Influence of ovariectomy on bone metabolism in very old rats.

Twenty-five 30-month-old Lou rats fed a diet (6 g/100 g BW/day) containing 0.9% Ca and 0.8% Pi were divided into five groups. Four groups were surgically ovariectomized. From day 2 until day 29 after ovariectomy, they were S.C. injected either with 17 beta estradiol (E2; 10 micrograms/kg BW/48 hours) or progesterone (P; 140 micrograms/kg BW/48 hours), or 17 beta estradiol + progesterone (E2P) at the same doses, or solvent alone (OVX). The fifth group was sham operated (SH) and injected with solvent. Urine was collected in metabolic cages from day 24 to 29 after ovx, and urinary pyridinoline (PYD) and deoxypyridinoline (DPD) excretion (markers of bone resorption) was measured by HPLC. All animals were killed 30 days after ovariectomy. Serum was then collected for measurement of osteocalcin (OC), alkaline phosphatase (ALP), parathyroid hormone (PTH), and calcitonin (CT). At necropsy, the success of ovariectomy was checked by marked atrophy of the uterine horns. Left and right femur were harvested for densitometric and mineral analysis, respectively. Ovariectomy had no significant effect upon plasma calcium and PTH concentrations. E2 or E2P treatment significantly increased plasma PTH and calcitonin concentrations. Plasma OC concentrations and ALP were not different in any of the groups. In contrast, urinary excretion of PYD and DPD was higher in OVX than in SH rats. Bone mineral density (BMD) of the distal femur was decreased by OVX, but was not different in the E2P and SH groups. A similar pattern was observed for the mineral or Ca content of whole femur. Thus, OVX decreased BMD and bone mineral content (BMC) in very old female rats. Plasma OC concentration and ALP activity failed to demonstrate any significant effect of OVX, whereas PYD and DPD were elevated. These results suggest that bone resorption is increased in OVX rats, even when supplemented with E2 or P alone. However, no significant difference was observed between SH and OVX rats treated with supplementation of both E2 and P. Thus, in very old rats, a combination of E2 and P is much more effective than E2 or P alone to prevent bone loss following ovariectomy.

Magnesium and blood pressure. I. Animal studies.

The relationship between experimental magnesium deficiency and blood pressure is complex and still the subject of much debate. The effect of Mg deficiency and blood pressure in Wistar rats receiving a Mg deficient diet (0.080 g/kg) for 40 weeks was examined. Deficient rats, when compared to controls, showed an initial transitory phase of hypotension, followed by normalization of blood pressure and then hypertension beginning after 15 weeks on the deficient diet. During the whole experimental period, heart rate was significantly increased in deficient rats as compared to controls. The fact that hypotension resulting from Mg deficiency of short duration can be inhibited by antihistamines and by indomethacin suggests that various mediators seen during the inflammatory period of Mg deficiency could be involved. Mg deficiency of long duration was accompanied by hypertension. When Mg-deficient rats received the control diet for a period of 3 weeks, Mg supplementation only partially corrected the hypertension. The hypertension was not a consequence of stimulation of the renin-angiotensin system since the plasma renin activity was not modified and ACE activity was reduced. These deficient rats showed a significantly lower vasopressor response to noradrenaline than control rats. Several factors such as increase in collagen, changes in elastin and arterial elasticity, total lipid content, and calcifications may account for the hyporesponsiveness to contractile agonists.(ABSTRACT TRUNCATED AT 250 WORDS)