High levels of caveolar cholesterol inhibit progesterone-induced genomic actions in human and guinea pig gallbladder muscle

Roles of cholesterol and bile salts in the pathogenesis of gallbladder hypomotility and inflammation: cholecystitis is not caused by cystic duct obstruction

A large number of human and animal studies have challenged the hypothesis that cystic duct obstruction by gallstones causes cholecystitis. These studies suggest that lithogenic bile that can deliver high cholesterol concentrations to the gallbladder wall causes hypomotility and creates a permissive environment that allows normal concentrations of hydrophobic bile salts to inflame the mucosa and impair muscle function inhibiting gallbladder emptying. High concentrations of cholesterol increase its diffusion rates through the gallbladder wall where they are incorporated into the sarcolemmae of muscle cells by caveolin proteins. High caveolar cholesterol levels inhibit tyrosine-induced phosphorylation of caveolin proteins required to transfer receptor-G protein complexes into recycling endosomes. The sequestration of these receptor-G protein complexes in the caveolae results in fewer receptors recycling to the sarcolemmae to be available for agonist binding. Lower internalization and recycling of CCK-1 and other receptors involved in muscle contraction explain gallbladder hypomotility. PGE2 receptors involved in cytoprotection are similarly affected. Cells with a defective cytoprotection failed to inactivate free radicals induced by normal concentrations of hydrophobic bile salts resulting in chronic inflammation that may lead to acute inflammation. Ursodeoxycholic acid salts (URSO) block these bile salts effects thereby preventing the generation of free radicals in muscle cells in vitro and development of cholecystitis in the ligated common bile duct in guinea pigs in vivo. Treatment with URSO improves muscle contraction and reduces the oxidative stress in patients with symptomatic cholesterol gallstones by lowering cholesterol concentrations and blocking the effects of hydrophobic bile salts on gallbladder tissues.

Physiology and Pathophysiology of the Biliary Tract: The Gallbladder and Sphincter of Oddi—A Review

The biliary tract collects, stores, concentrates, and delivers bile secreted by the liver. Its motility is controlled by neurohormonal mechanisms with the vagus and splanchnic nerves and the hormone cholecystokinin playing key roles. These neurohormonal mechanisms integrate the motility of the gallbladder and sphincter of Oddi (SO) with the gastrointestinal tract in the fasting and digestive phases. During fasting most of the hepatic bile is diverted toward the gallbladder by the resistance of the SO. The gallbladder allows the gradual entry of bile relaxing by passive and active mechanisms. During the digestive phase the gallbladder contracts, and the SO relaxes allowing bile to be released into the duodenum for the digestion and absorption of fats. Pathological processes manifested by recurrent episodes of upper abdominal pain affect both the gallbladder and SO. The gallbladder motility and cytoprotective functions are impaired by lithogenic hepatic bile with excess cholesterol allowing the hydrophobic bile salts to induce chronic cholecystitis. Laparoscopic cholecystectomy is the standard treatment. Three types of SO dyskinesia also cause biliary pain. Their pathophysiology is not completely known. The pain of types I and II usually respond to sphincterotomy, but the pain due to type III usually does not.

Progesterone inhibits L-type calcium currents in gallbladder smooth muscle cells

BACKGROUND AND AIM

The incidence of gallbladder stones is higher in women during pregnancy than in men. Progesterone can inhibit gallbladder motility and facilitate gallstone formation. However, the ionic mechanisms have not been fully illuminated. This study sought to investigate the effects of progesterone on L-type calcium currents and voltage-dependent potassium currents in gallbladder smooth muscle cells.

METHODS

Gallbladder smooth muscle cells were isolated by enzymatic digestion from adult guinea pigs. Ionic currents were recorded by the whole-cell patch clamp method.

RESULTS

Progesterone inhibited L-type calcium currents in a concentration-dependent manner. The characteristic of current-voltage curve was not significantly altered. The amplitude of calcium currents was gradually suppressed, reached a steady-state level within 4-6 min, and restored partly after washout. In the presence of protein kinase A (PKA) inhibitor, Rp-cAMP, the inhibitory effect induced by progesterone was apparently attenuated, whereas forskolin, a direct activator of adenylate cyclase, could suppress L-type calcium channel. However, progesterone did not significantly affect voltage-dependent potassium currents.

CONCLUSIONS

Progesterone inhibits L-type calcium channel by cAMP/PKA pathway in gallbladder smooth muscle cells. This may be an important mechanism for the gallbladder hypomotility induced by progesterone.

Effects of progesterone on motility and prostaglandin levels in the distal guinea pig colon

Progesterone (P4) inhibits the gastrointestinal muscle contraction by downregulating Galpha(q/11) proteins that mediate contraction, by upregulating Galpha(s) proteins that mediate relaxation, and by altering the pattern of cyclooxygenase (COX) enzymes and prostaglandins. We aimed to examine whether P4 treatment of guinea pigs in vivo affects basal colon motility [basal motility index (MI)] by altering the levels and actions of PGF(2alpha) and PGE(2). Guinea pigs were treated with intramuscular (IM) P4 for 4 days. The BASAL MI, the PGF(2alpha)-induced contraction, and PGE(2)-induced inhibition of contraction were examined in muscle strips and cells. The levels of PGF(2alpha) and PGE(2) were measured by radioimmunoassay. Treatment with P4 reduced the basal MI, the levels of PGF(2alpha), and PGF(2alpha)-induced contraction. P4 increased PGE(2) levels, and PGE(2) induced relaxation. Pretreatment with IM RU-486 (10 mg/kg per day), a P4 receptor antagonist, 1 h before P4 blocked the actions of P4. The PGF(2alpha) antagonist Al-1180 abolished basal MI and PGF(2alpha)-induced contraction. N-ethylmaleimide, which blocks unoccupied membrane receptors, blocked Ach and VIP actions but had no effect on PGF(2alpha) and PGE(2) effects. A COX-1 inhibitor decreased and a COX-2 inhibitor increased PGF(2alpha) levels; GTPgammaS increased and GDPbetaS decreased the levels of PGF(2alpha). Galpha(q/11) protein antibodies (Abs) reduced PGF(2alpha) levels, and Galpha(i3) Abs blocked its motor actions. Galphas Abs increased PGF(2alpha) but decreased PGE(2) levels. We concluded that P4 decreases basal MI by reducing PGF(2alpha) levels caused by downregulation of Galpha(q/11) and that PGF(2alpha)-induced contraction was blocked by downregulating Galpha(i3). P4 also decreased the basal MI by increasing PGE(2) levels, and PGE(2) induced relaxation by upregulating Galpha(s) proteins.