Changes in cyclic AMP level of rat thyroid by acute and chronic stimulation of thyrotropin in vivo

To assess a possible postmortem change in the level of cyclic AMP, the thyroids were snap-frozen at various time intervals after removal. Rats were fed a low-iodine diet (LID) with PTU for 2 weeks and a week after PTU discontinuation (PTU withdrawal). In all cases, the cyclic AMP level tended to increase as time elapsed from removing till fixing the thyroids, but in the PTU withdrawal group, the level was rapidly increased 2-fold after 5 min. In an acute experiment, the thyroids were removed under anesthesia and frozen rapidly. Intravenous administration of ovine thyrotropin (250 mU) and TRH (500 ng) brought about a rapid increase in the thyroidal level of cyclic AMP to 40% to 20% over the control level. Two weeks after PTU treatment, circulating thyrotropin was increased to a maximum of 19-fold and a further enhancement ("rebound") was observed after PTU withdrawal. PTU treatment led to an increase in the thyroidal level of cyclis AMP pre mug DNA to 60% over the control value. Following PTU withdrawal, the rise in the level of cyclic AMP returned to the normal level. However, there was no change in the concentration when it was expressed as per mg wet tissue weight. Therefore, the increase in the thyroidal concentration of cyclic AMP per mug of DNA may be due to an increase in volume of the follicular cells.

Cardiopulmonary dysfunctions caused by intravenous collagen-induced release of ADP and ATP from platelets

Bovine tendon collagen suspension (4.5 mg/kg) was injected rapidly into the femoral vein of 14 normal (untreated) and 8 busulfan treated rats. Trasient effects included decreased platelet counts and arterial PO2, increased central venous pressure, apnea, bradycardia and variable A-V block. These findings were most prominent within 1 minute after injection and subsided or disappeared by 10 minutes. During this period, ADP and ATP in platelet-free plasma from carotid arterial blood were measured in a liquid scientillation counter using the firefly luciferase assay. In normal (untreated) rats, collagen injection was followed by increases in plasma ADP and ATP, a rise in plasma hemoglobin and minimal changes of fibrinogen and hematcrit. Pathological observations indicated the platelet emboli in pulmonary vessels. In contrast, rats made thrombocytopenic by intraperitoneally infected busulfan prior to collagen injection had minimal or no change in platelet count, plasma ADP, ATP, hemoglobin, fibrinogen, or cardiopulmonary functions following collagen injection. These findings suggest that collagen injection causes release of ADP and ATP from platelets; released ADP induces platelets to form aggregates which lodge in the coronary and pulmonary microcirculations and elsewhere, resulting in thrombocytopenia and the cardiopulmonary dysfunction, in the presence of shear, of red cells with vessel surfaces altered by platelet aggregates.

Electron microscopic studies of the cartilage-pannus junction in rheumatoid arthritis

The junction between pannus and cartilage was examined in the rheumatoid joint. Three types of cartilage-pannus junction were observed. In one, proliferating small blood vessels, surrounded by highly cellular infiltrates, penetrated deeply into the cartilage. Degeneration of the cartilage was observed around the cellular accumulations. In the second, phagocytic and fibroblastic cells invaded the cartilage. In the third, fibrous pannus overlay the cartilage. Lysis of cartilage by infiltrating cells appeared to be a major cause of cartilage erosion in rheumatoid arthritis.

Cardiopulmonary dysfunctions caused by ADP-induced platelet aggregation

Intravenous (i.v.) injection of 0.1 mg/kg of ADP within one second in 13 rats caused a prompt drop in platelet count to 55.1 plus or minus 3.2% of the preinjection value with a statistical significance (p less than 0.01) at 30 seconds after the injection. At that time, mean arterial pressure and arterial PO2 decreased, while central venous pressure increased. Heart rate decreased with an appearance of sinus bradycardia and variable A-V block. Various respiratory effects such as shallow or slow respiration or apnea appeared. Such changes showed a tendency to recovery within 3 minutes. Splenectomy did not prevent these changes in 6 rats. In 6 thrombocytopenic and leukopenic rats treated with busulfan, these changes did not appear. Intra-arterial injection of the same amount of ADP induced almost no response. When ADP was injected twice 20 seconds apart in 10 rats, the second injection resulted in no effects or slight responses. In contrast, when 10 rats were injected twice 180 seconds apart, both the first and second injections showed the same effects on platelets and cardiopulmonary functions. The results suggests that the effects observed following I.V. ADP are probably due to transient obstruction of coronary and pulmonary microvessels by platelet aggregates. Reduced response following two successive injections may be due either to the reduced platelet count or to a refractory state induced by the first injection. ADP is probably rapidly metabolized in systemic microvascular beds.

Studies on the heterogeneity of labeled iodoprotein from iodine-replete and iodine-deficient rats as determined by susceptibility to proteolysis

Thyroid iodoprotein from rats fed a high-iodine diet (HID) or a low-iodine diet (LID) were labeled with radioiodine in vivo for periods ranging from 4 hr to several days. Standardized aliquots of thyroid homogenate from rats with various treatments were digested for 4 hr with 1% pancreatin or with 0.003% pancreatin after 30 min pretreatment with beta-mercaptoethanol (ME-P). Four-hr labeled iodoprotein from both LID and HID rats was equally susceptible to digestion with 1% pancreatin; however, such iodoprotein from LID rats was more susceptible to digestion with ME-P than that from HID rats. With increasing intervals up to 7 days between administering radioiodine and removing the thyroids, there was a progressive rise in the resistance to digestion in iodoprotein from LID rats, but only a slight increase in resistance in iodoprotein from HID rats. If propylthiouracil was added to the diet beginning 24 hr after radioiodine administration, there was a marked increase in the rate of development of resistance of iodoprotein to digestion. Radioautographs showed that the radioiodine was localized primarily in the peripheral follicles after 2 days PTU. Similar differences in susceptibility to digestion were found in purified thyrogobulin prepared from HID and LID rats. No change in susceptibility to digestion of thyroid iodoprotein with time after labeling was seen in hypophysectomized LID rats in which thyroid secretion and thyroglobulin turnover is known to proceed at an extremely slow rate. The data indicate that there are at least two types of iodinated thyroglobulin in the rat thyroid. One is readily susceptible to digestion and has a rapid turnover in the thyroid. The other is more resistant to digestion, has a slow rate of turnover and is located primarily in the peripheral follicles.