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The rat has been used as a model to study the significance of graft and host interactions in small bowel transplantation (SBTX). A mouse model of SBTX would allow investigators to apply the knowledge of the well-defined genetics in the mouse to this field of study. Therefore, we have developed a mouse model of heterotopic SBTX using syngeneic C57BL6/J mice. Animals were anesthetized with a combination of ketamine and xylazine. Donor animals underwent midline laparotomy, with isolation of a segment of bowel as an isograft for transplantation to a recipient animal. The bowel was flushed in situ prior to removal of the graft with a Carrel patch of aorta and portal vein. The recipient animal underwent midline laparotomy and preparation of its infrarenal aorta and inferior vena cava for end-to-side anastomosis of the graft with 10-0 nylon. After vascular reperfusion of the graft the ends of the isografted bowel were brought out as stomata. Successful grafts were later assessed for viability by laparotomy or histological examination at the time of sacrifice. Areas of technical difficulty in this model and issues that might improve the experimental results are discussed. This model should allow investigators to apply the well-defined genetics of the mouse to probe the challenging field of intestinal transplantation.

Choline acetyltransferase (CAT) catalyzes the biosynthesis of acetylcholine according to the chemical equation: Acetyl-CoA + Choline in equilibrium Acetylcholine + CoA. To demonstrate the neuronal relationship of this enzyme, CAT activity was measured in hearts to which the extrinsic innervation was completely interrupted by extirpation of the heart from a donor animal and transplantation in a heterotopic position into the recipient's abdominal cavity. After the animals were killed at 8 days, enzyme activity in the transplanted hearts was measured and compared with that of the recipient. Choline acetyltransferase activity decreased 98% in the right atrium of the transplanted denervated hearts, 94% in the SA node, 87% in the left atrium, 80% in the right ventricle, and about 50% in the interventricular septum and left ventricle. These data show that sectioning the extrinsic parasympathetic innervation to the heart results in variable decreases in CAT activity, a finding which confirms that CAT activity is related to the extrinsic cholinergic innervation. The extrinsic (preganglionic) component of the parasympathetic system is nonuniform and supplies predominantly the specialized regions of the heart with conduction tissue. The residual enzyme activity is related to intrinsic (postganglionic) parasympathetic neurons. The intrinsic component is uniformly distributed to both specialized and contractile regions of the heart.

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