Studies using isolated uterine and other preparations show bimatoprost and prostanoid FP agonists have different activity profiles

Abstract

1. The pharmacology of bimatoprost, a synthetic prostaglandin-amide, was examined in prostaglandin F(2alpha) (PGF(2alpha))-sensitive preparations. Bimatoprost potently contracted the rabbit isolated uterus (pEC(50)=7.92+/-0.16). In contrast, bimatoprost exhibited weak excitatory activity in human myometrium from pregnant and nonpregnant donors, mouse uterus, rat uterus, and endothelium-intact rabbit jugular veins, and did not stimulate DNA synthesis in mouse fibroblasts. 2. The possibility that the effects of bimatoprost may reflect partial agonism at prostanoid FP receptors was examined and the contractile effects of full agonists, 17-phenyl PGF(2alpha) (FP) and U-46619 (TP, a control), were determined in the absence and presence of 1 muM bimatoprost on the mouse uterus. Analyses of the agonist-agonist functional studies showed no antagonism, indicating that bimatoprost is not a partial agonist. 3. Bioassay metabolism studies of bimatoprost and latanoprost (FP receptor agonist prodrug) in the rabbit uterus were conducted using recipient mouse uterus. Results indicated that the potent responses to bimatoprost in the rabbit uterus are produced by the intact molecule and not by its putative free acid metabolite, 17-phenyl PGF(2alpha). Some hydrolysis of latanoprost to latanoprost free acid appears to have occurred in the rabbit uterus, according to biological detection. 4. The pharmacology of bimatoprost could not be explained by its interaction with known prostanoid FP receptors and was independent of species-, tissue-, or preparation-related factors. The potent contractile effects of bimatoprost in the rabbit uterus provide further pharmacological evidence for the presence of a novel receptor population that preferentially recognises bimatoprost.

Figure 1

Concentration–response curves for (a) bimatoprost, (b) 17-phenyl PGF_2α, (c) PGF_2α on contraction of rabbit, mouse, or rat isolated uterine preparations. Values are mean±s.e.m. of five to eight experiments, except on rabbit uterus where n=11 for bimatoprost and n=13 for PGF_2α.

Figure 2

Mean stimulatory dose–effect curves for bimatoprost and 17-phenyl PGF_2α in the superfused human isolated myometrium from (a) nonpregnant and (b) pregnant donors. Data are expressed as mean±s.e.m. of five experiments.

Figure 3

The activities of bimatoprost, 17-phenyl PGF_2α, and PGF_2α in histamine precontracted vascular endothelium-intact (a) and endothelium-denuded (b) rabbit isolated jugular vein preparations. Results are expressed as mean±s.e.m. of five to seven experiments.

Figure 4

Concentration–response curves for (a) theoretical additive effects of 17-phenyl PGF_2α and bimatoprost; 17-phenyl PGF_2α and U-46619 in the presence of vehicle or 1 μM bimatoprost and (b) PGF_2α and U-46619 in the presence of vehicle or 1 μM SQ 29548 in mouse isolated uterus. Results are expressed as mean±s.e.m. of five to six paired samples.

Figure 5

Effects of bimatoprost in mouse isolated uterine preparations (designated as Direct; n=8) were compared to those of bimatoprost and any potential active metabolites transferred from rabbit uterus media to the recipient mouse isolated uterus bioassay, graphed as final concentrations following 1 : 10 dilution (designated as Media; n=6). Results are expressed as mean±s.e.m.

Figure 6

Concentration–response curves for (a) latanoprost free acid and latanoprost in rabbit isolated uterus, (b) latanoprost free acid or latanoprost in the mouse isolated uterus (designated as Direct), compared to those of latanoprost and any potential active metabolites transferred from rabbit uterus media to the recipient mouse isolated uterus bioassay, graphed as final concentrations following 1 : 10 dilution (designated as Media). Results are expressed as mean±s.e.m. of five to six experiments.

Figure 7

Concentration–response curves for bimatoprost, 17-phenyl PGF_2α, fluprostenol, and PGF_2α on stimulation of DNA synthesis in mouse cultured Swiss 3T3 fibroblasts (n=3–4, except n=12 for PGF_2α). Values are expressed as mean±s.e.m. of (n) experiments.