Effects on pregnancy in mice of passive immunization against ovine LH and human chorionic gonadotrophin

Abstract

Mice given daily i.p. injections of immunoglobulins against ovine LH on Days 3-7 of pregnancy were devoid of implantation sites on Day 8 whereas mice treated with antibodies to hCG had embryos of normal number and appearance on Day 8. These antibody treatments reduced the mean ± s.d. serum progesterone concentrations from 65.4 ± 15.3 ng/ml (control globulins) to 8.6 ± 4.9 ng/ml (anti-LH) and 9.2 ± 3.1 ng/ml (anti-hCG) on Day 8 and had no differential effect on serum oestrogen levels on Day 4. However, the mice treated with anti-hCG did not litter; resorption of the embryos took place between Days 10 and 14 of pregnancy. Indirect immunofluorescence and quantitative immunoenzymic assays showed the presence of anti-ovine LH and anti-hCG reacting antigens in the mouse feto-placental unit. On Day 6, the values of reacting antigens (mean ± s.d. absorbance units/10 µm section of embryo) were 0.050 ± 0.002 with control globulins, 0.059 ± 0.002 with anti-hCG-Ig and 0.196 ± 0.018 with anti-LH-Ig; the corresponding values on Day 12 were 0.075 ± 0.009, 0.402 ± 0.02 and 0.416 ± 0.015. The quantitative disposition of the reacting antigens to the two types of anti-gonadotrophins seems to bear a temporal relationship to their respective antifertility action. The pregnancy terminating action of immunoglobulins to ovine LH (Days 6, 7 & 8) and hCG (Days 8, 9 & 10) was counteracted by administration of 2 mg medroxyprogesterone acetate on Days 6, 9 and 12, indicating the importance of progesterone in the maintenance of pregnancy in the mouse.