Proliferative effects of cholecystokinin in GH 3 pituitary cells mediated by CCK 2 receptors and potentiated by insulin

Proliferative effects of CCK peptides have been examined in rat anterior pituitary GH 3 cells, which express CCK 2 receptors. CCK‐8s, gastrin(1–17) and its glycine‐extended precursor G(1–17)‐Gly, previously reported to cause proliferation via putative novel sites on AR4‐2J and Swiss 3T3 cells, elicited significant dose dependent increases of similar magnitude in [ 3 H]thymidine incorporation over 3 days in serum‐free medium of 39±10% ( P <0.01, n =20), 37±8% ( P <0.01, n =27) and 41±6% ( P <0.01, n =36) respectively. CCK‐8s and gastrin potentially stimulated mitogenesis (EC 50 values 0.12 n M and 3.0 n M respectively), whilst G‐Gly displayed similar efficacy but markedly lower potency. L‐365,260 consistently blocked each peptide. The CCK 2 receptor affinity of G‐Gly in GH 3 cells was 1.09 μ M (1.01;1.17, n =6) and 5.53 μ M (3.71;5.99, n =4) in guinea‐pig cortex. 1 μ M G‐Gly weakly stimulated Ca 2+ increase, eliciting a 104±21% increase over basal Ca 2+ levels, and was blocked by 1 μ M L‐365,260 whilst CCK‐8s (100 n M ) produced a much larger Ca 2+ response (331±14%). Insulin dose dependently enhanced proliferative effects of CCK‐8s with a maximal leftwards shift of the CCK‐8s curve at 100 ng ml −1 (17 n M ) (EC 50 decreased 500 fold, from 0.1 n M to 0.2 p M ; P <0.0001). 10 μg ml −1 insulin was supramaximal reducing the EC 50 to 5 p M ( P =0.027) whilst 1 ng ml −1 insulin was ineffective. Insulin weakly displaced [ 125 I]BHCCK binding to GH 3 CCK 2 receptors (IC 50 3.6 μ M ). Results are consistent with mediation of G‐Gly effects via CCK 2 receptors in GH 3 cells and reinforce the role of CCK 2 receptors in control of cell growth. Effects of insulin in enhancing CCK proliferative potency may suggest that CCK 2 and insulin receptors converge on common intracellular targets and indicates that mitogenic stimuli are influenced by the combination of extracellular factors present.British Journal of Pharmacology (1999) 126 , 79–86; doi: 10.1038/sj.bjp.0702271