A hormonally controlled serum factor stimulating the thymidine uptake into lectin-activated lymphocytes

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Abstract
The in vitro stimulation of [3H]thymidine uptake into lectin-activated lymphocytes in the presence of various sera was studied. The mean precision of the assay is 5%, and study of the confidence intervals shows variations from 4-12%. Compared to a normal reference serum (fixed as 1 U/ml), the serum thymidine uptake stimulating activity (mean .+-. standard error of the mean) was 1.04 .+-. 0.07 U/ml in normal adult males, 2.63 .+-. 0.48 U/ml in acromegalic patients, 1.51 .+-. 0.13 U/ml in constitutional dwarfism and 0.37 .+-. 0.04 U/ml in untreated hypopituitary dwarfism with a significant difference between the groups (P < 0.001). In patients with hypopituitarism a single i.m. hGH [human growth hormone] dose (6 mg/m2) increased the thymidine uptake stimulating activity of serum within 24-48 h following injection. The effects of directly adding hGH, insulin and triiodothyronine to the assay were studied: pharmacological concentrations are required to produce only a slight effect. Physiological concentration of a purified preparation of somatomedin A stimulated thymidine uptake and its effect is increased in the presence of serum. [3H]Thymidine uptake into lectin-activated lymphocytes apparently is stimulated by a GH-dependent serum factor. This method should be proposed for an accurate and sensitive biological evaluation of serum thymidine uptake stimulating activity.