Thromboxane A2 and Prostacyclin Release in Bleeding Time Blood during Primary Haemostasis in Healthy Individuals

ABSTRACT It is generally believed that prostacyclin (PGI₂) generation is greatly stimulated when blood vessels are injured, even by minor trauma, such as venepuncture. The Simplate technique for measuring skin bleeding time was adapted to quantify by radioimmunoassay PGI₂ and thromboxane A₂ (TXA₂) in the emerging blood, as the stable degradation products 6-keto-prostaglandin F_1α (6-keto-PGF_1α) and thromboxane B₂ (TXB₂), both of which were measured in venous plasma as well as in serum (clotted at 37°C for 1 h). During bleeding, when platelets aggregate to occlude the injured vessels, the median TXB₂ level in the emerging bleeding time blood was 1.7 ng/ml. The median TXB₂ level in plasma was < 1 ng/ml and in serum 275 ng/ml. The levels of immunoreactive 6-keto-PGF_1α were always below determination limit in bleeding time blood (0.2 ng/ml) and in plasma (0.1 ng/ml), whereas in serum the levels ranged between 0.26 and 0.47 ng/ml. The fact that enhanced PGI₂ production in primary haemostasis in skin incisions could not be demonstrated calls for further investigations of possible PGI₂ production with more sensitive assays or in injured large vessels.     

Response of plasma norepinephrine and epinephrine to dynamic exercise in patients with congestive heart failure

The activity of the sympathetic nervous system is increased at rest in patients with congestive heart failure. To determine whether this augmentation is carried over during dynamic upright exercise, 14 patients with congestive heart failure were stressed maximally during upright bicycle ergometry. Plasma norepinephrine and epinephrine levels were measured in the basal upright (sitting) posture before and during maximal exercise. The results were compared with those in six healthy control subjects before and during maximal exercise. Plasma norepinephrine increased during exercise from a mean (± standard error of the mean) of 650 ± 95 to 1,721 ± pg/ml in the group with heart failure. This increase was significantly less (p < 0.001) than that in the control group (from 318 ± 36 to 3,230 ± 418 pg/ml). However, for equivalent levels of total body oxygen consumption (V?O₂), the group with heart failure had higher levels of plasma norepinephrine than the control group. Plasma epinephrine was similar in the two groups in the basal upright position (92 ±18 and 92 ± 26 pg/ml), but it increased more during exercise in the normal subjects (743 ± 210 pg/ml) than in the group with heart failure (167 ± 67 pg/ml) (p < 0.001). The percent increase in norepinephrine correlated with the percent change in V?O₂ in the group with heart failure (r = 0.62, p < 0.02), but the percent change in epinephrine did not.There is, therefore, a disturbance in the sympathetic nervous system during exercise in patients with congestive heart failure. Although norepinephrine increases in such patients to a greater extent than in normal subjects at lower levels of exercise, the extremely high levels of norepinephrine and epinephrine generated by normal subjects during maximal upright exercise do not occur in patients with heart failure.     

Periovulatory enhancement of spontaneous prolactin secretion in normal women

The role of endogenous estrogen in the regulation of prolactin secretion in man is controversial. To study this question further, spontaneous prolactin patterns were determined over 5 hr in 10 normal women during the early follicular and again during the periovulatory phases of the menstrual cycle. Steroid determinations revealed significant elevations in mean ±1 SE E₁ (113 ± 20 versus 55 ± 5 pg/ml), E₂ (144 ± 47 versus 48 ± 9 pg/ml), and 17-OHP (1,301 ± 266 versus 639 ± 46 pg/ml) during the periovulatory compared to the early follicular phase period. Each subject demonstrated increased mean plasma prolactin concentration during the higher estrogen state. Mean prolactin concentration (calculated from the individual mean values of samples obtained at 15 min intervals for 5 hr) during the midcycle study period was 10.7 ± 1.0 ng/ml compared to the early follicular phase period of 8.1 ± 1.0 ng/ml (p < 0.0005). The mean percent increment in plasma prolactin during the periovulatory period was 39% with a range of 9 to 117%. There was no correlation between mean prolactin and serum E₁, E₂, P, or 17-OHP levels during either study period. However, the incremental change in prolactin showed a positive correlation with the incremental increase in E₂ (correlation coefficient, r = 0.66, p < 0.05). In contrast, no significant correlation was present between mean incremental change in prolactin and E₁, P, or 17-OHP. These data suggest that enhanced cyclic estrogen secretion during the periovulatory phase of the menstrual cycle is associated with significantly increased serum prolactin concentrations.     

Platelet activation in patients with the Raynaud phenomenon

Background: The Raynaud phenomenon (RP) is an exaggerated and reversible vasospasm of small arteries triggered by cold or emotional stress. Primary RP (PRP) term is used when the underlying condition is unknown. An altered regulation in vascular tone and/or release of soluble mediators from activated platelets plays a role in PRP through an increased oxidative stress. We assessed platelet activation and oxidative stress in patients with PRP by measuring platelet PAC‐1, an index of glycoprotein (Gp) IIb/IIIa receptor activation, thromboxane A₂ (TXA₂), an index of platelet activation and 8‐epi‐prostaglandin F_2α (8‐epi‐PGF_2α), a marker of endogenous in vivo peroxidation. Methods: Eighteen asymptomatic patients with PRP (age 41.37 ± 16.94 years; 17 women, 1 man) and 18 healthy subjects (age of 35.11 ± 13.16 years; 16 women, 2 men) were studied. PAC‐1 was analysed by flow cytometry while circulating TXB₂, a stable metabolite of TXA₂ and 8‐epi‐PGF_2α levels were assessed by ELISA kit. Results: Our results show a significant platelet activation in PRP patients as indicated by increased PAC‐1 expression (65.29 ± 15.24%; P < 0.001), TXB₂ (1477.83 ± 454.04 pg/mL; P= 0.003) and 8‐epi‐PGF_2α circulating levels (42.50 ± 14.14 ng/mL; P < 0.001). An inverse correlation between the degree of PAC‐1 expression and TXB₂ levels (r=?0.527; P= 0.02) was also found in PRP patients, suggesting that downregulation of GpIIb/IIIa receptor expression may occur during thrombocytopoiesis, as a consequence of the chronic exposure to increased TXB₂ concentration. Conclusions: Our study for the first time shows a marked activation of GpIIb/IIIa receptor in asymptomatic patients with PRP and supports antiplatelet therapy in PRP patients.     

Arterial and coronary sinus catecholamines in the course of spontaneous coronary artery spasm

We studied plasma catecholamine levels in 10 patients with frequent spontaneous episodes of coronary artery spasm to evaluate the role of the sympathetic nervous system. Peripheral venous norepinephrine in supine and upright postures, urinary excretion of catecholamines, and functional testing of the sympathetic nervous system did not differ from the same measurements in control subjects. Arterial and coronary sinus levels of norepinephrine and epinephrine drawn early in ischemia were not elevated over baseline; coronary sinus norepinephrine levels were higher than those in arterial samples and rose from 315 ± 32 (pg/ml ± SE) at the onset of ST elevation to 490 ± 49 pg/ml late in ischemia (p < 0.05). Plasma epinephrine levels, higher in arterial than coronary sinus samples, also rose significantly only late in ischemia, from 44 ± 14 pg/ml to 148 ± 35 pg/ml (p < 0.05) in arterial blood and from 33 ± 10 pg/ml to 108 ± 29 pg/ml in coronary sinus samples (p < 0.05). Generalized sympathetic nervous system activation is not likely to be the sole cause of coronary artery spasm.     

Effect of angiotensin II infusion on a prostaglandin I2-metabolite and on left ventricular function

Summary Angiotensin Il's influence on circulating levels of prostaglandin I₂ metabolite 6-keto-PGF_1-alpha were determined during a pharmacological stress test of left ventricular function in 10 control subjects and 5 patients with coronary artery disease. Angiotensin II infusion (1.5±0.34 g/min) led to a significant increase of mean arterial blood pressure in both study groups (p<0.001). Heart rate decreased in control subjects (p<0.01) whereas in patients with coronary artery disease no significant change occurred. Global left ventricular ejection fraction determined by gated blood pool scanning decreased significantly in both study groups (p<0.05). The lack of reflex bradycardia in patients with coronary artery disease may be due to a compensatory increased sympathetic tone, prohibiting a more pronounced decline in ejection fraction.6-keto-PGF_1-alpha levels could be measured only in 6 of 15 persons. In the others they were below the limit of detection of the assay (70 pg/ml). During angiotensin II infusion 6-keto-PGF_1-alpha increased significantly and could be determined in all persons. Patients with coronary artery disease reached slightly higher 6-keto-PGF_1-alpha levels than controls (119±19 pg/ml versus 91.5±7 pg/ml; n.s.). Thus although angiotensin II infusion leads to vasoconstriction and increases peripheral resistance it also stimulates the production of vasodilating prostaglandins which may play a role in preserving microcirulation.     

Cardiovascular effects of transdermal nicotine in mildly hypertensive smokers

Smoking potentiates the enhanced cardiovascular risk of hypertensive patients. Although nicotine replacement therapy is safe when used by healthy individuals to quit smoking, there is no evidence that nicotine replacement therapy is safe in hypertensive smokers. In this crossover, single-blinded, placebo-controlled study, we compared for 4 h the acute effects of transdermal nicotine on the mean arterial pressure (MAP) and heart rate (HR) of mildly hypertensive smokers treated with hydrochlorothiazide with the responses in normotensive smokers and nonsmokers monitored with Finapres and ambulatory blood pressure systems. The plasma concentrations of thromboxane B₂ (TXB₂, the stable breakdown product of TXA₂) were also measured by ELISA to assess whether transdermal nicotine acutely affects TXA₂ production. The use of 21-mg nicotine patches increased the MAP and HR in nonsmokers (from 94 ± 4 mm Hg and 69 ± 3 beats/min to 117 ± 7 mm Hg and 83 ± 3 beats/min, respectively; P < .05) as well as the MAP in normotensive smokers (from 83 ± 4 to 106 ± 7 mm Hg; P < .05). However, MAP and HR remained unaltered in hypertensive smokers after transdermal nicotine. Higher basal TXB₂ levels were observed in hypertensive smokers compared with normotensive smokers and nonsmokers (2019 ± 402 v 670 ± 167 and 556 ± 68 pg/mL, respectively; P < .05). Transdermal nicotine increased the TXB₂ levels only in nonsmokers (P < .05). These data indicate that the use of transdermal nicotine in mildly hypertensive smokers is probably safe. Further studies involving other classes of hypertensive patients are warranted.     

Effect of nitrates on left ventricular size and function during exercise: Comparison of sublingual nitroglycerin and nitroglycerin paste

To compare the effects of sublingual nitroglycerin and nitroglycerin paste on left ventricular size and performance during supine bicycle exercise, equilibrium radionuclide angiography was performed in 36 persons classified into two groups of normal subjects and two groups of patients with angiographically proved coronary heart disease. Each group underwent a control exercise study, and then one group of normal subjects and one group of patients were restudied after the administration of 0.6 mg of nitroglycerin or 2 inches (5 cm) of nitroglycerin paste (but not both). Data were collected at rest and at peak exercise.In normal subjects exercise resulted in increased ejection fraction, decreased end-systolic volume and little change in end-diastolic volume. After either drug, volumes at rest markedly decreased, and during exercise, ejection fraction increased to levels comparable with pre-drug levels. After nitroglycerin paste the reduction in volume seen at rest persisted during exercise, but after sublingual nitroglycerin end-diastolic volume increased during exercise (88 ± 43 to 113 ± 30 ml [mean ± standard deviation]; p < 0.01). Peak exercise end-diastolic volume after nitroglycerin was still lower than that before nitroglycerin (113 ± 30 versus 120 ± 28 ml, p < 0.05).In patients with coronary disease, ejection fraction did not change during exercise, but both end-diastolic and end-systolic volumes increased. After either drug ejection fraction at rest was unchanged, although ventricular volumes were markedly lower (p < 0.05). Ejection fraction increased with exercise in both groups with coronary disease after either drug. After sublingual nitroglycerin, volumes increased during exercise although the peak exercise end-diastolic volume was still lower than the control value (113 ± 31 versus 145 ± 34 ml; p < 0.01). After paste administration, end-diastolic volume did not change during exercise, and end-systolic volume decreased (41 ± 20 to 36 ± 22 ml; p < 0.05).Thus, sublingual nitroglycerin and nitroglycerin paste improved left ventricular function during exercise. The effect of paste on end-diastolic volume appeared sustained, whereas that of sublingual nitroglycerin was transient, confirming the hypothesis that reduction in end-diastolic volume and, by implication, left ventricular wall tension, is a major mechanism of nitrate action.     

Alterations in left ventricular volumes and ejection fraction at rest and during exercise in patients with aortic regurgitation

This study was performed (1) to determine the changes in left ventricular volumes during exercise in patients with aortic regurgitation, and (2) to evaluate the importance of these alterations in characterizing left ventricular function in these patients. In 15 normal subjects (Group I) and in 17 patients with aortic regurgitation (Group II), left ventricular end-diastolic volume index, end-systolic volume index, ejection fraction and the ratio of peak systolic blood pressure to end-systolic volume index were measured at rest and during supine exercise. The patients with aortic regurgitation were classified into two groups on the basis of symptoms and chest radiographs: Group IIA, minimal or no symptoms, no cardiomegaly or pulmonary venous congestion; Group IIB, definite symptoms, with cardiomegaly and pulmonary venous congestion. Patients with aortic regurgitation had greater left ventricular end-diastolic and end-systolic volume indexes at rest and during exercise (p <0.05) than did normal subjects. During exercise, left ventricular end-diastolic volume index increased in normal subjects (53 ± 13 ml/m² [mean ± standard deviation] at rest, 67 ± 18 ml/m² during exercise, p <0.01), demonstrated a heterogeneous response in patients in Group IIA and increased in patients in Group IIB (180 ± 96 ml/m² at rest, 209 ± 102 ml/m² during exercise, p <0.05). During exercise, left ventricular end-systolic volume index decreased in normal subjects (18 ± 5 ml/m² at rest, $\text{15}\text{\$}\text{?}\text{6}$ ml/m² with exercise, p <0.01), increased in patients in Group IIB (82 ± 60 ml/m² at rest, 118 ± 93 ml/m² during exercise, p <0.05), and showed a variable response in those in Group IIA. At rest, left ventricular ejection fraction was similar in the three groups, but during exercise it increased in Group I (0.71 ± 0.07 at rest, 0.82 ± 0.07 with exercise, p <0.001), was unchanged in Group IIA and decreased in Group IIB (0.59 ± 0.15 at rest, 0.50 ± 0.16 during exercise, p <0.05). During exercise, there was an inverse relation between changes in left ventricular ejection fraction and endsystolic volume, but no relation between changes in end-diastolic volume and ejection fraction. Changes in the systolic pressure-volume ratio provided no more information than changes in end-systolic volume alone. Thus, abnormal alterations in left ventricular volumes occur during exercise in patients with aortic regurgitation and may be helpful in the further characterization of left ventricular performance in these patients.     

Binding and inactivation of prostacyclin (PGI2) by human erythrocytes

Summary . Prostacyclin (PGI₂), the most potent inhibitor of platelet aggregation known, is rapidly hydrolysed in aqueous solution at neutral pH to its inactive derivative 6-keto-PGF_1α. In previous studies (Willems et al, 1979), we found that PGI₂ is stabilized by plasma. Yet, PGI₂ is rapidly inactivated in vivo. These findings prompted us to study the fate of PGI₂ when incubated in whole human blood. After 20 min of incubation (at 37°C, pH 7·8), 29 ± 10% of the amount of PGI₂, added to whole blood, remained in the supernatant plasma whereas, under the same conditions, 80 ± 3% and 86 ± 2% were recovered when PGI₂ was added to platelet-rich plasma or cell-free plasma, respectively. When PGI₂ was incubated with washed erythrocytes resuspended in plasma, 20 ± 15% of the added PGI₂ remained in the supernatant after 10 min of incubation. These findings indicate that PGI₂, when incubated with whole blood, is preferentially bound to erythrocytes. To study the kinetics of binding in more detail, [³H]PGI₂ was incubated with washed erythrocytes resuspended in plasma. The binding was time- and concentration-dependent. The observed binding of label represented binding of [³H]PGI₂, because (1) acid-treated label did not bind to erythrocytes; (2) no substantial binding of [³H]6-keto-PGF_1α occurred, and (3) changes in the specific activity of the PGI₂ preparation did not alter the binding percentage of labelled PGI₂. The binding of [³H]PGI₂ was not influenced by PGE₁ or 6-keto-PGF_1α. Repeated incubations of erythrocytes with PGI₂ revealed that PGI₂ was rapidly degraded into a biologically inactive non-binding substance, presumably 6-keto-PGF_1α. Binding and metabolism of PGI₂ by erythrocytes may explain the apparent instability of PGI₂ in whole blood and provides an explanation for the rapid loss of the biological effects of PGI₂ on termination of the infusion.     

Very-low-dose twice-daily aspirin maintains platelet inhibition and improves haemostasis during dual-antiplatelet therapy for acute coronary syndrome

Higher aspirin doses may be inferior in ticagrelor-treated acute coronary syndrome (ACS) patients and reducing bleeding risk whilst maintaining antithrombotic benefits could improve outcomes. We characterized the pharmacodynamics of a novel dual-antiplatelet-therapy regimen consisting of very-low-dose twice-daily (BD) aspirin with standard-dose ticagrelor. A total of 20 ticagrelor-treated ACS patients entered a randomized crossover to take aspirin 20 mg BD (12-hourly) during one 14-day period and 75 mg once-daily (OD) in the other. After 14 days of treatment, serum thromboxane (TX)B₂ and light-transmittance aggregometry were assessed pre- and 2 h post-morning-dose, bleeding time was measured post-dose, and TXA₂ and prostacyclin stable metabolites were measured in urine collected 2 h post-morning-dose. Data are expressed as mean ± SD. After 14 days treatment, serum TXB₂ levels were significantly greater 2 h post-dosing with aspirin 20 mg BD vs. 75 mg OD (3.0 ± 3.6 ng/mL vs. 0.8 ± 1.9 ng/mL; p = 0.018) whereas pre-dosing levels were not significantly different (3.5 ± 4.1 ng/mL vs. 2.5 ± 3.1 ng/mL, p = 0.23). 1-mmol/L arachidonic acid-induced platelet aggregation was similarly inhibited by both regimens pre-dose (8.5 ± 14.3% vs. 5.1 ± 3.6%, p = 0.24) and post-dose (8.7 ± 14.2% vs. 6.6 ± 5.3%; p = 0.41). Post-dose bleeding time was shorter with 20 mg BD (680 ± 306 s vs. 834 ± 386 s, p = 0.02). Urinary prostacyclin and TX metabolite excretion were not significantly different. In conclusion, compared to aspirin 75 mg OD, aspirin 20 mg BD provided consistent inhibition of platelet TXA₂ release and aggregation, and improved post-dose hemostasis, in ticagrelor-treated ACS patients. Further studies are warranted to assess whether this regimen improves the balance of clinical efficacy and safety.     

Hypertriglyceridemia and hypoalphalipoproteinemia in azoospermic and oligospermic young men: Relationships of endogenous testosterone to triglyceride and high density lipoprotein cholesterol metabolism

Based upon the hypothesis that endogenous testosterone plays a significant role in triglyceride and high density lipoprotein cholesterol metabolism, the specific aim of this study in 9 azoospermic and 10 oligospermic subjects (compared to 20 fertile men) was to examine potential relationships between endogenous testosterone, luteinizing hormone, follicle stimulating hormone, lipids-lipoproteins, and lipoprotein lipases. The azoospermic and oligospermic men had much higher fasting plasma triglyceride levels (mean ± SD; 479 ± 258, 295 ± 119) than did normal controls (105 ± 31 mg/dl, p < 0.001, p < 0.001). The azoospermic and oligospermic subjects also had much lower mean high density lipoprotein cholesterol levels (C-HDL) than normals (27 ± 8 and 29 ± 7 versus 44 ± 7 mg/dl, p < 0.001, p < 0.001). Very low density lipoprotein's (VLDL) in vitro potency to activate lipoprotein lipase (U/mg of VLDL protein) was about one-third normal in the azoospermic subjects (57 ± 26 U/mg), and about one-half normal in the oligospermic subjects (86 ± 27), with values in the normals being 167 ± 58, p < 0.001, p < 0.001. Mean plasma testosterone levels were 3.4 ± 0.7 ng/ml in the azoospermic subjects, considerably lower than mean levels in normals (6.6 ± 2.0, p < 0.001), with intermediate levels in the oligospermic men (5.2 ± 1.7 ng/ml). Pooling the data for the azoospermic, oligospermic, and normal men, plasma testosterone levels were positively correlated with C-HDL (r = .42, p < 0.01) and inversely correlated with triglyceride (r = ?.50, p < 0.001) and very low density lipoprotein cholesterol (r = ?.37, p < 0.02). Plasma testosterone was also positively correlated with lipoprotein lipase activator potency, (r = .45, p < 0.01). These findings suggest that endogenous physiologic testosterone levels may play a role relative to regulation of triglyceride and C-HDL levels in men, and may also affect the hydrolytic susceptability of very low density lipoprotein molecules. Hypertriglyceridemia and low C-HDL levels in azoospermic and oligospermic men mandate quantitation of lipid-lipoprotein levels in infertility clinics to identify men at putatively increased risk for future coronary heart disease.     

Evidence for a physiologic role of pancreatic glucagon in human glucose homeostasis: Studies with somatostatin

To study the role of glucagon in human glucose homeostasis, experimental glucagon deficiency was produced by infusing somatostatin (i.v. 250 μg bolus, followed by infusion of 500 μg/hr) in six normal subjects and in two hypophysectomized patients—an insulin-dependent diabetic and a nondiabetic. In normal subjects, somatostatin lowered plasma glucagon from a mean (± SE) basal level of 85 ± 15 to 33 ± 10 pg/ml, p < 0.001. Concurrently, plasma glucose fell from $\text{90 ± 2 to 73 ± 3 mg}\text{100 ml}$, p < 0.001. Serum insulin and growth hormone fell slightly during somatostatin infusion, while plasma free fatty acids rose. In both hypophysectomized patients, somatostatin lowered plasma glucagon and glucose levels. In all subjects, after stopping somatostatin infusions, plasma glucagon and glucose returned promptly to control values, while serum growth hormone did not change. In additional in vitro studies, somatostatin (1 μg/ml) had no effect on muscle glucose uptake. Since it is known that somatostatin has no direct effect on hepatic glucose production, these results suggest that the fall in plasma glucose during somatostatin infusion resulted from inhibition of glucagon secretion, thus providing evidence that this hormone plays a physiologic role in the maintenance of fasting euglycemia in man.     

Biventricular function in sickle-cell anemia: Radionuclide angiographic and thallium-201 scintigraphic evaluation

Left ventricular (LV) and right ventricular (RV) function were evaluated at rest and during exercise using radionuclide ventriculography in 10 patients, aged 19–53 years, with sickle-cell anemia (SCA). Seven patients were in New York Heart Association functional class I and 3 were in class II. The resting LV ejection fraction (EF) was normal in 9 patients and the resting RVEF was normal in 4. LV dilation and high cardiac output were observed in 6 patients at rest. The LVEF during exercise was normal in all 10 patients, whereas only 2 patients had normal RVEF at rest and during exercise. The LVEF was lower in patients with SCA at rest (54 ± 4 % versus 61 ± 6%, p < 0.001) and exercise (66 ± 4% versus 74 ± 6%, p < 0.001) than in 42 age-matched normal subjects. Rest thallium-201 images from 9 patients showed abnormal RV uptake in 8 and normal LV uptake in 8.Thus, in adult patients with SCA, LV function was normal during exercise in all patients and at rest in all but 1 patient. The LVEF, however, was lower than that in age-matched normal subjects. RV function was abnormal in most patients at rest and during exercise. RV thallium-201 uptake suggested pressure or volume overload (or both), most likely due to pulmonary vaso-occlusive complications of the disease.     

A role for endogenous prostaglandins in defective glucose potentiation of nonglucose insulin secretagogues in diabetics

Noninsulin dependent diabetics have insulin responses to nonglucose secretagogues that are subnormal for their plasma glucose levels. Since endogenous prostaglandins have been implicated in the abnormal insulin responses to glucose in diabetics, the present study was performed to explore whether prostaglandins might also play a role in the defective insulin responses to nonglucose stimuli. We examined the effects of infusions of either prostaglandin E₂ (PGE₂) or sodium salicylate (SS), a PG synthesis inhibitor, on the acute insulin responses (AIR's) to arginine and isoproterenol and on the glucose potentiation of the insulin response to arginine in both normal and diabetic subjects. The AIR to arginine was augmented by SS in diabetics (SS = 61 ± 12 μU/ml, control = 37 ± 5 μU/ml, n = 11, p < .01). SS, however, had no effect on the AIR to arginine in normal subjects (SS = 39 ± 4 μU/ml, control = 34 ± 4 μU/ml, n = 6, p = ns). Similarly, SS augmented the AIR to an isoproterenol pulse in diabetics (SS = 38 ± 9 μU/ml, control = 18 ± 3, n = 9, p < .05) but not in normal subjects (SS = 19 ± 4 μU/ml, control = 21 ± 4 μU/ml, n = 8, p = ns), suggesting a SS-sensitive defect in the insulin response to these nonglucose stimuli in diabetics. Conversely, PGE₂ inhibited the AIR to arginine in diabetics (PGE = 28 ± 5 μU/ml, control = 39 ± 7 μU/ml, n = 7, p < .05), but not in normal subjects (PGE = 74 ± 7 μU/ml, control = 80 ± 14 μU/ml, n = 5, p = ns). The effect of SS on glucose potentiation of the AIR to arginine was studied by measuring the AIR to arginine at two different levels of plasma glucose, one before and one after an insulin infusion, with glucose potentiation defined as the ratio ΔAIR/Δprestimulus glucose. Glucose potentiation was significantly less in diabetics than in normals and SS significantly improved glucose potentiation toward normal values in diabetics but did not change glucose potentiation in normals. These findings suggest that endogenous PG's may play a role in the defective glucose potentiation of the AIR to nonglucose secretagogues in diabetics resulting in impaired insulin responses to these stimuli. This defect is partially reversible by an inhibitor of PG synthesis.     

Arterial-venous differences of plasma catecholamines in man

To investigate the relationship between forearm venous levels of catecholamines and systemic levels, simultaneous arterial and forearm vein blood samples were obtained from 14 subjects undergoing elective dental procedures and assayed with a sensitive and specific radioenzymatic assay. Baseline venous levels of norepinephrine were greater than arterial levels (305 ± 30 pg/ml versus 221 ± 18; ± SEM, p < .005). Conversely, arterial epinephrine levels were higher than venous (132 ± 17 pg/ml versus 80 ± 10; p < .005). There was a significant relationship between arterial and venous levels of both norepinephrine (r = .77, p < .01) and epinephrine (r = .67, p < .01). The arterial-venous epinephrine difference increased from the baseline value of 44 ± 14 pg/ml to 108 ± 16 (p < .005) by 3 min after subcutaneous injection of epinephrine (18 μg), but the arterial-venous difference returned to 65 ± 24 by 5 min after injection (p = NS versus baseline). These findings indicate that under the conditions of this study, forearm tissues produced more norepinephrine than they removed, but removed more epinephrine than they produced. Baseline venous and arterial levels were related; when epinephrine production was augmented, there was a short time lag for the venous epinephrine increase.     

Increased serum levels of macrophage colony-stimulating factor (M–CSF) in α-and β-thalassaemia syndromes: correlation with anaemia and monocyte activation

Abstract: Serum levels of M–CSF were determined by an ELISA method in 29 and 34 patients with HbH disease (α₁/α₂ or α₁/HbCS) or β⁰-thal/HbE, respectively, in 28 haematologically normal subjects and in five patients with anaemia due to iron deficiency or myelodysplasia. In HbH disease and β⁰-thal/HbE, M–CSF concentrations were significantly higher than those in the normal subjects [986 ± 138 and 1385 ± 133, respectively, vs. 500 ± 33 pg/ml (mean ± SEM); p <0.01, and p <0.001, respectively]. By contrast, in patients with anaemia due to iron deficiency, M–CSF levels were within the normal range. In HbH disease and in β⁰-thal/HbE, M–CSF levels correlated inversely with mean basal Hb values (r = –0.39, p = 0.05 and r = –0.60, p <0.001, respectively). In addition, in some of the HbH and β⁰-thal/HbE patients, monocyte ADCC activities towards red cells were tested and found to be approximately twice as high as those in normal controls [38.3±5.7 and 30.7 ± 4.6 vs. 17.8 ± 1.8 % specific lysis (mean ± SEM), respectively; p <0.01 and p <0.02, respectively]. When thalassaemic patients and normal controls were considered together there was a significant correlation between M–CSF levels and monocyte ADCC activities (r = 0.51, p <0.02). The results suggest that in HbH disease and in β⁰-thal/HbE, raised serum M–CSF contributes to the anaemia by enhancing the effector function of mononuclear phagocytes towards red cells.     

Renal effects on serum gastric inhibitory polypeptide (GIP)

Fasting and meal-stimulated serum immunoreactive gastric inhibitory polypeptide (GIP) concentrations were measured in normal subjects and in uremic patients undergoing chronic hemodialysis. Mean fasting GIP was higher in the uremic patients (1006 ± 145 (SE) pg/ml) than in the normal control subjects (132 ± 31 pg/ml, p < 0.001). Also, postcibal absolute and incremental serum GIP concentrations between 15 and 180 min were greater (p < 0.05) in the uremic patients than in the control subjects; in the former they failed to return to fasting levels 180 min after the meal. In a second study, using anesthetized normal dogs, simultaneous renal arterial and venous serum GIP concentrations were measured during an intraduodenal perfusion of glucose. The renal arterial-venous (A-V) GIP gradient became greater as serum arterial GIP concentrations increased. The correlation between renal A-V GIP gradient and renal arterial GIP concentration was quite good (r = 0.85), with a 39% maximum mean A-V reduction in serum GIP concentrations observed across the kidney. This large renal A-V GIP gradient observed under nonsteady conditions suggests that the kidney may be an important site for the removal of GIP from the circulation. Thus, the higher than normal fasting and stimulated serum GIP concentrations observed in uremic patients can be attributed, at least in part, to a loss of the renal extraction mechanism for GIP.     

Plasma catecholamine concentrations in hyperthyroidism and hypothyroidism

Using a modification of the fluorometric method of Anton and Sayre,⁴ we have measured the plasma epinephrine (E) and norepinephrine (NE) concentrations in patients with thyroid dysfunction. There was no significant difference in plasma E in hyperthyroid or hypothyroid subjects, the values being similar to those observed in normal subjects. There was a striking relationship between age and plasma NE in the euthyroid individuals (r = 0.685, p < 0.001, n = 41). Observed plasma NE concentrations were similar in control subjects (21.05 ± 1.6 ng/100 ml; mean ± SEM) and hyperthyroid patients (22.33 ± 2.0 ng/100 ml). However, plasma NE was significantly increased in hypothyroidism (35.46 ± 3.9 ng/100 ml; p < 0.01) and remained statistically different when the age factor was excluded (31.31 ± 2.67 ng/100 ml; p < 0.025). There was no correlation between plasma NE and serum thyroxine (T₄), free thyroxine (FT₄), or triiodothyronine (T₃), in any of the three groups studied. These data indicate that hyperthyrodism is accompanied by normal plasma NE concentrations and that hypothyroidism is associated with significantly increased plasma NE concentrations, possibly in an attempt to compensate for the lack of thyroid hormones.