Functional Role of α₁-Adrenoceptor Subtypes in Murine Ophthalmic Arteries

Abstract

These findings provide evidence that the α(1A)-AR subtype mediates adrenergic vasoconstriction in murine ophthalmic arteries.

The α1B‐adrenoceptor subtype mediates adrenergic vasoconstriction in mouse retinal arterioles with damaged endothelium

“…Using real‐time PCR, we recently demonstrated that murine ophthalmic arteries expressed mRNA for all three α 1 ‐adrenoceptor subtypes at similar levels (Gericke et al ., ). In the present study, we conducted analogous studies in isolated retinal arterioles with intact endothelium pooled from seven wild‐type mice of the same genetic background as those used in the previous study.…”

“…Several previous studies on mRNA and protein expression reported that the mRNA expression levels of individual α 1 ‐adrenoceptor subtypes were in fairly good agreement with their protein levels or their contribution to adrenergic vasoconstrictor responses (Rudner et al ., ; Hosoda et al ., ; Marti et al ., ; Jensen et al ., ). Other studies, including our own in murine ophthalmic arteries (Gericke et al ., ), however, demonstrated that the presence of mRNA or even protein of a particular α 1 ‐adrenoceptor subtype does not necessarily indicate the participation of that receptor subtype in vasoconstriction (Piascik et al ., ; Yang et al ., 1997; 1998; Hrometz et al ., ). The results of the present study represent another example of discrepancy between mRNA expression and the particular functional role of α 1 ‐adrenoceptor subtypes.…”

“…Because in retinal arterioles from α 1B ‐AR −/− mice, phenylpherine‐induced vasoconstriction was attenuated to a similar extent as by prazosin in arterioles from wild‐type mice, this response is obviously mediated mainly by the α 1B ‐adrenoceptor. The finding that α 1 ‐adrenoceptor‐mediated vasoconstriction in murine retinal arterioles is predominantly mediated by the α 1B subtype is particularly surprising, because in the murine ophthalmic artery, which is directly afferent to the retinal vasculature, the α 1A subtype mediates constrictive responses to α 1 ‐adrenoceptor stimuli when assessed under similar experimental conditions (Gericke et al ., ). Thus, our results demonstrate that smooth muscle cells of the retrobulbar (α 1A ‐adrenoceptor) and the retinal (α 1B ‐adrenoceptor) vasculature are under functional control of different α 1 ‐adrenoceptor subtypes.…”

“…Among adrenoceptors, the α 1 ‐adrenoceptor family is critically involved in the regulation of vascular tone and blood flow by mediating the vasoconstrictive effect of catecholamines. This functional role of α 1 ‐adrenoceptors was also demonstrated in ocular blood vessels, including retinal arterioles, from different species (Ferrari‐Dileo et al ., ; Ichikawa et al ., ; Gericke et al ., ; Mori et al ., ). Pharmacological studies and molecular cloning methods have identified three structurally distinct α 1 ‐adrenoceptor subtypes designated as α 1A , α 1B and α 1D (Hieble et al ., ).…”

The Dynamic Response of Intraocular Pressure and Ocular Pulse Amplitude to Acute Hemodynamic Changes in Normal and Glaucomatous Eyes

“…The pharmacologic action of PE is mediated by a-adrenoreceptors and their activation will tend to lower IOP through the reduction of aqueous humor production by its action on the ciliary body 42 and also through its vasoconstrictive action on the ophthalmic arteries owing to the artery's rich sympathetic innervation. 43,44 The nonselective activation of a 2 selective adrenergic receptor by PE may also have the effect of lowering IOP, similar to the action of the selective a 2 adrenergic agonists such as apraclonidine by decreasing aqueous production. 45,46 In effect, the stimulation of arterial hypertension by PE in our study is analogous to the sympathoadrenal activation of arterial hypertension observed during the stress response 47 as well as during isometric exercises.…”