Histamine receptors on rabbit blastocyst and endometrial cell membranes

Abstract

DESPITE much study, the role of histamine in ovum implantation remains unclear^1–5. Histamine action is mediated by H₁ and H₂ receptors^6,7, which are widely distributed on the cell membranes of mammalian tissues^8–14. However, no information is available about the histamine receptors on blastocyst or endometrial cell membranes. Recent evidence indicates that a certain lymphocyte subpopulation carries histamine receptors⁹ and has an important regulatory function in vitro^10–12 and in vivo^12,13 in mice^9–11, guinea pigs¹² and man¹³. Murine T cells, capable of regulating antibody secretion in vitro¹⁰, and precursors of T cells, capable of mediating cytotoxic effector cells¹¹, carry histamine receptors. The density of these receptors increases with cell maturation¹¹. Cell activation by histamine results in increased levels of intracellular cyclic AMP¹¹ and production of small molecular weight material, called histamine suppressor factor, capable of suppressing both cell proliferation and lymphokine production by sensitised lymphocytes following exposure to the antigen¹². Histamine suppression of delayed hypersensitivity in guinea pigs in vivo can be blocked completely or partially by H₂ and H₁ antagonists, respectively¹². Also, the administration of H₂ antagonists to man results in enhancement of delayed skin tests¹³. These observations indicate that lymphocytes carrying H₂ receptors acquire immunosuppressor potential on activation.