The effect of dietary calcium on vertebral bone mass in women is controversial. In a randomized study we have investigated the effect of dietary modification in the form of dairy products on vertebral bone mass in 30- to 42-yr-old premenopausal women over a 3-yr period. Twenty women increased their dietary calcium intake by an average of 610 mg/day (P less than 0.03) for 3 yr, while 17 age- and weight-matched women served as controls. Calcium intake was monitored by 3-day diet histories and 24-h urinary calcium excretion. The consumption of the dairy products did not alter serum calcium or PTH levels or the fasting urinary calcium to creatinine ratio. Twenty-four-hour urinary calcium excretion increased by 28% (P less than 0.03) in the supplemented women. Dairy product intake was accompanied by increased dietary fat intake, but there were no statistically significant changes in serum cholesterol, low density lipoprotein cholesterol, or high density lipoprotein cholesterol levels. The vertebral bone density in the women consuming increased calcium did not change over the 3-yr period (-0.4 +/- 0.9%). In contrast, the vertebral bone density in the control women declined (-2.9 +/- 0.8%; P less than 0.001) and was significantly lower than that in the supplemented group at 30 and 36 months. The study suggests that dietary modification in the form of dairy products retards vertebral bone loss in premenopausal women. Therefore, increased calcium intake in estrogen-replete premenopausal women may prevent age-related bone loss.

The effect of exercise on bone mass is unclear. To determine the skeletal effect of weight-bearing exercise in premenopausal women, we prospectively evaluated the effects of a weight-training program on lumbar spine bone mass in 10 women (mean +/- SEM, 36.2 +/- 1.3 yr) and compared the results with those in 7 sedentary women (40.4 +/- 1.6 yr). None of the women had previously participated in a weight-training program, and all ingested a 500-mg calcium supplement each day throughout the study. Axial loading and balance of large muscle groups were emphasized. Individual strength increased by 57 +/- 8% over 9 months. Despite the increase in muscle strength, lumbar spine bone density in the exercising women decreased by 2.90% at 4.5 months and 3.96% at 9 months (P = 0.01). In contrast, there was no change in lumbar density in the controls over the 9-month period. We conclude that short term weight training at this frequency and intensity decreases vertebral bone mass in premenopausal women.

The distribution of gonadotropin-releasing hormone (GnRH) was studied in the brain and infundibulum (INF) or median eminence of sheep utilizing a peroxidase-antiperoxidase immunohistochemical method. This procedure utilized a specific antiserum generated against GnRH conjugated to bovine serum albumin. In the rostral INF, the greatest concentration of GnRH positive axons was found in the medial region, mostly in the external layer dorsal to the hypophysial portal plexus. In the intermediate portion of the INF, the hormone was mainly observed in the external layer at the more dorsolateral areas ventral to the tuberoinfundibular sulcus. GnRH was generally located medially in the caudal portion of the INF and dorsomedially in the rostral infundibular stalk. Substantial amounts of reaction product were also noted in the internal layer throughout the entire rostrocaudal extent of the INF. The hormone was localized in axons throughout the brain from the septal and medial preoptic areas to the mammillary bodies. GnRH-positive perikarya were scattered in various regions of the infundibular (arcuate) and for the first time in the ventromedial nuclei of sheep hypothalamus. Preabsorption of the specific antiserum with synthetic GnRH abolished staining in both axons and perikarya, whereas preabsorption with thyrotropin-releasing hormone, oxytocin, arginine-vasopressin, and adrenocorticotrophic hormone did not affect staining intensity.

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