Purchase this article with an account.
KH Kulkarni, AM LeDay, CA Opere, SE Ohia; Pharmacology of Prejunctional Histamine Receptors on Sympathetic Nerves in Isolated Mammalian Irides . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1975.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
There is evidence that histamine can inhibit sympathetically-induced papillary dilation in cats by activation of H3-receptors (Koss and Hey, Naunyn-Schmiedeberg’s Arch. Pharmacol. 348: 141, 1993). It is, however, unclear whether this action is due to a direct effect of histamine on norepinephrine (NE) release from this tissue. Purpose: The aim of the present study was two-fold: (a) to examine the effect of exogenous histamine on NE release from bovine and human irides and (b) to classify the subtype of histamine receptors mediating this response in bovine irides. Methods: Isolated bovine and human irides were incubated in oxygenated Krebs solution containing 1.6 µM [3H]NE, and flurbiprofen (3 µM) for 1 hour. After incubation, tissues were prepared for studies of [3H]NE release using the superfusion method. Release of [3H]NE was elicited by 300 direct current pulses (supramaximal voltage, 2 ms pulse duration, 5 Hz) applied 84 minutes (S1) and 108 minutes (S2) after the onset of superfusion. Results: Histamine and other receptor selective agonists, R-α-methylhistamine (H3-) and imetit (H3-/H4-) caused a concentration-dependent inhibition of field-stimulated [3H]NE release from isolated bovine irides with the following rank order of potency: imetit ≷≷ R-α-methylhistamine ≷ histamine. All three agonist displayed a similar efficacy in inhibiting evoked [3H]NE release. An equimolar concentration of R-α-methylhistamine (1 µM) caused a similar degree of inhibition (35%) of electrically-induced [3H]NE release in both human and bovine irides. The inhibitory response produced by imetit (1 nM) was completely blocked by thioperamide (30 nM; H3-/H4-antagonist). Likewise, the inhibition caused by R-α-methylhistamine (1 µM) was abolished by clobenpropit (1 nM; H3-antagonist). Conclusion: We conclude that histamine can inhibit field stimulated [3H]NE release from isolated bovine and human irides. Furthermore, both prejunctional H3- and H4-receptors exist on sympathetic nerve terminals in the bovine irides. These heteroreceptors play an inhibitory role in the regulation of NE release from mammalian irides.
This PDF is available to Subscribers Only