Alterations of follicular microcirculation and apex structure during ovulation in the rat

Abstract

Objective: We utilized methods for intravital microscopy and microcirculation measurements to study changes during ovulation.

Study design: Immature gonadotrophin-primed rats were laparotomized and one ovary was examined for morphological alterations during a 3 h period (covering a period from 1h before to 27 h after hCG) through water-immersion lenses (maximum magnification 812×). Microcirculatory blood flow was assessed by measurements of blood cell velocity and laser Doppler flowmetry.

Results: Follicular hyperaemia was observed 30 min after hCG and then vasomotion was observed. A gradual decline of apical blood flow was seen, which later was associated with an avascular area over the top of the apex. Cells from the surface over the follicular apex were then detached from the exterior of the follicle and this phenomenon was initiated more than one hour prior to follicular rupture. The subsequent structural alterations varied with or without formation of a cone over the stigma. In ovulations with a stigma-cone, a translucent, irregular mass formed over the stigma. Prior to follicular rupture, granulosa cells and follicular fluid were extruded from the follicular cavity at a velocity of around 70 μm/s. Occasionally, intra-antral haemorrhage occurred prior to or during follicular rupture.

Conclusion: Characteristic features of ovulation in the rat are microcirculatory vasomotion, gradual formation of apical avascular area, specific changes of the stigma, and extrusion of the oocyte-granulosa cell complex with or without haemorrhage.