Tetrahydrobiopterin does not affect end-organ responsiveness to norepinephrine-mediated vasoconstriction in aged skin

We have recently demonstrated that tetrahydrobiopterin (BH4) augments reflex vasoconstriction (VC) in aged skin. Although this appears to occur through its role in norepinephrine (NE) biosynthesis, the extent with which vascular mechanisms are affected are unknown. We hypothesized that localized BH4 supplementation would not affect the VC response to exogenous NE when sympathetic nerves were blocked. Two microdialysis fibers were placed in bretylium tosylate pretreated (presynaptically blocks neurotransmitter release from sympathetic adrenergic nerve terminals; iontophoresis, 200 μA for 20 min) 3-cm2 forearm skin of 10 young (Y) and 10 older (O) subjects for perfusion of 1) Ringer (control) and 2) 5 mM BH4. While local skin temperature was clamped at 34°C, six concentrations of NE (10−12, 10−10, 10−8, 10−6, 10−4, 10−2 M) were infused at each drug-treated site. Cutaneous vascular conductance (CVC) was calculated (CVC = laser Doppler flux/mean arterial pressure) and normalized to baseline (%ΔCVCbase). Despite prejunctional adrenergic blockade, NE-mediated VC was blunted in aged skin at each NE dose (10−12: −12 ± 2 vs. −21 ± 2; 10−10: −15 ± 2 vs. −27 ± 1; 10−8: −22 ± 2 vs. −32 ± 2; 10−6: −27 ± 2 vs. −38 ± 1; 10−4: −52 ± 3 vs. −66 ± 5; 10−2: −62 ± 3 vs. −75 ± 4%ΔCVCbase; P < 0.01), and this response was not affected by pretreatment with BH4 ( P > 0.05). Localized BH4 did not affect end-organ responsiveness to exogenous NE, suggesting that the effects of BH4 on cutaneous VC are primarily isolated to the NE biosynthetic pathway.

Effects of Cocaine on the Placenta

Adverse perinatal outcomes of gravidas using cocaine is well documented, but the effects on the placenta have been difficult to elucidate due to confounding factors such as concurrent use of other drugs. This study compares pathologic findings of 26 placentas from women who used only cocaine during pregnancy with findings from 26 controls. All women were from a similar socio-economic class and were controlled for gestational age and tobacco use. None of the cocaine placentas were from women whose toxicology screens were positive for drugs other than cocaine. In the 26 cocaine placentas, there was 1 infarct, 3 chronic villitis, and 1 segmental fibrosis, with none present in the controls. In the control group, there was 1 decidual vasculopathy and 1 thrombus in a maternal vessel, but none were in the cocaine placentas. Each group had 1 thrombus in a fetal vessel. The study group showed 6 cases of chorioamnionitis and 1 funisitis; the control group had 10 and 4 cases, respectively. None of the above or seven other features showed a statistically significant difference between the cases and controls. Cocaine is a potent vasoconstrictive agent that blocks re-uptake of norepinephrine at the adrenergic nerve terminals. Our study suggests that cocaine does not cause an increased incidence of any of the 15 clearly recognizable placental features examined.

Galanin is localized in sympathetic neurons of the dog liver

Stimulation of canine hepatic nerves releases the neuropeptide galanin from the liver; therefore, galanin may be a sympathetic neurotransmitter in the dog liver. To test this hypothesis, we used immunocytochemistry to determine if galanin is localized in hepatic sympathetic nerves and we used hepatic sympathetic denervation to verify such localization. Liver sections from dogs were immunostained for both galanin and the sympathetic enzyme marker tyrosine hydroxylase (TH). Galanin-like immunoreactivity (GALIR) was colocalized with TH in many axons of nerve trunks as well as individual nerve fibers located both in the stroma of hepatic blood vessels and in the liver parenchyma. Neither galanin- nor TH-positive cell bodies were observed. Intraportal 6-hydroxydopamine (6-OHDA) infusion, a treatment that selectively destroys hepatic adrenergic nerve terminals, abolished the GALIR staining in parenchymal neurons but only moderately diminished the GALIR staining in the nerve fibers around blood vessels. To confirm that 6-OHDA pretreatment proportionally depleted galanin and norepinephrine in the liver, we measured both the liver content and the hepatic nerve-stimulated spillover of galanin and norepinephrine from the liver. Pretreatment with 6-OHDA reduced the content and spillover of both galanin and norepinephrine by >90%. Together, these results indicate that galanin in dog liver is primarily colocalized with norepinephrine in sympathetic nerves and may therefore function as a hepatic sympathetic neurotransmitter.

The mechanism of [3H]noradrenaline release by histamine and its analogs from the rat vas deferens

In this study the mechanism by which histamine and H1 and H2 agonists evoked an overflow of radioactivity from rat vasa deferentia preloaded with [3H]noradrenaline was investigated. The overflow evoked by the various agonists was unaffected by the presence of such receptor antagonists as propranolol, phentolamine, cimetidine, or scopolamine. On the other hand, the overflow evoked by all agonists except dimaprit was inhibited by mepyramine and by two well-known neuronal uptake inhibitors, cocaine and desipramine. The inhibition by mepyramine has been attributed to its effect on the neuronal uptake process. Metabolic profile studies showed that 3,4-dihydroxyphenylglycol (DOPEG) was the major constituent in the evoked overflow caused by histamine, 2-methylhistamine, 4-methylhistamine, and dimaprit and that the overflow evoked by 2-pyridylethylamine and 2-thiazolylethylamine consisted predominantly of unchanged noradrenaline. Based on these findings, it is concluded that all of the agonists tested evoke noradrenaline release intraneuronally by entering the adrenergic nerve terminals. While dimaprit might enter by passively diffusing into the adrenergic nerves, other agonists seem to use the neuronal uptake process. Noradrenaline released intraneuronally is subsequently degraded by neuronal monoamine oxidase to form DOPEG. However, there are qualitative and quantitative differences in the metabolic profile of the overflow evoked by various agonists. It is suggested that these differences could arise from their additional properties, such as their effect on the neuronal uptake process and (or) their ability to act as substrate for neuronal monoamine oxidase.Key words: noradrenaline, vas deferens, histamine, histamine H1 and H2 agonists.