At birth, the rat renal papilla has the structural composition of the mature inner stripe of the outer medulla. All loops of Henle have the configuration of short loops, and there are no ascending thin limbs. This study examines the role of apoptosis in the differentiation of the loop of Henle and the development of the ascending thin limb in the rat kidney. Kidneys of 20-day-old fetuses and 1-, 3-, 5-, 7-, 14-, and 21-day-old pups were preserved for immunohistochemistry and electron microscopy. Using a preembedding immunoperoxidase method, we identified thick ascending limbs by labeling with antibodies to the serotonin receptor, 5-HT1A, and descending thin limbs were identified by labeling with antibodies to aquaporin-1. Three methods were used to identify apoptotic cells as follows: 1) in situ nick end labeling using the ApopTag kit, 2) toluidine blue staining on plastic sections followed by etching, and 3) transmission electron microscopy. At birth, tubules with 5-HT1A immunoreactivity were present throughout the renal papilla, and there were no ascending thin limbs. From 1 to 14 days of age, staining for apoptosis was observed in numerous cells in the 5-HT1A-positive epithelium, beginning at the papillary tip and ascending to the border between outer and inner medulla. This was associated with transformation from a cuboidal to a squamous epithelium and subsequent disappearance of 5-HT1A immunostaining from the transformed cells. Electron microscopy confirmed the presence of apoptotic cells and phagocytosed apoptotic bodies in the thick ascending limb in the renal papilla. We conclude that the ascending thin limb is derived from the 5-HT1A-positive thick ascending limb by apoptotic deletion of thick ascending limb cells and transformation of the remaining tubule cells into the 5-HT1A-negative ascending thin limb.

Organ shortage continues to challenge the field of transplantation. One potential group of donors are those who have been transplant recipients themselves, or Organ Donation After Transplant (ODAT) donors. We conducted a retrospective cohort study to describe ODAT donors and to compare outcomes of ODAT grafts versus conventional grafts. From October 1, 1987 to June 30, 2015, 517 former recipients successfully donated 803 organs for transplant. Former kidney recipients generally survived a median of approximately 4 years before becoming an ODAT donor whereas liver, lung, and heart recipients generally survived less than a month prior to donation. In the period June 1, 2005 to December 31, 2014, liver grafts from ODAT donors had a significantly higher risk of graft failure compared to non-ODAT liver transplants (P = .008). Kidney grafts donated by ODAT donors whose initial transplant occurred >1 year prior were associated with significantly increased graft failure (P = .012). Despite increased risk of graft failure amongst certain ODAT grafts, 5-year survival was still high. ODAT donors should be considered another form of expanded criteria donor under these circumstances.