By binding iron in a Fenton-reactive form, intracellular hydroxyl radical production would ensue, but hydroxyl would be immediately trapped and scavenged by the minoxidil to generate a nitroxyl radical. It is presumed that this nitroxyl radical will be capable of reduction by glutathione to reform minoxidil. Such a process would cycle until the minoxidil is otherwise metabolized and would result in rapid glutathione depletion with glutathione disulphide formation and therefore with concomitant consumption of NADPH/ NADH and other reducing equivalents. Minoxidil inhibited PHD by interfering with the normal function of ascorbate, a cofactor of the enzyme, leading to a stabilization of HIF-1α protein and a subsequent activation of HIF-1. In an in vivo angiogenesis assay, millimolar minoxidil increased blood vessel formation in a VEGF-dependent manner. Minoxidil inhibition of PHD occurs via interrupting ascorbate binding to iron. The structural feature of positioning amines adjacent to nitric oxide may confer the ability of millimolar minoxidil to chelate iron, thereby inhibiting PHD. Minoxidil is capable of tetrahydrobiopterin inhibition as a cofactor for nitric oxide synthase.Minoxidil stimulates prostaglandin E2 production by activating COX-1 and prostaglandin endoperoxide synthase-1 but inhibits prostacyclin production. Additionally, expression of the prostaglandin E2 receptor, the most upregulated target gene in the β-catenin pathway of DP cells, was enhanced by minoxidil, which may enable hair follicles to grow continuously and maintain the anagen phase.Due to anti-fibrotic activity of minoxidil inhibition of enzyme lysyl hydroxylase present in fibroblast may result in synthesis of a hydroxylysine-deficient collagen.
Autonomic symptoms may include the presence of Red Ear Syndrome.Attacks hit the patient many times a day, from 5 times a day up to 40 times a day with an average of 11 a day. Mild background pain can persist between attacks. They come in bouts that last from 7 days to 1 year separated by remission periods that can last more than 3 months in episodic patients, or less than 3 months in chronic patients. Onset is in adulthood and the disorder may last indefinitely or spontaneously go into remission. Circadian mechanisms are likely involved in paroxysmal hemicrania due to its highly cyclic nature. No particular circannual recurrence characterizes symptomatic periods, although some patients can experience a seasonal preponderance. Causes
The causes of paroxysmal hemicrania are ultimately still unknown. Sympathetic symptoms such as miosis and ptosis might be linked with a generalized sympathetic dysfunction. Neuropathic mechanisms may be involved, since attacks can be triggered by mechanical stimulation. Perivascular neurogenic inflammatory processes can worsen symptoms or increase pain. Dilated blood vessels may contribute in stimulating trigeminal nociceptors directly, although they cannot be the origin of pain, since even suppression of vasodilation does not stop it once it’s started.Many secondary conditions have been reported to be possible causes of CPH, according to Mehta et al., most of which are arterial abrasions or tumors. These include aneurysms in the circle of Willis, middle cerebral artery infarction, parietal arteriovenous malformation, cavernous sinus and petrous ridge meningiomas, pituitary adenoma, Pancoast tumor, gangliocytoma of the sella turcica, and malignant frontal tumors.