Role of progesterone signaling in the regulation of G-protein levels in female chronic constipation

Background & Aims: Chronic constipation caused by slow transit is common in women with an F/M ratio of 9:1. The cause and mechanisms responsible for this syndrome are unknown. Progesterone has been suggested as a possible contributing factor. Our aim was to investigate the site and mechanisms responsible for this colonic motility disorder. Methods: Seven women with intractable constipation and slow transit time underwent colectomy and 6 women who underwent a left colectomy for adenocarcinoma (controls) were studied. Dissociated colonic circular muscle cells were obtained by enzymatic digestion. Changes in G-protein levels were measured by Western blot. The messenger RNA (mRNA) expression of Gαq and progesterone receptors was determined by reverse-transcription polymerase chain reaction and Northern blot. Results: Muscle cells from patients with chronic constipation exhibited impaired contraction in response to receptor-G-protein-dependent agonists (cholecystokinin [CCK], acetylcholine) and in response to the direct G-protein activator guanosine 5′-O-(3-thiophosphate). Contraction was normal with receptor-G-protein-independent agonists (diacylglycerol and KCl). Western blot showed down-regulation of Gαq/11 and up-regulation of Gαs proteins in patients with chronic constipation. The mRNA expression of Gαq was lower and the progesterone receptors were overexpressed in patients with chronic constipation compared with controls. These abnormalities were reproduced in vitro by pretreatment of normal colonic muscle cells with progesterone for 4 hours. Conclusions: Slow transit chronic constipation in women may be caused by down-regulation of contractile G proteins and up-regulation of inhibitory G proteins, probably caused by overexpression of progesterone receptors.