Human and rat growth hormones enhance guanylate cyclase activity

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Abstract
The objective of this investigation was to determine whether physiological levels of growth hormone have part of their mechanism of action through stimulation of guanylate cyclase (EC 4.6.1.2.). Rat and human growth hormones enhanced the activity of soluble guanylate cyclase two- to fourfold in rat gracilis anticus skeletal muscle, liver, lung, heart, pancreas, and kidney cortex at a concentration of 10 nM. Dose-response relationships revealed that more than half-maximal stimulation of guanylate cyclase activity was seen at a concentration as low as 10 nM and nonstimulation of guanylate cyclase activity was seen when the concentration was decreased to 1 nM. Maximal enhancement was seen at 100 nM of growth hormone, and there was no further enhancement when the concentration was increased to the micromolar or millimolar range. Thus, the data in this investigation indicate that at concentrations at which growth hormone is known to cause its growth-promoting effects, growth hormone does cause an enhancement of the activity of the guanylate cyclase-cyclic GMP system.