We have previously shown that short-term treatment (30 minutes) with follistatin (FST), a glycoprotein inhibitor of activins, reduced contraction caused by potassium (KCl) in vessels of the Spontaneously Hypertensive Rat (SHR) model of essential hypertension. This study specifically investigates the mechanisms through which FST inhibits KCl-induced vessel contraction in the SHR. Resistance mesenteric arteries taken from SHR or normotensive control WKY rats were tested in response to KCl using wire myography. Primary vascular smooth muscle cell (VSMC) cultures were established from WKY and SHR vessels. The fluorescent calcium sensor dye Fluo-4 AM and potassium tracking dye IPG-1 were then used to examine ion levels in the VSMCs. To determine whether FST effects were activin-mediated, neutralizing antibodies against activin A and B were used. Only activin A neutralization in the SHR reduced KCl-induced contraction as well as intracellular calcium rise, similarly to FST. Activin A (30 minute treatment) augmented KCl-induced contraction in both WKY and SHR vessels, but this was more pronounced in the SHR. There was an augmented KCl induced-intracellular calcium rise in SHR VSMC compared to WKY, which was decreased by FST. Inhibiting release of intracellular calcium stores did not attenuate KCl-induced calcium influx that was augmented by activin A or reduced by FST, but both of these effects were inhibited in calcium-free conditions. FST also significantly lowered the augmented KCl-induced intracellular potassium increase seen in SHR VSMC. Overall, FST reduces augmented KCl-induced contraction and rise in calcium and potassium levels in SHR vessels and VSMC. Taken together, these data suggest that FST may modulate L-type voltage gated Ca2+ channel (LTCC) or K-ATP channel activity. Neutralization studies support an important role for activin A, but not activin B, in mediating FST effects. Further studies will examine the mechanism by which FST modulates calcium influx. / Thesis / Master of Health Sciences (MSc) / We had shown that a protein called follistatin can reduce high blood pressure in rats. High blood pressure, or hypertension, is a condition that can lead to health problems such as heart failure, kidney disease and death, if not managed properly. We focused on a type of rat called the Spontaneously Hypertensive Rat (SHR), which has high blood pressure similar to what people experience. Our goal was to understand how follistatin works to lower blood pressure. To do this, we looked at how the blood vessels in these rats responded to a substance called potassium chloride (KCl), which causes blood vessels to contract as they do with high blood pressure. We found that follistatin reduced contraction of blood vessels caused by KCl. We also observed that calcium and potassium levels inside muscle cells of the blood vessels were lowered with follistatin, which could be one way follistatin prevents contraction and relaxes blood vessels. A better understanding of how drugs affect blood vessels will help us to create new treatments for high blood pressure.

Effects of neurokinin A (NKA) and substance P (SP) on coronary resistance vessels were studied in isolated guinea pig hearts perfused with isotonic buffer containing 20 mM KCl. Injections of NKA and SP caused dose-dependent reductions in perfusion pressure with ED50 values of 14.0 and 0.326 pmol, respectively. Blockade of nitric oxide synthesis or removal of the endothelium inhibited vasodilator responses to neurokinins. Infusions of NKA or SP caused tachyphylaxis and cross-desensitization to the other neurokinin but not to acetylcholine. Injections of 2.5 nmol NKA increased perfusion pressure by 31 ± 8% when given after tachyphylaxis developed to infused SP (2.5 nmol/100 μl/min). It was concluded that 1) neurokinins cause an endothelium-dependent relaxation of coronary resistance vessels by stimulating NK-1 receptors on endothelial cells, and 2) desensitization of the receptor mediating vasodilation unmasks a vasoconstrictor response to NKA.