Induction of Premature Birth in Rats by a Methionine Antagonist

Abstract

Pregnant rats injected with ethionine have shown a high incidence of resorption and stillbirth and pups born alive have been smaller than normal. Without precise knowledge of the time of conception it has not been known to what extent the low birth weight could be attributed to prematurity. The present study was designed to shed light on this question. Pregnant rats were injected with graded doses of ethionine up to and including the amount known to cause resorption or stillbirth. The date of conception was inferred from the first appearance of sperm in the vagina. Relatively small doses of ethionine caused premature birth with only a low incidence of resorption and stillbirth. The incidence of prematurity, and its degree, were directly related to the dose of ethionine. The premature pups grew faster than the control pups, thus correcting an initial weight deficit by the age of 3 months. Sub-lethal doses of ethionine given to non-pregnant animals did not adversely affect subsequent conception or gestation.