I. Leusen

Role of the endothelium in the vasodilator response of rat thoracic aorta to histamine

Despite their potent vasodilating action in vivo, acetylcholine and histamine often show a vasoconstricting action in vitro. As the endothelium has an important role in the vasodilating effect of acetylcholine, we investigated the possible role of the endothelium in the vasodilating effect of histamine in comparison to acetylcholine. Experiments were done on ring segments of rat thoracic aorta mounted for isometric tension measurements. We demonstrated that relaxation by histamine and acetylcholine of pre-contracted rat aorta segments required the presence of endothelial cells. Acetylcholine acting on muscarinic receptors, and histamine acting on H1-receptors seemed to initiate the production of mediator(s) from the endothelial cells, which leads to relaxation of the vascular smooth muscle cells. This production appeared to be depressed by ETYA and hydroquinone, and under hypoxic conditions.

Endothelium-dependent relaxation and hyperpolarization in aorta from control and renal hypertensive rats.

Endothelium-dependent relaxations are depressed in hypertension. In this study we investigated the possible involvement of endothelium-dependent smooth muscle hyperpolarization in this phenomenon. In isolated aortic segments from control rats, acetylcholine (10(-8)-10(-5) M) elicits relaxations after precontraction with norepinephrine (10(-7) M), and acetylcholine or carbachol (10(-5) M) induce smooth muscle hyperpolarization (10.6 +/- 0.9 mV). Both effects disappear after removal of the endothelium and are depressed by tetraethylammonium (3 x 10(-3) M), a rather nonspecific blocker of K+ channels, but not by glibenclamide (10(-5) M), a potent blocker of the ATP-regulated K+ channels, which has a marked effect on the relaxation induced by BRL 38227. The relaxation effect of acetylcholine is impaired in norepinephrine-contracted preparations from hypertensive rats but is not further depressed by tetraethylammonium. In aorta from hypertensive rats, hyperpolarization induced by carbachol was significantly reduced to a mean of only 21.8% of the values obtained in preparations from normotensive rats. From the relaxation-hyperpolarization relation obtained with BRL 38227 (opening K+ channels), it is derived that the endothelium-dependent hyperpolarization (approximately 10 mV) contributes for at least 20-30% of the maximal relaxation effect of acetylcholine on rat aorta. It is concluded that the diminished endothelium-dependent hyperpolarization may contribute to the depression of the endothelium-dependent relaxation in hypertension.

Release of endothelium-derived relaxing factor from human umbilical vessels.

The ability of human umbilical endothelial cells to release relaxing substance(s) in response to different agonists was investigated. Endothelium-denuded aortic rings of rats were used for the bioassay and tension recording. After precontraction, this preparation showed no response to histamine, acetylcholine, A 23187, or adenosine triphosphate while serotonin elicited further contraction. Superfusion of the precontracted preparations with the perfusate from umbilical veins and arteries stimulated with histamine (10(-7)-10(-5) M), A23187 (10(-7)-10(-6) M), or adenosine triphosphate (10(-5)-10(-4) M) elicited a relaxation. No relaxation was obtained with acetylcholine (10(-8)-10(-6) M) or serotonin (10(-8)-10(-6) M). The relaxation of bioassay aortic rings under the influence of the perfusate from histamine-stimulated umbilical vessels was inhibited by mepyramine (10(-5) M) but not by cimetidine (10(-4) M) suggesting the involvement of H1-receptors. The relaxation was also inhibited by increasing the transit time between the donor and the detector preparation, by methylene blue (5 X 10(-5) M), and by nordihydroguaiaretic acid (5 X 10(-5) M) but not by indomethacin (5 X 10(-5) M), and which have been reported for endothelium-derived relaxing factor. The involvement of umbilical endothelial cells in the relaxation response was further confirmed by studying precontracted, rubbed rat aortic rings seeded with cultured endothelial cells from human umbilical veins. Such preparations relaxed in response to histamine (10(-7)-10(-4) M) in contrast with the control preparations. No relaxations of these preparations were observed in response to acetylcholine (10(-9)-10(-6) M).(ABSTRACT TRUNCATED AT 250 WORDS)

The reactivity of isolated venous preparations to electrical stimulation

SummaryThe reactivity of spiral strips and isolated segments of the lateral saphenal vein of the dog was investigated. In a first series of experiments the influence of progressively increasing distension on the isotonic or isometric reactions of both preparations to a constant electrical stimulation was examined. It appeared that in every case the reaction first increases with progressive distension. Whenever the venous wall becomes overstretched, the amplitude of the reaction diminishes gradually. In a second series of experiments, spiral strips and isolated segments were prepared from the same veins and their sensitivity to increasing stimulation frequencies tested at the optimal point of their distension-reaction relation, both in isotonic and isometric conditions. From these experiments it appeared that the isotonic preparations are more sensitive than the isometric, and that the sensitivity of the isolated segment is also greater than that of the spiral strip.

Hemispheric blood flow in the rat after unilateral common carotid occlusion: evolution with time.

Acute occlusion of one common carotid artery in the anesthetized normocapnic rat results in a moderate cerebral blood flow (CBF) decrease in both cerebral hemispheres. No asymmetrical perfusion is observed when the overall flow in each hemisphere is considered. The increase in blood flow which normally occurs in hypercapnia is strongly impaired in the cerebral hemisphere on the occluded side resulting in an important asymmetrical hemispheric perfusion. The days (1, 5, 15, 30) following unilateral carotid occlusion normal control CBF values are found in both hemispheres in normocapnic conditions. Hemispheric perfusion asymmetry in hypercapnia also becomes progressively less pronounced with time but a slight asymmetry still persists one month after unilateral carotid occlusion.

CONTRIBUTION OF NITRIC-OXIDE TO THE ENDOTHELIUM-DEPENDENT HYPERPOLARIZATION IN RAT AORTA.

1. The effect of endogenous and exogenous nitric oxide on the membrane potential (Em) of smooth muscle cells of the thoracic aorta of rats was investigated. 2. In tissues with intact endothelium, application of ACh or carbachol generated a change of the membrane potential consisting of an initial hyperpolarization by 10‐12 mV, followed by a partial recovery toward a level which was at 10 min still 6‐8 mV more negative than in control conditions. 3. Application of NG‐nitro‐L‐arginine methylester (L‐NAME), an inhibitor of endogenous NO production, had no significant effect on the resting membrane potential. The initial peak endothelium‐dependent hyperpolarization elicited by ACh or carbachol was not significantly diminished. However, the recovery was more accentuated. Similarly, NG‐monomethyl‐L‐arginine (L‐NMMA) significantly diminished the second component of the endothelium‐dependent hyperpolarization without affecting the magnitude of the first transient peak Em change. 4. Nitroglycerin produced a small sustained hyperpolarization of 1‐2 mV, and the NO donor SIN‐1, the active metabolite of molsidomine, similarly increased Em by about 1 mV. Infusion of high doses of acidified NaNO2 solution caused a hyperpolarization smaller than that evoked by ACh or carbachol. 5. 8‐Bromo‐cyclic GMP caused little change of membrane potential. In the presence of 8‐Br‐cGMP, ACh evoked a membrane electrical response similar to that observed in the absence of the nucleotide. 6. It is concluded that, in the rat aorta, the initial peak endothelium‐dependent hyperpolarization observed under the influence of ACh or carbachol is not directly related to the synthesis of NO.(ABSTRACT TRUNCATED AT 250 WORDS)

LACTATE AND PYRUVATE IN THE BRAIN OF RATS DURING HYPERVENTILATION

AbstractExperiments on anesthetized and curarized rats under artificial ventilation show that during hyperventilation lactate and pyruvate are markedly increased both in blood and in brain. The lactate/pyruvate ratio which remains in blood the same as in control conditions, is systematically decreased in brain. During hypoxia (ventilation with 7 % oxygen in nitrogen) lactate rises markedly in blood and in brain. The lactate/pyruvate ratio which is strongly increased in blood shows a small rise in brain. These observations could indicate that a different mechanism is responsible for the rise of lactate in brain during hypoxia and hyperventilation. The important augmentation of lactate in brain during hyperventilation can give an explanation for the delayed rise which is seen in the lactate level in cerebrospinal fluid in these conditions.

Influence of age on the formation of 5α-androstanediol and 7α-hydroxy-testosterone by incubated rat testes

Abstract Testes from rats of different ages were incubated with or without tritiated testosterone. The exogenously-added or endogenously-produced testosterone is mainly metabolized to 7α-hydroxylated testosterone in adult animals, and to Set-reduced metabolites (especially 5α-androstanediol) in immature animals.

The biosynthesis of estrogens by cow follicles

Abstract Separated and recombined granulosa and thecal cells of ripening cow follicles were incubated in vitro in the presence of different steroid precursors involved in the Δ 4 and Δ 5 -pathways. The experiments indicate that both in the granulosa and the thecal cells the transformation of pregnenolone to androstenedione occurs predominantly through the Δ 5 -pathway. Although both cell types are able to transform androstenedione to estrogens, this capacity is very small in the thecal tissue as compared to the granulosa cells. Incubations of combined granulosa and thecal cells yielded larger amounts of estrogens than the incubations of each cell type separately, indicating a positive interaction between both cell types in the experimental conditions.

Effects of carbon dioxide, bicarbonate and pH on lactate and pyruvate in the brain of rats

SummaryThe influence of acute changes inPaCO2on lactate concentration in brain and blood was studied in hypercapnic and hypocapnic rats. Lactate in brain increases markedly whenPCO2is acutely decreased by severe hyperventilation. Compared with the observations in normal rats, the lactate response to an intense hypocapnia was decreased in animals maintained 24 hours in hypoxic alkalosis and increased after 24 hours hypercapnia. The results are discussed in relation to the hypothesis that the lactate concentration response in brain in these conditions is related to local pH. Incubation studies of brain tissue, in whichPCO2or (and) [HCO3−] were varied, show that lactate and pyruvate concentration and glucose consumption increase while the lactate/pyruvate ratio decreases when the pH of the incubation fluid is augmented. In an iso-pH system, lactate and pyruvate concentration, glucose consumption and L/P ratio increase with increasing [HCO3−]. The possible mechanisms and the possible importance of these metabolic variations are discussed.