PRESENCE OF THYROTROPIN RECEPTOR IN INFANT ADIPOCYTES

In healthy infants, the levels of TSH are known to peak at 50-100 time s adult values during the first days of life. In studies of isolated h uman infant adipocytes, we have earlier shown that bovine TSH (bTSH) h as a strong lipolytic effect, accompanied by a blunted response of adi pocytes to catecholamines. In this study, we used human recombinant TS H (hTSH), and incubation of adipocytes with hTSH induced a lipolytic r esponse similar to that obtained with the P-adrenergic receptor agonis t isoprenaline in adopters isolated from three infants. The lipolytic effect of hTSH was completely blocked by inhibitory TSH receptor (TSHR ) antibodies. The TSHR mediates the effects of TSH in the thyroid, and it has been detected in some extrathyroid tissues, but not in isolate d human adipocytes or childhood adipose tissue. In this study, we foun d TSHR RNA in infant and adult adipose tissues and isolated adipocytes with reverse transcriptase-PCR. The sequence of the amplified PCR pro duct agreed with the published sequence. Northern blot hybridization o n RNA prepared from infant adipose tissue showed a transcript of the e xpected size, and the expression of TSHR seemed higher in infant than in adult adipose tissue. In conclusion, this study indicates that TSH plays an active role in the metabolic adaptation after birth.