Extracorporeal biological perfusion of the isolated dog thyroid gland

The method of thyroid gland perfusion, in which the organ continues to function under physiological conditions, can be used to study the effects of various factors (transplantation, cryoconservation, antithyroid agents~ stimulating drugs) on individual parameters of thyroid function. Methods of perfusion of the surviving thyroid gland with buffered salt solutions [8-11] and also with blood, using a pulsating valve pump [14], developed previously cannot be regarded as adequate for these purposes. In this paper we describe a model of extracorporeal biological perfusion of the isolated thyroid gland which we have developed. The basis for development of the model was the principle of the scheme of perfusion of the testis [2, 3]. Considering the anatomical features of the dog thyroid gland, i.e., the total isolation of its two lobes, only the right lobe was perfused whereas the left remained in situ and served as the control. EXPERIMENTAL METHOD Experiments were carried out on dogs of both sexes weighing 20-35 kg. The animals were anesthetized with 0.005% fentanyl solution and 0.25% droperidol solution (2 ml of each, intramuscularly), followed by intravenous injection of 2.5% hexobarbital solution in a total dose of 5-7 mg/kg. The right lobe of the thyroid gland was mobilized on its vascular pedicle, consisting of a segment of the common carotid artery with the thyroid artery branching from it, through a longitudinal incision in the neck. The extra-thyroid branches of the thyroid artery were ligated and divided. Heparin was injected intravenously into the dogs in a dose of 250 U/kg body weight. The right lobe of the gland together with the segment of the common carotid artery was removed and transferred to a thermostatically controlled chamber whose temperature was kept constant at 37~ The segment of the common carotid artery was connected by means of polyethylene tubes to the central end of the divided right femoral artery, and its peripheral end was connected to the peripheral end of the divided left femoral artery (Fig. i). The veins of the gland were divided. Venous blood drained away freely into the chamber through perforations in the support beneath the gland, and it was collected in a special receiver and returned to the dog's blood stream. Blood from the left lobe of the thyroid gland (control) was collected from the dissected thyroid vein, which was divided and placed in a test tube. The dog's systolic arterial pressure was maintained throughout the experiment at 90-120 mm Hg. In the course of perfusion for 6 h the volume of plasma expanders (the Soviet dextran equivalent polyglucin, 0.9% NaCI) was 0.5 liter and the hematocrit index never fell below 40. The duration of ischemia of the extracorporeally perfused lobe of the gland did not exceed i0 min. Throughout perfusion a careful watch was maintained on the dog's hemodynamics. The perfused lobe of the gland was weighed before and after perfusion. Thyroid function was assessed by measurement of several parameters. The thyroxine and triiodothyronine levels (by radioimmunoassay using kits from Amersham International, England) and concentrations of glucose (orthotoluidine test) and lactic acid (enzyme assay) were determined in afferent and efferent thyroid blood. At the end of perfusion the thyroxine and triiodothyroni~e levels [1.2] and the glycogen (anthrone method) and lactic acid concentrations in the gland tissue were determined.