The Influence of Donor and Recipient Age and Sex on the Quantitative Transplantation of Monodispersed Rat Thyroid Cells*

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Abstract
We have previously reported a technique for the quantitative transplantation of monodispersed rat thyroid cells. In this study, the influence of the age and sexual status of the donor and recipient animals on the transplantation process has been examined using the number of cells required for the growth of 1 or more follicular units in 50% of the transplantation sites (follicular dose 50% or FD50) as the end point. The number of multifollicular clusters per 1000 inoculated cells was also explored. FD50 values in 5-week-old intact male recipients increased as the donor's age increased over the range of 4 weeks to 12 months. FD50 values in 5-week-old thyroidectomized male recipients were similar when donors were 4–8 weeks old, but were increased for cells from 52-week-old donors. The FD50 values of cells from 5-week-old donors was higher in 4-week-old intact recipients than in the 5- or 6-week-old recipients. In male recipients, the FD50 values were lower than in female recipients of 5 and 8 weeks of age. This sex-related effect was reduced by orchiectomy and ovariectomy. Generally, the frequency of multifollicular clusters per 1000 inoculated cells increased as the FD50 decreased. These results are discussed in the light of measurements of thyroidal DNA synthesis and TSH levels reported by others.