Developmental changes in the effects of carbachol and morphine on cGMP contents of plasma, heart, and lung of mice.

It is considered that carbachol increases plasma cGMP levels by acting on muscarinic receptors and morphine increases these levels by acting on opioid receptors, followed by stimulation of muscarinic receptors. We investigated the ability of carbachol and morphine to increase cGMP contents of plasma, heart, and lung and the guanylate cyclase activity of heart and lung homogenate in 1-, 2-, 3-, and 7-week-old mice. The increase in plasma cGMP levels induced by carbachol showed a peak at 2 and 3 weeks of age. The basal cGMP contents in heart and lung and their rise induced by carbachol, as well as the guanylate cyclase activity of these organs, were decreased in 7-week-old mice. The effects of morphine on the cGMP contents showed a similar developmental change, except for no effect in 1-week-old mice. These changes in the effects of carbachol and morphine may be the result of developmental changes of the muscarinic receptor--guanylate cyclase system and opioid receptors.