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Specimens of human rheumatoid and nonrheumatoid synovial lining were maintained in nonproliferative organ culture for 20 hours. The culture fluids were then assayed for prostaglandin E(2) (PGE(2)), thromboxane B(2) (TXB(2)), and 6-keto-prostaglandin F(1alpha) (6-keto-PGF(1alpha)) by specific radioimmunoassay. The presence of each of these substances was confirmed by gas chromatography and mass spectrometry. Rheumatoid tissue produced significantly more of each cyclo-oxygenase product than nonrheumatoid tissue.

5'-Nucleotidase (EC 3.1.3.5), a plasma membrane-bound enzyme, has been assayed in unfixed tissue sections of human synovium, activity being measured by scanning and integrating microdensitometry. Activity was markedly increased in the lining cells of the rheumatoid synovial membranes.

The synovial tissue in experimentally induced immune arthritis induced in the rabbit has been used as a model of rheumatoid arthritis to determine which cells may contribute to the growth of this tissue. Tissue from the challenged and from the unchallenged knee joints was taken, after the intra-articular injection of a small amount of tritiated thymidine, from rabbits up to 3 months after the arthritis was induced. DNA synthesis, as a measure of cell proliferative activity, was assessed firstly by measuring the labelling index in autoradiographs of sections of such tissue, and secondly by the DNA synthetic index obtained by Feulgen cytophotometry. These measurements were made separately on synoviocytes, on the structural cells of the stroma, on the cells lining the small blood vessels, and on the infiltrating inflammatory cells. The DNA synthetic activity of the synoviocytes, and of the stromal noninflammatory cells, was maximal between 3 and 7 days after challenge. The activity in the synoviocytes, in particular, remained raised for up to 84 days after the challenge. Thus these cells appear to be capable of contributing to the hyperplasia, but the contribution of other cells, deeper in the stroma, cannot be excluded.

The activities of two mitochondrial enzymes, succinate dehydrogenase and cytochrome oxidase, have been measured by quantitative cytochemistry and microdensitometry in the synoviocytes of rheumatoid and non-rheumatoid synovial lining cells. Although both tended to be higher in the former, there was no statistically significant difference in the activities of either enzyme in these tissues. However, when cytochrome oxidase activity was measured without exogenous cytochrome c, the activity in the rheumatoid synoviocytes was highly significantly elevated. It is suggested that these findings may indicate only that the cytochrome c-cytochrome oxidase complex in the rheumatoid cells is more stable, possibly because of the increased availability of phospholipids in these cells.

The DNA content per nucleus has been measured in the lining cells of 12 specimens of rheumatoid and 12 of nonrheumatoid synovial tissue. Optimal conditions for this reaction on these cells have been defined, and an index of DNA synthesis has been applied to give a quantitative measure of the degree of synthesis. This has given evidence of some DNA synthesis in both types of synoviocytes, compatible with the amount found in a slowly self-replacing tissue. There was no difference in the amount of synthesis in the rheumatoid and nonrheumatoid synoviocytes.

Synovial tissue from 3 patients with villonodular synovitis has been examined by quantitative cytochemistry. Considerable changes in the metabolism of the synoviocytes have been observed. These included a massive rise in the activity of glucose 6-phosphate dehydrogenase to levels even greater than those found in rheumatoid arthritis, and a significant rise in the activity of 2 glycolytic enzymes, glyceraldehyde 3-phosphate and lactate dehydrogenase. Lysosomal napthhylamidase showed raised activity with no latency. The sulphydryl content in the synoviocytes was raised, as was the amount of available phospholipid. This pattern of metabolic alterations is similar to that found in human rheumatoid synoviocytes.

There has been doubt as to whether elevated levels of parathyroid hormone, reported previously by radioimmunoassay, reflect increased concentrations of the biologically active hormone. The application of a recently developed, highly sensitive bioassay has shown considerable disparity between bioactivity and immunoreactivity in 5 rheumatic conditions and in normal subjects. Six patients with chondrocalcinosis had elevated levels; 3 of these did not have hypercalcaemia or any obvious cause other than possible subclinical hyperparathyroidism. One patient, assayed during an acute episode, had an elevated concentration of the hormone which reverted to normal when she was asymptomatic. Most patients with osteoarthrosis (13 our of 15) had low normal levels; 2 showed unexplained slightly elevated concentrations. Of 6 patients with haemochromatosis 3 had elevated levels, though this may have been related to the associated presence of diabetes mellitus. A third of patients with ankylosing spondylitis (10 out of 30) showed elevated parathyroid hormone levels but without hypercalcaemia. A number of spondylitic patients also showed anomalous results in this assay, possibly due to the presence of an antagonist. This would be consistent with the absence of clinical or biochemical evidence of hyperparathyroidism.

DNA synthesis has been measured both by Feulgen cytophotometry, quantified by the DNA synthesis index, and by tritiated thymidine autoradiography, quantified by the labelling index. In the early acute inflammation resulting from the intra-articular challenge of ovalbumin in sensitised rabbits both indices rose considerably, so that at least 1 in 10 synoviocytes was heavily labelled 3 days after challenge. The results are compatible with the concept that even such apparently differentiated synoviocytes are capable of cell division.

To examine the reported beneficial effect of zinc in rheumatoid arthritis, rheumatoid synovial tissue has been maintained in vitro in non-proliferative culture with or without zinc sulphate in the culture medium. Alkaline phosphatase activity was measured by microdensitometry of the cytochemical reaction in cryostat sections; the activity in blood vessels was measured separately from that in the supporting tissue below the synovial surface. Zinc enhanced this activity optimally at concentrations of between 10(-5) and 10(-4) mol/l.

A specific cytochemical reaction for freely available phospholipids has shown a raised concentration of such phospholipids in the lining cells of human synovial membranes removed from rheumatoid joints. Quantitative measurement, by microdensitometry, of the amount of reaction-product per cell showed that the rheumatoid synoviocytes contained almost three times the amount of free phospholipids present in the equivalent nonrheumatoid cells; statistically the difference was highly significant. Evidence from studies in which the bound phospholipids were 'unmasked' by methanol-chloroform confirmed the view that the increased content of freely available phospholipids was related to altered lipid-protein binding rather than to an increase in total phospholipids.

Human rheumatoid synovial lining cells have up to four times the capacity to oxidize glucose 6-phosphate, the first step of the hexose monophosphate pathway, as do the nonrheumatoid cells. The reducing equivalents produced by this system have many significant metabolic effects. Exposure of these cells by 10(-5) M prednisolone in vitro, or to 6 mg/day in vivo, causes some depression of this activity in the rheumatoid synovial lining cells; less than this dose of steroid, or the administration of nonsteroidal drugs in vivo, has little or no effect. The depression of activity produced by 6 mg/day does not bring this activity down to the value found in nonrheumatoid synoviocytes.

It was conceivable that the previously reported elevated pentose-shunt activity in human rheumatoid synoviocytes could be at the expense of glycolytic activity. To test this possibility the activities of glyceraldehyde 3-phosphate and lactate dehydrogenase, the two dehydrogenase enzymes of the latter pathway, have been investigated in the synovial lining cells in fresh sections of nonrheumatoid and rheumatoid synovial tissue. To measure the activity solely in the lining cells, apart from that in underlying infiltrating cells, quantitative cytochemical reactions have been used; the activities were measured by microdensitometry. The results showed highly and significantly increased activity of both enzymes in the rheumatoid cells. Increased activity was also found in synoviocytes in nonrheumatoid synovial tissue after trauma, so that the increased activity of these enzymes is not characteristic of the rheumatoid condition. However, the results indicate that the increased pentose shunt activity in rheumatoid synovial lining cells is not at the expense of glycolytic activity but may be part of an enhanced potential for utilising glucose 6-phosphate in these cells.