Histamine in the rabbit eye: distribution, synthesis, catabolism, and changes by light stimulation

Functional serotonin and histamine receptor subtypes in porcine ciliary artery in comparison with middle cerebral artery

Functional serotonin (5-HT) and histamine receptor subtypes were investigated in porcine middle cerebral and ciliary arteries. An H(1) antagonist, mepyramine, antagonized histamine-induced responses with pK(B) values of 8.91-9.10. In the presence of 1 muM mepyramine, however, histamine caused dilation through H(2) receptors in the middle cerebral but not in the ciliary artery. A 5-HT(2A) antagonist, ketanserin, antagonized 5-HT-induced responses, causing rightward shifts in the concentration-response curves with pK(B) values of 8.52-8.71. A 5-HT(1B) antagonist, SB224289, produced rightward shifts of the concentration-response curves to sumatriptan with pK(B) values (6.66) only in the middle cerebral artery. In contrast, a 5-HT(1D) antagonist, BRL15572, had no effect in either artery. An RT-PCR study demonstrated the gene expression of the mRNAs of all three receptors (5HT(1B), 5HT(1D) and 5HT(2A)) in both arteries. These results suggest that histamine-induced contraction is mediated only through functional H(1) receptor in these arteries. Interestingly, there are functional 5-HT(2A) and 5-HT(1B) receptor subtypes in the middle cerebral artery, whereas the only functional receptor is 5-HT(2A) in the ciliary artery. The difference may be important for treatment with 5-HT(1B/1D) agonists (e.g. for migraine) without ocular side effect.

Retinopetal axons in mammals: emphasis on histamine and serotonin

Since 1892, anatomical studies have demonstrated that the retinas of mammals, including humans, receive input from the brain via axons emerging from the optic nerve. There are only a small number of these retinopetal axons, but their branches in the inner retina are very extensive. More recently, the neurons in the brain stem that give rise to these axons have been localized, and their neurotransmitters have been identified. One set of retinopetal axons arises from perikarya in the posterior hypothalamus and uses histamine, and the other arises from perikarya in the dorsal raphe and uses serotonin. These serotonergic and histaminergic neurons are not specialized to supply the retina; rather, they are a subset of the neurons that project via collaterals to many other targets in the central nervous system, as well. They are components of the ascending arousal system, firing most rapidly when the animal is awake and active. The contributions of these retinopetal axons to vision may be predicted from the known effects of serotonin and histamine on retinal neurons. There is also evidence suggesting that retinopetal axons play a role in the etiology of retinal diseases.

Regulation of Norepinephrine Release from Isolated Bovine Irides by Histamine

In the present study, we investigated the effect of histamine on sympathetic neurotransmission from isolated, superfused bovine irides. We also studied the pharmacology of prejunctional histamine receptors that regulate the release of norepinephrine (NE) from this tissue. The effect of exogenous histamine and various histamine receptor agonists was examined on the release of [(3)H]-norepinephrine ([(3)H]NE) triggered by electrical field stimulation using the Superfusion Method. Histamine receptor agonists caused a concentration-dependent inhibition of field-stimulated [(3)H]NE overflow with the following rank order of potency: imetit > histamine > R-alpha-methylhistamine. In all cases, the inhibitory action of histamine receptor agonists was attenuated at high concentrations of these compounds. The histamine receptor antagonists, clobenpropit (H(3)-antagonist/H(4)-agonist) and thioperamide (H(3)-antagonist) blocked the inhibitory response elicited by R-alpha-methylhistamine and imetit, respectively. Inhibitory effects of R-alpha-methylhistamine and clonidine were not additive suggesting that prejunctional H(3)- and alpha(2)-adrenoceptors coexist at neurotransmitter release sites. We conclude that histamine produces an inhibitory action on sympathetic neurotransmission in the bovine iris, an effect mimicked by selective H(3)-receptor agonists and blocked by H(3)-antagonists.

Allergic and immunologic disorders of the eye. Part I: immunology of the eye

Immuno-ophthalmology evolved during the 20th century as a subspecialty linking ophthalmologists and immunologists. This emerging subspecialty has focused on the use of immunology to better understand and treat ocular disorders. To help the allergist/clinical immunologist better appreciate the growing field of immuno-ophthalmology, this 2-part review series (Part II: Ocular Allergy will appear in the December issue of the Journal) will provide an overview of the impact that immunology has had on our understanding and treatment of allergic and immunologic eye diseases. The current review will focus on mechanisms by which mast cells, T cells, eosinophils, cytokines, and other inflammatory constituents contribute to the unique features of eye disease and their link to allergic responses that occur in other organs of the body.

Effect of histamine and substance P on the rabbit and human iris sphincter muscle

BACKGROUND AND METHODS

In an attempt to clarify the functional action of histamine and substance P on atropine-resistant miosis, we isolated rabbit and human iris sphincter muscles and investigated their mechanical properties using the isometric tension recording method.

RESULTS

Substance P dose-dependently contracted the rabbit iris sphincter, but had no effect on the human iris sphincter. In the rabbit iris sphincter, histamine reduced the amplitude of twitch contraction evoked by field stimulation but had no effect on carbachol-induced contraction. Thioperamide, but not mepyramine or cimetidine, partially antagonized the histamine-induced reduction in the amplitude of twitch contractions. In the human iris sphincter, on the other hand, histamine dose-dependently provoked contraction and the amplitude of histamine-induced contraction was affected neither by atropine nor by indomethacin.

CONCLUSIONS

These results provide evidence that histamine has strong contractile effect on the human iris sphincter muscle; the rabbit iris sphincter muscle, however, apparently lacks functional histamine receptors. In rabbits, exogenously applied histamine only activates H3 receptors located on the cholinergic nerve terminal, hence the excitatory neuro-effector transmission is suppressed. Thus, histamine may have an important roles in atropine-resistant miosis in humans, but not in rabbits.

Histamine actions in dog retinal central arteries as compared to those in middle cerebral and temporal arteries

PURPOSE

Mechanisms underlying the relaxant response to histamine were compared in isolated dog retinal arteries (branch of internal and external carotid arteries), middle cerebral arteries (branch of internal carotid artery) and superficial temporal arteries (branch of external carotid artery).

METHODS

Changes in the isometric tension of helical strips of the arteries with and without the endothelium were recorded.

RESULTS

Histamine produced concentration-related biphasic (phasic and sustained) relaxations in retinal arterial strips contracted partially with prostaglandin (PG)F2 alpha. Relaxations induced by histamine were not dependent on the endothelium. Treatment with cimetidine attenuated the sustained relaxation, whereas chlorpheniramine or indomethacin depressed the phasic relaxation. In addition, the phasic relaxant response to histamine was attenuated by tranylcypromine, a PGI2 synthesis inhibitor. In contrast, the amine-induced relaxant responses in dog middle cerebral arterial branch and temporal arteries were markedly suppressed by cimetidine alone.

CONCLUSIONS

In dog retinal arteries, the phasic relaxation caused by histamine is mediated by PGI2 in association with activation of the H1 receptor subtype in subendothelial tissues, possibly smooth muscle, and the sustained relaxation is evoked by direct stimulation of the H2 receptor subtype in smooth muscle. The histamine-induced relaxation in temporal and distal middle cerebral arteries is associated solely with a stimulation of H2 receptors in smooth muscle.

Marked increase in [3H](R) alpha-methylhistamine binding in the superior colliculus of visually deprived rats after unilateral enucleation

The binding of [3H](R)alpha-methylhistamine to histamine H3-receptors in visual structures of unilaterally enucleated rats was examined by quantitative autoradiography to clarify the involvement of histamine neurons in the visual system. [3H](R)alpha-Methylhistamine binding in the visually deprived superior colliculus, contralateral to the enucleated eye, was significantly increased 5, 15, 30 and 45 days after unilateral enucleation. Slight time-dependent increases in ligand binding were observed in the visual cortex, but the change was significant only 45 days after unilateral enucleation. Unilateral enucleation had no significant effect in the dorsal lateral geniculate nucleus at any time after enucleation. Continuous injection of (S)-alpha-fluoromethylhistidine, a specific inhibitor of L-histidine decarboxylase, attenuated the effect of unilateral enucleation in the superior colliculus. These results suggest that retinal deafferentation induced an increase in histamine H3-receptor binding sites, probably by selective adjustment of histamine neurons in response to unilateral enucleation.

Immunocytochemical and biochemical studies of histamine in the retina of the turtle Pseudemys scripta

A combination of immunocytochemical and biochemical methods was used to study histamine in the turtle retina. Histamine-like immunoreactivity was localized within paraboloids of certain cone photoreceptors by use of two different antisera directed against histamine. Preincubation of eyecups in Ringer's containing 10 microM histamine selectively increased the immunoreactivity of these photoreceptor paraboloids. The present localization of histamine in paraboloids indicated that, although histamine is in photoreceptors of the turtle retina, it may play some metabolic or neuromodulatory role, and not function as a neurotransmitter.

Histamine H1-receptor in the retina: species differences

Histamine H1-receptors in membranes of the various mammalian retinas were studied by [3H]mepyramine binding assay. Specific [3H]mepyramine bindings to bovine, pig, dog and human retinas were observed with the dissociation constants (KD), 3.8 +/- 1.2 nM, 1.8 +/- 0.6 nM, 2.6 +/- 0.6 nM and 3.0 +/- 0.9 nM, respectively, which were similar to those found in brains. But there was no detectable specific binding in the guinea-pig and rabbit retinas. The number of binding sites (Bmax) ranged from negligible value to 290.7 +/- 51.7 fmole/mg protein(human retina). Some H1-antagonists acted as potent agents in competing with [3H]mepyramine binding to bovine and pig retinas. These results indicated that histamine H1-receptors exist in some mammalian retina and have similar characteristics to those in brain membranes, but they distributes in the wide difference of the binding capacities among the species, while in brain variations were smaller.

Histamine in the retina

Retina and choroid were rapidly and gently extracted from chickens, guinea-pigs, rats, rabbits and cows. They were frozen, weighted and pooled in 3% trichloroacetic acid in a refrigerator. Using a radioenzymic assay, histamine was found to be present in the retina of guinea-pig (4.26 +/- 0.677 nmol g-1), rabbit (1.08 +/- 0.422 nmol g-1) and cow (0.189 +/- 0.036 nmol g-1), but not detected in chicken and rat. In the choroid, histamine was found in all species except rat (chicken: 4.92 +/- 0.542 nmol g-1; guinea-pig: 121.5 +/- 4.46 nmol g-1; rabbit: 18.7 +/- 3.93 nmol g-1; cow; 0.36 +/- 0.095 nmol g-1). The study verifies the presence of histamine in the retina of some species, and thereby supports previous fluorometry assays.

3H-mepyramine binding and histamine-stimulated cAMP accumulation in mammalian retina

The specific binding of different amounts of 3H-mepyramine to the bovine retina revealed a quasi-hyperbolic curve which approached saturation at 3H-ligand concentration over 9-12 nM. Scatchard analysis of the binding data showed two binding sites with KD values of 0.76 nM and 7.3 nM and Bmax of 49.3 and 194.6 fmole/mg protein, respectively. In the guinea-pig brain 3H-mepyramine bound to a single population of binding sites with KD value of 1.6 nM and Bmax of 291 fmole/mg protein. Various H1-antihistamines were potent competitors of the 3H-mepyramine binding: there was a big difference in potency of d- and 1-chlorpheniramine in both membrane preparations. In the rabbit retina slices histamine, in contrast to dopamine, weakly stimulated cAMP accumulation. The data suggest that the mammalian retina may possess histamine receptors.

[3H]mepyramine binding to histamine H1 receptors in bovine retina

The promethazine-sensitive [3H]mepyramine binding was used to determine the presence of histamine H1 receptors in membranes from bovine retina. Specific mepyramine binding to retinal membranes was reversible, saturable and of high affinity. The apparent dissociation constant (KD = 2.2 +/- 0.4 nM) and the density of binding sites (Bmax = 60.9 +/- 5.1 fmol/mg protein), obtained in equilibrium studies, were similar to those found in bovine brain cortex. Binding was stereospecific and the inhibitory potencies of H1 and H2 antagonists indicated that [3H] mepyramine binding sites in the retina have characteristics of H1 receptors.