Human thyroid blood flow response to endogenous, exogenous human, and bovine thyrotrophin measured by electromagnetic flowmetry.

Human thyroid blood flow (TBF) was studied with electromagnetic flowmetry during operation. Measurements were made of the effect on TBF of injections of bovine TSH into one inferior thyroid artery in 6 patients; 6 other patients were given human TSH, and in 10 patients measurements were made both of TBF and endogenous TSH released after administration of TRH in a peripheral vein. The TBF increased after all three types of injection. The mean of the TBF maxima after bovine TSH was 2.26 +/- 0.35 (mean +/- SEM) relative to basal TBF, after human TSH 1.97 +/- 0.28, and after TRH 1.64 +/- 0.20. In the three groups combined it was 1.92 +/- 0.16. The TBF was often increased already during the first recording period 1-10 min after TSH or TRH administration. The mean TBF was approximately doubled at 30-50 min. There were considerable inter-individual variations in the latent time and maximum response of TBF, especially after human TSH, but we found no correlation between the response and the TSH serum concentration in any group. A prompt, but inter-individually varying, increase in TBF was confirmed. This increase is suggested to be secondary to an increased intrafollicular metabolic activity and not primarily regulating thyroid function.