Intestinal absorption of calcium-47 and strontium-85 in lactating rats

Determination of the Sr/Ca ratio of tooth samples by photoactivation analysis in Southern Turkey

A nuclear analytical technique, namely instrumental photon activation analysis (IPAA), was used to determine Sr and Ca concentrations in human teeth. This work was conducted using the first accelerator facility, an off-shelf clinical linear accelerator (cLINAC), in Turkey. The tooth samples supplied by the Akdeniz University Faculty of Dentistry were analyzed for determination of the Sr/Ca element ratio. The results were obtained to demonstrate the impact of socioeconomic changes on dietary habits. A calibration material (CM; a mixture of calcium and strontium oxides) was required for quantification of the analytical results. The tooth samples, together with the CM, were exposed to 18 MeV end-point energy bremsstrahlung photons from the cLINAC. Thereafter, the γ-ray spectra of the samples and the CM were obtained using high resolution γ spectroscopy. Variations in the Sr/Ca ratio in the teeth of patients fed with beef and fizzy beverages were investigated in this study.

The study of a physiological significance of prolactin in the regulation of calcium metabolism during pregnancy and lactation in rats

Since a pharmacological dose of prolactin has previously been reported to enhance calcium absorption and bone calcium turnover, the role of endogenous prolactin in the regulation of calcium metabolism was investigated in the balance studies of Wistar rats between days 17 and 20 of first (P1) and fourth (P4) pregnancy and between days 12 and 15 of lactation (L). Each group was divided into 3 subgroups: one subgroup was given 0.9% NaCl (control); one was given 0.3 mg bromocriptine/100 g body weight ip twice daily for 3 days (to suppress prolactin secretion); and one was given bromocriptine and 0.25 mg prolactin/100 g body weight sc daily for 3 days. All three groups received 1 mL/100 g body weight of 1.25 mM calcium gluconate containing 2 mCi (1 Ci = 37 GBq) 45Ca daily for 3 days. Compared with the two pregnant controls, the L group had higher food consumption and higher fecal calcium excretion and lower urinary calcium excretion (% intake). Bromocriptine administration increased total calcium excretion from 59% intake to 84 and 66% intake in P1 and P4, respectively, suggesting that endogenous prolactin decreased total calcium excretion. On the other hand, exogenous prolactin had no effect on the calcium balance of P1 but increased the total calcium excretion in P4 from 57 to 66% intake. In contrast, the calcium balance of lactating rats was not altered by suppression of endogenous prolactin secretion or exogenous prolactin. Considering bone 45Ca content as representing bone Ca turnover, a lower value of bone 45Ca content indicated an accelerated bone Ca turnover. It was found that bromocriptine had no effect in P1 but decreased bone Ca turnover rate in the P4 and L groups, indicating an accelerating effect of endogenous prolactin on bone Ca turnover in the P4 and L groups. Exogenous prolactin, on the other hand, decreased bone Ca turnover rate in every group. Muscle Ca turnover was affected by bromocriptine and exogenous prolactin in the same manner as bone 45Ca contents. Interestingly, the biphasic action of prolactin was demonstrated in both calcium absorption and bone calcium turnover. It could be concluded that during pregnancy and lactation, endogenous prolactin increases food consumption, fractional calcium absorption, and bone calcium turnover, apparently to increase calcium availability for fetal development and milk calcium secretion.Key words: bone turnover, bromocriptine, calcium absorption, calcium excretion, calcium retention, prolactin.

Rickets and soil strontium

The subjects of this study were children aged 6-60 months living in villages in the Ulas Health Region, Sivas. The villages were divided into two groups according to the amount of strontium in the soil: region 1, > 350 ppm, 650 children; region 2, < 350 ppm, 1596 children. Overall, the prevalence of one or more clinical signs of rickets was 22.9%. The prevalence in region 1 was 31.5% and that in region 2, 19.5%. These values were significantly different (p < 0.001). When other variables which may be relevant to the occurrence of rickets were taken into account, the difference in prevalence persisted. The results suggest that in villages where nutrition is mainly based on grain cereals the presence of strontium in the soil will increase the prevalence of rickets significantly. As a preventive measure, a greater proportion of the foods given to children in these villages should be derived from animal origin, and cereals and drinking water supplies should be obtained from villages with a low soil strontium content, or calcium supplements should be given.

Strontium-90 as an indicator of time since death: a pilot investigation

The results of a pilot investigation are presented. The study aimed to show that the presence of radioactive strontium-90 in human bone could be used as evidence of active uptake during life. In this way the time since death of the individual could be identified as occurring before or after the date when atmospheric levels of radioactive strontium were at a peak in the early 1960s. The results of this initial investigation were encouraging but further detailed analysis is required on a substantially larger sample of material spanning a more controlled time period.

Regulation of serum 1,25-dihydroxyvitamin D3 in lactating rats

To characterize further the mechanism(s) underlying the increased serum 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] concentration associated with lactation in the rat, we examined hormone biosynthesis [i.e., renal 25-hydroxyvitamin D-1 alpha-hydroxylase (1 alpha-hydroxylase) activity] and hormone disappearance in groups of lactating Holtzman rats and age- and sex-matched nonlactating controls. 1 alpha-Hydroxylase activity was significantly greater in kidneys from lactating rats (4.0 +/- 0.42 fmol.mg-1.min-1) on a basal diet than in those from nonmated females (1.4 +/- 0.08 fmol.mg-1.min-1), an increment sufficient to account for the observed fourfold elevation of 1,25(OH)2D3 in the dams. The increase occurs despite the lower serum 1,25(OH)2D3 levels in lactating than in nonlactating rats at 12 and 24 h after a bolus injection of 1,25(OH)2D3 (2 ng/g body wt). Elevation of serum 1,25(OH)2D3 is not a requisite consequence of lactation, however, because dams receiving supplemental calcium from food (1.6%) and water (0.3%) exhibited no increase of either serum 1,25(OH)2D3 or 1 alpha-hydroxylase activity compared with controls. In contrast, lactating rats that received a diet with only 0.1% calcium had 5-fold higher serum 1,25(OH)2D3 levels and 20-fold higher 1 alpha-hydroxylase activity than nonlactating rats on the same diet. We conclude that other factors in conjunction with lactation, but not the lactating state per se, promote the changes in 1,25(OH)2D3 metabolism observed.

Serum free 1,25-dihydroxyvitamin D and the free 1,25-dihydroxyvitamin D index during a longitudinal study of human pregnancy and lactation

The changes in three different indices of 1,25-dihydroxyvitamin D (1,25(OH)2D) biological activity were studied longitudinally in 35 women during late pregnancy and lactation and in 26 control women. Measurements were made of maternal serum total 1,25(OH)2D and free 1,25(OH)2D concentration (by centrifugal ultrafiltration) and the free 1,25(OH)2D index (the molar ratio of total 1,25(OH)2D and vitamin D binding protein (DBP]. During late pregnancy total 1,25(OH)2D concentrations were significantly elevated when compared to controls, as were free 1,25(OH)2D and DBP concentrations and the free 1,25(OH)2D index. Serum total 1,25(OH)2D, free 1,25(OH)2D and DBP concentrations all fell dramatically during the first 2 weeks of lactation with total 1,25(OH)2D and free 1,25(OH)2D concentrations falling to levels below those of controls. During the course of lactation both total 1,25(OH)2D and free 1,25(OH)2D levels rose significantly although they were not different from controls at 18 weeks of lactation. In contrast, the free 1,25(OH)2D index fell during the first 2 weeks of lactation, but remained at this level, significantly lower than controls. Neither urinary calcium excretion nor dietary calcium intake correlated with total or free 1,25(OH)2D, DBP, or the free 1,25(OH)2D index. The disagreement in the results of free 1,25(OH)2D concentration and free 1,25(OH)2D index demonstrates that these two approaches to measuring biologically active 1,25(OH)2D are not equivalent. In attempting to account for the increased calcium requirements of human reproduction we conclude that in pregnancy any of the 1,25(OH)2D measurements may be appropriate. In lactation, however, either 1,25(OH)2D is not a major factor or 1,25(OH)2D biological activity is inadequately represented by any of the currently available methods.

Bone strontium in pregnant and lactating females from archaeological samples

Because plants and animals consume or absorb different amounts of strontium and calcium, anthropologists are able to use strontium/calcium (Sr/Ca) ratios from archaeologically recovered human bone to estimate the relative contributions of meat and plants to paleodiets. Often females exhibit higher Sr/Ca ratios than males, a fact usually attributed to lower meat intake among women. However, in vivo and in vitro experiments with laboratory animals show that pregnancy and lactation elevate maternal bone strontium and depress maternal bone calcium because 1) strontium is discriminated against in favor of calcium in the transport of ions to the placenta and mammary glands and 2) pregnancy and lactation facilitate absorption of alkaline earth metals from the gut. In this study, bone Sr/Ca ratios and strontium concentrations were compared between reproductive-age females, postmenopausal females, and adult males from two late prehistoric Native American sites in Georgia: the King site (N = 43) and the Etowah site (N = 51). At the King site, the mean Sr/Ca ratio of females was over 14% greater than that of males. At Etowah, the mean strontium level of reproductive-age females exceeded that of postmenopausal females by almost 25%. Most of the difference, it is argued, is due to pregnancy and lactation. A dietary preference among pregnant and lactating women for foods high in alkaline earths, particularly nuts and corn, may also be partially responsible. Until we assess the influence variables other than nutrition exert on trace element concentrations, our reconstructions of paleodiets will be suspect.

Factors influencing the self-selection of calcium in lactating rats

The effect of varying litter size and preventing milk delivery on the self-selection of calcium in lactating rats was assessed in two experiments. In Experiment 1, two groups of lactating rats, one having a litter size adjusted to four pups (n = 10) on the day after parturition and the other a litter size adjusted to 16 pups (n = 9), were given ad lib access to a 2.4% solution of calcium lactate, demineralised water, and a calcium deficient diet. Calcium, water and food intake were compared for these two groups both before impregnation and during 16 days of lactation. Females nursing 16 pups increased their calcium and food intake over the course of lactation more than did mothers nursing four pups. In Experiment 2, female rats were divided into four groups consisting of 10 nonimpregnated, 10 impregnated, 10 impregnated galactophore-cut, and nine sham-operated impregnated animals. To maintain pup health, and thus equivalent suckling stimulation among groups, litters of 8 pups were switched between galactophore-cut, impregnated and colony foster mothers every twelve hours. Over the course of lactation galactophore-cut dams showed an increase in calcium intake compared to nonlactating females and further, took in similar quantities of calcium to both intact and sham-operated impregnated animals in the first week of lactation. These studies showed that female rats do selectively increase their calcium intake during lactation. Moreover, this increase varies as a function of litter size and persists in the absence of milk delivery.

Self-selection of calcium during pregnancy and lactation in rats

A modification of the two-choice diet paradigm was used to determine whether female rats would self-select high levels of calcium at different times in a reproductive episode. A 2 X 2 X 5 (reproductive state X diet X time) design was used to compare the relative calcium intake of impregnated and non-impregnated rats given ad lib access to a calcium deficient or calcium sufficient diet together with demineralised water and a 2.4% calcium lactate solution over five weeks. For the impregnated groups, this time period comprised three weeks of pregnancy and two weeks of lactation. The results showed that during lactation the impregnated animals maintained on the calcium deficient diet consumed a greater amount of calcium solution relative to water intake than any other group. This increase in relative calcium solution intake occurred early in lactation and appeared not to correlate with increases in milk production.

Bone chemistry and prehistoric diet: strontium studies of laboratory rats

Strontium analysis of prehistoric human bone for the reconstruction of past diets is a relatively new technique in anthropology. In order to evaluate certain assumptions of the method, diets with low and high levels of strontium were fed to male, virgin female, and pregnant female laboratory rats. Analysis of the femurs of these rats by inductively coupled plasma/atomic emission spectrometry indicates that dietary intake is directly reflected in levels of strontium in bone ash. When dietary strontium levels were low, the observed ratio for bone:diet in the laboratory rats averaged 0.26, a value similar to that observed by other investigators. Among the groups fed high levels of strontium, pregnant females accumulated the most and virgin females accumulated the least strontium in bone. Males were intermediate. Gender differences in bone strontium among prehistoric human populations are considered in these terms.

Calcium transport in small intestine during pregnancy and lactation

The factors involved in calcium homeostasis during the mammalian reproductive cycle and specifically in the control of active calcium transport in the intestine have not been thoroughly investigated. For this reason calcium transport in the intestine was measured in vitamin D-replete and vitamin D-deficient rats during pregnancy and lactation using the everted gut sac technique. In addition the changes in the plasma concentrations of calcium and 1,25-dihydroxyvitamin D were measured and correlated with transport. During the later stages of pregnancy and during lactation, the concentration of calcium in the plasma is reduced 10-30%. In turn, in the vitamin D-replete rat, the concentration of 1,25-dihydroxyvitamin D in the plasma increases from a control value of 26 pg/ml to 158 pg/ml at day 14 of lactation. Calcium transport in the intestine increases late in pregnancy, peaks during lactation, and then falls to control values by 3 wk postweaning in both vitamin D-replete and D-deficient animals. These findings strengthen the established relationship between 1,25-dihydroxyvitamin D and active calcium transport in the intestine as well as suggest that some factor(s) independent of vitamin D is stimulating intestinal calcium transport during the reproductive cycle.