IMMUNOREACTIVE THROMBOXANE SYNTHASE IS MEASURABLE IN-OVINE FETAL HYPOTHALAMUS AS EARLY AS 86 DAYS GESTATION

Thromboxane A(2) (TxA(2)) augments hypothalamus-pituitary-adrenal axis activity in both fetal and adult animals. We have proposed that TxA, acts as a neuromodulator within the brain to stimulate the release of corticotropin releasing hormone (CRH) or arginine vasopressin (AVP) in to the hypophyseal-portal blood(1). We performed the present experimen ts to identify immunoreactive thromboxane synthase (TxS) within fetal brain regions and to quantify developmental changes in the TxS immunor eactivity measurable within those regions. We found that immunoreactiv e TxS was present in fetal hypothalamus, pituitary, brainstem, and lun g. In fetal hypothalamus, we found immunoreactive TxS in three identif iable molecular weights, approximately 65, 42, and 35 kD. In fetal pit uitary and lung, we found the 65 and 35 kD forms, and in the brainstem we found only the 35 kD form. In fetal pituitary, there was a clear o ntogenetic change in TxS immunoreactivity. The 42 kD TxS immunoreactiv ity was not present in the youngest fetal sheep studied (86-90 days' g estation), but was expressed in the other age groups (125-128, 135-139 , 141-term, and postnatal ages). The other molecular weight forms appe ared to increase in the older fetuses, but the changes were not signif icant. In the hypothalamus, all three forms of TxS were measurable at all ages, and there was no significant change in relative abundance. W e conclude that immunoreactive TxS is present in the fetal brain throu ghout the last half of fetal gestation, but that the significance of m ultiple molecular weight forms is not clear.