Blood flow in the ovaries and ovarian follicles of Romanov and Préalpes-du-Sud ewes.

Radioactive microspheres (15 microns diameter) were used to measure capillary blood flow rates in the ovaries and ovarian follicles (Qf) in high fecund Romanov and low fecund Préalpes-du-Sud ewes at the preovulatory stage of the oestrous cycle. Additionally, assessments of the percentage of arterial blood passing through ovarian arterio-venous anastomoses were obtained. The mean +/- s.e.m. Qf per unit volume of theca [ml/min) x 10(4)/mm3) for non-atretic follicles in Romanov ewes was significantly greater (P less than 0.05) than that in Préalpes ewes (365.8 +/- 42.4, n = 19, compared with 241.3 +/- 30.1, n = 14). For each breed, the mean Qf value for non-atretic follicles was 8-10 times greater than that for atretic follicles. In Romanov ewes, total Qf [ml/min) x 10(4) and Qf per unit volume of theca was greatest in small-sized follicles (3.1-5.0 mm) while in Préalpes ewes, maximum flow was attained in larger-sized follicles (5.1-7.0 mm). The elevated Qf in small-sized follicles in Romanov ewes may be conducive to more follicles achieving maturation at a smaller diameter in this breed than occurs in the Préalpes ewes. The absence of flow through ovarian arterio-venous anastomoses in the Romanov, but not in the Préalpes, ewes suggests different mechanisms for controlling the distribution of the total ovarian blood supply in the 2 breeds.