Evidences for the presence of a somatomedin-like plasma factor(s) in the Japanese eel, Anguilla japonica.

The indirect action of growth hormone (GH) through a somatomedin-like plasma factor(s) on the synthesis of mucopolysaccharides in the ceratobranchial cartilages of the Japanese eel, Anguilla japonica, was studied by monitoring the uptake of [35S]sulfate in vitro. Addition of plasma obtained from intact eels significantly stimulated the sulfate uptake by the cartilages of hypophysectomized eel, whereas plasma from hypophysectomized eels had no effect. On the other hand, the plasma from hypophysectomized eels which had been injected with eel GH significantly stimulated the uptake. The maximal stimulating activity was found in the plasma 24 hr after a single injection of eel GH (2 micrograms/g). This stimulatory activity was dependent on the dose of GH injected. These findings indicate that GH elicits its effect on the cartilages indirectly through a GH-dependent plasma factor(s). The system established in the present study can provide as a biological assay for the somatomedin-like plasma factor(s).