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Biomedical subjects

D Porte

Publications and source records attributed to D Porte.

At least 217 records · Page 12Linked to original sources
PubMed1973

Glucagon release induced by pancreatic nerve stimulation in the dog.

A direct neural role in the regulation of immunoreactive glucagon (IRG) secretion has been investigated during stimulation of mixed autonomic nerves to the pancreas in anesthetized dogs. The responses were evaluated by measurement of blood flow and hormone concentration in the venous effluent from the stimulated region of pancreas. Electrical stimulation of the distal end of the discrete bundles of nerve fibers isolated along the superior pancreaticoduodenal artery was invariably followed by an increase in IRG output. With 10-min periods of nerve stimulation, the integrated response showed that the higher the control glucagon output, the greater was the increment. Atropinization did not influence the response to stimulation. That the preparation behaved in physiologic fashion was confirmed by a fall in IRG output, and a rise in immunoreactive insulin (IRI) output, during hyperglycemia induced by intravenous glucose (0.1 g/kg). The kinetics of this glucose effect on IRG showed characteristics opposite to those of nerve stimulation: the lower the control output, the less the decrement. Furthermore, during the control steady state, blood glucose concentration was tightly correlated with the IRI/IRG molar output ratio, the function relating the two parameters being markedly nonlinear. Injection or primed infusion of glucose diminished the IRG response to simultaneous nerve stimulation. Measurement of IRG was inferred to reflect response of pancreatic glucagon secretion on the basis of the site of sample collection (the superior pancreaticoduodenal vein), the absence of changes in arterial IRG, and similar responses being obtained using an antibody specific for pancreatic glucagon. THESE STUDIES SUPPORT A ROLE FOR THE AUTONOMIC NERVOUS SYSTEM IN THE CONTROL OF GLUCAGON SECRETION: direct nerve stimulation induces glucagon release. Such sympathetic activation may be interpreted as capable of shifting the sensitivity of the A cell to glucose in the direction of higher glycemia for a given glucagon output. The experimental model employed is valid for further studies of regulatory mechanisms of endocrine pancreatic function in vivo.

Animals↗
PubMed1973

Evidence for a common, saturable, triglyceride removal mechanism for chylomicrons and very low density lipoproteins in man.

Hypertriglyceridemic subjects were fed diets in which dietary fat calories were held constant, but carbohydrate calories were varied. Three subjects with fasting chylomicronemia (Type V) were given less carbohydrate and four subjects without fasting chylomicronemia (Type IV) were fed diets with more calories as carbohydrate. The restricted carbohydrate intake led to disappearance of chylomicronemia in those subjects who had chylomicronemia on a normal diet (Type V to IV). In those subjects without chylomicronemia, chylomicronemia appeared in response to increased carbohydrate intake (Type IV to V). Thus chylomicron concentrations in plasma were altered even though fat intake and presumably chylomicron input into plasma was kept constant. These findings provide evidence for saturation of chylomicron removal mechanisms by alteration of endogenous triglyceride-rich lipoprotein concentrations. They suggest that chylomicrons compete with very low density lipoproteins for similar removal mechanisms. The relationship between endogenous triglyceride concentration and the lipolytic activity in plasma following heparin was then evaluated with the use of long-term heparin infusions to release and maintain lipolytic activity in the circulation. 10 subjects were placed on fatfree diets to remove circulating dietary fat. The plasma lipolytic rate during the heparin infusion was measured consecutively on different days in individuals whose triglyceride concentrations were varied by either increasing or decreasing calories. The lipolytic rate was curvilinearly related to the plasma triglyceride concentrations. This curvilinear relationship followed Michaelis-Menton saturation kinetics over a wide range of triglyceride concentrations on fat-free, high-carbohydrate diets, in multiple studies in a group of individuals. These studies suggest that endogenous and exogenous triglyceride compete for a common, saturable, plasma triglyceride removal system related to lipoprotein lipase.

Adult↗
PubMed1973

Accelerated triglyceride secretion. A metabolic consequence of obesity.

A new animal model was developed to determine the effect of obesity upon endogenous triglyceride secretion. Desert sand rats (Psammomys obesus), rodents which become spontaneously obese and hyperinsulinemic when given ad lib. chow, were given intravenous Triton to allow in vivo measurement of triglyceride secretion rates (TGSR). In a group of 18 fasted animals of varying body weight and degrees of obesity, TGSR correlated significantly with body weight (r=0.68, P < 0.01) indicating that obesity was associated with accelerated endogenous release of triglyceride. In these same animals, basal plasma insulin levels correlated significantly with body weight (r=0.78, P < 0.001) and TGSR correlated significantly with mean plasma insulin levels (r=0.73, P < 0.001), suggesting that hyperinsulinemia may have been the mechanism through which obesity enhanced TGSR. No correlation was found between basal triglyceride level and either body weight, basal insulin, or TGSR which suggested that individual triglyceride removal rates among the animals may have been variable. To test this hypothesis, seven animals were studied prospectively before and after induction of obesity. There were significant increases (P < 0.02) in all parameters, i.e., weight, plasma insulin level, TGSR, and basal triglyceride level. Thus, when each animal was used as its own control, thereby minimizing the postulated factor of variable individual triglyceride removal, increments in basal triglyceride were shown to accompany the development of obesity, hyperinsulinemia, and accelerated triglyceride secretion. These data from studies in the sand rat offer in vivo evidence that obesity leads to accelerated triglyceride secretion, an effect which may be mediated by hyperinsulinemai, and which can be invoked as one possible mechanism to explain hypertriglyceridemia associated with obesity in man.

Animals↗
PubMed1972

Acute and steady-state insulin responses to glucose in nonobese diabetic subjects.

Previous observations in normal subjects have suggested that when 5-g glucose pulses (P) were given in the following sequence: before (P1) and 45 min after beginning a 300 mg/min glucose infusion (P2); during the 20th hr (P3) and 1 hr after the infusion was stopped (P4); the insulin responses were consistent with a simple two-pool model. One pool is a readily available small storage pool which is refilled by a second, larger, more slowly responding pool that controls basal and steady-state insulin output. The identical protocol was employed to evaluate the insulin responses in 13 nonobese diabetic subjects. DIABETICS HAD BASAL INSULIN LEVELS INDISTINGUISHABLE FROM NORMALS (DIABETICS: 10.7+/-4; normals: 10.7+/-5, mean +/-SD, muU/ml), but had significantly elevated basal glucose levels (diabetics: 161+/-27; normals: 88+/-7, mg/100 ml, P < 0.05). The mean early insulin response (3-5 min Delta IRI) after a 5 g glucose pulse (P1) was significantly diminished in diabetics (diabetics 6.4+/-9; normals: 32.5+/-14, muU/ml, P < 0.01) consistent with a defective storage pool output. The glucose disappearance rate, K(G), decreased in parallel with the early insulin response and the slope of the regression line between these two variables was virtually identical with that calculated from 16 normal subjects. Similar to normal subjects, during the short glucose infusion, the acute insulin response to P2 was diminished in diabetics (P < 0.02). In normal subjects after 20 hr of infusion, the rapid insulin responses to P3 are restored to the preinfusion P1 values, and 1 hr after the infusion was stopped, the responses to P4 are increased twofold (P < 0.001). Diabetics, however, demonstrated decreased early responses to P3 (P < 0.001) and no increased response to P4. In contrast to the diminished acute insulin responses to glucose pulses, diabetics have steady-state insulin levels after 20 hr of glucose infusion similar to those of normal subjects (diabetics: 25.7+/-13; normals: 32.5+/-14, muU/ml). Thus both basal and steady-state insulin levels of diabetics were comparable with those of normal subjects, which suggest that although the rapid insulin response from the storage pool output is defective in diabetics, the more slowly responding pool is intact.

Adolescent↗
PubMed1972

Studies of secretin-stimulated insulin responses in man.

Recent studies have suggested that secretin, like glucose, stimulates a rapid insulin response from a small storage pool. In order to evaluate the mechanism of the secretin-stimulated insulin response, small (15 U) rapidly administered intravenous injections (pulses) of secretin were given before, during, and after a 20 hr 300 mg/min glucose infusion. Contrary to previous studies demonstrating that the acute insulin response to a small (5 g) pulse of glucose given 45 min after the start of the glucose infusion was significantly diminished compared to the response to the preinfusion pulse, the acute insulin response (2-5 min Deltaimmuno-reactive insulin muU/ml) to 15-U secretin pulses exhibited a greater than twofold increase (before: 31.1+/-15.4; during: 71.2+/-40.4, muU/ml, mean +/-SD, P < 0.02). The increased response to secretin was also found after 20 hr of continuous glucose infusion, but was not observed 1 hr after cessation of the infusion when plasma glucose levels returned to control values. Thus, this increased response to secretin was glucose dependent. Four 150-U secretin pulses given at 30 min intervals elicited progressively and significantly diminished acute insulin responses with each succeeding pulse, consistent with depletion of the small storage pool. Similar to the observation that the magnitude of the insulin response to secretin was glucose dependent, the glucose-stimulated output appeared to be secretin dependent. Thus the acute insulin response to 5 g glucose was increased after secretin pretreatment (presecretin: 34.9+/-14.8; postsecretin: 50.5+/-22.5 muU/ml. P < 0.02) which suggests that secretin may either enlarge the storage pool stimulated by glucose or increase its sensitivity. The effect of epinephrine and propranolol on acute insulin responses to secretin and glucose was also different. 15-U secretin pulses were unaffected by infusions of either epinephrine (pre: 31.6+/-17.9; during: 27.8+/-16.6 muU/ml) or propranolol (pre: 12.8+/-8.4; during: 10.7+/-5.5 muU/ml). The results of these studies indicate that although both glucose and secretin stimulate a rapid insulin response, these responses are easily differentiated. The data suggest that glucose and secretin stimulate functionally separate storage pools of insulin, but that the acute response to either stimulus is partly determined by exposure to the other.

Epinephrine↗
PubMed1971

Epinephrine: selective inhibition of the acute insulin response to glucose.

An epinephrine infusion of 6 mug/min decreased the rapid insulin response to a 5 g glucose pulse by 96% (P < 0.001) compared with the preinfusion control. In contrast when an identical epinephrine infusion was superimposed on a prolonged glucose infusion, elevated steady-state insulin levels did not decrease, but increased from 26.9 +/-6 (mean +/-SD, muU/ml) to 56.8 +/-15 muU/ml (P < 0.05) in parallel with the epinephrine-induced hyperglycemia. Thus epinephrine inhibition of insulin secretion was observed during acute but not chronic glucose stimulation. To evaluate further the insulin responses during a prolonged glucose infusion, a 5 g glucose pulse was given before and 60 min later during a concomitant epinephrine infusion. Although the acute insulin response to the first glucose pulse was observed during the elevated steady-state glucose and insulin levels associated with the glucose infusion, epinephrine again inhibited the acute insulin response to the subsequent 5 g glucose pulse by 91% (P < 0.01). Thus epinephrine appears to inhibit selectively the rapid insulin response to glucose but not to influence insulin output stimulated by prolonged hyperglycemia. These observations provide further evidence for a model of insulin secretion which includes a small storage pool available for immediate release to a glucose challenge and a more slowly responding pool regulating insulin secretion in the basal and steady state.

Adult↗