Histamine formation by mouse preimplantation embryos.

Mouse embryos recovered on the 4th day of pregnancy produced histamine, as evidenced by the 14CO2 produced from carboxy labelled L-histidine, at the rate of 1.5 +/- 0.3 (s.e.m.) pmol/embryo per hour. Most (83.2 +/- 4.6%) of the embryos flushed from the oviducts on Day 3 of pregnancy (4--8-cell stage) developed into blastocysts within 48 h after being placed in culture. Inclusion of L-histidine hydrochloride (4.7 x 10(-4) M) in the culture medium did not alter this development but DL-alpha-methylhistidine (3.8 x 10(-4) M), an inhibitor of histidine decarboxylase, reduced the number of embryos developing into blastocysts to only 10.8 +/- 6.8%. A combination of L-histidine and DL-alpha-methylhistidine in the medium prevented the growth-retarding effect of the latter compound. The results indicate that mouse embryos can produce histamine and suggest that this is necessary for normal development.