Failure of propranolol to inhibit the epinephrine-induced enhancement of responses to sympathetic nerve stimulation in the rat mesenteric vascular bed.

Experiments were designed to characterize the nature of the epinephrine-induced potentiation of responses to sympathetic nerve stimulation in the Hooded Wistar rat. The responses to sympathetic nerve stimulation were determined in the isolated perfused mesenteric vascular bed preparation before and after infusion of epinephrine (at 0.27 or 2.

Elevated nerve growth factor levels in young spontaneously hypertensive rats.

It is generally agreed that sympathetic innervation of vascular tissues in spontaneously hypertensive rats (SHR) is greater than that existing in vascular tissues from normotensive Wistar-Kyoto (WKY) rats. One factor responsible for regulation of the growth of peripheral sympathetic nerves is the peptide nerve growth factor, which is released from effector cells. In the present study, an enzyme immunoassay was used to measure nerve growth factor levels in mesenteric arteries (densely innervated) and aortas (sparsely innervated) from both young (20-day-old) and mature (6-month-old) SHR and WKY rats.

Application of amperometric detection to the analysis of the diffusion and O-methylation of a catecholamine and a catechol steroid across the blood vessel wall.

A novel amperometric detection procedure was developed to determine the ability of the catechol, 2-hydroxyestradiol (2OHE2), to diffuse through and be O-methylated during its passage from the lumen to the adventitial surface of the rabbit ear artery. The diffusion and O-methylation of d-norepinephrine (d-NE) also was determined. When arteries were perfused with either 2OHE2 or d-NE (10 microM), the bulk of the material effluxing from the adventitial surface was O-methylated.

Adrenocorticotropin and corticosterone levels in pre-weanling spontaneously hypertensive rats.

Circulating plasma ACTH and corticosterone levels were measured in spontaneously hypertensive rats (SHR) and the corresponding, normotensive Wistar-Kyoto (WKY) strain at 10 and 20 days of age. In addition, stored levels of ACTH were measured in the pituitary glands of these animals. Circulating corticosterone levels were significantly lower, in both strains, at 10 days than at 20 days.

Time course of changes in the norepinephrine content of tissues from spontaneously hypertensive and Wistar Kyoto rats.

The change in norepinephrine (NE) content with age (from 2 days to 17 weeks old) was examined in a variety of tissues from spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) rats. NE content was determined by either a catechol-O-methyltransferase-based radioenzymatic assay or high performance liquid chromatography with electrochemical detection. Regardless of the age of the animal, NE content per gram of tissue was significantly greater in mesenteric arteries and kidneys from SHR compared to WKY tissues, whereas NE content per whole kidney was similar between the two rat strains.

Influence of cold-induced increases in sympathetic nerve activity on norepinephrine content in the vasculature of the spontaneously hypertensive rat.

In spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY), we have examined both the endogenous norepinephrine (NE) contents of caudal arteries, mesenteric arteries and cardiac tissue as well as the rates of decline of NE in these tissues after inhibition of NE synthesis. The endogenous NE contents of caudal and mesenteric arteries from SHR rats were greater than those from WKY rats. In contrast, the NE contents of hearts from SHR and WKY rats were similar.

Upregulation of the vascular alpha-1 receptor in malignant DOCA-salt hypertension.

In this investigation we describe regulation of the vascular alpha-1 receptor and functional properties of resistance vessels in malignant hypertensive DOCA-salt rats (DOCA-salt). Uninephrectomized control and DOCA-salt rats were maintained for 6 weeks; microscopic renal morphology provided an index of vascular injury. Radioligand binding studies indicated a striking increase in the density of mesenteric alpha-1 binding sites in DOCA-salt (542 +/- 44 fm/mg) vs.

A contrasting effect of the diabetic state upon the contractile responses of aortic preparations from the rat and rabbit.

Diabetes was induced in rats by a single intraperitoneal injection of streptozotocin (65 mg kg-1). Rabbits were rendered diabetic by injecting alloxan (100 mg kg-1) into the lateral ear vein. Diabetes was confirmed by a significant elevation of serum glucose in both species 8 weeks after injection.

The influence of oestrogen and oestrogen metabolites on the sensitivity of the isolated rabbit aorta to catecholamines.

In the present study the influence of oestradiol, catechol oestrogens, and O-methylated oestrogens was determined on the contractile responses of the isolated rabbit aorta to (-)-adrenaline. Oestradiol (40 mumol/l), 2-hydroxyoestradiol (2OHE2) (20 mumol/l), and 2-methoxyoestradiol (2MeOE2) (20 mumol/l) all sensitized the rabbit aorta to contractile responses to (-)-adrenaline. Similarly, the 2-hydroxy and 2-methoxy derivatives of oestrone and oestriol also sensitized the aorta to (-)-adrenaline-induced contractions.

Inhibition of tyrosine hydroxylase in rabbit mesenteric artery and vas deferens by catechol oestrogens.

In the present study we have investigated the effects of oestrogens, catechol oestrogens, and catecholamines on tyrosine hydroxylase (TH) activity derived from rabbit mesenteric artery and vas deferens. Both catechol oestrogens, 2-hydroxyoestradiol (2OHE2) and 2-hydroxyoesterone (2OHE1), inhibited TH activity in mesenteric artery and vas deferens in a concentration-dependent manner with potencies that were higher than those for noradrenaline but lower than that for dopamine. When added to the reaction medium along with increasing concentrations of a pterin cofactor (200 to 1,500 mumol/l DMPH4), the catechol oestrogens (200 mumol/l) increased the apparent Km for DMPH4 without altering the maximum velocity (Vmax) of the reaction.

Characterization of the O-methylation of catechol oestrogens by intact rabbit thoracic aorta and subcellular fractions thereof.

In the present study we investigated the O-methylation of catechol oestrogens by intact rabbit thoracic aorta and subcellular fractions thereof. The O-methylation of 2-hydroxyoestradiol (2OHE2) and 2-hydroxyoestriol (2OHE3) displayed saturation kinetics in the intact tissue. The apparent Km and Vmax values for the O-methylation of 2OHE2 were determined to be 0.

Perfusion of the intact and partially isolated rat mesenteric vascular bed: application to vessels from hypertensive and normotensive rats.

In the present study, we utilized 2 perfused mesenteric vascular bed preparations in an examination of the responses of mesenteric vessels from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. One preparation involved perfusion of the mesenteric vascular bed dissected free from the intestine. The second preparation was essentially similar, with the exception that the intestine and the small arterioles feeding the jejunum were intact.

O-methylation of isoproterenol by the endothelium of the rabbit thoracic aorta.

We have examined the influence of endothelial cell removal upon the O-methylation of the isomers of isoproterenol in the isolated rabbit aorta. Endothelial cells were removed by mechanically abrading isolated segments of rabbit aorta. The latter procedure resulted in the abolition of acetylcholine-mediated relaxation of tissues, a process dependent upon the presence of endothelial cells.

Evidence that 6-hydroxydopamine is an inhibitor of catechol-O-methyltransferase in intact tissue.

The effect of in-vitro sympathetic denervation on the O-methylation of 2-hydroxyoestradiol was examined using the rabbit thoracic aorta. Aortic segments were exposed to 6-hydroxydopamine (400 mg litre-1, 10 min), incubated in 2-hydroxyoestradiol (5 microM, 60 min), and the 2-methoxyoestradiol formed was quantified using HPLC with electrochemical detection. Pre-exposure to 6-hydroxydopamine reduced O-methylation by 90% in intact aortic strips.

Hypernoradrenergic innervation of the caudal artery of the spontaneously hypertensive rat: an influence upon neuroeffector mechanisms.

In the present studies we have established that the perfused caudal artery from spontaneously hypertensive (SH) rats responds to pharmacological and physiological stimuli in a manner similar to that described for other blood vessels from the SH rat. In addition, the responses of caudal arteries from SH rats to exogenous norepinephrine were similar to those of arteries removed from normotensive Kyoto Wistar rats. However, responses to sympathetic nerve stimulation at high, but not low, frequencies of stimulation were increased in arteries from the SH rat.

HPLC-ECD procedure for the measurement of O-methylation of catechol estrogens by vascular tissue.

A precolumn extraction procedure combined with high-performance liquid chromatography with electrochemical detection (HPLC-ECD) has been developed for the identification and quantitation of catechol estrogens, their immediate precursors (estrogens), and their 0-methylated metabolites. These compounds were isolated from Krebs solutions and from perchloric acid tissue extracts or whole tissues by simple solvent extraction prior to quantitation. The optimal conditions for detection by HPLC-ECD were those employing a radial compression module, a C18 Bondapak cartridge, and an isocratic mobile phase of ammonium phosphate (pH 3.

Nonintracellular, cell-associated O-methylation of isoproterenol in the isolated rabbit thoracic aorta.

The present study examines the subcellular site of catecholamine O-methylation in extraneuronal tissue. S-Adenosyl-l-methionine, a methyl donor that does not diffuse across biological membranes, was used to assess the participation of plasma membrane bound catechol-O-methyltransferase vs. cytoplasmic catechol-O-methyltransferase in the catecholamine O-methylating process.

The stereoselective O-methylation of isoprenaline in the isolated rabbit thoracic aorta.

This investigation examined the stereoselective nature of the steroid-sensitive extraneuronal O-methylation process for the isomers of isoprenaline in the rabbit aorta. The rate of O-methylation of (-)- and (+)-isoprenaline was linear with substrate concentration in the range 0.24 to 4.

Influence of blood sampling conditions upon histamine concentrations in rat plasma: a study of a complex relationship with plasma epinephrine.

The concentrations of histamine reported vary considerably from species to species. The present studies sought to determine if blood sampling techniques were at least in part responsible for this large variability. Since plasma catecholamines are influenced by the stress associated with blood sampling, these biogenic amines also were measured.

Altered catecholamine contents in vascular and nonvascular tissues in genetically hypertensive rats.

We have measured the catecholamine (CA) contents in hearts, mesenteric vasculature, abdominal aorta, inferior vena cava, vasa deferentia and salivary glands from genetically hypertensive rats (SHR) and normotensive Kyoto-Wistar rats (WKY). We noted differences between the norepinephrine (NE) contents of individual tissues from SHR and WKY rats and have used two different analytical procedures for the measurement of NE to confirm these differences. Comparisons between tissue contents of NE in SHR and WKY rats indicated a greater content of NE in the following tissues from the SHR: heart, mesenteric artery, abdominal aorta, inferior vena cava and vasa deferentia.

Non-radiochemical procedure for the measurement of O-methylation of the stereoisomers of isoprenaline.

A non-radiochemical procedure has been developed which permits the separation and measurement of isoprenaline (ISO) and the O-methylated metabolite, 3-methoxyisoprenaline (MeOISO). This methodology employs alumina chromatography and toluene solvent extraction to separate the catecholamine, ISO, from the O-methylated derivative, MeOISO. High-performance liquid chromatography with electrochemical detection has been used to quantify these compounds.

Neuronal deamination of endogenous and exogenous noradrenaline in the mesenteric artery of the spontaneously hypertensive rat.

The noradrenaline (NA) content of the mesenteric arteries from spontaneously-hypertensive rats (SHR) are greater than those in arteries from normotensive Kyoto Wistar rats (WKY). The possibility that impaired neuronal monoamine oxidase (MAO) activity in mesenteric arteries from SHR rats was responsible for the differences in NA content was explored. The in-vitro formation of dihydroxyphenylethylene glycol (DOPEG) by intact segments of mesenteric arteries was used as an index of neuronal MAO activity.

Changes in adrenal microsomal cytochrome(s) P-450 with aging in the guinea pig.

Studies were carried out to investigate the mechanism(s) responsible for the changes in adrenal microsomal mixed function oxidase activity which occur with aging (30-200 days) in guinea pigs. With aging, the rate os metabolism of xenobiotics [ethylmorphine and benzo(a)pyrene] by adrenal microsomes increased 3- to 5-fold. Steroid 17 alpha- and 21-hydroxylations, when expressed per mg protein, were similar in immature (30 days old) and mature (200 days old) animals.