Pseudopregnancy and the decidual response in the obese Zucker rat: a reexamination

The ability to induce the pseudopregnant (psp) state and the decidual response (DR) in the obese Zucker rat was reexamined. Lean and obese rats were cervically stimulated on the evening of proestrus or morning of estrus. This procedure lengthened the period of vaginal diestrus in both groups to approximately 13 days. The percentage of obese rats (70.0%) that became psp was not significantly different from that of lean rats (72.2%). To test sensitivity to a decidual stimulus, sesame oil was injected into the lumen of uteri of psp rats on Day 4 of vaginal diestrus. Treated uterine horns of all rats decidualized. The mean percentage increases in weights of Day 9 decidualized horns were not significantly different between obese and lean rats (752 +/- 85% SE and 875 +/- 133%, respectively). These data contradict previous reports that obese rats do not become psp following cervical stimulation, and that their uteri do not develop a typical DR. Although it is recognized that the reproductive capacity of the obese female Zucker rat is severely limited, this study describes aspects of reproductive function that are less abnormal than previously reported. The ability of the obese Zucker rat to become psp following cervical stimulation suggests that the progestational state of pregnancy might be induced reflexly. Furthermore, the ability of its uterus to respond to a decidual stimulus suggests that the obese Zucker rat may be able to support implantation.