E.N. Su

Continued progression of retinopathy despite spontaneous recovery to normoglycemia in a long-term study of streptozotocin-induced diabetes in rats

Abstractu2002· Background: This long-term (2.3 years) study determines the temporal relationship between systemic glucose levels and the progression of diabetic retinopathy during the natural course of streptozotocin-induced diabetes in rats.u2002· Methods: Of 367 rats, 200 were randomly assigned into a group injected with streptozotocin (50 mg.kg–1) and 167 into a control group. Subsets of the rats were killed at 6, 28, 40, 65, 90 and >100 weeks post induction to allow the severity of retinopathy to be assessed quantitatively and qualitatively by trypsin digests of the retinal vasculature. Concurrently blood glucose, body weight and death rate were monitored.u2002· Results: Three glycemic phases were observed in the streptozotocin rats. In phase 1 (0 to 36–40 weeks) hyperglycemia was established and maintained. In phase 2 (36–40 to 84–90 weeks) normoglycemia was restored, and maintained during phase 3 (84–90 to 120 weeks). Control rats were normoglycemic throughout. The retinal microangiopathy was marked at 28 weeks during phase 1, developed more slowly in phase 2 and continued to worsen with loss of capillaries in all retinas and saccular microaneurysms present in 50% of retinas in phase 3. Cumulative death rate in streptozotocin rats also followed three phases, with maximum vulnerability occurring between 28 and 40 weeks. Body weight was significantly lower in streptozotocin rats throughout, increasing slowly in phase 1, then more rapidly during and after spontaneous glycemic recovery.u2002· Conclusion: The worsening retinopathy, despite sustained recovery to normoglycemia, implies that good glucose control alone does not stop the progression of the retinal microangiopathy at this late stage.

Changes in vitreal oxygen tension distribution in the streptozotocin diabetic rat

SummaryMeasurements of vitreal oxygen tension have been made for the first time in the streptozotocin-induced diabetic rat eye. A total of 36 Sprague Dawley rats were divided into a control (n=18) and streptozotocin injected group (n=18), and after 5–6 weeks of established hyperglycaemia, an acute experiment was performed in which vitreal oxygen tension profiles were determined with oxygen sensitive microelectrodes. The control rats had significant oxygen tension gradients in the vitreous close to retinal arteries with relatively flat oxygen tension profiles close to retinal veins and intermediate regions. All control rats had a substantial arteriovenous oxygen tension difference when measurements were made on retinal arteries and veins. In contrast the oxygen tension profiles measured in the vitreous of streptozotocin rats showed markedly reduced oxygen gradients in the vicinity of retinal arteries and a smaller arteriovenous oxygen tension difference. In both groups of rats, for distances of 500 μm and greater from the retina (mid vitreous) a plateau oxygen tension value was observed. No significant difference was found in this mean mid vitreous value between the control rats and diabetic rats under the same systemic conditions. We conclude that there are significant changes in oxygen tension near retinal arteries in streptozotocin-induced diabetes before any histopathological changes are evident.

An in vivo and in vitro comparison of the effects of vasoactive mediators on pulpal blood vessels in rat incisors

The effects of endogenous vasoactive substances were evaluated in anaesthetized rats using a laser Doppler flowmeter to monitor changes in pulpal blood flow, as well as directly in isolated pulpal arteriole preparations utilising a microperfusion and monitoring system to observe changes in vessel diameter. In anaesthetized rats, while systemic arterial blood pressure remained relatively stable, intra-arterial delivery of adrenaline (epinephrine) (A), noradrenaline (norepinephrine) (NA), phenylephrine (PHE), dopamine (DOPA), 5-hydroxytryptamine (5-HT), or endothelin-1 (ET-1) produced a dose-dependent reduction in pulpal blood flow (order of potency: ET-1>>A=NA>PHE=DOPA=5-HT); acetylcholine induced a dose-dependent increase in pulpal blood flow; histamine, isoproterenol and adenosine produced no significant changes. In isolated arteriole preparations, intraluminal delivery of A, NA, PHE, DOPA or 5-HT produced dose-dependent vasoconstriction (A=NA>PHE=DOPA=5-HT). Acetylcholine relaxed NA-precontracted vessels dose-dependently. Histamine and isoproterenol produced a small vasodilatation. Intraluminal ET-1 produced a small vasoconstriction at 10(-8)M, whereas extraluminal ET-1 produced a dose-dependent vasoconstriction from 10(-10)M and above. Intraluminal adenosine failed to dilate vessels precontracted with ET-1, whereas extraluminal adenosine caused a complete relaxation. These combined in vivo and in vitro data suggest that, in the rat incisor, the pulpal microcirculation is capable of functional regulation and that pulpal blood flow may be modulated by endothelium-related factors, metabolic (tissue-related) factors, as well as humoral (blood-borne) factors.

Histamine Induces Opposing Vasoactive Effects at Different Levels of the Ocular Vasculature

Purpose: To characterize the vasoactive properties and receptors of histamine in porcine retinal arterioles compared to that in the long posterior ciliary artery. Methods: Isolated perfused porcine retinal arterioles were used to study vessel diameter in response to histamine (10−10 to 10−4 M). Ring segments from the long posterior ciliary artery were used to study contractile force in response to histamine. Results: Histamine-induced vasodilatation in pig retinal arterioles but contraction in the long posterior ciliary artery. In retinal arterioles, the involvement of H2 receptors was implied by the attenuation of the histamine response in the presence of cimetidine. Further attenuation of the histamine response by pyrilamine suggests the involvement of H1 receptors. In retinal arterioles denuded of endothelial cells, the histamine response was only slightly reduced.Conclusion: Histamine induces opposing vasoactive effects at different levels of the porcine ocular vasculature.

Agonist-induced vasoactive responses in isolated perfused porcine dental pulpal arterioles

A novel isolated perfused pulpal arteriole preparation and microperfusion system was used to evaluate the direct vasoactive responses of pulpal arterioles to selected agonists. Short lengths of porcine pulpal arterioles (101.7+/-2.2 microm o.d., n=105) were dissected out and placed in an environment-controlled bath on the stage of an inverted microscope. Both ends of the vessel were cannulated and perfused at a controlled rate through the lumen. The diameter of the vessel was measured online. Following equilibration, the vessel was challenged with various agonists: adrenaline (epinephrine), noradrenaline (norepinephrine), phenylephrine, dopamine, isoproterenol, 5-hydroxytryptamine, histamine and adenosine. The endothelium-dependent vasodilator acetylcholine was used to evaluate endothelial cell function. Adrenaline, noradrenaline, phenylephrine, 5-hydroxytryptamine and dopamine caused dose-dependent contractions (adrenaline=noradrenaline>phenylephrine>dopamine>5-hydroxytryptamine). Isoproterenol and histamine provoked a dose-dependent dilation. Adenosine produced pronounced vasodilatation in vessels precontracted with 10(-8)M endothelin-1. Functional adrenergic, histamine, 5-hydroxytryptamine and adenosine receptors are, therefore, present in porcine pulpal arterioles. The isolated perfused pulpal arteriole preparation may prove valuable in understanding local control mechanisms of pulpal microcirculation.