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1. Experiments were performed in anaesthetized rabbits to examine the effects of calcitonin gene-related peptide (CGRP) and the CGRP antagonist CGRP8-37 on blood flow to the medial collateral ligament of the knee joint. 2. Topical application of CGRP (10(-13) to 10(-9) mol) to the exposed external surface of eight knee joints resulted in dose-dependent dilatation of vessels in both the ligament and the joint capsule. The magnitude of this response varied significantly in different regions of the medial collateral ligament, with the 10(-9) mol dose of CGRP giving the maximum response (101.5 +/- 25.3% increase) at the femoral insertion site of the medial collateral ligament and lowest (23.1 +/- 8.8%) at the tibial insertion site. 3. Topical application of CGRP8-37 (0.1, 1 and 10 nmol) produced dose-dependent constriction of vessels in the ligament and the joint capsule in five knees, with a trend towards the greatest effect occurring at the femoral insertion site (45.8 +/- 8.1% reduction in blood flow). With the 10 nmol dose, the vasoconstrictor response at the femoral insertion site differed significantly (P<0.05) from the responses obtained at the tibial insertion and joint capsule sites. 4. Topical application of CGRP8-37 (0.1, 1 and 10 nmol) to four chronically denervated knees produced substantially smaller vasoconstrictor responses at all sites. At the femoral insertion site, where 10 nmol CGRP8-37 normally produces a 45.8 +/- 8.1% reduction in blood flow (n=8), ten days following denervation this response was reduced to 6.5 +/- 6.1%, this difference being significant (P=0.01). 5. Adrenaline was applied topically to augment blood vessel tone, in order to establish how effectively co-administration of CGRP would offset this increase in tone. Adrenaline (10(-10) mol) produced vasoconstriction at all sites (n=6). In the capsule this vasoconstriction was virtually abolished when CGRP (10(-9) mol) was co-administered with adrenaline but in the ligament vasodilatation occurred at all sites. This vasodilatation was significantly greater at the femoral insertion site compared to the tibial insertion and mid ligament sites (P<0.05 for both) and the capsule (P<0.01). 6. Topical application of substance P (10(-10) or 10(-9) mol) failed to elicit dilatation of ligament blood vessels. 7. These results suggest that endogenous CGRP may play an important role in regulating blood flow to different structures in and around the knee joint.

Coloured microspheres were used to determine standardized blood flow in an established model of medial collateral ligament injury in the adult rabbit knee. Resting blood flow in the ligament was ascertained to be on the order of 0.68 +/- 0.08 ml/min/100 g (mean +/- SEM) in normal rabbit knees, although errors in flow estimates of this magnitude may be quite high. In healing medial collateral ligament, however, flow had increased markedly 3 weeks after injury (21.45 +/- 5.48 ml/min/100 g). Flows in sham-operated control medial collateral ligaments were not significantly increased compared with those in control normal ligaments. Six weeks after injury, blood flow in the ligament remained elevated (16.90 +/- 3.20 ml/min/100 g) and was similarly elevated in other neighbouring joint tissues (i.e., ipsilateral synovial fat pad). The increase in flow to ipsilateral noninjured articular tissues did not persist beyond 6 weeks, but flow in the healing medial collateral ligament scar tended to remain elevated after 17 weeks (4.20 +/- 1.79 ml/min/100 g), although this did not achieve statistical significance. We conclude from these data that it is possible to measure the increase in blood flow in injured and healing articular tissues using the coloured microspheres technique and that ligament injury is a potent stimulus for increasing blood flow. Coloured microsphere measurements of blood flow to joint connective tissues may offer a valuable approach to future investigations of joint injury and arthritis.

This study evaluates the dose-dependent accuracy of the radionuclide-labeled microsphere technique for blood flow evaluation in nerve, tendon, and ligament. In eight dogs, blood flows were determined for nerve, nerve graft, tendon, and ligament tissue by simultaneous injection of high- and low-dose microspheres with different radiolabels. The results demonstrated no significant differences in blood flow as measured from the small number of microspheres (less than 400) and the high number (more than 400) for nerve and tendon tissue. For nerve tissue, microsphere counts of 50 to 100, 100 to 200, 200 to 300, and more than 300 produced mean percentage errors of 12.74% (n = 5, SEM = 4.52), 5.45% (n = 13, SEM = 1.22), 10.22% (n = 6, SEM = 4.37), and 17.08% (n = 12, SEM = 3.30), respectively. For tendon tissue, the same microsphere subdivisions had mean percentage errors of 7.47% (n = 4, SEM = 2.66), 3.63% (n = 6, SEM = 1.34), 15.54% (n = 4, SEM = 4.43), and 12.91% (n = 1), respectively. For ligament tissue, percentage errors were consistently higher; microsphere counts of 30 to 100, 100 to 200, and 200 to 300 produced mean errors of 20.14% (n = 4, SEM = 6.38), 18.66% (n = 4, SEM = 6.24), and 25.78% (n = 2, SEM = 1.97), respectively. Although there was no direct relationship between percentage error and number of microspheres retrieved, we suggest that microsphere counts in the range of 100 to 200 should be considered acceptable for nerve and tendon in the canine. Ligament tissue seems to be less well suited to the microsphere technique; however, further study is warranted.