Effect of hysterectomy on serum luteinizing hormone concentrations and on corpus luteum function in the rat

Serum progesterone, follicle stimulating hormone (FSH) and luteinizing hormone (LH) concentrations were estimated in intact and hysterectomized pseudopregnant rats. Progesterone concentrations increased significantly from day 2 of pseudopregnancy (PSP) onwards, and a plateau was reached on days 4 and 5. No significant differences in progesterone concentrations between intact and long-term hysterectomized animals were observed until day 10 of PSP. In the intact rats, progesterone concentrations decreased after day 8, but in the hysterectomized rats they remained elevated until days 18-20 of PSP. No differences between FSH concentrations in intact and hysterectomized rats were found. In hysterectomized rats, however, LH concentrations were significantly lower than those in the intact rats on days 2-7 of PSP. When hysterectomy was performed on day 2 of PSP (acute hysterectomy) lower LH concentrations were also found in the hysterectomized animals compared with sham-operated animals. No differences in progesterone concentrations were found between sham-operated controls and acutely hysterectomized animals on days 3-8 of PSP. It was found that LH concentrations in ovariectomized long-term hysterectomized rats were lower than those in ovariectomized, but otherwise intact, animals. In contrast to its effect on tonic LH secretion, long-term hysterectomy had no influence on the surge of LH during the afternoon of proestrus. In both intact and long-term hysterectomized rats the duration of PSP was not significantly altered after transplantation of an ovary under the kidney capsule and the removal of the ovaries in situ. It is concluded that hysterectomy leads to a decreased LH secretion by the pituitary gland, but has no influence on the maximal progesterone concentrations during PSP. The significance of these findings, particularly with regard to the prolongation of PSP after hysterectomy, is discussed.