Chronic Uterine Distention in Progestin-Treated Rabbits. ∗ †

Summary

In mature, progestin-treated rabbits, growth resulting from distention is regularly obtained, but greater degrees of distention are necessary to produce growth responses comparable to that obtained in untreated, ovariectomized rabbits with smaller amounts of stretching. It is probable that progestin, through its property of reducing myometrial tonicity, may reduce the tension of the tissues about the pellets to such an extent that greater degrees of stretching are required in order to produce a degree of tension equal to that obtained by less distention in untreated, ovariecto-mized rabbits. Hence, an appropriate amount of tension appears to be an essential condition for uterine enlargement to take place as a result of distention. In oestrin-treated rabbits, however, the dis-tention-growth response is much reduced. 3 This has been attributed to impairment of the blood supply about the sites of distention, resulting from the great increase in tonicity of the myometrium due to oestrin. Thus distention appears to be an adequate stimulus for uterine growth when a small degree of tension is produced, but not if the tension is so great as to interfere with the nutrition (blood supply) of the tissues.