Nitric oxide regulates alkaline phosphatase activity in rat fracture callus explant cultures.
Nitric oxide (NO) is synthesised by a group of enzymes called nitric oxide synthases (NOS) and oxidizes to its stable end-products nitrite (NO2-) and nitrate (NO3-) We have previously reported in an in vivo rat model that NO is an important regulator for rat bone fracture healing. This study examines the effects of NO on alkaline phosphatase (ALP) activity in a rat fracture callus explant culture system. Explants of rat femoral fracture callus from days 4, 7, 14 and 28 post fracture induced NO2 release and ALP activity in a biphasic temporal manner, with the highest activity on day 7 and the lowest activity on day 14. Inhibition of NOS by co-incubation with an NOS inhibitor, S-(2-aminoethyl) isothiouronium bromide hydrobromide (AETU), inhibited ALP activity by an average of 50% at each time point (P <0.01). Supplementation with NO donor 3-morpholinosydnonomine hydrochloride (SIN-1) at low doses (25 and 0.025 microM) increased ALP activity by 20% (P < 0.01). ALP mRNA and histochemical ALP activity were localised to osteoblast-like and chondrocyte-like cells within fracture callus. The current study provides evidence that NO plays a regulatory role in ALP activity during rat fracture healing.
Department of Endocrinology, St George Hospital Campus, University of New South Wales, Australia.
H
H
Namkung-Matthai
A
A
Diwan
R S
RS
Mason
G A
GA
Murrell
T
T
Diamond
D000469:Alkaline Phosphatase / Q000378:metabolism*; D000818:Animals; D002146:Bony Callus / Q000166:cytology / Q000201:enzymology / Q000473:pathology / Q000502:physiology*; D005264:Femoral Fractures / Q000201:enzymology / Q000473:pathology / Q000503:physiopathology*; D009569:Nitric Oxide / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D009924:Organ Culture Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D000469:Alkaline Phosphatase