Endogenous urea secretion into the sheep gastrointestinal tract.

Urea turnover and the proportion of endogenous urea secreted and excreted in the saliva, the bile, the pancreatic juice and the urine and directly across the wall of the digestive tract was studied in 6 experiments, after a single i.v. dose of labelled 15N, in two adult sheep weighing 49 and 50 kg, with permanent biliary and pancreatic fistulus and with an exteriorized right parotid duct. It was found that, of the total amount of endogenous urea secreted into the animals' digestive tract (0.2694+/-0.0138 mg/min/kg b.w.), 10.27+/-0.94% reached the contents in the saliva, 2.12+/-0.28% in the bile and 0.66+/-0.08% in the pancreatic juice, and that 86.95+/-2.1% was secreted into the gastrointestinal tract, across its wall, from the blood capillaries. Exogenous turnover amounted to 0.3228+/-0.192 mg/min/kg. Of the total amount of 476.6 mg i.v. injected 15N urea, 274.1+/-8.86 mg was excreted in the urine 5.1+/-0.9 mg in the bile, 3.19+/-0.06 mg in the pancreatic juice, 4.96+/-0.76 mg via the right parotid gland and 9.34+/-1.09 mg in the faeces. The results show that the quantitatively most important part of the recirculation of endogenous urea is its passage from the blood across the wall of the gastrointestinal tract into its contents.     

Effect of exogenous and endogenous insulin on the secretory response of the pancreas to the octapeptide of cholecystokinin (CCK8) in normal rats

The author studied the effect of insulin on CCK8-stimulated secretion by the pancreas. CCK8 (0.6 nmol.kg-1) was administered to normal anaesthetized rats 30 min after the intravenous injection of insulin (10 U.kg-1), glucose (2 g.kg-1) or NaCl (controls). Pancreatic juice was collected from the intubated common bile duct. In rats given exogenous insulin, there were no statistically significant differences in total protein, amylase and trypsinogen output after CCK8 compared with the controls. In rats in which endogenous insulin secretion was stimulated with glucose, the amylase response to CCK8 was not significantly different from the control animals, but the trypsinogen response was significantly lower. The results show that insulin, in some still unknown manner, inhibits the trypsinogen secretory response to CCK8. In addition, they confirm data claiming that the synthesis and secretion of pancreatic amylase require a given critical ratio of insulin to glucose, or of insulin to the factor stimulating pancreatic secretion.     

Cholecystokinin and gastrointestinal cancer

The gut hormone cholecystokinin exerts various actions on the gastrointestinal tract, including the regulation of growth. The hormone has been reported to induce hypertrophy and hyperplasia of the pancreas and to enhance chemically-induced pancreatic carcinogenesis in animals. Stimulation of endogenous cholecystokinin secretion through the induction of deficiency of intraintestinal proteases and bile salts by trypsin-inhibiting nutrients, bile salt-binding drugs or surgical intervention is also capable of stimulating growth and tumour development in the rat. In man, factors suggested to increase the risk of pancreatic cancer, such as a high-fat and high-protein diet or gastrectomy, are known to stimulate plasma cholecystokinin secretion. Receptors for cholecystokinin have been demonstrated on human pancreatic adenocarcinomas, and cholecystokinin has been demonstrated to enhance the growth of xenografted pancreatic cancer and to inhibit growth of gastric and bile duct cancer. The recently developed cholecystokinin-receptor antagonists inhibit not only pancreatic growth but also pancreatic carcinogenesis in animals. These new drugs may be valuable new tools for inhibiting pancreatic cancer growth in humans.     

The influence of potato fibre on exocrine pancreatic secretions and on plasma levels of insulin,secretin and cholecystokinin in growing pigs

The effect of a potato fibre preparation on exocrine pancreatic secretions and on gastrointestinal hormone levels in plasma was studied in three 8 weeks old piglets that were surgically fitted with a jugular vein catheter for blood sampling, a pancreatic duct catheter and a T‐shaped duodenal cannula for collection of pancreatic juice. The animals were fed for 2 weeks a control diet (experimental period 1), thereafter for 2 weeks the control diet supplemented with 2% potato fibre (experimental period 2) and for another 2 weeks the control diet again (experimental period 3). Additionally, intraduodenal (i.d.) infusions of the experimental diet, the control diet and potato fibre as well as i.v. infusions of a solution containing cholecystokinin (CCK) and secretin were administered.

Potato fibre in the diet evoked in tendency an increase in the volume of secretion of pancreatic juice and a significant increase both in the mean values of the total protein content and total activities of lipase, trypsin and a‐amylase when compared to the control diet. The i.d. infusion of the control diet, experimental diet and fibre infusate as well as the i.V. administration of the hormone infusate led to a spontaneous secretory response of the exocrine pancreas. Besides gastrointestinal hormones, such as CCK, other factors such as short chain fatty acids may be involved in the regulation of the exocrine pancreas.     

Enterohepatic circulation in hamsters with an extracorporeal bile duct.

The present study describes a novel technique for investigations of the enterohepatic circulation in the hamster with an extracorporeal bile duct that allows long-term bile collection in the free-moving animal. The animals recovered for 7 days after the operation before the external loop was cut and bile was collected over a period of 78 h. Under these optimal conditions, initial bile flow (651 +/- 89 microliters per 100 g.h-1) and the secretion rates of biliary lipids were several-fold higher than reported in an earlier study using the acute fistula hamster. Biliary cholesterol secretion amounted to 369 +/- 32 nmol per 100 g.h-1, phospholipid secretion was 2.6 +/- 0.3 mumol per 100 g.h-1, and total bile acid secretion was 31.9 +/- 2.2 mumol per 100 g.h-1. A clearcut diurnal rhythm was demonstrated for bile flow and all biliary constituents. After 9 h the depletion of the bile acid pool was complete and cholic acid synthesis derepressed 1.4-fold from a basal rate of 818 nmol per 100 g.h-1, whereas the derepression of chenodeoxycholic acid synthesis was even less pronounced. Biliary cholesterol output increased 2.2-fold, but the phospholipid secretion was constant during the full experiment. It may be concluded that the technique of an extracorporeal bile duct in the free-moving animal allows studies of bile secretion under optimal conditions. Most likely the bile secretion rates given above approach the physiological rates in the hamster.     

Effect of diversion of bile-pancreatic juice to the ileum on pancreatic secretion and adaptation in the rat

Cannulas were implanted to collect bile and pancreatic juice, and the collected secretions were pumped back into the intestine at the level of the duodenum or the proximal ileum. The effect of 6 days of such treatment on pancreatic secretion and on pancreatic growth was determined. The effect on pancreatic secretion was studied by measuring the pancreatic secretory response to a stimulus, provided by acute diversion of bile-pancreatic juice from the proximal intestine. Trophic effects were studied in a separate group of rats by measuring pancreatic weight, protein content, and chymotrypsin activity after an overnight fast. Stimulated pancreatic secretion was 2.1 times greater for protein output and 3.4 times greater for fluid output in rats with chronic diversion of bile-pancreatic juice to the ileum. Pancreatic weight, protein content, and chymotrypsin activity were increased 2.6, 2.9, and 4.8 times, respectively, by chronic diversion of bile-pancreatic juice to the ileum. These results indicate that pancreatic hypertrophy and hyperplasia reported in rats with bile-pancreatic duct transposition to the ileum are the result of loss of feed-back inhibition from bile-pancreatic juice in the proximal intestine.     

Interactions between bile and pancreatic juice diversions on cholecystokinin release and pancreas in conscious rats

Pancreatic exocrine secretion in the conscious rat is regulated by proteases secreted by the pancreas, and cholecystokinin (CCK) is known to be involved in its mechanism. It has also been reported that the absence of either pancreatic juice or bile in the duodenum could stimulate pancreatic secretion. Therefore, differences in CCK release responding to the exclusion of bile, pancreatic juice (PJ), or both bile and pancreatic juice (BPJ) from the intestine were examined by using a bioassay for cholecystokinin. Plasma CCK levels were increased by all three treatments compared with the basal value, the order of their effects being BPJ greater than PJ greater than bile diversion, and CCK concentrations produced by BPJ diversion were much greater than can be explained as simply summed effect of exclusions of bile and PJ. Pancreatic exocrine secretions were significantly increased by PJ and BPJ diversions, but the effect of bile diversion on the pancreas was not statistically significant. An additional infusion of CR-1409 (0.1 mg/rat), one of CCK receptor antagonists, inhibited exocrine function stimulated by BPJ diversion. We conclude (i) BPJ diversion is the strongest endogenous stimulant on CCK release; (ii) the potentiation between bile and PJ diversions is induced on CCK release; (iii) pancreatic protein secretion during BPJ diversion is mainly modulated by CCK.     

The effect of oleate on pancreatic and bile secretion in the conscious rat

The effects of sodium oleate infused into either the duodenum or the terminal ileum on bile and pancreatic secretion were examined in the conscious rat. Rats were prepared with cannulae draining pure bile and pancreatic juice separately, and with an ileal and two duodenal cannulae. A 40 mM taurocholate solution containing 7 mg/ml bovine trypsin was infused into the duodenum throughout the experiment to replace diverted bile-pancreatic juice to maintain the normal regulation of pancreatic secretion. The intraduodenal infusion of sodium oleate significantly increased pancreatic juice flow, protein, and bicarbonate outputs, whereas it did not affect bile secretion. Intravenous infusion of proglumide (300 mg/kg/hr) did not inhibit pancreatic secretion stimulated by intraduodenal infusion of sodium oleate. An intravenous infusion of atropine (100 micrograms/kg/hr) attenuated protein and fluid secretions but not that of bicarbonate in response to intraduodenal oleate. In contrast, the intraileal infusion of oleate had no effect on pancreatic secretion, whereas it decreased bile flow, bicarbonate, and bile salt outputs. In conclusion, sodium oleate introduced in the duodenum stimulates pancreatic secretion but oleate in the terminal ileum inhibits bile secretion.     

Hepatic bile and pancreatic exocrine secretions evoked by gastrointestinal peptides in sheep

The secretory response of hepatic bile and exocrine pancreas to gastrointestinal peptides has been studied in chronically cannulated sheep. Pancreatic juice flow and protein output were evoked dose dependently by intraportal injection of secretin, CCK-8, caerulein, VIP and neurotensin. However, biliary secretion was evoked by only secretin. Biliary and pancreatic exocrine secretions were enhanced by delivered gastric juice into the duodenum as followed by the increased plasma concentration of immunoreactive secretin (IRS). Results suggest that secretin is the major peptide that regulates pancreatic exocrine secretion and hepatic bile production in the sheep.     

Endogenous praecaecal and total tract losses of nitrogen in pancreatic duct-ligated minipigs

The pancreatic duct-ligated minipig (PL) is an established model of pancreatic exocrine insufficiency (PEI) with a significant decrease of nutrient digestibility. This study aimed to quantify and compare endogenous losses of nitrogen (N) (ileal and faecal) in minipigs receiving an almost N-free diet. Altogether, 12 Göttingen minipigs (7 PL and 5 control animals) fitted with an re-entrant ileo-caecal fistula were used. In Study 1, ileal digesta was collected over a period of 12 h on seven consecutive days, including one 24 h collection, when animals were fed a diet containing 0.49 g N/kg dry matter (DM). In Study 2, faeces were collected for 10 consecutive days. In Group PL, the amount and DM content of ileal digesta were higher (p < 0.05), while N concentration was lower than in the Control. The ileo-caecal N flux [g/kg DM intake] was about 2.5 times higher in Group PL (5.47 ± 1.15) than in the Control (1.91 ± 0.59) (p < 0.05). The amount of faeces did not differ, but faecal N losses were higher in Group PL (p < 0.05). Endogenous faecal N losses [g N/kg DM intake] of the Control group (1.17 ± 0.72) were comparable with earlier studies, while those of Group PL were 2.6 times higher (3.09 ± 1.34). In contrast, urinary excretion of N did not differ between the Control and Group PL. In conclusion, PEI caused markedly increased endogenous N losses. Therefore, the impact of reduced digestibility of nutrients on endogenous N losses might be relevant for apparent protein digestibility rates and should be taken into account.     

The ghrelin pentapeptide inhibits the secretion of pancreatic juice in rats.

Ghrelin, a 28 amino acids polypeptide was recognized as an endogenous ligand for the growth hormone secretagogue receptor. It turned out that the entire sequence of ghrelin is not necessary for performing the above-mentioned functions. It was suggested that 5 residues (Gly-Ser-Ser(n-octanoyl)-Phe, pentaghrelin) constituted functionally active part of the full-length polypeptide. Ghrelin-28 was found to inhibit pancreatic enzyme output in rats, though the effect of pentaghrelin was not studied so far. The study aimed to determine the involvement of pentaghrelin in pancreatic juice secretion in anaesthetized rats. Male Wistar rats (220 +/- 20 g body weight, b. wt.) were anesthetized, the external jugular vein and common biliary-pancreatic duct were cannulated. Pentaghrelin boluses (i.v., 1.2, 12, and 50 nmol kg(-1) b. wt.) were injected every 30 min with or without CCK-8 infusion, duodenal mucosal CCK(1) receptor blockade with tarazepide, vagotomy and capsaicin pretreatment. Pentaghrelin boluses reduced the volume of pancreatic-biliary juice, protein and trypsin outputs both under basal and CCK-8-stimulated conditions in a dose-dependent manner. However, exogenous pentaghrelin failed to affect the pancreatic secretion in rats subjected to vagotomy, capsaicin deactivation of afferents or pretreatment with Tarazepide. In conclusion, pentaghrelin may control exocrine pancreas secretion by affecting duodenal neurohormonal mechanism(s) involving CCK and vagal nerves in rats.     

Compensation of exocrine pancreatic insufficiency during its partial, subtotal and total resection

Chronic experiments on dogs have shown that the damage of extra-secretory pancreatic function by duct ligation caused marked compensatory changes of stomach function. The increase in gastric juice secretion and gastric juice proteolytic activity was accompanied by the reduction in its acidity. In addition to quantitative changes, qualitative shifts were revealed (amylolytic activity in strongly acid pH-reaction), never observed in the gastric juice of intact animals. Partial pancreas resection (up to 75%) both in control and test animals 10-14 months after pancreatic duct ligation was not accompanied by significant changes in gastric juice secretion. Total pancreas resection in dogs with previous pancreatic duct ligation caused neither prompt animal death, as in the control, nor the inhibition of compensatory reactions of gastric juice secretion.     

Biliary and pancreatic exocrine secretions via endogenous secretin by intestinal infusion of propionate and propionate analogues in piglets

1. The secretory responses of hepatic bile and exocrine pancreas by intraduodenal infusion of propionate (PA), 3Cl-PA, 2Cl-PA, 3Br-PA and 2Br-PA solutions were examined in anesthetized piglets. 2. Pancreatic juice and protein secretions were enhanced by infusion of PA and PA analogue solutions of pH 2.0 following increase of plasma secretin level but not pH 7.0. The order of response time was as follows: 3Br-PA greater than 2Cl-PA greater than 2Br-PA greater than 3Cl-PA greater than PA. 3. The response of bile flow depended on endogenous secretin and showed almost the same pattern as that of pancreatic juice secretion. 4. The results suggested that pancreatic exocrine secretion via endogenous secretin was not always dependent on the dissociation constant of weak acids.     

Three-day continuous drainage of pancreatic juice in the cortisone-treated conscious rat: Analysis of enzyme activities and ultrastructural changes

Summary We have investigated the short-term effects of hydrocortisone (60 mg/kg per day) and placebo on basal and stimulated pancreatic secretion in the conscious rat. Volume and enzyme secretion were determined; fine structural changes were examined simultaneously.The pancreatic and bile ducts were cannulated separately; pancreatic juice was drained via an isolated fistula, and bile was recirculated into the duodenum. The application of hydrocortisone led to an almost complete inhibition of the secretory response of the exocrine pancreas when stimulated with 0.25 U secretin in combination with 5 × 10^-8 g caerulein per h. It strongly affected the secretion rates of volume, protein, lipase, chymotrypsin, trypsin and carboxypeptidase, whereas the secretion rate of alpha-amylase continued to show a slight increase after stimulation.After stimulation with secretin and caerulein, the hydrocortisone-treated animals showed a higher density of zymogen granules in the acinar cell and an increase in the number of autophagic vacuoles in comparison to the equally stimulated placebo-treated rats.It is concluded that the short-term inhibition of pancreatic secretion by hydrocortisone occurs largely as a result of an inhibition of cellular enzyme discharge.Supported by the Deutsche Forschungsgemeinschaft, Ga 279     

吗啡和纳洛酮对酸化十二指肠引起狗胰液分泌的影响

本工作用制备 Thomas 胰瘘和胃痿的5条狗进行慢性实验。实验时用0.1N 盐酸灌入十二指肠以刺激胰液分泌,并分別注射吗啡或/和纳洛酮,观察它们对胰液分泌和对胰液中碳酸氢盐和蛋白质浓度的影响。另外我们还观察了吗啡和纳洛酮对6条狗离体胰主导管紧张性的影响。结果表明:(1)吗啡抑制了胰液分泌量,对胰液中碳酸氢盐和蛋白质浓度无影响,由于分泌量减少故两者的排出量显著减少(P<0.05),(2)纳洛酮本身对胰液分泌量和碳酸氢盐及蛋白质浓度均无影响;(3)纳洛酮可以加强吗啡抑制胰液分泌的作用(P<0.01);(4)吗啡能增加狗的离体胰主导管肌条的紧张性,纳洛酮不能阻断或翻转吗啡的这一效应,相反能加强其效应。本工作表明,吗啡抑制酸化十二指肠所引起的胰碳酸氢盐和蛋白质排出量,其机制可能是吗啡刺激胰导管收缩,而纳洛酮则加强吗啡的这种抑制效应。     

Effect of dietary fibre on nitrogen retention and fibre associated threonine losses in growing pigs

Apart from being an energy source, dietary fibre is also discussed to act as anti-nutritional factor reducing apparent precaecal protein and amino acid (AA) digestibility due to reduced absorption or increased endogenous secretion or both. However, the amounts of protein and AA of endogenous origin determined at the terminal ileum in cannulated animals do not represent the total losses associated with endogenous secretion. A high proportion of secreted protein is reabsorbed and does not reach the terminal ileum, and losses occur during synthesis of endogenous protein. Therefore, the present study used an alternative indirect approach, taking the reduction of nitrogen (N) retention in a threonine (Thr) limited diet as a sensitive indicator for fibre-associated Thr losses. Two experiments were conducted with 12 castrated male pigs each between 37 and 75 kg body weight to measure the effect of the intake of Thr and 150 and 300 g/d fibre from wheat bran (Exp. 1), or 150 g/d fibre from rape seed, cassava leaves, and cassava root peels, respectively (Exp. 2), on N retention. During two (Exp. 1) and three (Exp. 2) balance periods the animals were subjected to the dietary treatments according to a cross-over design. All animals received 1350 g/d of a wheat-soybean-based diet supplemented with free AA to ensure Thr being the first-limiting AA. To determine the effect of Thr on N retention, intake of the basal diet was reduced to 1150 g/d and supplemented with corn starch to reach equal energy intake and an unchanged AA pattern. With increasing BW additional starch was added to all diets to ensure a constant energy intake of 1.25 MJ ME/kg BW(0.75). Since the fibre sources contained small amounts of Thr, N retentions were corrected for precaecal digestible Thr intake originating from the fibre sources according to the Thr effect on N retention as determined in experiment 1. Corrected N retentions were affected by fibre level (p = 0.007) and source (p < 0.001). Fibre-associated Thr losses amounted to 3.3, 3.2, 1.2, and 1.1 g/kg fibre from wheat bran, rapeseed, cassava leaf, and cassava root peel, respectively. It is concluded that Thr losses per gram of dietary fibre depend on the fibre source and that fibre concentration and source in pig diets should be considered as a factor affecting Thr requirement.     

Effect of dietary fibre on nitrogen retention and fibre associated threonine losses in growing pigs

Apart from being an energy source, dietary fibre is also discussed to act as anti-nutritional factor reducing apparent precaecal protein and amino acid (AA) digestibility due to reduced absorption or increased endogenous secretion or both. However, the amounts of protein and AA of endogenous origin determined at the terminal ileum in cannulated animals do not represent the total losses associated with endogenous secretion. A high proportion of secreted protein is reabsorbed and does not reach the terminal ileum, and losses occur during synthesis of endogenous protein. Therefore, the present study used an alternative indirect approach, taking the reduction of nitrogen (N) retention in a threonine (Thr) limited diet as a sensitive indicator for fibre-associated Thr losses. Two experiments were conducted with 12 castrated male pigs each between 37 and 75 kg body weight to measure the effect of the intake of Thr and 150 and 300 g/d fibre from wheat bran (Exp. 1), or 150 g/d fibre from rape seed, cassava leaves, and cassava root peels, respectively (Exp. 2), on N retention. During two (Exp. 1) and three (Exp. 2) balance periods the animals were subjected to the dietary treatments according to a cross-over design. All animals received 1350 g/d of a wheat–soybean-based diet supplemented with free AA to ensure Thr being the first-limiting AA. To determine the effect of Thr on N retention, intake of the basal diet was reduced to 1150 g/d and supplemented with corn starch to reach equal energy intake and an unchanged AA pattern. With increasing BW additional starch was added to all diets to ensure a constant energy intake of 1.25 MJ ME/kg BW^0.75. Since the fibre sources contained small amounts of Thr, N retentions were corrected for precaecal digestible Thr intake originating from the fibre sources according to the Thr effect on N retention as determined in experiment 1. Corrected N retentions were affected by fibre level (p = 0.007) and source (p < 0.001). Fibre-associated Thr losses amounted to 3.3, 3.2, 1.2, and 1.1 g/kg fibre from wheat bran, rapeseed, cassava leaf, and cassava root peel, respectively. It is concluded that Thr losses per gram of dietary fibre depend on the fibre source and that fibre concentration and source in pig diets should be considered as a factor affecting Thr requirement.     

Pancreatic exocrine secretion in the pig following test meals of different composition and intra-duodenal loads of glucose and maltose.

Eleven pigs were fitted with pancreatic and duodenal fistulae, and pancreatic juice collected permanently. Amylase, chymotrypsin, lipase and total proteins were determined in juice collected within 2 and 6 hours after different test-meals or intraduodenal loads of glucose and maltose. In the pancreatic juice of pigs adapted to a high-lipid diet and submitted to a high-carbohydrate test-meal the activity of amylase was increased by 50%. When the consumption of the high-lipid meal was associated with an intraduodenal load of 100 g of glucose all the enzyme activities were stimulated when compared to the effect of meal alone, but only the activity of amylase was significantly increased (+ 82%). In the juice of pigs adapted to a balanced diet and submitted to intraduodenal loads of 150 ml of water, 50 g of glucose, 50 g of maltose and 150 g of maltose, the enzyme activities remained almost constant with the load of water and 50 g of maltose but with 50 g of glucose and 150 g of maltose loads, amylase activity was increased by 20% and 30% respectively. It is suggested, that the exocrine pancreas of the pig adapts itself rapidly to the changes in the size of the intestinal pool of starch hydrolysis products.     

Nitrate reductase activity,biomass, yield,and quality in cotton in response to nitrogen fertilization

In the production of cotton (Gossypium hirsutum L.), nitrogen fertilization is one of the most costly crop practices, but important to reach high yields. However, high nitrogen (N) content in plants does not always translate into a high fibre production. One way of assessing the efficiency of the N fertilizer is through the enzymatic activity of the nitrate reductase (NR). This is a key enzyme in N assimilation, whose activity is regulated by a number of endogenous and exogenous factors that determine yield. The aim of this study was to assess the effect of N fertilization on yield, fibre quality, biomass, and NR enzymatic activity in vivo in the cotton variety Fiber Max 989. The evaluated application rates were 0, 50, 100, and 150 kg/ha of N, using urea as a source (46% N) in a randomizedblock design with three replicates. At harvest, the maximum yield of seed cotton and the greatest accumulation of total foliar biomass through time was reached after applying 150 kg N/ha. The different N-application rates did not affect the components of cotton-fibre quality. The activity of endogenous NR was greater on plants where 150 kg N/ha were applied. The highest cotton yield and N contents were obtained on these plants. Therefore, the NR activity in vivo could be used as a bioindicator of the N nutritional level in cotton.     

The effects of dietary nitrogen on reproductive development in the female boll weevil, Anthonomus grandis

ABSTRACT. The role of dietary nitrogen in reproductive development was investigated in the female boll weevil, Anthonomus grandis (Boh.)(Coleoptera: Curculionidae). Artificial diets were employed containing 1.7%, 2.6% and 4.0% N. Each diet was labelled with a ¹⁴C-amino acid mixture and standardized relative to cpm and N per mg of diet dry weight. Egg production, diet consumption, nitrogen consumption and nitrogen utilization were measured by recovering the cpm in the faeces, ovaries plus eggs and the carcass.
Females given the 4% N diet initiated oviposition on day 4 with maximum egg production of 11 eggs/day/female occurring on day 6. Females on the 2.6% N diet also initiated oviposition on day 4, but the time necessary to reach maximum egg production was extended. Egg production by these females eventually equalled the total production of the group on the 4% N diet. This was achieved by consuming more diet per female and dedicating a higher percentage of the absorbed diet to egg formation. With the 1.7% N diet, females showed both a delay and a decrease in total egg production because of reduced feeding and a reduced commitment of consumed nutrients to oöcyte maturation.
Switching dietary nitrogen concentrations after the initiation of oviposition resulted in changes in consumption and reproductive allocation within 48 h.