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  • Title: Insulin sensitivity is unaltered by the use of the Norplant subdermal implant contraceptive.
    Author: Koopersmith TB, Lobo RA.
    Journal: Contraception; 1995 Mar; 51(3):197-200. PubMed ID: 7621688.
    Abstract:
    Prior evaluations of carbohydrate metabolism in Norplant implant users, using the oral glucose tolerance test, have shown mild but clinically insignificant deterioration of insulin sensitivity. Using the more sensitive insulin tolerance test, the effects of the Norplant implant system on insulin sensitivity was studied in normal women. Insulin tolerance tests were performed before Norplant implant insertion in ten ovulatory female volunteers and repeated after 12 weeks of use. Both fasting glucose and fasting insulin values were similar before and after the use of Norplant implants. There was no significant difference in either the Kitt glucose value or the Kitt insulin value at baseline and at 3 months of use. Furthermore, the insulin-to-glucose ratio did not differ before and after the use of Norplant implants. There was a significant correlation with BMI and Kitt glucose value (r = -0.45, p < .05), as well as between fasting insulin and BMI (r = 0.6, p = 0.006). In the first three months of use, the levonorgestrel-containing implant system, Norplant, does not affect sensitivity to insulin or glucose in normal, nondiabetic women. 10 ovulatory women aged 18-34 from the family planning clinic of the University of Southern California Medical Center who had requested the use of the contraceptive implant, Norplant, were recruited for a clinical study. It aimed to determine whether the release of levonorgestrel (LNG) from the implants would affect carbohydrate metabolism. The researchers used the more sensitive insulin tolerance test (ITT) rather than the oral glucose tolerance test to measure carbohydrate metabolism. They conducted the ITT before insertion of the implants (in the luteal phase in 7 cases and the follicular phase in 3 cases) and after 12 weeks of Norplant use. The women had a high carbohydrate diet for 3 days before each ITT followed by an overnight fast. Body mass index (BMI) and the fractional disappearance rate for plasma insulin (Kitt insulin) after intravenous insulin injection were negatively correlated (r = -0.447, p = 0.049). Fasting insulin and BMI had a positive correlation (r = 0.596, p = 0.006). The mean fasting glucose and fasting insulin values did not change significantly after Norplant use (84.6 vs. 84.7 mg/dl and 7.3 vs. 9.8 uU/ml, respectively). The insulin-to-glucose ratios also did not change significantly (11.7 vs. 8.2 uU x 100/mg). Neither the Kitt glucose value (plasma glucose disappearance) nor the Kitt insulin value differed significantly after Norplant use (3.59 vs. 3.49 and 7.57 vs. 7.95, respectively). The Kitt glucose value and the Kitt insulin value increased as the serum LNG levels decreased (r = -0.697, p = 0.025 and r = -0.643, p = 0.043, respectively). Norplant users with serum LNG levels of 200-400 pg/ml (most women) had normal Kitt glucose and Kitt insulin levels. The Kitt glucose and Kitt insulin levels may be adversely affected, however, in women with extremely high serum LNG levels. These findings suggest that LNG implants do not adversely affect carbohydrate metabolism in normal nondiabetic women during the first 3 months of use.
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