Luteal oxytocin-containing secretory granules have been isolated and characterized in terms of their physicochemical parameters. The isopynic sedimentation density (1·03 ±0·003 g/ml) and sedimentation coefficient (1670 S, 0·32 mol sucrose/l, 4 °C) of these granules have been estimated. Based upon these estimates, the average vesicle diameter (258 ± 17 nm) and vesicle weight (9·92 ±0·67 fg/vesicle) were calculated. The exchangeable water content (58·2%) of these granules was determined using density gradients prepared with deuterium oxide. Luteal oxytocin-containing granules displayed similar physicochemical characteristics to those reported for neurohypophysial peptide-containing granules, with the exception of particle size. Luteal granules were 1·3 times greater in diameter than neurohypophysial granules.
J. Endocr. (1988) 116, 267–272