Effect of Hypothalamic Extracts on the Incorporation of [3H]-Thymidine by Pituitary Cells in Culture

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Abstract
Rat hypothalamic extracts stimulated the incorporation of [3H]-thymidine into DNA derived from cultured rat pituitary cells, after 24 h and 48 h of incubation. A 3- to 5-fold increase in the incorporation of [3H]-thymidine was observed in the presence of hypothalamic extracts. This stimulatory activity was significantly decreased by heating or dialysis. Rat cerebral cortical extracts also stimulated this incorporation but to a lesser extent than hypothalamic extracts. Hydroxyurea (25 mM) completely inhibited the incorporation of [3H]-thymidine by pituitary cells. The synthetic hypothalamic hormones, LHRH [luteinizing hormone releasing hormone], TRH [thyrotropin releasing hormone] and somatostatin, had no significant effects, whereas estradiol (40 nM) had a significant inhibitory effect.