Effect of dietary calcium on cadmium absorption and retention in suckling rats

The effect of calcium supplementation on absorption and retention of cadmium in the suckling period was evaluated in Wistar rat pups of both sexes. Animals were maintained in the litters with the mother rats and supplemented with 1%, 3% or 6% calcium (as CaHPO₄×2H₂O) in cow's milk by artificial feeding from day of birth 6 through 14. All rats were exposed to cadmium (as CdCl₂×H₂O) either orally or parenterally. Oral cadmium dose of 0.5 mg/kg body weight a day was administered through nine-day period of calcium supplementation and parenteral cadmium dose was injected subcutaneously in a single dose of 0.5 mg Cd/kg body weight prior to calcium supplementation. On experimental day 10 (at the age of pups of 15 days) all animals were killed and the liver, kidneys, brain and carcass (body without organs and skin) were removed for element analyses. Cadmium and essential elements calcium, zinc and iron were analysed in the tissues by atomic absorption spectrometry. Results showed that after oral exposure cadmium concentrations in all calcium-supplemented groups were significantly decreased in the organs and carcass and that the effect was dose-related. No such effect of calcium was found after parenteral cadmium exposure. Calcium supplementation per se significantly increased calcium concentration in the carcass and had no effect on iron in organs and zinc in carcass. It was concluded that calcium supplementation during the suckling period could be an efficient way of reducing oral cadmium absorption and retention without affecting tissue essential trace element concentrations.     

Reduction of 141Ce absorption in suckling rats

The influence of diet or its ingredients on 141Ce absorption and retention was investigated in six-day-old rats. Animals were fed over 8h with cow's milk, rat diet or a mixture of rat diet ingredients (fish meal, sunflower meal, alfalfa, cane molasses and premix) labelled with 141Ce. Whole-body radioactivity was determined in a double crystal scintillation counter every 24 h over a six-day period. Gut, liver, kidney and femur retention and cerium distribution in the gut was determined at the end of the experiment. Compared to milk diet, administration of rat diet or ingredients caused respectively 3 and 7.5 times lower whole body retention. Carcass retention was reduced by rat diet or ingredients 2-3 times and intestinal retention 3 and 8 times respectively. Irrespective of the dietary treatment the main site of cerium intestinal retention was the ileum. Our present results indicate that some compounds of rat diet might be considered as a means of reducing cerium absorption and intestinal retention in the very young.     

Discrimination between strontium and calcium in suckling rats

Discrimination between strontium (Sr) and calcium (Ca) was examined in suckling rats and compared with that in older rats after weaning. Concentrations of Sr and Ca and the Sr/Ca ratios in serum and femur of 10-d old and 21-d old rats were determined. The Sr concentrations and Sr/Ca ratios in the serum and femur of 10-d old rats were lower than those of 21-d old rats, that could be explained by the fact that 10-d old rats ingested only maternal milk in which the Sr/Ca ratio was much lower than the laboratory diet. The relative ratios of Sr/Ca in serum and femur to that in the diet were found to be higher in 10-d old rats compared with those in 21-d old rats, and also higher than those in the older rats after weaning, as described in our previous publication. This result may reflect that discrimination between Sr and Ca during intestinal absorption is lacking in very young animals before weaning and develops after this age. Renal discrimination between Sr and Ca in the suckling rats at 10 d of age was evaluated by determining the relationship between the relative clearances of Ca and Sr. The mathematical model proposed by Walser and Robinson was applied on these results and the parameter for the equation, that is, the discrimination constant, was shown to be higher in 10-d old rats compared to those in young (7 wk of age) and adult (25 wk of age) rats. This result suggests that the discrimination of Sr in favor of Ca during the tubular reabsorptive process may not be fully developed in the very young rats before weaning.     

The absorption of antibody by the duodenum and jejunum in young rats

Experiments were performed to test the capacity of parts of the small intestine of rats aged27–29 days to absorb homologous antibody and transmit it to the circulation. No antibody absorption occurs after the oral administration of immune serum to rats of this age, for the postnatal transfer of immunity normally terminates at about20–21 days.
Antibody is readily absorbed and transmitted to the circulation from homologous immune serum introduced into the duodenum of27–28 day animals, after removal of the duodenal contents by flushing out with warm saline. Absorption and transmission occurs in some animals even if the duodenal contents are not previously removed. The animals used in these experiments were left with their mothers until shortly before the operation.
No transmission of antibody occurred when comparable experiments were performed on young rats aged27–28 days that had been weaned at the usual age of20–21 days.
Similar experiments were performed on the first segment of the jejunum. The results obtained are discussed in relation to the pinocytic activity of the epithelial components of the duodenum-jejunum.     

A comparison of the effects of suckling or transient dopamine antagonism on thyrotropin-releasing hormone and suckling induced prolactin release in lactating rats

Prolactin (PRL) release was studied in mid-lactational female rats by comparing the stimulatory influence of suckling to a drug protocol that mimics the effect of suckling on the anterior pituitary (AP). Animals that nursed pups for 15 minutes and were allowed to suckle again 60 minutes later for 10 minutes, released PRL effectively during both nursing episodes; however, in animals that received the dopamine (DA) agonist 2-Br-alpha-ergocryptine maleate (CB-154, 0.5 mg/rat i.v.) at the end of the first nursing period did not show an increase in plasma PRL to a second suckling stimulation by the pups. When thyrotropin releasing hormone (TRH) was substituted for the second suckling period in CB-154 treated rats, a slight increase in plasma PRL occurred 5 minutes after the injection. In a third study we transiently blocked the action of DA at the AP by injecting the DA antagonist domperidone (0.01 mg/rat i.v.), followed 5 minutes later by the administration of CB-154. One hour later animals were either allowed to suckle pups for 10 minutes or were injected with TRH. Treatment with TRH resulted in an 11 fold increase in plasma PRL but suckling was completely ineffective in inducing PRL release. These data suggest that the lack of PRL release to suckling in CB-154 treated rats was due to inhibitory effects of CB-154 on neural mechanisms which link nursing to PRL release. In addition, the data show that pharmacologic DA antagonism affects TRH releasable PRL more than does suckling. This may be due to a reduction, by suckling, of the pool of PRL that is available to be released by TRH administration.     

Anterior pituitary and plasma prolactin in rats after 2 to 90 minutes of suckling.

Separation of litter for 6 hr resulted in plasma PRL levels of 48 +/- 5.8 and 45 +/- 5.7 ng per ml and AP PRL concentrations of 6.1 +/- 0.6 and 6.3 +/- 0.5 mug per mg AP in early (4-8 days) and late (20-22 days) lactation, respectively. After a 6-hr separation period, suckling for 2, 30, 60, and 90 min resulted in highly significant increases in the plasma PRL level in early lactaiton. Increases in plasma PRL levels were not seen in late lactation except in the 30-min suckled group. In both stages of lactation the AP PRL concentrations in the suckled groups were significantly lower than in the nonsuckled groups.     

The effect of dietary selenium supplementation on cadmium absorption and retention in suckling rats

Selenium (Se) reduces cadmium (Cd) toxicity in adult animals, but its effects in newborn animals are still unknown. This study investigated Cd (as CdCl₂) absorption, distribution, and retention in suckling rats receiving oral Se supplementation (as Na₂SeO₃) in equimolar doses (8 μmol Cd and/or Se per kg b.w./day). Selenium was given either before and during Cd exposure (Se_pre + Cd group; pre-treatment group) or only during Cd exposure (Se + Cd group). Rats were treated from postnatal day (PND) 6–14 as follows: controls (H₂O, PND 6–14), Se (PND 10–14), Cd (PND 10–14), Se_pre + Cd (Se PND 6–14 + Cd PND 10–14) and Se + Cd (Se + Cd PND 10–14). Selenium supplementation, especially pre-treatment, decreased Cd levels in the blood, brain, liver and kidney of suckling rats. Selenium levels in plasma, brain, and kidney also decreased. These findings suggest that higher Se intake could efficiently reduce Cd retention during the suckling period.     

Potential-dependent calcium channels in rabbit jejunum

Potential-dependent calcium channels have been studied in the isolated rabbit jejunum. A biphasic response was observed, a transient and rapid contraction followed by partial relaxation and a sustained contraction attaining a plateau state. These are similar to the phasic and tonic responses observed in the isolated smooth muscles of other species. Both the responses are susceptible to blockade by the calcium antagonists bepridil, diltiazem, nifedipine, PN 200-110 (isradipine), and verapamil. Two calcium pools or the presence of two channels affecting the two responses are proposed.     

Amino acid absorption in jejunum of rats in vivo--a kinetic comparison of distal resection effects

Jejunal absorption of leucine and cycloleucine by sham and 50% distal resected rats in vivo was studied by measuring the passive component and the active transport. After 5 months postresection the total amino acid absorption was increased. The mass-transfer coefficients of the passive process (obtained in presence of methionine) were higher in remnant jejunum than that in control rats, whereas the active transport remained unaltered after resection. When the kinetic constants of the saturable and non-saturable components were corrected for the unstirred water layer effects, the "real KD" increased in the resected group, whilst similar values for the "real Km and Jmax" were obtained.     

Release of oxytocin and prolactin in response to suckling.

The oxytocin and prolactin responses to suckling were measured in 10 women in early (n = 5) and established lactation (n = 5). Oxytocin was released in a pulsatile manner during suckling in all women, but the response was not related to milk volume, prolactin response, or parity of the mother. In all 10 women plasma oxytocin concentrations increased three to 10 minutes before suckling began. In five women this occurred in response to the baby crying, in three it coincided with the baby becoming restless in expectation of the feed, while in two it corresponded with the mother preparing for the feed. There was no prolactin response to stimuli other than stimulation of the nipple associated with suckling. These results clearly indicate that the milk ejection reflex, with release of oxytocin, occurs in most women before the tactile stimulus of suckling. A second release of oxytocin follows in response to the suckling stimulus itself. Thus it is important that care is taken to protect breast feeding mothers from stress not only during suckling but also immediately before nursing, when conditioned releases of oxytocin will occur.     

Intestinal iron absorption during suckling in mammals

The maintenance of appropriate iron levels is important for mammalian health, particularly during the rapid growth period following birth. Too little iron can lead to irreversible damage to the developing central nervous system and too much iron at this point can have adverse long term consequences, possibly due to excessive free radical production. In order to maintain iron levels, intestinal iron absorption is very efficient in young mammals, such that almost all of the iron in breast milk is utilized. However this high level of absorption is unable to be down regulated in response to excess iron as it can be in adults, implying that different regulatory processes are involved during suckling. Various mechanisms have been proposed to explain this high absorption, including enhanced expression of the proteins involved in iron absorption in adults (particularly DMT1 and ferroportin), non-specific uptake via pinocytosis, and the uptake of lactoferrin bound iron by the lactoferrin receptor. However, at present the precise mechanism is unclear. It is possible that all of these components contribute to the high intestinal iron absorption seen during suckling, or a novel, as yet undescribed, mechanism could be involved. This review summarises the evidence for and against each of the mechanisms described above and highlights how little is known about iron homeostasis in this vital stage of development.     

Ingestion of raffinose promotes calcium absorption in the large intestine of rats

We examined the effects of feeding raffinose on intestinal calcium absorption in ovariectomized rats by two separate experiments. In experiment 1, female Sprague-Dawley rats (6 wk old) were divided into two groups: sham operation and ovariectomy, and fed diets with or without raffinose (30 g/kg diet) for 4 wk. In experiment 2, ovariectomized rats with cecocolonectomy or transsection and reanastomosis (sham) were divided into two groups as in experiment 1 and fed the same diets for 3 wk. In experiment 1, calcium absorption was lower in the ovariectomized rats than in the sham rats but calcium absorption in rats fed the raffinose diet was higher than that in rats fed the raffinose-free diet. In experiment 2, increased calcium absorption in the raffinose group was abolished by cecocolonectomy. The impaired absorption in ovariectomized rats was restored by feeding raffinose. The large intestine is involved in the beneficial effects of raffinose.     

Effect of shellfish calcium on the apparent absorption of calcium and bone metabolism in ovariectomized rats

Fossil shellfish powder (FS) and Ezo giant scallop shell powder (EG) were rendered soluble with lactate and citrate under decompression (FSEx and EGEx, respectively) and we examined the effects of lactate-citrate solubilization of FS and EG on mineral absorption, tissue mineral contents, serum biochemical indices and bone mineral density (BMD) in ovariectomized (OVX) rats. The apparent absorption ratios of minerals tended to be high in the rats fed with the solubilized mineral sources, those in the FSEx group being significantly higher than in the FS group. There was no significant difference in the tibia mineral content among the OVX groups. BMD at the distal femoral diaphysis was significantly increased by FSEx and EGEx feeding. It is suggested that solubilization with lactate and citrate under decompression increased the solubility and bioavailability of calcium from such natural sources of shellfish calcium as FS and EG.     

The effect of calcium on lead absorption in rats.

The effects of Ca2+ on lead absorption as PbCl2 and 203PbCl2 were studied in rats. 1. Doubling of dietary calcium with Ca3(PO4)2 significantly decreased lead absorption as assessed by 203Pb retention, tissue lead concentration, urinary excretion of delta-aminolaevulinate and increased activities of delta-aminolaevulinate dehydratase and ferrochelatase. 2. Similar effects on lead absorption were shown by the Ca2+ salts, Cl-, CO32-, PO43-, SO42-, gluconate and glycerophosphate. 3. CaCl2 and calcium glycerophosphate were found to be most effective in decreasing lead absorption when administered immediately before lead dosage. 4. A negative exponential relationship was found between CaCl2 concentration and 203Pb absorption at 120h. The result suggest that, above 4 mmol of administered calcium, residual lead absorption is unaffected by increasing gastrointestinal calcium concentrations. 5. Increased systemic calcium had no effect on lead retention. 6. Calcium in the concentrations found in domestic hard-water supplies significantly decreased absorption of a solution of 203Pb dissolved in it compared with absorption of 203Pb dissolved in soft or distilled water. 7. Milk and skimmed milk were found to have no effect on 203Pb absorption in rats.