Alteration of Sensitivity of Adrenergic Vascular Responses after Prolonged Exposure to Agonists via Osmotic Minipump

Vascular Reactivity to Adrenergic Agents and Neuronal and Vascular Catecholamine Levels in Spontaneously Hypertensive Rats

“…This increase in norepinephrine appears to have caused subsensitivity of the alpha receptors and diminished contractile response. We re cently showed that the alpha receptors in the normal Holtzman rat can be desensitized by week-long exposure to phenylephrine via minipump; however, this desensitization was also accompanied by an increase in the sensi tivity of beta receptors to the relaxant effects of isoproterenol [10]. These animals remained normotensive.…”

“…In our previous studies [10], normal Holtzman rats exposed to isoproterenol for 1 week had desensitization of beta receptors but no elevation of blood pressure, even though the heart rate was increased. Our present studies with SHR therefore appear to indicate that desensitization of the beta re ceptor may play only a small part in the establishment of hypertension, but supersen sitivity of this receptor in response to alpha desensitization in Holtzman rats may dimin ish or prevent the onset of hypertension.…”

The alpha-1 Adrenergic Receptors

“…Exposure of tissues to various alpha-adrenergic receptor agonists in vitro Abel et al, 1980) decreases their contractile responsiveness to alpha-adrenergic receptor agonists, although in vivo exposure (Sun and Hanig, 1983) decreases the maximum response. Using radioligand binding assays, have found that chronic in vivo treatment with epinephrine decreased the density but not the affinity of alpha-adrenergic receptors in rat mesenteric arteries.…”

“…(1985), with permission of the publisher. been reported to decrease the responsiveness of isolated tissues to receptor stimulation (Fleish and Titus, 1973;Sun and Hanig, 1983;Kenakin and Beek, 1984) and decrease the density of betaadrenergic receptors in many tissues (Mukherjee and Lefkowitz, 1977;Wolfe et al, 1978).…”