Biomedical subjects

R J Head

Publications and source records attributed to R J Head.

At least 55 records · Page 3Linked to original sources

PubMed1989

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. The vessel wall offered a considerable barrier to the diffusion of both NE and 2OHE2, because the concentrations of NE and 2OHE2 found in the solution perfusing the adventitial surface were as much as 1,000-fold lower than their concentration in the intralumenal perfusion stream. It is concluded that the blood vessel wall offers a significant physical and metabolic barrier to the penetration of unchanged 2OHE2 and NE.

Animals↗

PubMed1989

Determinants of smooth muscle sensitivity.

1. Deviation supersensitivity and post-junctional supersensitivity are important determinants in the control of the response of smooth muscle. 2. Post-junctional supersensitivity is a process whereby effector cells have augmented responsiveness as a consequence of an impaired physiological stimulus. Deviation supersensitivity which occurs as a result of inhibition of sites of loss or inactivation of the transmitter substance noradrenaline and its analogues also produces an enhanced response of smooth muscle cell preparations. 3. The enzymes monoamine oxidase and catechol-O-methyl transferase are irreversible site of loss of noradrenaline. Functional impairment of these enzymes results in deviation supersensitivity. 4. The complexities involved in unravelling the contribution of noradrenaline metabolizing enzymes to deviation supersensitivity are highlighted with emphasis upon the pioneering work of Professor de la Lande in this field.

Animals↗

PubMed1989

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. The nerve growth factor content of mesenteric arteries and aortas from 20-day-old SHR was significantly greater than that present in corresponding tissues from WKY rats. In contrast, the nerve growth factor content found in mesenteric arteries and aortas of adult SHR did not differ significantly from that found in the corresponding adult WKY rat tissues. Moreover, when the tissues were obtained from adult animals, nerve growth factor levels were substantially higher in mesenteric arteries compared with aortas, regardless of the rat strain. These results support the hypothesis that the greater nerve growth factor content of vascular tissues from young SHR is involved in the early increased sympathetic innervation of blood vessels in this animal model of hypertension.

Animals↗

PubMed1989

Hypernoradrenergic innervation: its relationship to functional and hyperplastic changes in the vasculature of the spontaneously hypertensive rat.

There is now compelling evidence indicating that there is a greater sympathetic innervation of blood vessels in the spontaneously hypertensive rat (SHR) when compared with the innervation of corresponding vessels in the normotensive genetic control rat (WKY). In selected vascular beds in the SHR, increased sympathetic innervation occurs immediately after birth and prior to the expression of hypertension in the animal. In contrast, the available evidence suggests that the sympathetic innervation of cardiac tissue in SHR and WKY are similar in young and adult rats. The functional significance of the enhanced sympathetic innervation of blood vessels in the SHR with regard to the development or maintenance of hypertension relates in two ways to the well-established phenomena of vascular smooth muscle cell hypertrophy and hyperplasia, which are thought to be the pathophysiological basis for the increased peripheral vascular resistance and elevated blood pressure in this animal model of hypertension. First, the enhanced innervation of blood vessels in the SHR leads to an augmented release of the vasoconstrictor transmitter noradrenaline (NA). The predicted consequences of this augmented release of NA upon vascular contraction are modulated by the presence of a larger number of sites for neuronal inactivation (i.e. reuptake sites) of NA by virtue of the presence of the increased innervation. Second, and of more significance, is the inter-relationship between hypernoradrenergic innervation and vascular smooth muscle hyperplasia, as the early appearance of such changes is a powerful indicator for the subsequent expression of hypertension in the SHR. In view of the substantial evidence that implicates vascular smooth muscle cells in regulating the degree of their sympathetic innervation and confirms the influence of sympathetic nerves upon vascular smooth muscle hyperplastic change, attention is drawn to the role of trophic factors in providing the setting for the development of hypertension in the SHR.

Animals↗

PubMed1988

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. After synthesis inhibition with alpha-methyl-p-tyrosine (300 mg/kg i.p.), the NE contents of hearts and mesenteric arteries decreased in a monoexponential fashion. The rates of decline of NE were similar for corresponding tissues from SHR and WKY rats. Cold stress, reported to selectively activate sympathetic discharge, did not influence the rates of decline of NE in mesenteric arteries of either SHR or WKY animals. In contrast, cold exposure dramatically accelerated the rate of decline of NE in cardiac tissue from both SHR and WKY rats. It is concluded that in mesenteric arteries from SHR rats there is a larger pool of NE with turnover characteristics not dissimilar from that prevailing in vessels from normotensive animals. The failure of cold stress to modify the rates of decline of NE in mesenteric and caudal arteries of SHR and WKY rats suggests that these arteries are under considerable sympathetic influence at ambient temperature. The results support the view that the hypernoradrenergic innervation found in SHR blood vessels, together with normal functioning of the sympathetic nervous system, may have the potential for producing a heightened peripheral vascular resistance in this model.

Animals↗

PubMed1988

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. The time course of enhanced NE content in caudal arteries and aortas from SHR followed the development of hypertension. In the spleen, NE content per gram of tissue was elevated in young SHR; however, in adult rats NE content was not significantly different between the two rat strains. Because spleens from WKY rats were substantially larger, total NE content per spleen was significantly greater in tissues from WKY rats. Cardiac contents of NE were similar in SHR and WKY rats at all ages examined. Adrenal epinephrine concentrations were similar in SHR and WKY rats, whereas NE content was elevated in the SHR at 46 and 81 days of age. The results of the present study demonstrate that the appearance of increased NE levels in some SHR tissues occurs before the development of hypertension in this model. If NE content is a valid index of sympathetic innervation, enhanced innervation may contribute to the vascular medial hypertrophy observed in young SHR and the elevation of blood pressure in these rats.

Animals↗

PubMed1987

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. The largest degree of sensitization was seen in the presence of the 2-methoxysteroids. Oestradiol and 2OHE2 did not increase responses of the aorta to (-)-noradrenaline, while slight potentiation of contraction was seen in the presence of 2MeOE3. The potentiating effect of 2OHE2 on contractile responses to (-)-adrenaline was abolished by prior treatment of the tissue with a COMT inhibitor (U-0521, 55 mumol/l). Conversely, pretreatment of the tissue with 2OHE2 prevented the augmented aortic contraction to (-)-adrenaline usually seen after inhibition of COMT. The non-additive nature of the sensitization seen after combined treatment with 2OHE2 and U-0521 was qualitatively similar to that seen following combined exposure to maximally effective concentrations of U-0521 and an inhibitor of extraneuronal uptake (hydrocortisone 100 mumol/l). Oestradiol and 2MeOE2 reduced the formation of both the 3H-O-methylated, 3H-deaminated and the 3H-O-methylated deaminated metabolites of 3H-(-)-adrenaline (0.15 mumol/l) during exposure of the aorta to the tritiated catecholamine.(ABSTRACT TRUNCATED AT 250 WORDS)

2-Methoxyestradiol↗

PubMed1987

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. Similar results were obtained with the addition of noradrenaline (200 mumol/l) and dopamine (120 mu/mol). Apparent Ki values obtained for the catecholamines and catechol oestrogens were within the same order of magnitude and varied from 30 mumol/l for dopamine and 2OHE2 to 183 mumol/l for 2OHE1. Oestradiol (E2) and 2-methoxyoestradiol (2MeOE2), i.e., oestrogens that do not possess a catechol moiety, exhibited only weak inhibitory effects on TH activity. At the highest concentration tested (1 mmol/l), they did not reduce enzyme activity below 58% of control values. Kinetic analysis revealed that these two oestrogens did not consistently affect either the Vmax of hydroxylation or the Km for DMPH4. It is concluded that catechol oestrogens inhibit TH activity with a potency comparable to noradrenaline and dopamine. This inhibition is by competition with the pterin cofactor. Oestrogens that to not possess a catechol moiety are not effective inhibitors of TH.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1987

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 maximum contraction to noradrenaline (NA), 5-hydroxytryptamine (5-HT) and KCl was markedly diminished in thoracic aortic rings (AR) from diabetic rats with no change in the EC50 of the agonists. There were no differences in the contractile properties of AR from diabetic rabbits to NA, 5-HT or KCl. Diabetes did not alter the responsiveness of AR from the rat to angiotensin II (AII). However, AR from diabetic rabbits displayed a decreased maximal contraction and an increased EC50 to AII. The magnitude of the acetylcholine-induced relaxation to precontracted AR was not different between diabetic and control rats and rabbits. The contractile responses of AR to NA, 5-HT and KCl were depressed in diabetic rats, regardless of the control tissue to which they were compared. The decrease in maximal contraction to NA, 5-HT and KCl seen in diabetic animals was prevented by insulin replacement. The results demonstrated that while both rats and rabbits exhibited a similar degree of hyperglycemia after treatment with a diabetogenic agent, aortic preparations from the rabbit are not affected in the same way as the aorta from the diabetic rat when exposed to NA, 5-HT and KCl. This feature may be related to the marked differences between the extent of sympathetic innervation of the aorta in the rabbit and rat. Furthermore, the decrease in maximal contraction in rat aorta was non-specific with respect to agonists since it could also be demonstrated with KCl. Therefore, it follows that the diabetic state may affect processes responsible for contraction beyond the level of receptor activation.

Acetylcholine↗

PubMed1987

Norepinephrine depletion and sensitivity changes in rat heart induced by pretreatment with reserpine.

Depletion of norepinephrine, sensitivity to isoproterenol and sensitivity to tyramine in rat atria were investigated after various doses and schedules of pretreatment of rats with reserpine. Virtually complete depletion of norepinephrine occurred in both right and left atria and ventricles after doses of 1.0 mg/kg/day of reserpine for one or more days of pretreatment. A smaller dose, 0.3 mg/kg/day, produced lesser depletion, and a larger dose, 2.5 mg/kg/day, caused severe central nervous system depression and high mortality. Chronic treatment (5 days or longer) with the 1.0-mg/kg/day dose produced supersensitivity of right atria to the chronotropic, but not inotropic, responses to isoproterenol. Chronic treatment with this dose for 7 days produced inotropic supersensitivity in left atria. Most of the schedules of pretreatment with reserpine depressed the maximum response to tyramine. However, the data indicate that the tyramine-releasable norepinephrine was not a consistent reflection of the total norepinephrine pool, even when depletion was very pronounced. The effects of depletion of cardiac stores of norepinephrine with reserpine in comparison with the effects of cardiac sympathectomy are discussed.

Animals↗

PubMed1986

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 0.91 mumol/l and 104 pmol g-1 min-1, respectively, when 2OHE2 was used as substrate; and 1.14 mumol/l and 188 pmol g-1 min-1 when 2OHE3 was used as substrate. The inhibitors of the extraneuronal uptake process (viz; phenoxybenzamine 33 mumol/l; normetanephrine, 46 mumol/l; and deoxycorticosterone acetate 27 mumol/l) failed to inhibit the O-methylation of either 2OHE2 (3.4 mumol/l) or 2OHE3 (3.4 mumol/l) in intact segments of the rabbit thoracic aorta. (-)-Isoprenaline (40 mumol/l) abolished the O-methylation of 2OHE2 (3.4 mumol/l) and markedly reduced that of 2OHE3 (3.4 mumol/l). Pretreatment of tissues with phenoxybenzamine (33 mumol/l) partially restored the O-methylation of 2OHE2 and 2OHE3 in the presence of (-)-isoprenaline (40 mumol/l). The O-methylation of 2OHE2 (5 mumol/l) was significantly reduced in segments of aorta in which the endothelium was removed. The latter reduction could not be attributed to damage to components of the vessel media. The O-methylation of 2OHE2 and (-)-isoprenaline by subcellular fractions of the rabbit aorta also was examined. Both the microsomal and cytosolic fractions were shown to O-methylate 2OHE2 and (-)-isoprenaline, providing evidence for the existence of membrane-bound and soluble forms of COMT in the rabbit aorta. The O-methylation of 2OHE2 by cytosolic and microsomal fractions of the aorta was determined and compared to that of (-)-isoprenaline. The kinetic constants for the O-methylation of 2OHE2 by cytosolic (Km: 0.27 mumol/l; V max: 112 pmol g-1 min-1) and microsomal (Km: 0.15 mumol/l; Vmax: 161 pmol g-1 min-1) fractions were similar. In contrast, the kinetic constants for the O-methylation of isoprenaline by cytosolic (Km: 121 mumol/l; Vmax: 174 pmol g-1 min-1) and membranal (Km: 0.91 mumol/l; Vmax: 105 pmol g-1 min-1) fractions were very different. It is concluded that catechol oestrogens are excellent substrates for catechol-O-methyltransferase (COMT) in the rabbit aorta. Their O-methylation can occur in endothelial structures as well as in the smooth muscle-containing medial sections of the vessel.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1986

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. However, O-methylation was also reduced (81%) in rabbit aorta that had been surgically denervated before exposure to 6-hydroxydopamine. Furthermore, the O-methylation of 2-hydroxyoestradiol (20 microM, 15 min) by partially purified soluble catechol-O-methyltransferase was inhibited by 6-hydroxydopamine (400 mg litre-1) by 95% and 51% in the absence and presence of antioxidant, respectively. These results suggest that the inhibition of catechol-O-methyltransferase by 6-hydroxydopamine reported for the purified enzyme, applies to the intact tissue and that the inhibition is dependent on oxidation of the 6-hydroxydopamine. Subsequent experiments using dialysis techniques demonstrated that the inhibition of soluble catechol-O-methyltransferase by 6-hydroxydopamine was irreversible in part, but the degree of irreversibility was influenced by pH and by the extent of in-vitro oxidation of 6-hydroxydopamine.

Animals↗

PubMed1986

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. In addition, histological staining and electron-microscopic analysis indicated the presence of endothelial cells in tissues not subjected to mechanical abrasion and the absence of endothelial cells in tissues subjected to abrasion. Moreover, ultrastructural analysis revealed that the influence of abrasion was limited to the luminal side of the internal elastic lamina. The removal of endothelial cells from the isolated rabbit aorta was associated with a decrease (approximately 30%) in the O-methylation of the isomers of isoproterenol. Inhibition of the extraneuronal uptake process with deoxycorticosterone (DOCA) produced a predicted decrease in the O-methylation of isoproterenol in tissues with the endothelium intact. In the absence of endothelial cells, the inhibition of the O-methylation of isoproterenol mediated by DOCA persisted. The results suggest that the O-methylation of catecholamines can occur in both medial and endothelial structures in this blood vessel and support the results of immunohistochemical studies that suggested a presence of catechol-O-methyltransferase in vascular endothelial structures. In addition, the findings exclude a possibility that the extraneuronal uptake process for catecholamines resides exclusively in endothelial structures. The functional consequences of vascular endothelial cell O-methylation are discussed.

Acetylcholine↗

PubMed1986

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. The results suggested that the small vessels offer a significant contribution to the mechanical resistance to perfusion in the mesenteric vasculature and are important in the neurogenic responses of this preparation. In contrast, the arterioles in the arcade supplying the jejunum play only a minor role in the responses of the mesenteric vascular bed to intraluminally injected vasoactive substances. It was found that mesenteric preparations from SHR rats responded more forcefully to intraluminally administered norepinephrine and potassium, regardless of whether the intestine was absent or present. Similarly, the responses of mesenteric preparations to electrical nerve stimulation were greater in preparations from SHR rats, particularly when the intestine was present. It is concluded that the perfused mesenteric vasculature from SHR rats is more responsive to vasoactive substances and nerve stimulation and that this feature is not exclusively dependent upon a contribution to contraction by the arterioles supplying the jejunum.

Animals↗

PubMed1985

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 4.7 mumol X 1(-1). There was marked preference for the O-methylation of (-)-isoprenaline rather than (+)-isoprenaline at low (less than 0.94 mumol X 1(-1) substrate concentrations. In contrast, at concentrations equal to or greater than 9.4 mumol X 1(-1) the rates of O-methylation of (-)- and (+)-isoprenaline were similar. Phenoxybenzamine (30 mumol X 1(-1) inhibited but did not abolish the O-methylation of both (-)- and (+)-isoprenaline when the isomers were present in a concentration range of 0.24 mumol X 1(-1) to 9.4 mumol X 1(-1). Phenoxybenzamine did not significantly influence the O-methylation of either (-)- or (+)-isoprenaline when the isomers were present at a concentration of 24 mumol X 1(-1). Deoxycorticosterone acetate (DOCA) produced an equipotent and marked inhibition of the O-methylation of both (-)- and (+)-isoprenaline at a low (0.24 mumol X 1(-1) substrate concentration. When higher substrate concentrations were used, there was a significantly greater resistance to the inhibition of O-methylation of (-)-isoprenaline than was the case for (+)-isoprenaline. At a concentration of 9.4 mumol X 1(-1), the steroid failed to inhibit the O-methylation of (-)-isoprenaline but was effective in inhibiting the O-methylation of (+)-isoprenaline.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1985

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 3.0) combined with 30-70% acetonitrile. A biological application of this procedure includes the investigation of the 0-methylation of catechol estrogens by vascular tissue. In the present study, the 0-methylation of 2-hydroxyestradiol by rabbit aorta has been examined. The 0-methylation in segments of thoracic aorta was significantly less than that in abdominal aortic segments, but was reproducible along the length of the thoracic aorta.

Animals↗

PubMed1985

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. A modest elevation of NE [but not epinephrine (E)] was observed in adrenal glands from SHR rats. The NE contents of salivary glands from SHR and WKY rats were indistinguishable from each other. The results suggest that there may exist a generalized increase in NE contents in the peripheral vasculature of SHR rats. Furthermore, this increase is also present in the vasa deferentia, but not the salivary gland. The results draw attention to altered concentrations of NE in vascular and selected nonvascular tissues in the SHR.

Adrenal Glands↗

PubMed1985

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. Segments of rabbit thoracic aorta incubated with [methyl-3H]-S-adenosyl-l-methionine and isoproterenol generate [3H]methoxy-isoproterenol. The formation of [3H]methoxy-isoproterenol from [methyl-3H]-S-adenosyl-l-methionine was proportional to the isoproterenol concentrations in the range of 0.1 to 1.0 microM. There was a marked preference for the O-methylation of the (+)- rather than the (-)-isomer of isoproterenol. The O-methylation of isoproterenol in the presence of [methyl-3H]-S-adenosyl-l-methionine was stimulated as much as 8-fold by the removal of calcium ions from the incubation solutions. In contrast, the O-methylation of (+)-[3H]isoproterenol by endogenous, intracellular S-adenosyl-l-methionine was only slightly inhibited by the removal of calcium ions from incubation solutions. The formation of [3H]methoxy-isoproterenol from [methyl-3H]-S-adenosyl-l-methionine and isoproterenol was not inhibited by pretreatment of tissues with phenoxybenzamine (32 microM) or treatment with metanephrine (27 mumol 1(-1] or deoxycorticosterone acetate (27 microM), i.e., drug treatments that inhibit the extraneuronal uptake and O-methylation of [3H]-isoproterenol by endogenous intracellular S-adenosyl-l-methionine. The results of this study provide evidence for a nonintracellular, cell-associated site of O-methylation of isoproterenol in the rabbit aorta.

Animals↗