Growth hormone releasing and inhibin-like activity in rat uterus: an in vitro study

Cytosol from uteri of intact rats stimulated growth hormone (GH) release from anterior pituitary cells in vitro. Cytosol from uteri from ovariectomized (OVX) animals had the same effect, but approximately 30-times less. Estradiol treatment in vivo increased such activity in the uteri of OVX rats. To characterize and partially purify this GH releasing activity, crude extracts from uteri of intact and OVX rats, from liver, and plasma were fractionated on Sephadex G-100 superfine columns and the effects of different fractions on the synthesis and release of GH studied and compared to the effects on the synthesis of thyrotropin (TSH), follitropin (FSH), and lutotropin (LH). Fractions containing molecules with high molecular weight (MW greater than or equal to 40,000, HMWF) in these tissues and plasma stimulated GH release. Furthermore, fractions containing molecules with lower MW (10,000-20,000, LMWF) from intact uteri and plasma, but not from uteri of OVX rats and liver had similar GH-releasing activity. LMWF from uteri of both intact and OVX rats but not from plasma and liver inhibited FSH synthesis without having any effects on LH synthesis. Tissue and plasma fractions did not show any effects on TSH and LH synthesis. It was concluded that the rat uterus contained two GH-releasing activities: one which was associated with HMWF and the other one with LMWF. The GH-releasing activity in LMWF was probably induced by estradiol and secreted into the plasma. Furthermore, inhibin-like activity was present in LMWF from uteries.