Changes in noradrenergic vesicle markers of rabbit oviducts during progesterone treatment

The effect of progesterone (P) on norepinephrine (NE), [3H] norepinephrine ([3H]NE) and dopamine beta-hydroxylase (DBH) in noradrenergic vesicles from rabbit oviducts was studied after daily injections of the hormone during different periods (4, 7 and 15 days). Progesterone induced a concomitant increase in NE and DBH activity and [3H]NE uptake. To study the mechanism involved in such effects, 4 tissue fractions were obtained by differential centrifugation of the oviducts of which the vesicular fraction was applied over continuous sucrose gradients (0.3-2 M). The changes induced by P in markers of tissue and gradient fractions showed an increase of the NE storage capacity which could be ascribed to an increase in the number of storage vesicles, and/or to a higher extravesicular storage capacity. The occurrence of these mechanisms during pregnancy or after P treatment could account for the (long-lasting) high levels of NE observed in such instances.