DEVELOPMENT OF A MODIFIED CRYOPRESERVATIO N TECHNIQUE FOR PARATHYROIDTISSUE IN AN ANIMAL-MODEL

A modified cryopreservation technique for parathyroid tissue was inves tigated in an animal model. The modified technique was compared with a previously described method [10, 11] using a programmed freezer and a lso with other simplified cryopreservation techniques [1, 8]. Total pa rathyroidectomy was performed in 90 Sprague-Dawley rats, which were al located to 7 groups. Group I had no autotransplantation (n = 10) and g roup II underwent immediate autotransplantation of one parathyroid gla nd (n = 17). In the other five groups of rats the parathyroids were cr yopreserved and one gland was reimplanted after 10 days' storage in li quid nitrogen (LN) at -196 degrees C. The following techniques for cry opreservation of the parathyroid glands were used. Group III: immediat e placement in LN, n = 7; group IV: immediate placement in a freezer a t -20 degrees C, transfer to LN after 2 h, ii = 12; group V: immediate placement in a freezer at -80 degrees C, transfer to LN after :! h, n = 13. group VI: manually controlled freezing initially at a rate of 1 degrees C/min to -25 degrees C, and subsequently at 10 degrees C/min to -70 degrees C before transfer to LN [8], n = 19, group VII: program med freezing at a controlled rate of 1 degrees C/min to -80 degrees C prior to transfer to LN [10, 1 1], n = 12. Serum calcium concentration s were determined over a period of 60 days. Furthermore, the individua l difference in the calcium concentration was assessed for each rat on the basis of the calcium levels recorded preoperatively and at day 60 . By 60 days after immediate autotransplantation (group II), in 15 out of 17 rats (88%) serum calcium concentrations had returned to normal values. Serum calcium had normalized by day 60 in 1 out of 7 rats (14% ) in group III, 6 out of 12 rats (50%) in group IV, 7 out of 13 rats ( 54%) in group V, 4 out of 19 rats (21%) in group VI, 7 out of 12 rats (58%) in group VII, and in none of the 10 rats without autotransplanta tion (group I). In group II median calcium concentrations of 2.35 mmol /l and 2.32 mmol/l were determined preoperatively and on day 60, respe ctively. The median value of 0.02 mmol/l estimated for the individual calcium differences was not statistically significant. After cryoprese rvation the median individual calcium concentration difference was sma llest in group IV at 0.14 mmol/l (median calcium level: 2.35 mmol/l pr eoperatively, 2.23 mmol/l day 60). After programmed freezing the media n difference was 0.28 mmol/l (median calcium level: 2.48 mmol/l preope ratively, 2.25 mmol/l day 60), 0.92, mmol/l in group I, 0.72 mmol/l in group III, 0.23 mmol/l in group V and 0.39 mmol/l in group VI. In the present experimental study, rat parathyroid glands were successfully autografted after cryopreservation using the described modified techni que of freezing the glands by immediate placement in a freezer at -20 degrees C and transfer to LN after 2 h. The results were comparable to those obtained after controlled freezing in a programmed freezer and superior to results reported for simplified cryopreservation technique s. The suitability of this technique for human parathyroid tissue will be evaluated in a further study.