Effects of human insulin‐like growth factor‐I on release of growth hormone by rainbow trout (Oncorhynchus mykiss) pituitary cells

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Abstract
A recombinant human IGF-I (rhIGF-I) was applied to primary cultures of rainbow trout pituitary cells. In wells containing 3 × 104 and 6 × 104 cells/well, rhIGF-I inhibited basal GH release both in short (6 h) and long (12 and 24 h) exposures. The decline in GH release was dose-dependent over the range of 0.01 and 100 mM. The combination of rhIGF-I and low concentrations of synthetic somatostatin14 (SRIF) enhanced the inhibitory effect of rhIGF-I in an additive manner. Any appreciable effect of rhIGF-I on PRL release was not evidenced. To our knowledge, this report demonstrates for the first time the participation of IGFs on the inhibitory component of fish GH regulation.