Postmenopausal bone loss is primarily due to estrogen deficiency. Recent clinical observation demonstrate that GH increases bone mass in GH deficient patients. The present study investigates whether estrogen regulates GH action and GH receptor expression in osteoblasts. 17 beta-estradiol or GH added to the culture medium as single substances did not influence rat osteosarcoma cell proliferation nor human osteoblast-like (hOB) cell proliferation. However, together they synergistically induced osteoblast proliferation (rat osteosarcoma cells 160.1 +/- 15.5% of control cells; human osteoblast-like cells 159.6 +/- 5.1% of control cells). 17 beta-estradiol stimulated 125I-GH binding and GH receptor (GHR) mRNA levels in rat osteosarcoma cells. The stimulatory effect of estradiol was time dependent, reaching a peak after 8 h of incubation with 17 beta-estradiol (binding 216.9 +/- 27.8% and mRNA 374.6 +/- 30.8% of control). The finding that estradiol stimulated 125I-GH binding was confirmed in human osteoblast-like cells. In these cells, 17 beta-estradiol (10(-12) M) increased 125I-GH binding to 203.8 +/- 3.6% of control levels. We conclude that estrogen stimulates GH activity as well as GH binding and GHR mRNA levels in osteoblasts. These findings indicate that estrogen potentiates the effect of GH at the receptor level.
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- Author: JC Netelenbos x
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MC Slootweg, D Swolin, JC Netelenbos, OG Isaksson, and C Ohlsson
EJ Giltay, EJ Duschek, MB Katan, PL Zock, SJ Neele, and JC Netelenbos
Estrogens may affect the essential n-6 and n-3 fatty acids arachidonic acid (AA; C20:4n-6) and docosahexaenoic acid (DHA; C22:6n-3). Therefore, we investigated the long-term effects of hormone replacement therapy and raloxifene, a selective estrogen-receptor modulator, in two randomized, double-blind, placebo-controlled studies. In study I, 95 healthy, non-hysterectomized, early postmenopausal women (age range 47-59 years) received one of the following treatments: daily raloxifene 60 mg (n=24), daily raloxifene 150 mg (n=23), 0.625 mg conjugated equine estrogens (CEE) plus 2.5 mg medroxyprogesterone acetate (MPA; n=24), or placebo (n=24). In study II, 30 men (age range 60-69 years) received daily 120 mg raloxifene (n=15) or placebo (n=15). In study I, plasma cholesteryl ester fatty acids were measured at baseline and after 6, 12, and 24 months in 83 (drop out rate 13%), 73 (23%), and 70 (25%) women respectively. In study II, fatty acids were measured at baseline and after 3 months in 29 men (drop out rate 3%). In postmenopausal women, administration of 150 mg raloxifene increased AA by a mean of +6.1% (P=0.055, not significant). Administration of CEE plus MPA increased AA by +14.1% (P<0.0005). Mean changes in DHA were +22.1% (P=0.003) and +14.9% (P=0.047) respectively, as compared with placebo. In men, 120 mg raloxifene for 3 months did not significantly affect AA (-5.2%; P=0.342) or DHA (+4.0%; P=0.755), but it increased testosterone levels by +19.8% (P=0.006). Administration of raloxifene 150 mg/day as well as CEE plus MPA to postmenopausal women increases the proportion of AA and DHA in plasma cholesteryl esters during a follow-up of 2 years. Short term administration of raloxifene in elderly men did not affect AA or DHA. The synthesis of AA and DHA from precursors may be enhanced through an estrogen receptor-dependent pathway.
