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Biomedical subjects

D S Gregory

Publications and source records attributed to D S Gregory.

26 records · Page 2Linked to original sources
PubMed1989

A circadian rhythm of aqueous flow underlies the circadian rhythm of IOP in NZW rabbits.

There is a daily rhythm of aqueous flow in New Zealand White rabbits entrained to 12 hr light:12 hr dark. The phase of the rhythm of flow is determined by the phase of the light:dark cycle, and the rhythm persists in constant dark. Therefore, in New Zealand White rabbits the rhythm of aqueous flow, like the rhythm of intraocular pressure, is circadian. The range of the circadian rhythm of flow suggests it plays a major role in producing the circadian rhythm of intraocular pressure. This animal model provides a powerful tool for studying endogenous mechanisms which regulate aqueous humor formation and intraocular pressure.

Animals↗
PubMed1987

Interaction between alpha 2- and beta 2-adrenergic receptors in rabbit ciliary processes.

The interaction between the alpha 2- and beta 2-adrenergic receptors of ciliary processes has been studied by examining dose-response curves for adrenergic agonist stimulation of cyclic AMP production by intact, excised rabbit ciliary processes. Stimulation of cyclic AMP production by 1-isoproterenol is maximum from 0.1 to 1.0 microM; at higher concentrations stimulation decreases and approaches basal levels. Decreased cyclic AMP production at high concentrations of isoproterenol is blocked by the specific alpha 2-adrenergic antagonist, yohimbine, but not by the alpha 1-adrenergic antagonist, prazosin. Ciliary processes from animals after bilateral cervical ganglionectomy also show reduced cyclic AMP production at high concentrations of isoproterenol and this reduction is blocked by yohimbine, but not prazosin. This experiment suggests that the inhibition at high concentrations of isoproterenol is mediated by postsynaptic alpha 2-adrenergic receptors. Cyclic AMP production is relatively insensitive to epinephrine and norepinephrine, but their responses are potentiated by yohimbine. Catecholamines and clonidine, a specific alpha 2-adrenergic agonist, exhibit dose-dependent inhibition of forskolin-stimulated cyclic AMP production by ciliary processes. I50s from the dose-response curves are consistent with the characteristic binding affinities of these adrenergic agonists for alpha 2-adrenergic receptors: clonidine = epinephrine greater than norepinephrine greater than isoproterenol. Inhibition of forskolin-stimulated cyclic AMP production by clonidine is blocked by yohimbine but not by prazosin.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Agonists↗
PubMed1987

Adrenergic decentralization modifies the circadian rhythm of intraocular pressure.

The effect of unilateral decentralization on the circadian rhythm of IOP was examined in rabbits to determine whether postganglionic sympathetic nerves to the eye can play a role in regulating the circadian rhythm of IOP in the absence of input from the central nervous system. Decentralization produced a marked reduction of the dark phase increase of IOP, but had little effect on IOP during the light phase. Therefore, circadian signals from the central nervous system, which contribute to the dark phase increase of IOP, arrive at the cervical ganglia by way of preganglionic fibers of the sympathetic chain and travel to the eye through postganglionic adrenergic nerves.

Animals↗
PubMed1985

Cervical ganglionectomy alters the circadian rhythm of intraocular pressure in New Zealand White rabbits.

A circadian rhythm of intraocular pressure in rabbits could provide a useful model for understanding the daily rhythm of intraocular pressure in humans and for studying mechanisms which regulate intraocular pressure. Our results confirm earlier work showing that New Zealand White rabbits housed in an environment with a lighting cycle of 12 hours light and 12 hours dark have a rhythm of intraocular pressure, and that this rhythm persists in constant dark. We show further that the cycle of light and dark is the zeitgeber for entrainment of the rhythm of intraocular pressure, and therefore persistence of this rhythm in constant dark establishes it as a circadian rhythm. Cervical ganglionectomy demonstrated that intact sympathetic innervation to the eye is required for maintenance of the normal circadian rhythm of intraocular pressure in rabbits. Intraocular pressure in sympathectomized eyes is no different from control eyes during the light, but is significantly reduced during the dark.

Animals↗
PubMed1980

Beta-adrenergic receptors in ciliary processes of the rabbit.

Identification and characterization of beta-adrenergic receptors were attempted in particulate membrane fractions derived from isolated ciliary processes (CP) of rabbit eyes. High-affinity binding sites for 125I-hydroxybenzylpindolol (125I-HYP), a beta-adrenergic antagonist, were identified in particulate membrane fractions of homogenized CP that were recovered from discontinuous sucrose density gradients. Adenylate cyclase activity was recovered in the same fraction as the 125I-HYP binding sites. The dissociation constant of 125I-HYP for the high affinity site is 0.25 nM, with a minimum capacity of about 35 fmol/mg of protein. Adrenergic agonists and antagonists, including timolol, 1-alprenolol, d,1-propranolol, 1-isoproterenol, 1-epinephrine, and phentolamine, were examined for their ability to displace 125I-HYP from its binding site. The results were consistent with the identification of the high-affinity 125I-HYP binding sites as beta-adrenergic receptors. This is the first report which identifies by ligand binding techniques beta-adrenergic receptors in CP exclusive of iridial or other uveal tissue and supports the possibility of direct action of beta-adrenergic agents on the formation of aqueous humor.

Adenylyl Cyclases↗