The effect of MS on nitric oxide (NO) end products (NO2- and NO3-), and endothelial cell constitutive NOS (ecNOS) and inducible NOS (iNOS) mRNA expression was examined in cultured brain endothelial cells from newborn pig cerebral microvessels; grown to confluence and treated with MS (100 ng/ml media), naloxone (100 ng/ml media), or morphine+naloxone (100 ng/ml media). The control cells were treated with an equivalent volume of saline. The cells were exposed to drug or saline for 6, 24, 48 & 96 hrs. At the end of each experimental time (n=6 flasks), media was analyzed for the sum of NO2-+NO3-levels(μM) by the Greiss method. The cells were examined for ecNOS and iNOS mRNA expression by reverse transcriptase-polymerase chain reaction (RT-PCR). MS exposure resulted in a significant decrease in NO end products at all time intervals. NO end products did not change with naloxone exposure and naloxone+morphine decreased NO end products at 6 and 48 hrs of exposure (table).

Table 1 No caption available.

Data are expressed as mean±SEM (*p<0.05,**p<0.01). In the control group, ecNOS mRNA increased steadily over time and peaked at 24 hrs (44%, p<0.05). No change in iNOS mRNA expression was detected over time in the control group. However, in the MS-treated group ecNOS mRNA expression decreased significantly at 48 hrs (49%,p<0.05) compared to time 0 and the control group. In addition, iNOS expression decreased significantly at 6 hrs (44%, p<0.05) versus control. These data indicate that MS decreases NO production in brain endothelial cells. NO does not play a role in the vascular responses to MS.