Effect of serum on vascular smooth muscle function

Serum contains many biologically active factors influencing cell growth and is commonly used as a culture medium supplement. It has not generally been appreciated that serum can affect vascular tone. We have observed that the contractile response of aortic rings previously exposed to 10% fetal bovine serum (FBS) for 24 hours and then stimulated with phenylephrine (0.01-1microM) or angiotensin II (1microM) is significantly diminished compared to 1) rings incubated in FBS for only 6 hours, 2) aortic rings previously incubated in 1% FBS or 3) aortic rings incubated in 10% bovine serum albumin for 24 hours. A similar attenuated response was also seen when the vascular aortic rings were incubated in heat inactivated adult bovine serum. To test whether prostaglandins might be induced by factors contained in serum and account for the diminished stimulated contractile response, rings were incubated for 24 hours in media containing 10% FBS with either indomethacin 10microM, corticosterone 100nM or 11-dehydrocorticosterone 100nM. These agents are known to affect prostaglandin synthesis. Contractile responses were then measured accordingly. In each series, the previously attenuated contractile response to phenylephrine and to angiotensin II was fully restored with prostaglandin synthesis inhibition. Thus, factors contained in serum are capable of blunting the stimulated contractile response of rat aortic vessels. These serum factors appear to act by inducing prostaglandin synthesis in vascular tissue.