Neural and Local Regulation of Blood Flow and Synovial Fluid PO2 in the Rabbit Knee Joint

Najafipour, Hamid (1993) Neural and Local Regulation of Blood Flow and Synovial Fluid PO2 in the Rabbit Knee Joint. PhD thesis, University of Glasgow.

Abstract

Synovial fluid, in addition to its lubricating action of moving structures, provides nutrients to avascular structures such as articular cartilage (McKibbin & Maroudas, 1979), and also to the knee ligaments (Renzoni et aL, 1984), within the joint. As synovial fluid formation is critically dependent on synovial blood flow (Levick, 1987), those factors which regulate flow in the synovial vascular bed are clearly important in this process. The first objective of this research was to measure knee joint blood flow quantitatively and also assess the effect of sympathetic nerves in the regulation of joint blood flow. Secondly, to investigate and characterize the type of adrenoceptors mediating the sympathetic control of joint blood flow, and other mediators involved in nerve mediated changes in articular blood flow. Thirdly, to assess the possible role of the endothelium in regulation of joint blood flow and modulation of sympathetic nerve-mediated changes in joint blood flow. Finally to perform all the mentioned procedures in an experimentally induced acutely inflamed knee joints to determine the effect of inflammation on these regulatory mechanisms and factors. The second objective of this study was to measure, in both normal and inflamed knee joints, the synovial PO2 directly in its place; and also assess the correlation between the joint blood flow and oxygen tension in the synovial fluid and the extent to which this correlation may be affected by the process of inflammation. Experiments were performed on rabbits. Acute inflammation was induced by intra-articular injection of carrageenan. Quantitative measurement of joint blood flow was conducted by the radiolabelled microsphere technique. Relative changes in blood flow were assessed by laser Doppler flowmetry, and a polarographic oxygen elecrode (and oxygen meter) was used to measure synovial PO2 and its changes during the course of experiments. The results of this investigation indicate that: 1). The microsphere technique and laser Doppler flowmetry are suitable methods for quantitative and continuous measurement of joint blood flow respectively, and the process of inflammation increases joint blood flow significantly. Despite this increase in blood flow, synovial PO2 which in normal joint is much lower than the arterial PO2, even decreases more in the inflamed joints. 2). Sympathetic nerves innervate the blood vessels of the posterior capsule of the knee joint and play an important role in regulation of joint blood flow. alpha2 adrenoceptors predominate in this vascular bed and mediate vasoconstrictor responses to nerve stimulation. No evidence of pimergic co-transmission was obtained. The process of inflammation reduced the effectiveness of sympathetic nervous system in regulation of joint blood flow. 3). Nerve-mediated vasodilator responses appeared to have two components, a beta-adrenoceptor component which is mediated by postjunctional beta1 adrenoceptors which found to predominate in this vascular bed, and a substance P mediated component which is produced by the release of neuropeptide, substance P, presumably from the unmyelinated sensory nerve endings. 4). Vascular endothelium keeps the joint blood vessels of both normal and inflamed joints in a state of active dilatation by release of nitric oxide (NO) and therefore plays a major role in local regulation of joint blood flow. NO also counteracts the sympathetic vasoconstrictor responses, but it showed no modulatory effect on nerve-mediated vasodilator responses. 5). Prostaglandins are important local factors in regulation of joint blood flow in both normal and inflamed joints. They seemed to have no modulatory effect on sympathetic regulation of blood flow to this vascular bed. PGE2 receptors are present on knee joint blood vessels but they down regulate during the process of inflammation. 6). A polarographic oxygen electrode provided a new and suitable method for quantitative and continuous measurement of oxygen partial pressure in the synovial fluid of both normal and inflamed knee joints. A high correlation between changes in joint blood flow and synovial PO2 was found in both joints.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: W R Ferrell
• Keywords: Physiology
• Date of Award: 1993
• Depositing User: Enlighten Team
• Unique ID: glathesis:1993-75334
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Nov 2019 20:50
• Last Modified: 19 Nov 2019 20:50
• URI: https://theses.gla.ac.uk/id/eprint/75334