A priming effect of luteinizing hormone releasing hormone on bovine pituitary cells in vitro.

The capacity of pituitary glands to release luteinizing hormone (LH) in response to LHreleasing hormone (LHRH) in vivo may be increased by previous frequent exposures to small quantities of LHRH. This phenomenon, called LHRH self-priming, may play an important role in the control of LH secretion. Our initial objective was to determine whether LHRH selfpriming occurs via a direct effect on bovine pituitary cells. Subsequently, we studied the effects of interval between LHRH exposures and source of pituitary glands (steers versus cows) on LHRH self-priming. Cells from bovine anterior pituitary glands were dispersed and mixed with Sephadex-G25, and the mixture was poured into glass columnS. Columns were superfused and effluent medium was assayed for LH. Challenges were .1 ng LHRH/ml or 0 ng LHRH/ml (sham) each for 10 minutes. In one experiment, quantity of LH released by a second exposure to LHRH averaged 124 + 6 ng/ml, which was greater than that released in response to an LHRH challenge (90 +4) given 40 min earlier. In a second experiment, variables were LHRH sequence (sham-LHRH versus LHRH-LHRH) and interval between challenges (40, 80, 160 and 320 min), Quantities of LH released in response to LHRH following the sham challenge or the first of two LHRH challenges were not different. However, LH released by a second LHRH challenge was 48, 39 and 48% greater (P<.01) than that released by the first when the interval between challenges was 40, 80 and 160 min, respectively. But when the interval was 320 min, no LHRH self-priming