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Biomedical subjects

F P Field

Publications and source records attributed to F P Field.

32 records · Page 2Linked to original sources
PubMed1980

Effect of isomers of octopamine on in vitro reactivity of vascular smooth muscle of rats.

The vascular reactivity to DL-ortho-, meta-, and para-octopamine was tested in vitro in aortic smooth muscle of the rat. When reactivities were compared on a molar basis with L-phenylephrine, an alpha-adrenergic agonist, the potencies of the three isomers were: 0.7500, 0.0075 and 0.0038 times that of phenylephrine for the m-, p- and o-isomer, respectively, Thus, of the three isomers, DL-m-octopamine had the greatest alpha-adrenergic activity in vitro as it did in vivo in earlier studies. Additional studies showed L-phenylephrine to induce about one-third the vascular response induced by L-norepinephrine.

Animals↗
PubMed1979

Use of an iodide-specific electrode to study lactoperoxidase-catalyzed iodination of l-tyrosine.

An in vitro method employing an iodide-specific electrode for monitoring lactoperoxidase-catalyzed iodination is described. The method utilized lactoperoxidase, potassium iodide, and a glucose--glucose oxidase system for the generation of hydrogen peroxide and l-tyrosine. As iodination of l-tyrosine proceeded, the free iodide concentration in solution decreased and was monitored by an iodide-specific electrode. The iodide electrode was reliable when compared to a 131I-method for measuring free iodide changes in solution. Increasing concentrations of resorcinol, a well-known inhibitor of thyroid peroxidase-catalyzed iodination, in the reaction mixture resulted in graded inhibition of the initial rate of lactoperoxidase-catalyzed l-tyrosine iodination. This in vitro system can be used to assess inhibitory activity of various antithyroid substances.

Catalysis↗
PubMed1979

Effect of clonidine on the contractile responsiveness of aortic smooth muscle to norepinephrine.

A length-tension relationship was established for aortic smooth muscle of rats by means of membrane depolarization with KCl. Maximal tension was developed by aortic rings when the preload initial tension was 8--9 g. Two aortic rings (4 mm thick) were removed from segments of the aorta cut 1.5 (upper) and 2.4 cm (lower) below the aortic arch. Upper rings appeared to develop a greater tension than lower rings during depolarization with KCl. However, in spite of this quantitative difference between rings from upper and lower segments of the aorta, there were no qualitative differences observed. Clonidine, an antihypertensive agent, induced a contraction in aortic smooth muscle, apparently by way of alpha-adrenoreceptor stimulation. Clonidine also attenuated significantly the development of active tension by norepinephrine but did not inhibit significantly the development of active tension following membrane depolarization with KCl. This suggests that there is a partial antagonism between norepinephrine and clonidine, presumably at the site of the receptors on smooth muscle, and that clonidine does not interfere with the contractile mechanism, per se.

Animals↗
PubMed1978

beta-Cyclodextrin as an aid to peritoneal dialysis. Renal toxicity of beta-cyclodextrin in the rat.

A peritoneal dialysate containing beta-cyclodextrin has been shown to accelerate the removal of intravenously administered phenobarbital in rats. It was found that high concentrations of beta-cyclodextrin were toxic to the animals in the single exchange technique employed. The renal toxicity was estimated by measuring blood urea nitrogen values in the rats following oral and intraperitoneal administration of the cyclic amylose.

Amylose↗
PubMed1977

Effect of chronic exposure to cold on some responses to catecholamines.

An objective of these studies was to test the responsiveness of cold-adapted (8 wk, 5 degrees C) rats to a specific beta-adrenergic agonist. Twenty-four hours after removal from cold, increases in tail skin temperature (Tsk) and colonic temperature (Tco) were measured for 2 h in air at 25 degrees C following subcutaneous (sc) administration of 28, 70 or 136 mug d,l-isoproterenol sulfate dihydrate/kg body wt to restrained male rats. Cold-adapted rats responded to each dose of isoproterenol with greater increases in Tsk than controls. Tco of both groups increased at the two highest doses, but cold-adapted rats showed a greater rise. Thus, cold-adapted rats showed greater metabolic (Tco) and vascular (Tsk) responsiveness to the beta-adrenergic agonist, isoproterenol, than nonadapted controls. No effect of the alpha-adrenergic agonist, phenylephrine (50 or 100 mug/kg body weight, sc), was observed on Tco or Tsk. A second objective was to study the tension developed by aortic smooth muscle rings of cold-adapted and control rats both during stimulation of alpha-adrenergic receptors by norepinephrine and membrane depolarization by KCl. Adaptation to cold air appeared to suppress alpha-adrenergic responsiveness in aortic segments but did not alter responsiveness to KCl. This suggests an unchanged contractile mechanism in aortic rings of cold-adapted rats and a reduced responsiveness either at the level of the alpha-receptor or at a site immediately beyond.

Adaptation, Physiological↗
PubMed1976

Effect of hypothyroidism on responsiveness to beta-adrenergic stimulation.

Chronic administration of aminotriazole (0.5 g/kg food) to rats was accompanied by a reduced responsiveness to acute administration of the beta-adrenergic agonist, l-isoproterenol (50-100 mug/kg, sc). The responses tested included water intake, change in heart rate in the anesthetized and unanesthetized rat, change in mean blood pressure, and change in blood glucose concentration. In addition, the increase in tail skin temperature accompanying administration of epinephrine (1 mg/kg, sc) was significantly reduced in the hypothyroid group. Administration of l-thyroxine (25 mug/kg per day, ip) to aminotriazole-treated rats prevented the reduction in responsiveness to beta-adrenergic stimulation. Thus, an interaction appears to exist between the level of thyroid activity and responsiveness to beta-adrenergic agonists in rats.

Adrenergic beta-Agonists↗
PubMed1976

Effect of orange juice consumption on urinary pH.

The effect of orange juice consumption on urinary pH was studied in seven adult male subjects, each of whom served as his own control. The diet of the subjects was standardized during the work-day. The effects of two regimens of orange juice were studied: 1500 ml divided into five 300-ml portions during the day, and 300 ml once in the morning. Urine was collected, its pH recorded, and titrated with HCl to determine the mEq of base excreted per unit time. The consumption of 300 ml of orange juice did not significantly alter urinary pH. The consumption of 1500 of orange juice changed the urinary pH by an average of one pH unit. A change of this magnitude could cause clinically significant variation in the overall excretion pattern of acidic or basic drugs.

Adult↗
PubMed1975

Reduced beta-adrenergic responsiveness in hypothyroid rats.

The beta-adrenergic agonist isoproterenol (100-200 mug/kg body wt sc) induces vasodilation and an increase in skin temperature of the tail of the euthyroid but not the hypothyroid rat. Administration of thyroxine (25 mug/kg body wt per day) to rats made hypothyroid by means of the antithyroid drug aminotriazole (0.5 g/kg of foof) returned responsiveness to control level. Reduced responsiveness to isoproterenol occurred between 1 and 5 wk of treatment with aminotriazole. Increase in tail skin temperature induced in euthyroid rats by isoproterenol was blocked by administration of propranolol (7.5 mg/kg ip). Other beta-adrenergic-induced responses, including increased water intake and increased plasma glucose concentration, also were reduced in hypothyroid rats and returned to control level by administration of thyroxine. Thus, hypothyroidism appears to be accompanied by a reduced beta-adrenergic responsiveness as assessed by changes in tail skin temperature, water intake, and plasma glucose concentration after injection of isoproterenol. Since administration of thyroxine returned the responses of hypothyroid rats to control levels, it appears that thyroxine is important in maintaining beta-adrenergic responsiveness under these conditions.

Animals↗
PubMedDate not supplied

Vascular reactivity in the spontaneously hypertensive rat. Effect of high pressure stress and extracellular calcium.

The role of extracellular calcium and high blood pressure stress in altered vascular adrenergic responsiveness in rings of femoral artery from spontaneously hypertensive rats (SHR) was investigated. A model in which partial ligation of the external iliac artery prevents the increase in blood pressure to the ipsilateral femoral artery was used to assess the effect of the increase in pressure stress on these alterations. Age-matched (5-week-old) male Wistar-Kyoto rats (WKY) and SHR were used in the study. Partial ligation was performed before a substantial increase in blood pressure occurred (6 weeks of age), and studies on vascular reactivity were carried out at 10 to 12 weeks of age when the SHR were considered hypertensive (indirect systolic blood pressure greater than 150 mm Hg). Maximal contractility of rings of unprotected femoral artery from the SHR in response to KCl in either a normal (2.5 mM) or low (0.25 mM) calcium Krebs solution was significantly greater (p less than 0.05) than was that of protected vessels from the SHR or protected and unprotected vessels from the WKY; however, no difference in the sensitivity to KCl was observed. Isoproterenol-induced relaxation was significantly attenuated in rings of vascular smooth muscle from unprotected femoral arteries of the SHR (p less than 0.05), while the responses of protected vessels from the SHR were similar to controls. Equilibration of vascular smooth muscle in a low calcium Krebs solution resulted in an increase in beta-adrenergic mediated relaxation in all groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗