Effect of indomethacin on capillary growth and microvasculature in chronically stimulated rat skeletal muscles

1. Capillary proliferation and microvessel diameters were studied in rat an kle flexors subjected to chronic electrical stimulation by implanted electr odes (10 Hz, 0.3 ms pulse width, up to 6 V, 8 h day(-1)) for 2 or 7 days wi th or without concurrent indomethacin treatment (similar to 2 mg day(-1) in drinking water) to study the role of prostaglandins in the microcirculatio n in relation to capillary growth. 2.Diameters of terminal arterioles, capillaries and confluent venules were measured in epi-illuminated muscles, together with capillary red cell veloc ity, to evaluate whether changes in capillary pressure and/or shear stress participate in capillary growth via release of prostaglandins. 3. Cell proliferation was detected following bromodeoxyuridine (BrdU) incor poration and immune-staining of frozen sections. Labelling was assessed as the percentage of all interstitial nuclei (Haematoxylin-stained) that were BrdU positive. By comparison with serial sections stained for alkaline phos phatase, from which the capillary-to-fibre ratio (C:F) was obtained, labell ing was derived for nuclei colocalised either to capillaries or to other no n-capillary interstitial cells. 4. C:F increased to 1.89 +/- 0.06 from 1.47 +/- 0.04 in controls only after 7 days stimulation; indomethacin reduced this to 1.55 +/- 0.07. Capillary labelling increased from 2.9 +/- 0.5% in controls to 11.3 +/- 2.2 % after 2 days stimulation and 10.6 +/- 0.8% after 7 days. The increase was attenuat ed by indomethacin at both time points (to 5.8 +/- 1.6% and 4.2 +/- 0.5%, r espectively). 5. Non-capillary interstitial labelling (2.0 +/- 0.4% in controls) increase d to 9.5 +/- 2.7% after 2 days stimulation and was back to normal after 7 d ays (3.2 +/- 0.07 %). Indomethacin depressed the increase at 2 days to 4.0 +/- 1.3% and had no effect at 7 days (2.9 +/- 0.13%). Labelling in sham-ope rated rats with or without indomethacin or in vehicle-treated animals was n o different from controls. 6. Arteriolar and venular diameters were increased by 2 days of stimulation but unchanged after 7 days. Indomethacin increased diameters of arterioles after 2 days and venules after 7 days in sham-operated animals, but had no effect an diameters of either vessel type in stimulated muscles. 7. Capillary diameters did not change during acute muscle contractions wher eas red cell velocity diet. Calculated shear stress in capillaries was ther eby increased by 75%. 8. Thus during chronic electrical stimulation both capillary growth and the cell proliferation that I,recedes it were attenuated by indomethacin. Tran sient stimulation-induced increases in arteriolar and venular diameters, wh ich were unaffected by indomethacin, do not implicate increased capillary p ressure as a factor in prostaglandin release and capillary growth. Estimati ons of increases in capillary shear stress during muscle contractions and o f a 45 % higher value even at rest after chronic stimulation for 7 days sug gest that shear stress is a more likely stimulus for prostaglandin release in chronically stimulated muscles.