be independent of gender. These results suggest that T-3 and hypothalamic/par acrine factors may independently control PPII activity in adenohypophysis, in either male or female animals.