Luteinizing hormone-releasing hormone in thymus and hypothalamus of rat fetuses: Suppressing effect of antagonist and of antibodies on concanavalin A-induced proliferation of thymocytes

The effect of endogenous luteinizing hormone-releasing hormone (LHRH) on th e proliferation induced by concanavalin A (Con A) in rat fetal thymocytes w as studied. A selective antagonist (2 mug per fetus) or antibodies to LHRH (20 mul per fetus) were injected in utero into 20-day-old rat fetuses, and this resulted in a two- or fivefold decrease in the Con A-induced prolifera tion of thymocytes, respectively. In combined culture of the antagonist (10 (-5)-10(-6) M) with fetal thymocytes, the proliferative response was not de creased. The concentration of LHRH was determined by radioimmunoassay in ti ssues of immunocompetent organs and in blood serum of 18- and 21-day-old fe tuses, and the hormone was found in the hypothalamus, thymus, and periphera l blood. The initially low level of LHRH in the thymus increased by 65 and 40%, respectively, on the first day after birth and became similar to the l evel in the hypothalamus. In the fetal blood serum, the LHRH level was sign ificantly higher than in the thymus and hypothalamus of fetuses of the same age. The hormone concentration was greatest in the 18-day-old fetuses, and it decreased twofold by the 21st day. The findings indicate that LHRH is i nvolved in regulation of T-cell immunity even during prenatal ontogenesis.