Pathways

Newer dopamine receptor agonists such as quinagolide and Cabergoline are shown to effectively inhibit prolactin secretion with improved efficacy over Bromocriptine. These drugs are effective in patients who are intolerant or resistant to Bromocriptine. Quinagolide exists as a racemate and its relevant clinical activity is mediated predominantly by the (-) enantiomer. It is typically present in the hydrochloride salt form and is marketed as oral tablets. Quinagolide is a non-ergot-derived selective dopamine D2 receptor agonist used for the treatment of elevated levels of prolactin or hyperprolactinaemia. Quinagolide achieves long-lasting reduction in prolactin levels in a dose-proportional effect via selectively targeting D2 receptors as an agonist. It potently suppresses both basal and stimulated serum prolactin levels by exerting a strong inhibitory effect on the secretion of the anterior pituitary hormone prolactin. Prolactin secretion from the lactotroph cells present in the anterior pituitary gland is under tonic inhibitory control mediated by dopaminergic signalling via D2 receptors. Quinagolide selectively binds to D2 receptors expressed on the surface of lactotroph cells with high affinity which results in reduced adenylyl cyclase activity, reduced intracellular cyclic adenosine monophosphate and inhibited prolactin secretion. It also binds to D1 receptors but with low affinity and little clinical relevance.

Metabolites of Quinagolide are predicted with biotransformer.

Quinapril is angiotensin-converting enzyme (ACE) inhibitor for the conversion of angiotensin I into angiotensin II. Angiotensin II is a critical circulating peptide hormone that has powerful vasoconstrictive effects and increases blood pressure. Quinapril is used to treat hypertension, high blood pressure, congestive heart failure, and chronic renal failure as it decreases blood pressure. Quinapril is converted into Quinaprilat through the liver after being ingested which travels in the blood to inhibit ACE which is from the lungs. Angiotensin has many vasoconstrictive effects by binding to angiotensin II type 1 receptor (AT1) in blood vessels, kidneys, hypothalamus, and posterior pituitary. In blood vessels, AT1 receptors cause vasoconstriction in the tunica media layer of smooth muscle surrounding blood vessels increasing blood pressure. Less angiotensin II that is circulating lowers the constriction of these blood vessels. AT1 receptors in the kidney are responsible for the production of aldosterone which increases salt and water retention which increases blood volume. Less angiotensin II reduces aldosterone production allowing water retention to not increase. AT1 receptors in the hypothalamus are on astrocytes which inhibit the excitatory amino acid transporter 3 from up-taking glutamate back into astrocytes. Glutamate is responsible for the activation of NMDA receptors on paraventricular nucleus neurons (PVN neurons) that lead to thirst sensation. Since angiotensin II levels are lowered, the inhibition of the uptake transporter is not limited decreasing the amount of glutamate activating NMDA on PVN neurons that make the individual crave drinking less. This lowers the blood volume as well. Lastly, the AT1 receptors on posterior pituitary gland are responsible for the release of vasopressin. Vasopressin is an anti-diuretic hormone that cases water reabsorption in the kidney as well as causing smooth muscle contraction in blood vessels increasing blood pressure. Less angiotensin II activating vasopressin release inhibits blood pressure from increasing. Overall, Quinapril inhibits the conversion of angiotensin I into angiotensin II, a powerful vasoconstrictor and mediator of high blood pressure so decreasing levels of angiotensin will help reduce blood pressure from climbing in individuals.

Quinapril (trade name: Accupril) belongs to the class of drugs known as angiotensin-converting enzyme (ACE) inhibitors and is used primarily to lower high blood pressure (hypertension). This drug can also be used in the treatment of congestive heart failure and type II diabetes. Quinapril is a prodrug which, following oral administration, undergoes biotransformation in vivo into its active form quinaprilat via cleavage of its ester group by the liver. Angiotensin-converting enzyme (ACE) is a component of the body's renin–angiotensin–aldosterone system (RAAS) and cleaves inactive angiotensin I into the active vasoconstrictor angiotensin II. ACE (or kininase II) also degrades the potent vasodilator bradykinin. Consequently, ACE inhibitors decrease angiotensin II concentrations and increase bradykinin concentrations resulting in blood vessel dilation and thereby lowering blood pressure.

Quinapril (trade name: Accupril) belongs to the class of drugs known as angiotensin-converting enzyme (ACE) inhibitors and is used primarily to lower high blood pressure (hypertension). This drug can also be used in the treatment of congestive heart failure and type II diabetes. Quinapril is a prodrug which, following oral administration, undergoes biotransformation in vivo into its active form quinaprilat via cleavage of its ester group by the liver. Angiotensin-converting enzyme (ACE) is a component of the body's renin–angiotensin–aldosterone system (RAAS) and cleaves inactive angiotensin I into the active vasoconstrictor angiotensin II. ACE (or kininase II) also degrades the potent vasodilator bradykinin. Consequently, ACE inhibitors decrease angiotensin II concentrations and increase bradykinin concentrations resulting in blood vessel dilation and thereby lowering blood pressure.

Quinethazone is an oral thiazide-like diuretic drug that acts in the kidney, specifically in the distal convoluted tubule of the nephron. It is used in the treatment of hypertension. In the distal convoluted tubule (DCT), the regulation of ions such as sodium, potassium, calcium, chloride, and magnesium occurs. In epithelial cells of the DCT, the basolateral membrane consists of the Na+/K+ ATPase, which pumps Na+ into the interstitium-blood area and K+ into the epithelial cell; the Na+/Ca2+ exchanger, which pumps Na+ into the cell and Ca2+ into the interstitium-blood; and the chloride transporter which transports chloride into the interstitium-blood. The apical membrane contains a calcium channel that transports calcium from the lumen into the epithelial cell, a potassium channel that transports K+ out of the epithelial cell, and a Na+/Cl- cotransporter which transports Na+ and Cl- into the epithelial cell. Quinethazone targets this Na+/Cl- cotransporter. Quinethazone is transported from the blood into the epithelial cells. In the cell, it has access to the Na+/Cl- transporter and inhibits it preventing Na+ and Cl- reabsorption. The inhibition of Na+ reabsorption results in a low cytosolic concentration of Na+ and increases the solute concentration of the lumen. This decreases the lumen-epithelial cell concentration gradient and as a result, less water would be reabsorbed from the urine. This effect is valued in conditions such as hypertension because it allows more water to be excreted in the urine rather than be absorbed in the blood which increases blood volume. Since less Na+ is available for the Na+/K+ ATPase function, K+ accumulates in the cell and the ATP-sensitive inward rectifier potassium channel(IKATP) transports this excess K+ into the lumen, thus increasing K+ excretion. Side effects such as nausea, dizziness, hypokalemia, and dry mouth can occur from taking Quinethazone. This drug is administered as an oral tablet.

Quinethazone, also known under the brand-name Hydromox, is a pharmacologically-active small molecule that belongs to a class of drugs called thiazides. Thiazides and thiazide-like drugs are diuretics commonly employed to control hypertension. The short term mechanism of action is relatively well-understood: thiazides inhibit sodium-chloride co-transport into the renal distal convoluted tubule of the nephron and therefore increase fluid loss which decreases extracellular fluid (ECF), plasma volume, and ultimately blood pressure. In the case of quinethazone, it inhibits the sodium-chloride symporter, solute carrier family 12 member 3. Thiazides also inhibit sodium ion transport. However, the long-term mechanism of action isn’t as well-characterized and it is thought that other processes beyond regulating plasma and ECF volumes are involved as these two volumes return to baseline within 4-6 weeks of first use of thiazides.