Objective: To study the effects of different types of continuous hormone replacement therapy on carbohydrate metabolism.
Method: Postmenopausal women were treated with conjugated estrogens, 0.625 mg/medroxyprogesterone acetate, 2.5 or 5 mg (CEE/MPA) or tibolone 2.5 mg daily for 13 28-day cycles. Serum glucose and insulin were measured before and during a 75 g oral glucose tolerance test (OGTT) at baseline and after 3, 6 and 13 cycles and areas under the curve (AUC) were calculated. Sex hormone-binding globulin (SHBG) was measured as an additional marker of nutritional and insulin status.
Results: Neither CEE/MPA 2.5mg nor tibolone had any effects on carbohydrate metabolism while AUC(insulin), AUC(glucose) and also body mass index (BMI) increased after 13 cycles of treatment in the CEE/MPA 5 mg group. SHBG increased significantly during CEE/MPA treatment and decreased significantly during treatment with tibolone. The effects on SHBG were less pronounced in the CEE/MPA 5mg group. Pretreatment SHBG showed significant negative correlations to BMI and to variables that may reflect a certain degree of insulin resistance, the most pronounced being fasting glucose. Changes in SHBG during treatment with tibolone were negatively correlated to pretreatment SHBG and positively to BMI, AUC(insulin) and fasting insulin resistance index, while no such correlations were found in the CEE/MPA groups. There were no correlations between changes in AUC(insulin) and AUC(glucose) on one hand and basal variables or treatment SHBG on the other in the CEE/MPA groups.
Conclusion: The effects of tibolone and CEE/MPA on carbohydrate metabolism were considered to have clinical significance only for CEE/MPA 5mg, indicating a less favourable role of the higher progestagen dose. The results further support the important role of metabolic and insulin status in the physiological regulation of SHBG and also indicate that the suppressive effect of tibolone on circulating SHBG is mainly depends on pretreatment SHBG levels. SHBG does not reflect changes in carbohydrate metabolism during CEE/MPA treatment.