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J H Strubbe

Publications and source records attributed to J H Strubbe.

At least 55 records · Page 3Linked to original sources
PubMed1988

Insulin responses and glucose levels in plasma and cerebrospinal fluid during fasting and refeeding in the rat.

The present experiments were designed to investigate the rate of penetration of insulin from the plasma into the cerebrospinal fluid (CSF) during 24 hr of fasting and refeeding in the light phase. The results show that under these conditions basal CSF-immunoreactive insulin (IRI) levels were positively correlated with plasma IRI levels. Basal plasma IRI fell during a fast but was similar to prefast control after one day of refeeding. Although CSF-IRI levels rose during glucose infusion, CSF-IRI was not elevated by glucose during a fast. During refeeding, CSF-IRI responses returned toward control, prefeeding values. This study suggests a decreased transport of insulin from plasma to CSF during fasting. The lower CSF-IRI levels achieved under these conditions may determine meal size by allowing larger meals after a fast.

Animals↗
PubMed1988

[Hormonal modifications induced by food intake contribute to the regulation of the body weight and to metabolic variations].

In the rat the energy content of the body is subject to homeostatic control. The level of energy content depends on internal and external conditions. In the adult individual food intake is matched exactly to energy expenditure. Food intake leads to profound alterations in several hormonal plasma levels affecting metabolism e.g. insulin, glucagon and catecholamines. These hormones play an important feedback role in the storage and depletion of reserve tissues such as liver and fat cells. In this paper it is discussed that messages reporting energy content of the body may influence feeding motivation and that the CNS and especially the hypothalamus plays a directing role in this respect. Among these motivation setting messages the pancreatic hormones insulin and glucagon may be prominent factors in respectively long- and short-term regulation of food intake.

Adipose Tissue↗
PubMed1987

Daily variation of food-induced changes in blood glucose and insulin in the rat and the control by the suprachiasmatic nucleus and the vagus nerve.

Rats were provided with permanent cardiac catheters allowing free movement and blood sampling without anaesthesia. During food intake the increments of plasma insulin and blood glucose were smaller and more slowly increasing in the light phase than during the dark phase. After vagal blockade the increase in both blood glucose and plasma insulin was reduced. Since this effect was more prominent in the dark phase it suggests that during this phase vagal activity may stimulate an increase in glucose inflow into the blood by activating transport and digestion of food. Electrolytic lesions of the nucleus suprachiasmaticus caused disappearance of the circadian variation of insulin and glucose responses. In this situation in both phases rapid increments of insulin and glucose occurred similar to the controls during the dark phase. It is suggested that the nucleus suprachiasmaticus directly or indirectly controls vagal activity, which determines via its influence on the gastrointestinal tract the circadian variation in blood glucose and plasma insulin responses after food intake.

Animals↗
PubMed1986

Daily rhythms of feeding in the genetically obese and lean Zucker rats.

Feeding patterns were examined in obese (fa/fa) and lean (Fa/-) adult Zucker rats over the light-dark cycle during 14 days. Obese rats eat more than lean rats especially during the dark phase. Light and dark feeding expressed as percentage of 24 hr intake showed no significant differences between the lean and obese groups. The higher food intake in obese rats is mainly caused by larger meals since obese rats ate fewer meals than lean rats. Only for the obese group differences were observed between mean meal size in light and dark phase. There is some indication that the circadian controlled temporal distribution of meals is different in obese rats compared to lean rats since obese rats eat fewer but larger meals during the first half of the dark phase. During this phase meal size increases gradually in the obese rats, suggesting that the circadian influence on feeding motivation is increased.

Animals↗
PubMed1986

Reduced insulin secretion after short-term food deprivation in rats plays a key role in the adaptive interaction of glucose and free fatty acid utilization.

The present study was undertaken to investigate the effects of short-term fasting periods up to 24 hr on insulin secretory responses of the B-cell to glucose and the consequences for FFA and glucose availability in the circulation. Conscious male rats provided with permanently implanted heart catheters received glucose infusions at midday, lasting for 20 min, in the nearly ad lib condition (i.e., 6 hr of non feeding during daytime) and after extending the fasting period to 12, 18 and 24 hr. Basal preinfusion insulin levels and insulin responses to glucose decreased gradually during these fasting periods. Basal blood glucose dropped only significantly after 24 hr of fasting whereas basal FFA levels increased gradually from 6 hr of fasting onwards. After prolonged fasting insulin released during glucose infusion became more effective in suppressing plasma FFA levels. While our data suggest that the sensitivity to the antilipolytic action of insulin is increased, the decreased responsiveness of the B-cell after moderate fasting periods may result in a drop of basal insulin levels. This facilitates the switch from glucose to FFA metabolism for most tissues already, when the first meals are missed. The results suggest that this physiological process is important to save the glycogen stores as long as possible as fuel for the central nervous system, and also to support basic energy requiring processes adequately.

Animals↗
PubMed1986

Interaction between circadian and caloric control of feeding behavior in the rat.

Feeding at the beginning of the night is probably dependent on the rat's immediate energy requirements while feeding at the end may have an anticipatory function. This latter feeding peak may be mainly controlled by a circadian pacemaker. The aim of this study was to investigate the relative contribution of satiety signals and circadian pacemakers in the control of feeding behavior. Food intake was monitored after infusion of liquid food into the stomach during several parts of the day-night cycle to prevent a possible influence of oral sensations. It is demonstrated that intragastric infusion is more effective in suppressing intake during daytime and the first half of the dark phase than during the second half of the dark phase. Suppressions of food intake are mainly due to delaying the first occurrence of food ingestion, whereas the size of that meal is less affected. During the last period of the night no significant delay could be brought about. These experiments suggest that in the rat a circadian pacemaker dominates feeding motivation during the end of the night thereby strongly interacting with caloric control of feeding behavior.

Animals↗
PubMed1986

Effect of skeleton photoperiod and food availability on the circadian pattern of feeding and drinking in rats.

Feeding and drinking behavior were measured in rats maintained under a 12:12 light-dark (LD) cycle or skeleton photoperiod (SPP). Feeding and drinking were closely associated during the normal LD cycle but under SPP conditions an increased feeding activity during the subjective day was not accompanied by an equivalent increment of water intake. This indicates a stronger coupling of drinking to the subjective night. A restriction of food availability to the subjective light phase did not cause an accompanying complete shift in drinking behavior. These results suggest that drinking is largely dependent on the influence of a circadian oscillator and this association is not disrupted by changes in feeding schedule. A change in food access to the subjective light phase caused partial but not permanent desynchronization between feeding and drinking behavior. Synchrony was reestablished within one day once food was available ad lib. Complete return to the original feeding and drinking patterning took 3 days. It is suggested that separate slave oscillators controlling feeding and drinking are governed by a hypothesized "master" circadian oscillator which remains definitely entrained to the original rhythm by the light pulses of the SPP condition.

Animals↗
PubMed1986

Meal-induced increases in parasympathetic and sympathetic activity elicit simultaneous rises in plasma insulin and free fatty acids.

The aim of this study was to investigate sympathetic and parasympathetic activity during food intake in rats by measuring plasma norepinephrine (NE), epinephrine (E), insulin, free fatty acids. (FFA), glycerol and blood glucose. Therefore male Wistar rats were implanted with silastic jugular vein cannulas so that blood could be withdrawn from freely moving animals. Blood samples were frequently taken before, during and after intake of a test meal. The effects of the blood sampling procedure on above mentioned blood compounds was also determined. Insulin increased considerably within the first minutes of food intake before a rise in blood glucose which is mediated by a vagal mechanism. An increase in plasma NE could be observed during the whole period of ingestive behavior whereas E increased considerably only in the first minute. Plasma FFA level was augmented sharply during food intake and a few minutes afterwards, whereas plasma glycerol levels did not change. After termination of food intake sympathetic activation disappeared and both plasma FFA and glycerol levels declined significantly below levels as observed in control rats. In contrast, plasma insulin and blood glucose increased considerably. It is concluded that food intake in rats causes a simultaneous increase in both sympathetic and parasympathetic activity and because of that a rise in plasma FFA and insulin respectively. It is argued that augmented sympathetic activity elicits a rise in plasma FFA levels, which is not mediated by increased lipolysis but by either decreased FFA utilization or reduced reesterification.

Animals↗
PubMed1982

Effects of pancreas transplantation on insulin secretion in the rat during ingestion of varying glucose loads.

Following alloxan induced diabetes in rats, transplantation of neonatal pancreases under the kidney capsule was successfully carried out. The insulin response to oral ingestion of 150 and 750 mg of glucose was studied. The responses in controls and in rats 40 days after transplantation demonstrated a load-dependent increment of plasma insulin responses which was not related to the similar glucose responses. In control rats a part of the insulin response had occurred at 1 min, i.e. 2 min before the rise in blood glucose. After transplantation in the absence of this nervously triggered response, blood glucose rose faster than in control rats from 3 to 5 min after start of ingestion (p less than 0.01). In non-transplanted rats regenerating a part of their original pancreas within one week, glucose intolerance was seen 10 min after glucose ingestion, probably due to the lack of adequate secondary phase release. This study shows that maintenance of a normal glucose tolerance curve to glucose ingestion depends on at least two factors. First, an anticipatory nervously triggered insulin secretion. Second, a load dependent humoral potentiation of glucose stimulated insulin release.

Animals↗
PubMed1982

Circadian pacemaker control of feeding in the rat, at dawn.

Previous studies suggest that feeding at dusk is probably dependent on the rat's immediate energy requirements, while feeding at dawn may have an 'anticipatory' function. However, little is known regarding the relative contribution of habit, energy deficits and circadian pacemakers in the expression of feeding behavior. The aim of the present study was to investigate the involvement of, and interplay between, habit, pacemaker synchronization and energy deficits in the occurrence of dawn feeding in rats. Light onset exerts a strong control over the timing of dawn feeding. The motivation to feed at dawn persists even when access to food is prevented during this period, and shows accompanying shifts with changes in light onset. Rats compensate their caloric deficit imposed by food restriction at dawn by eating earlier in the light phase. This feeding probably occurs in response to feedback mechanisms signalling an energy deficit. The rapid shift in dawn feeding with changes in light onset and food restriction, and its quick reappearance after discontinuing food restriction, argue against habit formation as solely responsible for the occurrence and maintenance of dawn feeding. Habit formation does play a secondary role in the maintenance, but occurs within the 'boundaries' set by the pacemaker. These experiments show that the timing and maintenance of dawn feeding are under the control of a circadian pacemaker which can be shifted by light onset only.

Animals↗
PubMed1978

Plasma insulin patterns in the unanesthetized rat during intracardial infusion and spontaneous ingestion of graded loads of glucose.

Rats were provided with double permanent heart catheters, allowing simultaneous infusion and rapid blood sampling in the freely moving animals. Intracardial glucose infusion (75, 150, and 300 mg) over 15-min periods induced biphasic plasma insulin responses, their onset and magnitude being correlated with the blood glucose increments. The insulin-ogenic index decreased at increasing infused loads. After spontaneous oral ingestion of 75, 150, 300, and 750 mg glucose over 2 min or less, plasma insulin increased rapidly during the initial 4 to 8 min. At the highest leads this was followed by a gradual further increase until 15 min. The rapid insulin response increased with the ingested load. About half of this response had occurred already at 2 min, i.e., prior to the first rise of blood glucose at 3 min. Maximum blood glucose levels (125-135 mg/dl) occurred between 8 and 15 min and did not correlate with the ingested loads. The insulinogenic index increased at higher oral loads. It is suggested that the plasma insulin response to glucose ingestion results from successive and cumulative operation of anticipatory nervously triggered insulin secretion, anticipatory loaded-dependent potentiation of secretory stimulation by rising blood glucose, and further adjustment of the secretion rate until blood glucose declines. The possible mechanisms are discussed.

Administration, Oral↗
PubMed1978

Bile secretion and bile composition in the freely moving, unanaesthetized rat with a permanent biliary drainage: influence of food intake on bile flow.

1. In freely moving, unanesthetized rats bile flow was measured continuously over the whole day--night cycle. Bile composition was analysed and the influence of food intake on bile flow was investigated. 2. In both sexes a distinct circadian variation of bile production was observed. The mean night-time production was 50% higher than the day-time value for female rats and 38% for male rats. In the morning when the light was switched on, a sharp decrease in secretion rate was prominent and bile flow gradually increased in the afternoon. 3. The pattern of food intake was positively correlated with the pattern of food bile secretion. During fasting only the general level of bile flow decreased, but the circadian variation persisted. Refeeding again increased the mean level of bile flow. 4. The chenodeoxycholate/cholate ratio in these rats with permanent bile fistulae was higher than in rats with "acute" bile fistulae and changed during the day--night cycle. The ratio decreased from 1.01 at 05.00 hours to a minimum of 0.41 at 15.00 hours. 5. During the day--night cycle the sodium, potassium, calcium and cholesterol concentrations were relatively constant. The total bile salt concentration was only slightly changed, so that both the bile salt-dependent fraction and the bile salt-independent fraction were subject to about the same circadian variations.

Animals↗