INTERACTION OF LHRH WITH GROWTH HORMONE-RELEASING FACTOR-DEPENDENT AND FACTOR-INDEPENDENT POSTNATAL-DEVELOPMENT OF SOMATOTROPHS IN RAT PITUITARY CELL AGGREGATES

Addition of LHRH for 40 h to aggregate cell cultures of 14-day-old rat pituitary significantly decreased the number of [H-3]thymidine ([H-3] T)-incorporating cells which immunostained for GH protein as well as t he number of [H-3]T-labelled cells expressing GH mRNA detectable by in situ hybridization with a digoxigenin-labelled riboprobe. The effect at the level of GH protein was seen at a dose of 1 nM LHRH. However, t he effect at the GH mRNA level required a higher dose of LHRH (10 nM) or a longer incubation time (64 h). Treatment of the cultures for 40 h with 0.1 nM GH-releasing factor (GRF) provoked a 54% increase in the number of [H-3]T-labelled cells containing GH mRNA and a 30% increase in the number of cells immunostained for GH protein. The latter effect s of GRF were completely blocked by simultaneous addition of LHRH (1 n M) to the cultures. In the absence of GRF, LHRH (1 nM) also had an inh ibitory effect on the total number of cells containing GH mRNA and a c omparable effect on the total number of cells stained for GH protein. The present data show that LHRH is capable of inhibiting the GRF-indep endent as well as the GRF-dependent development of somatotrophs in pos tnatal rat pituitary in culture.