Nitric oxide is a paracrine signal molecule because NO

A. is slow to diffuse

B. is produced in very small quantiites

C. is unstable, with a short half life

D. binds to cell surface receptors that are

veryplentiful.

C. is unstable, with a short half life

Explanation:

Paracrine hormones are the hormones that act on neighboring cells only. These hormones or chemicals are largely unstable and have a brief life as do not visit the distantly placed target cells. For instance, somatostatin is secreted by D cells of the pancreas. It acts in a paracrine manner and inhibits the discharge of hormones from the neighboring beta and alpha cell.

Likewise, one of the functions of unstable NO gas is to serve as a vasodilator. It is released by epithelium cells and serves to dilate arterioles and relax precapillary sphincters. Then it is degraded.