Evidence for functional arterio-venous anastomoses in the ovaries of sheep

Abstract

Vessels with histological features characteristic of arterio--venous anastomoses were found in the stroma but not in CL. In 5 conscious ewes at the mid-luteal stage of the oestrous cycle, ovarian blood flow was significantly greater (P less than 0.025) with microspheres of 50 than of 15 micrometers diameter in ovaries without CL (0.23 +/- 0.04 (s.e.m.) and 0.11 +/- 0.02 ml/min, respectively), but not in ovaries with CL (4.42 +/- 0.86 and 3.73 +/- 0.70 ml/min, respectively). In 5 similar but anaesthetized ewes, the portion of each ovarian artery within the ovarian vascular pedicle was bypassed with re-entrant catheters through which microspheres were perfused. A greater proportion (P less than 0.01) of 50 than of 15 micrometers microspheres was retained in ovaries with (90 and 79%) or without (82 and 45%) a CL. It is concluded that functional arterio--venous anastomoses are present in sheep ovaries.

Blood flow in the ovary and adjacent structures of the non-pregnant sheep

“…In accordance with our results Mattner et al (1981) recently reported a lack of AV shunts in CL of sheep ovaries of midluteal phase. However, in the non-luteal compartments these authors re¬ ported a significantly larger entrapment of 50 µ than of 15 µ microspheres which were infused into the ovarian artery.…”

“…However, in the non-luteal compartments these authors re¬ ported a significantly larger entrapment of 50 µ than of 15 µ microspheres which were infused into the ovarian artery. The reason for the discre¬ pancy between our results and those of Mattner et al (1981) cannot at present be fully established. A meticulous analysis of a number of methodological factors, such as differences in intravascular distri¬ bution, tendency of aggregation and sedimentation rate of different sized microspheres, arterial infu¬ sion pressures anaesthesia etc., may shed some light on this problem.…”

“…In the present study the large diameter and length of the catheters as well as the elevation of them were kept constant in all animals in attempts to minimize artifactual variations of flow. The values of ovarian blood flow found by direct meas¬ urements correlated well with those found in the surgically intact sheep ovary using radioactive microspheres (Mattner et al 1981;Janson, unpubl. observ. ).…”

Luteolysis in the pig: studies into the mechanism of action of prostaglandin F2[alpha]

“…Systemic progesterone levels, however, did not decline until 6 hours after prostaglandin Fjtt administration (Nett et al, 1976). The earlier decline in luteal blood flow than total ovarian blood flow is likely due to the presence of ovarian arterio-venous anastomoses which shunt blood away from the corpus luteum towards the ovarian stroma during the early stages of luteolysis (Mattner et al,, 1981). These observations suggested that the rapid decline in luteal blood flow induced by prostaglandin F^a treatment might be the initial trigger for luteolysis, however, the cause and effect relationship has been difficult to establish (Einer-Jensen and McCracken, 1981) .…”