Insulin modulation of luteinizing hormone secretion in normal female volunteers and lean polycystic ovary syndrome patients.
OBJECTIVE
Endocrine features of polycystic ovary syndrome (PCOS) include altered ovarian steroidogenesis, hyperinsulinemia and abnormal luteinizing hormone (LH) secretion. This study was undertaken to further evaluate the role of insulin to modulate LH secretion in lean PCOS patients with normal insulin sensitivity and normal volunteers.


METHODS
The study was performed in five nonobese patients diagnosed with PCOS on the basis of amenorrhea and a polycystic morphology at ovarian ultrasound, and 5 normal controls in early to mid-follicular phase and matched for weight and age. All subjects were phenotyped, and then admitted for 12 h of frequent (q 10') blood sampling on two separate occasions, once for a baseline study and the other time for a hyperinsulinemic and euglycemic clamp study. LH was measured in samples obtained throughout each admission in order to perform LH pulse analysis.


RESULTS
Baseline LH secretion in PCOS subjects was significantly different from controls: they had higher LH levels, higher LH/FSH ratios as well as a faster LH pulse frequency than normal women. Insulin administration did not affect the pattern of LH secretion of PCOS patients, whereas it significantly increased the LH pulse frequency while decreasing the LH interpulse intervals in the controls.


CONCLUSIONS
These data confirm that an abnormal pattern of LH secretion characteristic of PCOS can be observed in lean patients, and appears independent of peripheral insulin levels. Furthermore, our results in lean controls provide the first direct evidence that peripheral insulin can modulate the activity of hypothalamic gonadotropin-releasing hormone (GnRH) neurons in the human.
Moret
Mallory
M
Service of Endocrinology, Diabetology and Metabolism, University Hospital, University of Lausanne, Lausanne, Switzerland.
Stettler
Rodrigue
R
Rodieux
Frederique
F
Gaillard
Rolf C
RC
Waeber
Gérard
G
Wirthner
Daniel
D
Giusti
Vittorio
V
Tappy
Luc
L
Pralong
Francois P
FP
D000328:Adult; D005260:Female; D015309:Glucose Clamp Technique; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism; D006801:Humans; D007031:Hypothalamus / Q000378:metabolism; D007328:Insulin / Q000008:administration & dosage* / Q000097:blood / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000097:blood / Q000187:drug effects / Q000378:metabolism*; D011085:Polycystic Ovary Syndrome / Q000378:metabolism*; D013851:Thinness
D007328:Insulin; D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone