prostaglandin-g2 and Hypertension

Acute, severe increases in arterial blood pressure cause sustained cerebral arteriolar dilation, abnormal reactivity to carbon dioxide and to changes in blood pressure, abolition of endothelium-dependent dilation from acetylcholine, discrete morphological lesions of the endothelium and vascular smooth muscle, and breakdown of the blood-brain barrier to plasma proteins. The dilation, abnormal reactivity, and morphological abnormalities are inhibited by pretreatment with cyclooxygenase inhibitors or with free radical scavengers. Superoxide dismutase-inhibitable reduction of nitroblue tetrazolium applied to the brain surface was detectable both during hypertension and one hour after hypertension subsided. Nitroblue tetrazolium reduction is also reduced by inhibitors of the anion channel. The abnormalities seen after hypertension are reproduced by topical application of arachidonate. The results are consistent with the view that acute hypertension induces generation of superoxide anion radical in association with accelerated arachidonate metabolism via cyclooxygenase. This radical enters cerebral extracellular space via the anion channel and gives rise to hydrogen peroxide and hydroxyl radical. All three radicals are capable of causing vasodilation by relaxation of cerebral vascular smooth muscle. The hydroxyl radical is the most likely candidate for vascular wall damage. The significance of this mechanism in chronic experimental hypertension or its relevance to human disease is not known.

Topics: Animals; Arachidonic Acid; Arachidonic Acids; Arterioles; Blood Proteins; Blood-Brain Barrier; Bradykinin; Brain; Brain Injuries; Cardiovascular Agents; Catalase; Cerebrovascular Circulation; Cerebrovascular Disorders; Cyclooxygenase Inhibitors; Endothelium; Free Radicals; Hydrogen Peroxide; Hydroxides; Hydroxyl Radical; Hypertension; Leukocytes; Leukotrienes; Lipid Peroxides; Muscle, Smooth, Vascular; Peroxidases; Prostaglandin-Endoperoxide Synthases; Prostaglandins G; Superoxide Dismutase; Superoxides; Vasodilation; Xanthine Oxidase

The activity of basal 24-hour urinary kallikrein activity (UKA), prostaglandin E2 (U. PGE2) and thromboxane B2 (U. TxB2) and their relationship to natriuresis (U. Sodium), urinary aldosterone (U. Aldosterone) and plasma renin activity (in supine position: PRA1; in standing position: PRA2) were evaluated in 20 patients with early-moderate hemodynamically defined (first pass and gate blood pool radionuclide angiocardiography) essential hypertension (H) and in 13 age-matched normotensive patients (N). In basal conditions, UKA and PRA2 were significantly reduced (p less than 0.005 and p less than 0.05, respectively) in H compared with N. However, no differences between N and H were found for U. TxB2, U. PGE2, U. Aldosterone, U. Sodium, and PRA1. All parameters were also evaluated both in H and N before and after the administration of furosemide (40 mg i.v.). In H, but not in N, furosemide induced an increase of UKA (p less than 0.05), U. TxB2 (p less than 0.05) and U. Sodium (p less than 0.001). In both H and N furosemide caused a significant rise of PRA1 (p less than 0.001 in H and p less than 0.01 in N) and PRA2 (p less than 0.001 in H and p less than 0.05 in N). In H a significant correlation was found between percent increases of U. Sodium and U. Kallikrein (r = 0.54, p less than 0.01) and between percent differences of PGE2 and TxB2 (r = 0.59, p less than 0.01). It is proposed that reduction of basal UKA may be an early evidence of the first stages of hypertension, i.e., in absence of renal and cardiovascular alteration. The finding is not accompanied by significant changes in urinary excretion of arachidonic acid metabolites and aldosterone. Finally, any relation between UKA values and systemic hemodynamics is lacking.

Topics: Aldosterone; Female; Furosemide; Hemodynamics; Humans; Hypertension; Kallikreins; Male; Middle Aged; Natriuresis; Prostaglandin Endoperoxides; Prostaglandins G; Renin; Thromboxane B2