The effects of salt and meclofenamate administration on the hypertension of spontaneously hypertensive rats

Age and the antihypertensive effect of aspirin in rats

1. We previously showed that chronic exposure to aspirin (100 mg kg-1 daily, by mouth) is effective in preventing the onset of hypertension in young (28-84 day old) spontaneously hypertensive rats (SHRs). This is contrary to what others have reported using older SHRs. 2. Renal prostaglandin F2 alpha was also reduced in young SHRs and Wistar-Okamoto strain rats (WKYs) exposed to aspirin. 3. In the present study we extended the period of aspirin treatment in young rats to beyond 84 days of age. We found that aspirin lost its antihypertensive effect in SHR and WKY rats at 110 +/- 7 days of age regardless of whether the exposure to aspirin had begun at age 28, 49 or 87 days. 4. We conclude that the loss of antihypertensive effect of aspirin in the SHR and in older WKY rats, is determined by some factor(s) probably not related to prostaglandin F2 alpha, which reaches full expression in the 110 +/- 7 day old rat, or is fully dissipated at this age. 5. The anti-PGF2 alpha activity of aspirin in the SHR and WKY rat was short-lived and apparently unrelated in time to the antihypertensive effect of aspirin.

Arachidonic acid metabolites, hypertension and arteriosclerosis

The level of arterial blood pressure is set by complete interactions of several mechanisms which influence both blood flow in and resistance of the vascular system. An imbalance favouring elevation of vascular resistance or extracellular volume will result in hypertension. Such alterations may include increased activity of the sympathetic nervous system, of the renin-angiotensin system, or excessive secretion of mineralocorticoids. Of equal importance may be a reduced activity of blood pressure-lowering factors such as prostaglandins and the kallikrein-kinin system. This paper describes the possible significance of prostaglandins in the pathophysiology of hypertension and in degenerative vascular disease, based on their involvement in the control of vascular resistance, renal regulation of extracellular volume and platelet-vessel wall interactions. An abnormality in the biosyn-thesis of certain prostaglandin endoperoxide metabolites may lead to hypertension even without an increase in the activity of the classic blood-pressure-elevating systems. The contribution of prostaglandins for the development of hypertension and degenerative vascular disease may be based on an inherent abnormality of the prostaglandin system, as well as on the effects of major risk factors such as dietary intake of sodium and fat on prostaglandin synthesis. Specific blockade or stimulation of distinct biosynthetic pathways leading to antagonistically acting prostaglandins and nutritional manipulation of precursor fatty acids should lead to a better understanding of the pathomechanisms involved and may offer new strategies for therapy or prevention of these cardiovascular disorders.