• Thymus;
  • weight;
  • lymphocytes;
  • mating

ABSTRACT: Eleven groups, each of ten Sprague-Dawley female rats, were sacrificed at 12 to 13 weeks of age; one group of virgins, the others at two-day intervals during the first ten days after either inbred or outbred mating. Observations were made on thymus weight, total white cell count, and thymic white cell density.

Compared with the virgin group no significant differences were observed in the thymic weight at any stage after either inbred or outbred mating. In contrast the total white cell counts were significantly greater than the virgin count on the second postcoital day after both inbred and outbred mating.

These increased total counts were maintained until the end of the observation period and were associated with significant increases in the thymic white cell densities. These observations suggest that mating and implantation initiate and sustain a mechanism of lymphocyte accumulation in the rat thymus.