Autoradiographic localization of radioactivity from [3-H]oxytocin in the rat mammary gland and oviduct.

[3-H]Oxytocin was incubated in vitro with pieces of oviduct and mammary gland and the tissue were subjected to autoradiography. Radioactivity was localized only in smooth muscle cells of the oviduct and in regions of mammary tissue where myoepithelial cells are found. In contrast, radioactivity was not concentrated in any region of skeletal muscle, a nontarget tissue for oxytocin. The localization of radioactivity in oviduct and mammary cells was absent when the tissues were incubated with [3-H]oxytocin and an excess of unlabeled oxytocin. These findings provide evidence for the presence of specific and high affinity receptors for oxytocin in its target tissues.     

The Role of the Membrane Potential of Endothelial and Smooth Muscle Cells in the Regulation of Coronary Blood Flow

Membrane Potential of Coronary Endothelial and Smooth Muscle Cells. In the mammalian heart the supply of oxygen and energy-rich substrates through the coronary arterioles is continuously adapted to the variations of cardiac work. The coronary resistance arteries and the surrounding myocardium form a functional unit with multiple interactions between coronary endothelial cells, smooth muscle cells, perivascular nerves, and cardiac muscle cells. We describe the mechanisms underlying the electrical and chemical communication between the different cell types, the ionic channels contributing to the resting potential of endothelial and smooth muscle cells, and the mechanisms responsible for modulation of the resting potential. The main conclusion of our analysis is that the membrane potential of coronary endothelial and smooth muscle cells is one of the major determinants of coronary blood flow, and that modulation of the membrane potential provides a way to dilate or constrict coronary resistance arteries. It is proposed that the membrane potential of the myo-endothelial regulatory unit, i.e., of the endothelial cells and the underlying smooth muscle cells in the terminal arterioles, may function as an integrator of the numerous local and global vasodilator and constrictor signals that provide for the adaptation of coronary blood flow to the metabolic demands of the heart.     

High Frequency Phenomena in Regurgitant Jets

Color Doppler echocardiography is accepted as a useful tool for evaluating valvular regurgitation but, so far, it does not allow for a precise quantification of the regurgitant volume since it is limited by the combination of velocity ambiguities, a limited resolution, and a low frame rate. The low frame rate is imposed by the sector angle, the packet size, the pulse repetition rate, the line density, and the sequential analysis of the ultrasound emissions. On the other hand, the images are supposed to depict pulsatile jets surrounded by high frequency pulsatile vortices. The present study was designed to search for the presence of high frequency phenomena in turbulent jets and to analyze the influence of the low frame rate on the jet images. An in vitro study using an aliasing-free laser Doppler and a hydraulic model simulating intracardiac jets was carried out. An analysis of flow events with a high bandwidth (500 Hz) was conducted using M-mode color displays of the velocities. It showed: (1) on the centerline, a slow propagation of the front of the jet, and low frequency velocity fluctuations (< 50 Hz); and (2) at the opposite, in the boundary layer of the jet, very rapid fluctuations with frequencies comprised between 50 and 500 Hz. On two-dimensional color images of laser Doppler data, the size of the central laminar core appeared strongly modified by a decrease in frame rate up to the maximum one commonly used in color Doppler (30 frames / sec) as well by a decrease in line density. These data demonstrate that higher frame rate could improve the accuracy of ultrasound color Doppler flow mapping.