X-ray, light and electron microscopic observations in experimental lymphostasis of the liver

Experimental lymph stasis demonstrates the hepatic lymph vessel system by unfolding of the branching lymphatics. The lymphatics are limited to the interlobular connective tissue. The lymphatic wall consists of a flat endothelium without pores and without a continuous basal membrane. The endothelial cells show overlapping processes and are suspended in a net of delicate filaments. Lymph and bile stasis produce separation of the endothelial junctions. Only reversible changes of liver parenchyma are seen after pure lymphostasis. The storage of tantalum powder by the liver is reduced by the Imphostatic edema. The significance of lymph stasis resides primarily in its existence as an additional stressor. Simultaneous lymph and bile stasis definitely speeded up the cirrhotic process. The experimental models should lead to a greater emphasis of the importance of the hepatic lymphatic drainage system, and especially of lymphostasis as an important additional factor in pathogenesis of human diseases.

Pancreatic insulin secretion following intrapancreatic infusion of amino acid

Both protein ingestion and amino acid infusion are known to stimulate insulin secretion. The mechanism of this response has been attributed to increased plasma amino acid concentration. The present studies were undertaken to determine whether this-secretory response is due to a direct effect of amino acids on the islet cells or whether it is mediated through some other indirect mechanism. Accordingly, pancreatic infusion studies were conducted to help resolve this question.

Casein hydrolysate (1 gm.) infused into the pancreatico-duodenal artery of dogs for one-half hour provoked an immediate secretion of insulin into the portal vein. Femoral arterial insulin concentration also rose within five minutes, although hyperglycemia was not observed until the end of the infusion. An insulin response of similar magnitude was achieved by pancreatic glucose infusion (1 gm.). Simultaneous administration of epinephrine (30 μg.) inhibited the insulin responses to both glucose and amino acid. Combined infusion of casein hydrolysate and glucose (0.5 gm. each) produced a greater insulin response than the sum of the individual responses, suggesting glucose-amino acid synergism. Intraportal infusion of casein hydrolysate produced no significant insulin response in either portal venous or femoral arterial plasma.

These studies suggest that the insulin response associated with ingested or parenteral protein represents a direct amino acid effect on the islets of Langerhans. They also suggest that the amino acid concentration in the pancreas may be as important as glucose in control of insulin secretion.

Potentiation of the plasma insulin response to glucose by prior administration of alcohol. An apparent islet-priming effect

Ethyl alcohol which has been reported to be without effect on insulin secretion apparently modifies beta-cell function nevertheless, as indicated by the plasma insulin responses to glucose loading after prior administration of alcohol. Glucose was injected intravenously in nine young adults on three separate occasions at intervals of at least two weeks. During the twelve hours preceding each test the subjects received ethanol either by mouth or by vein or, as a control, no ethanol. Plasma insulin and glucose concentrations were not noticeably affected by the ethanol alone but alcohol pretreatment was followed in all instances by heightened plasma insulin responses to the glycemic pulse stimulus and by accelerated rates of plasma glucose disappearance. The mean plasma insulin response was increased 50 per cent by the alcohol, irrespective of the route of administration. Unlike recognized insulin secretogogues, therefore, ethanol appears to augment insulin secretion only on demand. The route of administration appeared not to be a factor in determining the magnitude of the alcohol effect. Other alcohol effects included blunting of the plasma pyruvate and exaggeration of the plasma lactate elevations after glucose.

Relationship between meal size and frequency and plasma insulin response in man

The effect of varying the size of a meal on plasma insulin was determined in eight normal male adults. The effect of consuming one half of a meal at 0 time and one half at two hours later was also studied. Each subject was studied on four days, one day when he consumed a whole meal (580 calories) of natural foodstuffs; one day, one-half the meal; one day, one quarter of the meal, and one day when he consumed one half the meal at 0 time and the remainder two hours later. When fractions of the meals were ingested, all ingredients were decreased proportionately. As meal size was increased, a log-dose relationship was observed to characterize the comparison of meal size ingested to plasma insulin response. When on the fourth day the subjects consumed the meal in fractions, the mean sum of the plasma insulin responses was identical to that observed when the meal was eaten at one time. The results suggest that over a four-hour period, the plasma insulin response is a function of the magnitude of the load of calories requiring disposition and that the response does not appear to be influenced by the frequency with which the calories are ingested.

Insulin response to ingested protein in diabetes

The ingestion of protein by normal human subjects has been shown recently to represent a stimulus to the secretion of insulin. This response is probably related to the postprandial rise in plasma amino acid concentration.

Since disordered protein synthesis may contribute to the pathogenesis of diabetes and its complications, the insulin response to ingested protein (casein or gelatin, 50-100 gm.) was compared in twenty-eight normals and ten maturity-onset diabetics. Insulin response (microunits-minutes, μU.-min.) was considered to be the area included by that portion of the plasma insulin response curve above projected basal insulin secretion. Following protein ingestion the diabetics showed a mean insulin response (± S.E.M.) of 3,425 ± 367 μU.-min., compared with 1,005 ± 136 in the normals, a 3.4-fold difference (p < 0.01). In neither group were there significant or consistent changes in plasma glucose concentration. The fall in free fatty acids was comparable and no difference was seen in the plasma amino acid nitrogen curves.

These data indicate that the insulin response to ingested protein is excessive in diabetes. The mechanism of the hyperresponse would seem to lie within the beta cell since no abnormality of the presumed amino acid stimulus was demonstrated.