Biochemical Variables in Pre- and Postmenopausal Women: Reconciling the Calcium and Estrogen Hypotheses

Abstract

There is controversy as to whether the rise in urinary calcium at the menopause is the cause or the result of the rise in bone resorption at that time. In an attempt to resolve this issue, we have compared the relevant biochemical variables in 102 premenopausal volunteers (mean age 37 years; range 21-52) and 86 apparently normal postmenopausal women (mean age 55 years; range 40-60). We measured the fasting serum calcium, creatinine, proteins, electrolytes and intact parathyroid hormone (PTH), and the urinary calcium and creatinine both after an overnight fast and in a 24-h collection. We calculated serum calcium fractions, creatinine clearance and the notional tubular maximum reabsorptive capacity for calcium. Creatinine excretion and clearance were lower in the post- than in the premenopausal women after correction for surface area and age. Total serum calcium was higher in the post- than in the premenopausal women but this was accounted for by the higher ligand concentrations in the former. Fasting and 24-h urinary calcium were also higher in the post- than in the premenopausal women due in part to the former's higher filtered load of calcium (due to their higher serum complexed calcium) but mainly to their reduced tubular reabsorption of calcium despite their slightly raised serum PTH. Our analysis resolves the rise in urinary calcium at the menopause into its two components: increased filtered load and reduced tubular reabsorption. The changes in these two variables, neither of which can be attributed to increased bone resorption, produce an increase in calcium requirement that is sufficient to account for postmenopausal bone loss. However, the translation of this menopausal increase in calcium requirement into an increase in bone resorption at near-normal serum PTH levels requires some menopause-dependent change in the responsiveness of the bone to calcium demand. We suggest that this change may occur at the level of the osteoclasts and that estrogen may modify the calcium feedback setpoint in these cells in a manner analogous to calcitonin. This model resolves the apparent conflict between the estrogen and calcium hypotheses and explains the synergism between these two treatment modalities.

Decreases in urine specific gravity and urinary creatinine in elderly women

“…Dietary intake of meat (combination of animal meat, poultry and fish) of the ‡70-year-old women (133 g/day) was, however, only insignificantly (P>0.10) lower than that of younger people (e.g., 175 g/day for 15-19-year-old women, at which the intake was highest among women of a whole age range) due to wide inter-individual variation (the ASD being nearly equal to the AM) (Ministry The present analysis made it clear that menopause is an influential factor of CR, the power being comparable to that of age (Table 7). The finding that urinary CR was lower among post-menopausal women than among pre-menopausal women was as previously reported; for example, Nordin et al (1991) observed that average CR in spot urine samples from post-menopausal women was significantly (P<0.01) lower than that from pre-menopausal subjects, and the same was also the case when CR levels were compared in 24-h urine samples, although statistical power for the difference varied depending on the studies (Nordin et al 1993(Nordin et al , 1999.…”

Studies on Effect of Atenolol and Enalapril on Serum Electrolytes in Pre and Postmenopausal Women with Essential Hypertension

“…[16] The present study showed significant reduction in serum calcium in premenopausal hypertensive patients which is in agreement to other research findings. [17] An increase in concentration of serum calcium was observed in postmenopausal hypertensive women and this may be due to higher filtered load of calcium mainly because of their reduced reabsorption of calcium. A direct effect of Section: Biochemistry calcium is reported on the peripheral vascular tone.…”

“…[18] A research study by Nordin et al have stated that urinary calcium in post-menopause is increased because of two components increased filtered load and reduced tubular re-absorption. [17] A rise in the level of serum calcium, potassium and parallel decrease in the level of serum sodium was observed after supplementing ACE-inhibitor, enalapril and β-blocker, atenolol which is necessary for decreasing blood pressure in pre and postmenopausal women. [19] A study conducted for analysis of relationship between sodium status and ACE-inhibitor efficacy reported that sodium depletion boosts renin secretion from the juxtaglomerular cells which leads to increase in the hypotensive effect of ACE-inhibitor.…”

Role of Non-Contrast CT in Management of Urolithiasis

“…These results were comparable to a study by Fowler 23 , where ultrasound identified hydronephrosis in 95%, ureteral dilation in 89% and perirenal fluid in 23% of the patients as in present study. As previously highlighted, due to low individual sensitivities and specificities, the KUB should always be paired with another imaging modality such ultrasound 24 . In the present study X-ray KUB when combined with USG, correctly diagnosed urolithiasis in 35 (70%) of the 39 patients with urolithiasis.…”