Some Mammalian Endocrine Tissues or Cells Can Be Experimentally Transplanted

Some mammalian endocrine tissues or cells can be experimentally transplanted to other well-vascularized sites (such as the oral mucosa) in genetically similar hosts and the tissue's function continues normally and with proper regulation. The pars distalis is not a good candidate for such transplantation studies for which one of the following reasons?

A) More severe rejection of neurally related tissue occurs compared with other endocrine organs.
B) Its hormonal source is unavailable after its axonal connections to the hypothalamus are disrupted.
C) Its cells stop functioning when separated from the hypothalamo-hypophyseal portal system.
D) Neogenesis of blood vessels into this tissue will not occur at the transplant site.
E) The vascular wall of the superior hypophyseal arteries is unique.