Protamine does not affect the formation of cGMP or cAMP in pig vascular smooth muscle cells in response to vasodilators.
OBJECTIVE
Protamine has recently been shown to have a direct vasodilator action in isolated vascular tissue. As one possible mechanism for this action, it has been hypothesized that protamine might increase the response of vascular smooth muscle to the endothelium-derived relaxing factor, nitric oxide. In this study, we tested this hypothesis and examined the effect of protamine on other guanosine 3'5'-cyclic monophosphate (cGMP)- and adenosine 3'5'-cyclic monophosphate (cAMP)-dependent processes.


METHODS
Prospective, repeated measures analysis of concentration-response curves.


METHODS
Anesthesia research laboratory in an academic medical center.


METHODS
Cultured coronary artery smooth muscle cells from pig heart.


METHODS
Sodium nitroprusside was used to mimic the action of the endothelium-derived relaxing factor by stimulating the soluble guanylyl cyclase and increasing intracellular cGMP. Atrial natriuretic peptide was used to stimulate the particulate guanylyl cyclase. Isoproterenol and forskolin were used to increase intracellular cAMP. The responses to these agents were determined in the presence and absence of protamine.


RESULTS
In cultured vascular smooth muscle cells, sodium nitroprusside increased cGMP, the second messenger for endothelium-derived relaxing factor, in a concentration-dependent manner. In cells treated with protamine (32 to 250 micrograms/mL), we could detect no effect of protamine on basal intracellular levels of cGMP until a concentration of 250 micrograms/mL of protamine was used. At this concentration, protamine increased basal cGMP concentrations from 4.2 +/- 0.3 to 9.0 +/- 0.6 pmol/mg protein (p < .001). The response of intracellular cGMP to sodium nitroprusside in cells treated with 250 micrograms/mL or other concentrations of protamine was not different from control. Likewise, we could detect no effect of protamine on intracellular cGMP stimulated with the atrial natriuretic peptide or on cAMP stimulated with the beta-adrenergic receptor agonist, isoproterenol, or with forskolin.


CONCLUSIONS
These experiments show that protamine does not alter the responses of the intracellular second messengers, cGMP and cAMP, to the vasodilators sodium nitroprusside, atrial natriuretic peptide, isoproterenol, and forskolin. These results do not support the hypothesis that protamine sensitizes vascular smooth muscle cells to the endothelium-derived relaxing factor, nitric oxide.
Castresana
M R
MR
Department of Anesthesiology and Critical Care Medicine, Medical Center of Central Georgia, Macon, USA.
Zhang
L M
LM
Newman
W H
WH
D000704:Analysis of Variance; D000818:Animals; D009320:Atrial Natriuretic Factor / Q000494:pharmacology; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis*; D006152:Cyclic GMP / Q000096:biosynthesis*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D007545:Isoproterenol / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D009599:Nitroprusside / Q000494:pharmacology; D011446:Prospective Studies; D011479:Protamines / Q000494:pharmacology*; D013552:Swine; D014665:Vasodilator Agents / Q000494:pharmacology*
D011479:Protamines; D014665:Vasodilator Agents; D009599:Nitroprusside; D005576:Colforsin; D009320:Atrial Natriuretic Factor; D000242:Cyclic AMP; D006152:Cyclic GMP; D007545:Isoproterenol