Osteoblast-derived cells express functional glucose-dependent insulinotropic peptide receptors.

Glucose-dependent insulinotropic peptide (GIP) is a 42-amino acid peptide synthesized and secreted from endocrine cells in the small intestine. The role of GIP in coupling nutrient intake and insulin secretion, the incretin effect, is well known. We report that GIP receptor messenger RNA and protein are present in normal bone and osteoblast-like cell lines, and that high affinity receptors for GIP can be demonstrated by [125I]GIP binding studies. When applied to osteoblast-like cells (SaOS2), GIP stimulated increases in cellular cAMP content and intracellular calcium, with both responses being dose dependent. Moreover, administration of GIP results in elevated expression of collagen type I messenger RNA as well as an increase in alkaline phosphatase activity. Both of these effects reflect anabolic actions of presumptive osteoblasts. These results provide the first evidence that GIP receptors are present in bone and osteoblast-like cells and that GIP modulates the function of these cells.

Alendronate and estrogen effects in postmenopausal women with low bone mineral density. Alendronate/Estrogen Study Group.

The bisphosphonate alendronate and conjugated equine estrogens are both widely used for the treatment of postmenopausal osteoporosis. Acting by different mechanisms, these two agents decrease bone resorption and thereby increase or preserve bone mineral density (BMD). The comparative and combined effects of these medications have not been rigorously studied. This prospective, double blind, placebo-controlled, randomized clinical trial examined the effects of oral alendronate and conjugated estrogen, in combination and separately, on BMD, biochemical markers of bone turnover, safety, and tolerability in 425 hysterectomized postmenopausal women with low bone mass. In addition, bone biopsy with histomorphometry was performed in a subset of subjects. Treatment included placebo, alendronate (10 mg daily), conjugated equine estrogen (CEE; 0.625 mg daily), or alendronate (10 mg daily) plus CEE (0.625 mg daily) for 2 yr. All of the women received a supplement of 500 mg calcium daily. At 2 yr, placebo-treated patients showed a mean 0.6% loss in lumbar spine BMD, compared with mean increases in women receiving alendronate, CEE, and alendronate plus CEE of 6.0% (P < 0.001 vs. placebo), 6.0% (P < 0.001 vs. placebo), and 8.3% (P < 0.001 vs. placebo and CEE; P = 0.022 vs. alendronate), respectively. The corresponding changes in total proximal femur bone mineral density were +4.0%, +3.4%, +4.7%, and +0.3% for the alendronate, estrogen, alendronate plus estrogen, and placebo groups, respectively. Both alendronate and CEE significantly decreased biochemical markers of bone turnover, specifically urinary N-telopeptide of type I collagen and serum bone-specific alkaline phosphatase. The alendronate plus CEE combination produced slightly greater decreases in these markers than either treatment alone, but the mean absolute values remained within the normal premenopausal range. Alendronate, alone or in combination with CEE, was well tolerated. In the subset of patients who underwent bone biopsies, histomorphometry showed normal bone histology with the expected decrease in bone turnover, which was somewhat more pronounced in the combination group. Thus, alendronate and estrogen produced favorable effects on BMD. Combined use of alendronate and estrogen produced somewhat larger increases in BMD than either agent alone and was well tolerated.

Glucose-dependent insulinotropic peptide is an integrative hormone with osteotropic effects.

Glucose-dependent insulinotropic peptide (GIP) is a gut-derived hormone known to be important in modulating glucose-induced insulin secretion. In addition, GIP receptors are widely distributed and may have effects on multiple other tissues: fat cells, adrenal glands, endothelium and brain. We have demonstrated recently that GIP also has anabolic effects on bone-derived cells. We now demonstrate that GIP administration prevents the bone loss associated with ovariectomy. We propose that GIP plays a unique role in signaling the bone about nutrient availability, indicating the importance of the gut hormones in directing absorbed nutrients to the bone, and suggesting the concept of an 'entero-osseous axis'. Thus, GIP plays an integrative role helping coordinate efficient and targeted nutrient absorption and distribution.

Hyponatremic emergencies.

Hyponatremia is a common clinical problem and can result in severe morbidity and even death. Understanding the pathophysiology of hyponatremic encephalopathy is central to accurate diagnosis and management. This article reviews the controversies surrounding the treatment of hyponatremia with special emphasis on risk to benefit ratio of different therapeutic strategies.

Glucocorticoid-induced osteoporosis: pathogenesis, prevention and treatment.

Glucocorticoids (GC) are widely used for anti-inflammatory and immunosuppressive therapy. Thirty to 50% of GC-treated patients develop osteoporosis. Potential mechanisms of GC-induced osteoporosis (GC-OP) include abnormalities in calcium balance, vitamin D metabolism, parathyroid hormone release and activity, prostaglandin E2 and cytokine synthesis, interference with c-fos and p-53 expression in osteoblasts, and hypogonadism. Early diagnosis and detection of patients at risk are accomplished with rapid, safe and non-invasive bone density measurements. Preventive measures include maintaining a positive calcium balance, vitamin D supplementation (if indicated) and treatment of hypogonadism. The shortest duration and the smallest doses possible of GC for a particular condition are advisable. For high-risk patients and those with established GC-OP calcitonin or bisphosphonate therapy is recommended.

Plasma prolactin concentration in gilts reared in confinement.

Plasma prolactin concentrations were determined in confinement-reared gilts, which were subsequently exposed to boars and/or relocated to pasture lots. At an average age of 181 days, an indwelling vascular cannula was surgically implanted, and 28 gilts were assigned randomly to either control (remained in confinement) or treatment (relocated to pasture) groups. Nine of the gilts in each group were exposed to a mature boar twice daily. Furthermore, the experiment was divided between April (n=17 gilts) and September (11 gilts). Blood samples were drawn at the time of surgical implantation and twice daily thereafter. Plasma concentrations of prolactin were quantified by validated radio-immunoassay procedures. Samples which were collected at surgery had significantly more prolactin than post-surgical samples in 25 of 28 gilts. The overall average for the post-surgical concentration of prolactin was 2.7 ng/ml, and there was no effect of continued confinement versus relocation to pasture lots. There was a tendency for boar exposure to reduce prolactin levels in relocated gilts but not in control gilts. There was also a tendency for plasma prolactin to be greater in September than in April, especially in control gilts. Overall these results indicate that plasma prolactin levels do not reflect the delay of puberty in confinement-reared gilts or the induction of puberty caused by relocation to pasture lots.

Prolactin and colibacillus-induced fluid transport in ligated intestinal segments.

Two experiments, using the ligated intestinal segment technique, were conducted to determine whether the pituitary hormone prolactin (PRL) could reduce Escherichia coli-induced fluid loss into the small intestine of 2- to 3-week-old pigs. Inoculation of 10(6) to 10(8) enteropathogenic E coli organisms into ligated jejunal segments caused a significant accumulation of luminal fluid within 12 hours. In the first experiment, intraluminal inoculation with 0.5 mg of ovine PRL along with the bacteria did not have any effect on fluid accumulation. Systemic IV treatment of the animals with 1.0 mg of ovine PRL at 3-hour intervals, beginning either immediately after or 9 to 10 hours before intestinal ligation, did not significantly (P less than 0.05) reduce fluid accumulation as compared with control animals. In the second experiment, IM administration of 100 microgram of thyrotropin-releasing hormone (TRH) at 3-hour intervals, beginning 6 hours before intestinal ligation, significantly (P less than 0.05) increased circulating PRL concentrations, as measured by radioimmunoassay. However, TRH treatment did not reduce the accumulation of luminal fluid in E coli-inoculated segments.

Hypercalcemia due to hard water used for home hemodialysis.

We have described two patients from the same rural community in Georgia who had hypercalcemia during home hemodialysis. In the first patient the diagnosis was not considered until after the patient complained of the poor taste of her home tap water and of the white residue it left on her cooking utensils; other causes of hypercalcemia had been ruled out. The diagnosis was confirmed when samples of tap water that had passed through the in-line deionizer showed low to high calcium concentrations. Calcium concentrations were high after the deionizer filters had been in place for some time but within the acceptable guidelines for the type of filters used. The second patient, seen shortly after the first, had also received dialysis with hard water and also had hypercalcemia despite the use of an in-line deionizer. These cases suggest that dialysis-induced hypercalcemia can occur during home hemodialysis despite seemingly adequate pretreatment of the water source.

Comparative effects of thyroxine and/or retinoic acid treatment in vivo on growth hormone synthesis and release by pituitaries from thyroidectomized rats.

Thyroid hormones and retinoic acid (RA) coregulate growth hormone (GH) synthesis and release from cultured pituitary tumor cells by interacting with nuclear receptors that activate GH gene transcription. Whether these two compounds share overlapping GH regulatory activities in vivo is unclear. Therefore we compared the effects of in vivo replacement therapy with thyroxine (T4) and/or retinoic acid (RA) on GH synthesis and release in pituitaries from hypothyroid rats. Three weeks after thyroidectomy, male rats (100-150 grams, body weight) received 7 days of intraperitoneal T4 (20 ug/kg/day) and/or RA (500 ug/kg/day) or vehicle. Isolated pituitary fragments were incubated for 3 h with [14C]leucine followed by 2 h with [3H]leucine and 3 nM rat growth hormone-releasing hormone (GHRH). Basal synthesis, GHRH-induced release of stored [14C]GH, and GHRH-stimulated release of newly synthesized [3H]GH were assessed by specific immunopercipitation of media and tissue homogenates. T4 increased the synthesis of GH in the absence and presence of GHRH. T4, but not RA, increased the absolute amount of stored and newly synthesized GH released by GHRH. Neither T4 nor RA altered the percent of stored GH released by GHRH, however, both independently or additively decreased the percent of newly synthesized GH released by GHRH. In summary, treatment of hypothyroidism with T4 increased GH synthesis and absolute release. Interestingly the fractional release of GH was unchanged or decreased by T4 treatment. RA treatment had no effect on GH synthesis or absolute release, but like T4 it decreased the fractional release of newly synthesized GH. Thus T4 and RA did not share similar regulatory effects on GH synthesis and stored GH release but did have similar effects on the fractional release of newly synthesized GH in pituitaries from thyroidectomized male rats.

Absorption of orally administered bovine prolactin by neonatal rats.

Neonatal rats received by esophageal administration 400 ng bovine prolactin (bPRL) in 0.5 ml of diluent. Blood serum was collected by decapitation at intervals of 15, 30, 45 and 90 min after administration. Pooled samples of rat sera were assayed for the presence of immuno-reactive bPRL using radioimmunoassay procedures validated for that purpose. Significant quantities of bPRL were detected in sera from 7- and 8-day-old rats at 30 and 45 min after oral administration. However, there was no bPRL detected in sera from 7-day-old rats at 15 or 90 min after administration. There was also an absence of detectable bPRL at 45 min after administration in rats between 9 and 14 days of age. Rats older than 8 days apparently lose the ability to absorb oral bPRL or become more able to degrade the hormone.

Dietary arginine, insulin secretion, glucose tolerance and liver lipids during repletion of protein-depleted rats.

Male Sprague-Dawley rats (approximately 500 g) were fed a very low protein diet (0.5% lactalbumin) for 14 weeks. The average weight loss was 195 g. Following protein depletion the rats were randomly assigned to 5 groups and repleted for 15 days with a purified diet containing 20% protein equivalent as L-amino acids with arginine comprising 0, 0.25, 0.5, 0.75 or 1.0% of the total diet. The absence of dietary arginine during repletion significantly reduced weight gain and efficiency of feed utilization with no apparent change in feed intake. Livers of animals fed 0 and 0.25% arginine were slightly heavier and contained a greater concentration of total lipids than livers from other groups. Intravenous glucose tolerance tests performed on the animals fed 0, 0.5 and 1.0% arginine gave k coefficients for glucose disappearance which were significantly greater (P less than .01) for 1.0% arginine (0.12) than for 0.5% arginine (.056) or 0% arginine (.045). Plasma insulin for the 1.0% arginine group peaked at 5 min following glucose injection, and declined steadily to near basal levels at 45 min. Plasma insulin for animals repleted with 0 and 0.5% arginine was elevated to a lesser degree than for 1.0% arginine by 5 min but remained above basal levels throughout the experiment and there was a concurrent decrease in the rate of glucose disappearance. The insulinogenic index (formula: see text) was significantly greater (P less than .01) with 1.0% and 0.5% arginine than with 0% arginine. These data suggest that glucose intolerance during arginine deficiency is related to decreased insulin release immediately following glucose administration and possibly a mild insulin resistance.

Acute management of cancer-related hypercalcemia.

OBJECTIVE: To review the pathogenesis and pharmacologic treatment of acute hypercalcemia associated with malignancy. DATA SOURCES: A MEDLINE search (1966 to 1995) of the English-language literature pertaining to acute hypercalcemia was performed. Additional literature was obtained from reference lists of articles identified through the search. STUDY SELECTION AND DATA EXTRACTION: All articles discussing the etiology and medical management of cancer-related acute hypercalcemia were considered in this review. Clinical trials reporting efficacy and safety of antihypercalcemic agents were also included. Information selected in the review was based on the discretion of the authors. DATA SYNTHESIS: Hypercalcemia is a life-threatening disorder associated with malignancy. It occurs in approximately 10-20% of patients with cancer. A variety of medications have been used in the management of hypercalcemia including bisphosphonates, calcitonin, furosemide, gallium nitrate, glucocorticoids, NaCl 0.9%, and plicamycin. Each of these agents has been reviewed with consideration of pharmacologic mechanism of action, evaluation of clinical trials, recommended dosages, efficacy, safety, cost, and role in treating cancer-related acute hypercalcemia. CONCLUSIONS: Immediate management of cancer-related acute hypercalcemia to prevent death and provide symptomatic relief is warranted. Severity determined by symptoms, calcium concentrations, and the overall status of the patient are important considerations in selecting appropriate therapy. Although the specific role of individual agents may vary, hydration remains the cornerstone of therapy. NaCl 0.9%, calcitonin, and pamidronate disodium have established roles as dominant first-line agents for the management of acute hypercalcemia associated with malignancy.

Effects of dietary lipid saturation on prolactin secretion, carcinogen metabolism and mammary carcinogenesis in rats.

Isoenergetic diets containing 20% corn oil, 20% beef tallow, or an equal mixture of 10% corn oil and 10% beef tallow (mixed fat) were fed to 30 rats per diet for 28 weeks following weaning. DMBA [7,12-dimethylbenz(a)anthracene] was administered (1.75 mg/100 g body weight) in a single oral dose after 4 weeks of feeding. After 28 weeks, 70% of the rats fed corn oil had mammary tumors versus 47% for mixed fat and 30% for tallow. Diet had no effect on the number of tumors per tumor-bearing rat or the proportion of tumors that were adenocarcinomas. Other rats assigned to each of the three diets were killed at the time corresponding to DMBA administration for examination of hepatic mixed-function oxidase activity. NADPH cytochrome c reductase activity and cytochrome P-450 content were higher in rats fed corn oil or mixed fat rather than tallow. However, no significant differences in aryl hydrocarbon hydroxylase, glutathione transferase, and uridine-diphosphoglucuronide transferase activities were observed. The effects of dietary fat saturation on enzyme activity failed to show a clear association with DMBA carcinogenesis. In other rats assigned to the three dietary treatments for 4 or 16 weeks, lipid saturation did not change serum prolactin (PRL) concentrations during diestrus or proestrus. PRL secretion was examined following a provocative stimulus (perphenazine) in rats fed the experimental diets for 4 or 10-22 weeks. Although perphenazine increased serum PRL and depleted the pituitary of PRL, differences in dietary lipid saturation caused no significant changes in these indices. These data show that the incidence of mammary tumors in rats fed high fat diets (20% by weight) was greater in those fed corn oil compared to beef tallow. The effect of dietary lipid source on tumorigenesis was not associated with changes in carcinogen-metabolizing enzyme activity or PRL secretion.

Arginine requirement of mature protein-malnourished rats for maximal rate of repletion.

Male Sprague-Dawley rats (initial weight 400 g) were fed a 0.5% lactalbumin diet containing required amounts of all other known essential nutrients for 14 weeks. The body weights averaged 250 g after depletion when the animals were randomly assigned to four groups of four or five. Rats of one group were killed for baseline analyses on day 0 of repletion. The remaining three groups were repleted for 14 days with a complete L-amino acid diet containing 20% protein equivalent and 0, 0.75 or 1.5% Arg . HCl. Daily feed intakes averaged 11, 15 and 17 g and daily weight gains were 3.3, 7.4 and 8.3 g, respectively. Average values for corresponding groups were: nitrogen balance--116, 187 and 190 mg/day; urinary orotate--4.6, 0.8 and 0.15 mg/day; carcass lipid--27, 37 and 40 g/100 g dry matter. Liver weights per 100 g body weight for 0 arginine exceeded other groups by 40%. There were no differences in creatinine index, nor in plasma concentrations of insulin, glucagon and albumin. The maximal rate of recovery from protein-calorie malnutrition of mature rats required an exogenous source of arginine. Urinary orotic acid excretion provided a reliable measure for determining when arginine needs for maximal rate of repletion were not met.

The combined effects of dietary fat and estrogen on survival, 7,12-dimethylbenz(a)anthracene-induced breast cancer and prolactin metabolism in rats.

The relationships between dietary fat concentration (10 or 40% of energy), fat source (corn oil or beef tallow) and estrogen (control, ovariectomy or ovariectomy with estrogen replacement) to 7,12-dimethylbenz(a)anthracene (DMBA)-induced breast carcinogenesis and survival in rats were studied in a 2 x 2 x 3 factorial experiment. Female Sprague-Dawley rats given DMBA (2.5 mg/100 g body wt, intragastric) at 55 d of age were randomly allocated to three groups 48 h later: sham ovariectomy (control), ovariectomy (OVX) or ovariectomy with a subcutaneous estrogen implant (OVX+E). Each group was subdivided into dietary groups fed 10 and 40% of energy as corn oil or beef tallow for 70 wk. OVX+E rats exhibited serum estrogen concentrations in excess of physiologic values. Survival at 70 wk for the 3 hormonal groups was control 51%, OVX 67% and OVX+E 13%. Mortality in controls was doubled by feeding a high fat diet; no diet effect was detected in OVX or OVX+E rats. Palpable tumors developed in 74, 14 and 60% of control, OVX and OVX+E rats, respectively. High fat diets approximately doubled the hazard of developing a palpable tumor. Adenocarcinoma prevalence was 58, 12 and 63% in control, OVX and OVX+E rats, respectively. The odds of having any tumor, an adenocarcinoma or an adenoma were multiplied by 3.6, 2.8 and 2.3, respectively, for rats fed high vs. low fat. Additional studies showed that diet had no effect on serum prolactin or estrogen concentrations or metabolism and clearance of intravenously administered radiolabeled prolactin. We demonstrated that high dietary fat concentration enhances breast carcinogenesis independently of cyclic ovarian function, although the presence of estrogen may be a prerequisite for significant dietary modulation. The effect of fat on breast cancer is not mediated by major changes in systemic prolactin metabolism.

Dietary fat and protein intake differ in modulation of prostate tumor growth, prolactin secretion and metabolism, and prostate gland prolactin binding capacity in rats.

The combined effects of dietary fat and protein concentration on prostate tumor growth and endocrine homeostasis were evaluated in male rats. A 2 x 2 factorial experiment examined the effects of protein (5 and 20% of energy as casein) and fat (10 and 40% of energy as corn oil) on the growth of the Dunning R3327-H transplantable prostate adenocarcinoma in Copenhagen x Fisher F1 rats. Rats fed protein-restricted diets for 20 wk exhibited lower energy intakes, final body weights and tumor growth rates. Weanling male Sprague-Dawley rats fed protein-restricted diets for 4 wk had serum concentrations of prolactin, growth hormone and testosterone which were 68, 17 and 85% of controls, respectively. After 16 wk of feeding, there were no effects of dietary protein on serum hormone concentrations despite reduced energy intake and body weight. The metabolic clearance rate of serum prolactin was lower in rats fed the low protein diets for 4 or 16 wk; however, no differences were noted when adjusted for body weight. In vivo studies employing intravenously injected 125I-labeled prolactin revealed slight alterations in the metabolism of circulating prolactin monomer or binding to serum proteins in protein-restricted rats. The maximal binding capacity of prolactin receptors on the prostate membrane fraction was 42% lower in rats fed diets restricted in protein despite normal serum hormone concentrations at 16 wk. Dietary fat had no effect on tumor growth or prolactin homeostasis although a slightly greater serum testosterone was noted in rats fed high fat diets. In contrast, restriction of dietary protein caused significant changes in energy intake, serum hormone concentrations, prolactin metabolism, prostatic prolactin binding capacity and prostate tumor growth rates. These studies support the hypothesis that dietary protein and energy intake, particularly during periods of rapid growth and development, may alter prostate biology and modulate the risk of future prostate cancer progression.