Bimatoprost mildly stimulates the rate of aqueous humor flow during the day (13%) and at night (14%), its ocular hypotensive action is due primarily to a 26% reduction in the tonographic resistance to outflow. Bimatoprost enhances the pressure-sensitive outflow pathway.  Bimatoprost displaces [3H]prostaglandin F(2alpha) from FP receptors with K(i) of 6.31 μM. Bimatoprost rapidly mobilizes intracellular Ca(2+) via cloned human FP receptors expressed in human embryonic kidney cells and via native FP receptors in 3T3 mouse fibroblasts with EC(50) of 2.94 μM and 2.2 μM.  Bimatoprost up-regulates Cyr61 mRNA expression in the cat iris. Bimatoprost-induced up-regulation of Cyr61 mRNA expression is not because of the activation of the prostaglandin FP receptor but a different receptor.  Bimatoprost consistently evokes responses in different cells within the same tissue preparation, whereas prostaglandin F(2 alpha) and 17-phenyl prostaglandin F(2 alpha) elicites signaling responses in the same cells. Bimatoprost selectively stimulates intracellular calcium signaling in different cat iris sphincter cells. 
Bimatoprost is the ethyl amide derivative of 17-phenyl trinor PGF2α, a potent prostaglandin FP receptor agonist. Bimatoprost elicits an immediate, robust spike in [Ca2+] that rapidly decayes back to baseline levels. Bimatoprost possess direct agonist activities at the rat, mouse, and human FP prostanoid receptor.