Observations on the Responses of Rats with Spontaneous Hypertension and Control Rats to Pressor Drugs and to Hexamethonium

Abstract

• A difficulty in studying the pathogenesis of essential hypertension is that spontaneous hypertension is not frequent in experimental animals. Most experimenters have used animals in which hypertension has been induced, usually by the production of renal ischemia. As essential hypertension in man is inheritable, an attempt was made to develop a spontaneous hypertension by selective breeding from rats with overaverage blood pressures. Eventually a strain of Wistar rats with overaverage blood pressures was obtained by Smirk and Hall 1 ; about 25 per cent of buck rats had tail blood pressures exceeding 140 mm. Hg and a few were above 160 mm. Hg. Since this article was published, the colony has improved and over 50 per cent of buck rats have systolic blood pressures exceeding 150 mm. Hg.We are unaware of any long series of experiments on animals with spontaneous hypertension, although Alexander et al.2 found the response to the cold pressor test was increased in the families of rabbits with spontaneous hypertension.Divergent conclusions have been published concerning the comparative responsiveness of hypertensives and normotensives, both human and experimental. The responses to several pressor drugs are stated to be larger in hypertensive than in normotensive rats by Sturtevant. 3 Olsen et al. 4 found an enhanced response to epinephrine and norepinephrine in renal hypertensive rats, whereas the responses to tyramine and phenethylamine were similar in hypertensives and normotensives. While the average responses to epinephrine and angiotensin of DCA-treated hypertensive

Cardiovascular Effects Of Chronic Nitric Oxide Synthase Inhibition In Genetically Hypertensive Rats

“…The response to NA in vivo was unaffected by L ‐NAME and similar in GH and N rats, the latter finding similar to previous studies. 33,34 Changes in HR in response to NA were similar in the different experimental groups, indicating that baroreflex activity is similar and, therefore, could not have masked differences in constrictor response. In the hindquarter, the response to NA was larger in GH rats, which is consistent with other findings in this and the mesenteric vascular bed.…”

Blood Pressure, Plasma and Pituitary Prolactin Responses to Bromocriptine in New Zealand Genetically Hypertensive and Normotensive Rats

“…Increased vascular reactivity has also been shown in the intact adult GHR (Phelan et al 1962) and in the pithed GHR rat preparation (Jones et al 1976). Phelan et al (1 979) showed specifically that vascular reactivity to adrenaline and noradrenaline was enhanced in young GHR.…”

Trimethylamine-N-Oxide: A Carnitine-Derived Metabolite That Prolongs the Hypertensive Effect of Angiotensin II in Rats

“…We decided to use a low-dose Ang II infusion protocol because rats infused with a high-dose Ang II show strong hypertensive response 13,14 , and it has been shown that animals with high blood pressure fail to respond to pressor compounds 15,16 . We found that infusion of Ang II alone significantly increased BP for the first 5 days of infusion, while the concomitant infusion of Ang II and TMAO produced sustained increase in BP, which suggests that TMAO prolonged the hypertensive effect of Ang II.…”