LH pulsatility and response to a single s.c. injection of buserelin in polycystic ovary syndrome

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Abstract
The present study was undertaken in order to determine whether patients with polycystic ovary syndrome (PCOS) have LH pulse frequency and/or amplitude higher than those in normal cycling women during the follicular phase, and, if so, to establish possible factors which might influence LH secretion in PCOS. The study was conducted on 14 PCO patients (aged 19–30 years), who were subdivided according to the data on their cycle abnormality into 2 groups: amenorrheic (Am-PCOS, n = 9) and oligomenorrheic (O-PCOS, n = 5). LH pulsatility was assessed in the early follicular phase in controls (n = 5) and O-PCOS and at any time in Am-PCOS. Blood samples were taken every 10 minutes for 4 hours. Pulse analyses of LH data were performed using the Munro program. The buserelin test was performed on the same day by injection of 40 μg of buserelin (blood samples were taken every 60 minutes for the following 10 hours). Eleven PCO patients and 12 control subjects had an oral glucose tolerance test (oGTT) (blood samples were taken every 60 minutes for glucose, insulin and C-peptide measurements). Both mean LH pulse frequency and mean pulse intervals were not distinguishably different in PCO women (Am and O) and controls. In contrast, the mean pulse amplitude was significantly higher in the Am-PCOS group than in O-PCOS women and controls (p < 0.02 and p < 0.001, respectively). A significant positive correlation was established between nadir LH concentrations and LH pulse amplitude (r = +0.966, p < 0.001). The LH response to buserelin stimulation was significantly higher in Am-PCOS than in O-PCOS (p < 0.004). A highly significant positive correlation was observed between LH pulse amplitude and insulin response during oGTT (p < 0.001) in PCO subjects. Basal (prebuserelin) LH concentrations correlated significantly with fasting insulin levels (p < 0.008) and insulin and C-peptide responses to oGTT. These results allow us to conclude the following: 1. An increased LH pulse amplitude and an exaggerated LH response to buserelin observed in amenorrheic PCO subjects compared to those in oligomenorrheic PCO subjects fail to support the hypothesis of an intrinsic hypothalamo-pituitary abnormality. 2. The relationship between fasting and glucose-stimulated insulin levels with LH nadir concentrations, pulse amplitude and response to buserelin suggests an etiological role of insulin in the pathogenesis ofPCOS.

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