Pamidronate Reduces PTH-mediated bone loss in a gene transfer model of hyperparathyroidism in rats

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Abstract
We Evaluated Spinal And Femoral Bone Mass And Density Utilizing Dual-Energy X-Ray Absorptiometry (Dexa) In Rats In Which Severe Hyperparathyroidism Was Produced By The Expression Of The Gene For Human Pth-(1–84) (Hpth). This Gene Was Incorporated Into A Retroviral Vector That Was Transfected Into Fibroblasts Which Were Subsequently Injected Into Their Peritoneal Cavities. Further, We Examined The Effect Of The Administration Of Pamidronate On Bone Mass And Density In The Presence Of Extremely High Concentrations Of Hpth. Three Groups Of Rats Were Studied. Groups 1 And 2 Receive The Hpth-Secreting Fibroblasts; Group 2 Subsequently Received Pamidronate (2.5 Mg/Kg Iv) 18 And 27 Days After Receiving The Fibroblasts. These Animals Developed Levels Of Hpth > 1.0 μg/Liter And Became Hypercalcemia Within 20 Days. These Animals Became Lethargic And Were Significantly Lower In Weight Than Age-Matched Controls (Group 3, P < 0.05). After Accounting For The Animal Weight There Was A Further Significant Decrease In Bone Mineral Content And Density (Bmc And Bmd) On Day 29 Attributable To Hpth-Mediated Bone Loss. Treatment With Pamidronate Resulted In A Higher Bmc Of The Lumbar Spine Than In The Untreated Animals, With Elevated Concentrations Of Hpth. The Bmd Was Significantly Higher At Both The Lumbar Spine And Femur In The Pamidronate-Treated Animals (P < 0.05). The Cv Of Paired Measurements Of Bmd Was 2.7% At The Spine And 1.5% Of A Femur, Respectively. The Bmc Of The Lumbar Spine And Femur Was Closely Correlated With The Ashed Weight Of The Same Bones (R = 0.92 And 0.85, Respectively).