A critical step in the formation of cholesterol gallstones in nucleation (i.e., the formation of cholesterol monohydrate crystals from supersaturated bile). The rate of nucleation of cholesterol depends upon a critical balance between pronucleating and antinucleating factors in bile. Mucin, a high molecular weight glycoprotein secreted by the gallbladder and biliary duct epithelium, is a pronucleating agent in experimental and human gallstone disease. Gallbladder mucin shares with other epithelial mucins the ability to bind lipids and bile pigment. The hydrophobic binding sites in the polypeptide core of mucin may provide a favorable environment for nucleation of cholesterol monohydrate from supersaturated bile. In nearly all animal models of cholelithiasis, mucin hypersecretion is prominent. The stimulus for gallbladder mucin hypersecretion appears to be a component of lithogenic bile. Prostaglandins regulate mucin release in gallbladder epithelium in vitro and probably in vivo. In the cholesterol-fed prairie dog, blockage of mucin release with aspirin inhibits gallstone formation. These findings suggest that inhibition of mucin release may prevent cholesterol stone formation during high-risk periods or after dissolution therapy with bile salts.

Animals↗

PubMedDate not supplied

Rapid NMR cardiography with a half-echo M-mode method.

A real-time NMR cardiac profiling pulse sequence has been developed that incorporates two-dimensional (2D) selective excitation and a half-echo readout. The time resolution has been improved by a factor of two relative to the previous flow-compensated, full-echo version. The technique produces a 2D plot of "beam"-axis position versus time, analogous to M-mode echocardiography. In human subjects, details of valve leaflet motion, intracardiac flow, wall motion, and wall thickening may be observed along optimal lines of sight selected interactively. The pulse sequence uses a low-tip-angle 2D selective-excitation pulse derived from a spiral k-space trajectory to excite a narrow cylinder of magnetization, followed by a half-echo readout gradient oriented along the axis of the cylinder. One-dimensional Fourier transformation of the acquired signal results in a magnetization profile along the length of the cylinder, or beam. The pulse sequence is effectively flow compensated without any additional gradient lobes, because the rapid oscillation in the gradient wave forms of the 2D excitation pulse produces relatively small net gradient moments, and the shortened readout gradient has minimal first-order moment relative to center echo. The signal from moving blood can alternatively be velocity encoded by the addition of bipolar gradients along any of the three axes, producing Doppler-like traces of intracardiac blood flow.

Echocardiography↗

PubMedDate not supplied

Regional planning of primary health care services.

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California↗